Voltage to PWM chip (similar to class D)?

[Joerg]

Folks,

Does anyone know an IC that can turn a control voltage into PWM and can
handle PWM frequencies in the 50-1000kHz range? Similar to a class D
driver but has to go down to DC. The changes in control would be
restricted to the audio spectrum below 15kHz.

The LTC6992 does this nicely but isn't precise enough. Same with
555-style timers or switcher chips. I am looking for better 1% and
ideally a lot better, including nonlinearity, drift, warts and all. A uC
is not suitable either because it should be simple and I need very fine
control granularity, down to around 0.1%.

Can't use short-lived consumer chips for radios and TV sets and such.

--
Regards, Joerg

http://www.analogconsultants.com/

[Jim Thompson]

On Thu, 29 May 2014 14:20:26 -0700, Joerg <inv...@invalid.invalid>
wrote:

I can design you a chip >:-}

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

[Lasse Langwadt Christensen]

does it have to be pwm?

not hysteretic, deltasigma or UcD ?

http://www.hypex.nl/technology/ucd.html

-Lasse

[jurb...@gmail.com]

>"PWM frequencies in the 50-1000kHz range?..."

Is it fifty or a thousand ? It makes a difference.

[John Larkin]

On Thu, 29 May 2014 14:20:26 -0700, Joerg <inv...@invalid.invalid>
wrote:

How about a sawtooth or triangle waveform and a comparator. Close a
feedback loop around that, with a PWM to DC converter; the PWM-DC part
can be made very linear.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[Lasse Langwadt Christensen]

Den torsdag den 29. maj 2014 23.53.48 UTC+2 skrev John Larkin:
> On Thu, 29 May 2014 14:20:26 -0700, Joerg <inv...@invalid.invalid>
>
> wrote:
>
>
>
> >Folks,
>
> >
>
> >Does anyone know an IC that can turn a control voltage into PWM and can
>
> >handle PWM frequencies in the 50-1000kHz range? Similar to a class D
>
> >driver but has to go down to DC. The changes in control would be
>
> >restricted to the audio spectrum below 15kHz.
>
> >
>
> >The LTC6992 does this nicely but isn't precise enough. Same with
>
> >555-style timers or switcher chips. I am looking for better 1% and
>
> >ideally a lot better, including nonlinearity, drift, warts and all. A uC
>
> >is not suitable either because it should be simple and I need very fine
>
> >control granularity, down to around 0.1%.
>
> >
>
> >Can't use short-lived consumer chips for radios and TV sets and such.
>
>
>
> How about a sawtooth or triangle waveform and a comparator. Close a
>
> feedback loop around that, with a PWM to DC converter; the PWM-DC part
>
> can be made very linear.
>

put loop around integrator,comparator and flipflop and you have deltasigma

cut down to the bone,

Version 4
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WIRE 496 -64 64 -64
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SYMBOL voltage 208 240 R0
WINDOW 123 0 0 Left 2
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SYMATTR Value PULSE(0 1 0 1n 1n 500n 1000n)
SYMBOL res 592 160 R90
WINDOW 0 0 56 VBottom 2
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SYMATTR Value 1k
SYMBOL cap 624 240 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C2
SYMATTR Value 10n
TEXT -130 488 Left 2 !.tran 100m

[Phil Hobbs]

How about a CMOS 555 with a current source to charge the capacitor?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

[Joerg]

This one has to be PWM but we can possible delinearize upfront (possibly
...). Better would be a clean 1:1 PWM.

[Joerg]

jurb...@gmail.com wrote:
>> "PWM frequencies in the 50-1000kHz range?..."
>
> Is it fifty or a thousand ? It makes a difference.
>

Sorry, 50kHz to 1000kHz.

[Joerg]

John Larkin wrote:
> On Thu, 29 May 2014 14:20:26 -0700, Joerg <inv...@invalid.invalid>
> wrote:
>
>> Folks,
>>
>> Does anyone know an IC that can turn a control voltage into PWM and can
>> handle PWM frequencies in the 50-1000kHz range? Similar to a class D
>> driver but has to go down to DC. The changes in control would be
>> restricted to the audio spectrum below 15kHz.
>>
>> The LTC6992 does this nicely but isn't precise enough. Same with
>> 555-style timers or switcher chips. I am looking for better 1% and
>> ideally a lot better, including nonlinearity, drift, warts and all. A uC
>> is not suitable either because it should be simple and I need very fine
>> control granularity, down to around 0.1%.
>>
>> Can't use short-lived consumer chips for radios and TV sets and such.
>
> How about a sawtooth or triangle waveform and a comparator. Close a
> feedback loop around that, with a PWM to DC converter; the PWM-DC part
> can be made very linear.
>

That's what I wanted to avoid for real estate reasons. But if I hafta
I'll do it.

[Joerg]

Phil Hobbs wrote:
> On 5/29/2014 5:20 PM, Joerg wrote:
>> Folks,
>>
>> Does anyone know an IC that can turn a control voltage into PWM and can
>> handle PWM frequencies in the 50-1000kHz range? Similar to a class D
>> driver but has to go down to DC. The changes in control would be
>> restricted to the audio spectrum below 15kHz.
>>
>> The LTC6992 does this nicely but isn't precise enough. Same with
>> 555-style timers or switcher chips. I am looking for better 1% and
>> ideally a lot better, including nonlinearity, drift, warts and all. A uC
>> is not suitable either because it should be simple and I need very fine
>> control granularity, down to around 0.1%.
>>
>> Can't use short-lived consumer chips for radios and TV sets and such.
>>
>
> How about a CMOS 555 with a current source to charge the capacitor?
>

That could be done but would gradually lead me to the circuit complexity
(size) of a comparator solution. Because I'd have to control the current
source over a wide range and very precisely.

I was hoping I'd not be the only one needing a precise voltage-to-PWM
function.

[John Larkin]

If you want 0.1% accuracy, you might be able to do it open-loop, with a very
linear ramp, but it will be hard at that frequency. If you only want 0.1%
resolution ("granularity"?) it's not so bad.

Can you use delta-sigma? There are some integrated d-s modulators around.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

[Joerg]

I could but then I'd have to build a one-shot that stretches the pulses
into a very precise length and that's almost the same kind of challenge
as building my own PWM generator (needs too much space).

[Tim Wescott]

Hey! Microprocessors are simple! You just need to learn some valuable
skills, that's all.

http://www.c-for-dummies.com/

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

[Reinhardt Behm]

But generating a PWM at 1MHz with a resolution of 0.1% mean you need a base
frequency for your counter of 1GHz. I don't know any CPU that could do that.

--
Reinhardt Behm

[Lasse Langwadt Christensen]

why would you need a one-shot? the output is clocked

something like the AD7401, if you want to be sure a flipflop on the output


-Lasse

[Lasse Langwadt Christensen]

he did say the input was limited to 15KHz, so 2*15K*1000 >= 30MHz

plenty of cpus that can do that

-Lasse

[John Larkin]

Someone, TI I think, has a ARM with nanosecond-resolution PWM outputs. But Joerg
seems to want an analog input.

Digital delay generators generally use a clocked coarse width generator with
analog interpolation down to picoseconds. Too complex for this app.

[Maynard A. Philbrook Jr.]

In article <5387D833...@electrooptical.net>,
ho...@electrooptical.net says...

>
> On 5/29/2014 5:20 PM, Joerg wrote:
> > Folks,
> >
> > Does anyone know an IC that can turn a control voltage into PWM and can
> > handle PWM frequencies in the 50-1000kHz range? Similar to a class D
> > driver but has to go down to DC. The changes in control would be
> > restricted to the audio spectrum below 15kHz.
> >
> > The LTC6992 does this nicely but isn't precise enough. Same with
> > 555-style timers or switcher chips. I am looking for better 1% and
> > ideally a lot better, including nonlinearity, drift, warts and all. A uC
> > is not suitable either because it should be simple and I need very fine
> > control granularity, down to around 0.1%.
> >
> > Can't use short-lived consumer chips for radios and TV sets and such.
> >
>
> How about a CMOS 555 with a current source to charge the capacitor?
>
> Cheers
>
> Phil Hobbs

Yeah, have a tube of those 1 cell voltage capable Cmos versions. They
don't handle the upper voltage well but they sure do work well in one
cell applications.

Jamie

[Tim Wescott]

Some MCUs follow the PWM section with a selectable delay line, which
gives you sub-clock PWM resolution.

But often you can stand higher error in the higher frequencies than you
can at DC. In that case you can put a sigma-delta modulator between your
drive number and your PWM. I do this often in control loops, because it
works well, it's easy, and it's cheap.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

[Tim Wescott]

TI also sells a DSP-ish chip that has a PWM output with a final delay-
line stage that gives you finer clock resolution.

I know Joerg wants an analog input. _I_ want to tweak Joerg a bit!

[Tim Wescott]

On Thu, 29 May 2014 14:20:26 -0700, Joerg wrote:

A 555 or other teeny thing wrapped with integrating feedback, to hold the
average at precisely what you want? It kinda violates your "one chip"
desire, but at least it can be done with a minimum of small parts.

[whit3rd]

On Thursday, May 29, 2014 6:07:45 PM UTC-7, Joerg wrote:

> John Larkin wrote:

> > How about a sawtooth or triangle waveform and a comparator. Close a
> > feedback loop around that, with a PWM to DC converter; the PWM-DC part
> > can be made very linear.

> That's what I wanted to avoid for real estate reasons.

It's only a dual comparator and a transistor! The first comparator is set
up as a Schmitt trigger with thresholds at +Vs and -Vs; its output drives
a resistor to the base, capacitor from collector to base, emitter to V-.
That makes a triangle wave. The second comparator takes signal in
on one input, and triangle wave on the other, and you're done.

[Joerg]

It's possible but when assuming a master clock of 20MHz going in and I'd
want, say, a 1k granularity that would result in an effective PWM of
only 20kHz. Unless I am understanding something wrong in the datasheet.

http://www.analog.com/static/imported-files/data_sheets/AD7401.pdf

What I'd essentially need is a class D audio modulator but without the
DC cut-off. Unfortunately that's as rare as it is on audio CODECs where
only a few such as the AD1939 can go down to DC without onerous offset
issues or huge drift.

[dagmarg...@yahoo.com]

On Thursday, May 29, 2014 9:10:45 PM UTC-4, Joerg wrote:
> Phil Hobbs wrote:
> > On 5/29/2014 5:20 PM, Joerg wrote:
> >> Folks,
> >>
> >> Does anyone know an IC that can turn a control voltage into PWM and can
> >> handle PWM frequencies in the 50-1000kHz range? Similar to a class D
> >> driver but has to go down to DC. The changes in control would be
> >> restricted to the audio spectrum below 15kHz.
> >>
> >> The LTC6992 does this nicely but isn't precise enough. Same with
> >> 555-style timers or switcher chips. I am looking for better 1% and
> >> ideally a lot better, including nonlinearity, drift, warts and all. A uC
> >> is not suitable either because it should be simple and I need very fine
> >> control granularity, down to around 0.1%.
> >>
> >> Can't use short-lived consumer chips for radios and TV sets and such.
> >>
> >
> > How about a CMOS 555 with a current source to charge the capacitor?
> >
> That could be done but would gradually lead me to the circuit complexity
> (size) of a comparator solution. Because I'd have to control the current
> source over a wide range and very precisely.

The current source would be fixed, not variable "over a wide range."
That's trivial.

555 comparator drift might be a problem, but there might be precision
versions without it.

The 555 is cheap and small enough that it's almost worth using just
for the internal logic...


Cheers,
James Arthur

[Joerg]

Tim Wescott wrote:
> On Fri, 30 May 2014 09:32:27 -0600, Reinhardt Behm wrote:
>
>> Tim Wescott wrote:
>>
>>> On Thu, 29 May 2014 14:20:26 -0700, Joerg wrote:
>>>
>>>> Folks,
>>>>
>>>> Does anyone know an IC that can turn a control voltage into PWM and
>>>> can handle PWM frequencies in the 50-1000kHz range? Similar to a class
>>>> D driver but has to go down to DC. The changes in control would be
>>>> restricted to the audio spectrum below 15kHz.
>>>>
>>>> The LTC6992 does this nicely but isn't precise enough. Same with
>>>> 555-style timers or switcher chips. I am looking for better 1% and
>>>> ideally a lot better, including nonlinearity, drift, warts and all. A
>>>> uC is not suitable either because it should be simple and I need very
>>>> fine control granularity, down to around 0.1%.
>>>>
>>>> Can't use short-lived consumer chips for radios and TV sets and such.
>>> Hey! Microprocessors are simple! You just need to learn some valuable
>>> skills, that's all.
>>>
>>> http://www.c-for-dummies.com/
>> But generating a PWM at 1MHz with a resolution of 0.1% mean you need a
>> base frequency for your counter of 1GHz. I don't know any CPU that could
>> do that.
>
> Some MCUs follow the PWM section with a selectable delay line, which
> gives you sub-clock PWM resolution.
>

If that's the usual silicon delay line deal I don't want it. Took my
lumps there, or rather a client did and when they called me in all I
could do is rip it all out and design an analog solution. The digital
delay section had the noise performance of a pressure-assist loo during
the flush :-)

> But often you can stand higher error in the higher frequencies than you
> can at DC. In that case you can put a sigma-delta modulator between your
> drive number and your PWM. I do this often in control loops, because it
> works well, it's easy, and it's cheap.
>

Which IC do you use for generating the PWM? Creating a number would be
as easy as dropping in an ADC. Most sigma-delta chiops I've seen use a
fairly low clock frequency and you don't get the granularity needed at a
sufficnetly hig PWM frequency. I could drop the upper frequency to
500kHz if hard-pressed but not a lot lower.

[Joerg]

But their timers won't run faster than MLCK and that seriously limits
the granularity if the PWM has to pipe out at a MHz. I'd need almost a
Giggeehoitz. Not that it can't be done but that's a really fat CPU.

[Joerg]

Digital is ok but 1000:1 granularity at a MHz or at least half a MHz
would require a fat processor with really good timer resources.

>> Digital delay generators generally use a clocked coarse width generator
>> with analog interpolation down to picoseconds. Too complex for this app.
>

Not too complex but all the phase noise measurements I did on digital
delay lines so far almost made me throw up.

> TI also sells a DSP-ish chip that has a PWM output with a final delay-
> line stage that gives you finer clock resolution.
>
> I know Joerg wants an analog input. _I_ want to tweak Joerg a bit!
>

My wife's already trying that since a few decades :-)

[Joerg]

I am going to do something like that (but probably not with a 555) if
nothing single-chip comes up. That's the reason for this thread, to see
if there isn't anything out there. I mean, every class-D amp must have a
super-linear PWM generator. It's just that most have the power stages
built in (would be ok, can be left idle) and have lousy or no DC
performance (would not be ok).

[dagmarg...@yahoo.com]

On Friday, May 30, 2014 12:45:25 PM UTC-4, Joerg wrote:

>
> Digital is ok but 1000:1 granularity at a MHz or at least half a MHz
> would require a fat processor with really good timer resources.

Okay, that narrows the field--too fast for a 555!

It's going to be hard to get good linearity from any consumer
part, and it's hard to imagine who'd need it other than class-D
audio.

Cheers,
James Arthur

[Maynard A. Philbrook Jr.]

In article <a697758c-89a9-446b...@googlegroups.com>,
whi...@gmail.com says...

yes, a fixed frequency PWM 0..100% generator, use that myself. :)

Jamie

[Joerg]

Sure, I know how to do it analog. But it's not quite as simple as it
looks. Offsets, drift, regulators for super-stable rails et cetera. I
thought there's got to be a solution-in-a-can because of all the class D
amps these days. But the problem seems to be DC because audio doesn't
need that. So maybe there isn't a suitable IC.

[Joerg]

dagmarg...@yahoo.com wrote:
> On Thursday, May 29, 2014 9:10:45 PM UTC-4, Joerg wrote:
>> Phil Hobbs wrote:
>>> On 5/29/2014 5:20 PM, Joerg wrote:
>>>> Folks,
>>>>
>>>> Does anyone know an IC that can turn a control voltage into PWM and can
>>>> handle PWM frequencies in the 50-1000kHz range? Similar to a class D
>>>> driver but has to go down to DC. The changes in control would be
>>>> restricted to the audio spectrum below 15kHz.
>>>>
>>>> The LTC6992 does this nicely but isn't precise enough. Same with
>>>> 555-style timers or switcher chips. I am looking for better 1% and
>>>> ideally a lot better, including nonlinearity, drift, warts and all. A uC
>>>> is not suitable either because it should be simple and I need very fine
>>>> control granularity, down to around 0.1%.
>>>>
>>>> Can't use short-lived consumer chips for radios and TV sets and such.
>>>>
>>> How about a CMOS 555 with a current source to charge the capacitor?
>>>
>> That could be done but would gradually lead me to the circuit complexity
>> (size) of a comparator solution. Because I'd have to control the current
>> source over a wide range and very precisely.
>
> The current source would be fixed, not variable "over a wide range."
> That's trivial.
>

Then the comparator in the IC must do the job and be good, and they
normally aren't.

> 555 comparator drift might be a problem, but there might be precision
> versions without it.
>

That's the trade-off.

> The 555 is cheap and small enough that it's almost worth using just
> for the internal logic...
>

Yes, or go with an analog solution like whit3rd mentioned. But then
you'll have to make sure the offsets and all that are handled which
makes it all not as trivial and low in real estate as it looks.

[Joerg]

That's the reason for starting this thread: Class D. They use PWM in the
hundreds of MHZ in order to get away with small magnetics yet it's quite
linear.

The DC stability is the issue, most audio ICs barely have any to write
home about.

[Lasse Langwadt Christensen]

with DS is hard to talk about pwm frequency, it has noise shaping so the
switching noise gets pushed to higher frequencies. i.e if you are exactly midrange the "pwm frequency" would be 10MHz

with a brick wall reconstructions filter you would normally gain 3dB every
time you double the sampling frequency, with a second order deltasigma you
gain ~15dB, first order ~9dB

>
> http://www.analog.com/static/imported-files/data_sheets/AD7401.pdf
>
> What I'd essentially need is a class D audio modulator but without the
>
> DC cut-off. Unfortunately that's as rare as it is on audio CODECs where
>
> only a few such as the AD1939 can go down to DC without onerous offset
>
> issues or huge drift.
>

if you can live with the higher switching frequency I think deltasigma
would do that

-Lasse

[Joerg]

I can't live with a switching frequency that gets much past a MHz in
certain areas. It will cause large losses in the attached power
electronics. I'd like the PWM to be at least somewhat constant in
frequency. It isn't critical though, if it varies even 50% that would be
ok. But not a lot more.

[Tim Wescott]

Are you sure they aren't digital inside, with 2nd- or 3rd-order sigma-
deltas to make up the bit count?

[Tim Wescott]

You originally said 50-1000kHz. At 50, I'd use an ST ARM-core micro
running at 48 or 50MHz.

If _all_ you're doing is generating PWM at 500kHz you could probably
still do that. You'd get 1% or 2% steps in your PWM (some of those chips
limit the PWM clock to 1/2 the core clock). To get delta-sigma you'd
need to use DMA, though, which is getting beyond simple for most folks.

On the bright side, at a 500kHz PWM frequency and a 15kHz "I care"
bandwidth, a simple 1st-order delta-sigma modulator would buy you roughly
five bits of precision -- at that point, your error drivers are probably
asymmetries in the power circuitry, rather than the actual behavior of
the PWM.

[Tim Wescott]

On Fri, 30 May 2014 09:47:56 -0700, Joerg wrote:

No DC performance can't be fixed -- but lousy DC performance could be
fixed with feedback, assuming there's an appropriate loop frequency to
make it easy, yet have enough authority at low frequencies to clean up
the crap.

(And no microprocessor -- see, I can propose analog solutions to analog
problems).

[Joerg]

Yes, that's the range I need this to be able to operate in.

> If _all_ you're doing is generating PWM at 500kHz you could probably
> still do that. You'd get 1% or 2% steps in your PWM (some of those chips
> limit the PWM clock to 1/2 the core clock). To get delta-sigma you'd
> need to use DMA, though, which is getting beyond simple for most folks.
>

It has to have 0.1% granularity or better.

> On the bright side, at a 500kHz PWM frequency and a 15kHz "I care"
> bandwidth, a simple 1st-order delta-sigma modulator would buy you roughly
> five bits of precision -- at that point, your error drivers are probably
> asymmetries in the power circuitry, rather than the actual behavior of
> the PWM.
>

Not really. My most recent project contains a uC-generated PWM at 12-bit
granularity. Of course, that can only run at 2kHz. We could still double
the master clock for a 4kHz PWM at same granularity but the power
consumption penalty would be too much for this application.

[Joerg]

Mostly not sure because they are usually releasing very little
information about the modulator. But they sure are good in noise
performance and granularity. Not always quite up to par with linear amps
but close.

[Joerg]

That's a problem, my signal path goes all the way to DC and the loop
would be a pain.

> (And no microprocessor -- see, I can propose analog solutions to analog
> problems).
>

And I did a project with a uC in there last month. Plus one the month
before. But ... other than prescribing how I want the code to flow and
what the individual chunks of it should do the programming was done by
others.

I like things analog if possible. Like my new mountain bike (which by
now looks like it came back from a war zone), in contrast to cars those
do not contain any uC. On higher-end road bikes that is already starting
to change where some have electronic shifting. Couldn't believe it.

[George Herold]

On Friday, May 30, 2014 11:32:27 AM UTC-4, Reinhardt Behm wrote:
> Tim Wescott wrote:

<snip>

>
> > Hey! Microprocessors are simple! You just need to learn some valuable
> > skills, that's all.
> >
> > http://www.c-for-dummies.com/
>
> But generating a PWM at 1MHz with a resolution of 0.1% mean you need a base
> frequency for your counter of 1GHz. I don't know any CPU that could do that.

Only if you needed it "right away", if you could average 100 cycles,
then you could do it with 10MHz.

George H.
>
> --
> Reinhardt Behm

[rickman]

On 5/30/2014 10:15 AM, Joerg wrote:
> John Larkin wrote:
>> On Thu, 29 May 2014 18:07:45 -0700, Joerg <inv...@invalid.invalid> wrote:
>>

>>> John Larkin wrote:
>>>> On Thu, 29 May 2014 14:20:26 -0700, Joerg <inv...@invalid.invalid>

>>>> wrote:
>>>>
>>>>> Folks,
>>>>>
>>>>> Does anyone know an IC that can turn a control voltage into PWM and can
>>>>> handle PWM frequencies in the 50-1000kHz range? Similar to a class D
>>>>> driver but has to go down to DC. The changes in control would be
>>>>> restricted to the audio spectrum below 15kHz.
>>>>>
>>>>> The LTC6992 does this nicely but isn't precise enough. Same with
>>>>> 555-style timers or switcher chips. I am looking for better 1% and
>>>>> ideally a lot better, including nonlinearity, drift, warts and all. A uC
>>>>> is not suitable either because it should be simple and I need very fine
>>>>> control granularity, down to around 0.1%.
>>>>>
>>>>> Can't use short-lived consumer chips for radios and TV sets and such.

>>>> How about a sawtooth or triangle waveform and a comparator. Close a
>>>> feedback loop around that, with a PWM to DC converter; the PWM-DC part
>>>> can be made very linear.
>>>>
>>> That's what I wanted to avoid for real estate reasons. But if I hafta
>>> I'll do it.
>>
>> If you want 0.1% accuracy, you might be able to do it open-loop, with a very
>> linear ramp, but it will be hard at that frequency. If you only want 0.1%
>> resolution ("granularity"?) it's not so bad.
>>
>> Can you use delta-sigma? There are some integrated d-s modulators around.
>>
>
> I could but then I'd have to build a one-shot that stretches the pulses
> into a very precise length and that's almost the same kind of challenge
> as building my own PWM generator (needs too much space).

Can the pulse width be dithered or does each pulse width have to adjust
to within 0.1% of the needed value? I think a digital solution could do
this if you just need the average pulse width to match.

--

Rick

[rickman]

This is starting to sound like a job for FPGAman! Where's my cape?
Durn, at the cleaners after that messy SERDES job.

--

Rick

[George Herold]

On Friday, May 30, 2014 1:00:16 PM UTC-4, Joerg wrote:
> dagmarg...@yahoo.com wrote:
>
> > On Friday, May 30, 2014 12:45:25 PM UTC-4, Joerg wrote:
>
> >
>
> >> Digital is ok but 1000:1 granularity at a MHz or at least half a MHz
>
> >> would require a fat processor with really good timer resources.
>
> >
>
> > Okay, that narrows the field--too fast for a 555!
>
> >
>
> > It's going to be hard to get good linearity from any consumer
> > part, and it's hard to imagine who'd need it other than class-D
> > audio.
>
> That's the reason for starting this thread: Class D. They use PWM in th

> hundreds of MHZ in order to get away with small magnetics yet it's quite
> linear.
>
> The DC stability is the issue, most audio ICs barely have any to write
> home about.

Well I don't really know what I'm suggesting,
but can you patch up the DC response of an audio IC?
(maybe someone already did that?)
George H.

[Joerg]

Dither is a problem. If it's dithering between 2-3 consecutive pulses,
maybe, but it would be a serious compromise.

This does not mean I am ruling anything out at this point, it's just
that I'd first like to see if there is a class-D chip that can be
pressed into service. Thise have very clean PWM, just not down to DC
because offset voltages and stuff aren't important for audio.

[Joerg]

I bet an FPGA with some minor analog sprinkles around it could do this
job nicely. But that would be like using a Porsche to go to the grocery
store.

[John Larkin]

That's sort of a variation on delta-sigma: PWM, but dither it one
clock to interpolate the output. Full delta-sigma has too many
transitions.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[Joerg]

With some CODECs you can. However, so far all the ones I looked at
except for the AD1939 have sloppy offset specs. But this was for another
project, it can't do PWM.

[Joerg]

That would have the phase noise performance of a steam locomotive :-)

[John Larkin]

We have one product where we used 16 channels of 1 GHz SERDES to make
the equivalent of 16 PWMs, each with 1 ns resolution. We can make
pulses of any delay and width by streaming clever patterns into the
SERDES fifos.

[rickman]

And what is wrong with that? Porche makes a mom-mobile! FPGAs come in
lean, mean sizes for any budget. If you are short on board space they
even come in some pretty teeny-tiny packages if you don't mind very fine
pitch BGA type things. Otherwise they just come in small packages.

Actually a digital approach would need either the comparator that you
seem to not like or an ADC which might be a better match. If you need
up to a 1 MHz pulse rate I assume you would need a 1 MHz ADC sample rate
which is not too hard, but it would start to use a few mA. It's been a
while since I've looked at ADCs at that rate but I know they are not
hard to find, especially with only 10 or 12 bits.

The rest is easy... 1 GHz clock might be a bit tricky in one of the
very low power FPGAs, but maybe. The dual latches used for DDR work
might just enable this on a pretty low power device. It would be an
interesting design task. Either way one of the conventional FPGAs could
handle this easily I'm sure and the smaller ones don't suck so much
power. I could poke around a bit if you are interested.

--

Rick

[Joerg]

rickman wrote:
> On 5/30/2014 3:02 PM, Joerg wrote:
>> rickman wrote:
>>> On 5/30/2014 12:42 PM, Joerg wrote:
>>>> Lasse Langwadt Christensen wrote:
>>>>> Den fredag den 30. maj 2014 17.32.27 UTC+2 skrev Reinhardt Behm:
>>>
>>>>>>
>>>>>> But generating a PWM at 1MHz with a resolution of 0.1% mean you need
>>>>>> a base
>>>>>> frequency for your counter of 1GHz. I don't know any CPU that could
>>>>>> do that.
>>>>>
>>>>> he did say the input was limited to 15KHz, so 2*15K*1000 >= 30MHz
>>>>> plenty of cpus that can do that
>>>>>
>>>>
>>>> But their timers won't run faster than MLCK and that seriously limits
>>>> the granularity if the PWM has to pipe out at a MHz. I'd need almost a
>>>> Giggeehoitz. Not that it can't be done but that's a really fat CPU.
>>>
>>> This is starting to sound like a job for FPGAman! Where's my cape?
>>> Durn, at the cleaners after that messy SERDES job.
>>>
>>
>> I bet an FPGA with some minor analog sprinkles around it could do this
>> job nicely. But that would be like using a Porsche to go to the grocery
>> store.
>

> And what is wrong with that? Porche makes a mom-mobile! ...


For the ritzy crowd with beaucoup disposable income, yes.


> ... FPGAs come in

> lean, mean sizes for any budget. If you are short on board space they
> even come in some pretty teeny-tiny packages if you don't mind very fine
> pitch BGA type things. Otherwise they just come in small packages.
>

It is like shooting a fly with a 50mm canon. The fly will be killed dead
for sure, as John Wayne would say, but it's overkill. We have no people
who can program FPGA. It ain't in the budget (yet).

> Actually a digital approach would need either the comparator that you
> seem to not like or an ADC which might be a better match. If you need
> up to a 1 MHz pulse rate I assume you would need a 1 MHz ADC sample rate
> which is not too hard, but it would start to use a few mA. It's been a
> while since I've looked at ADCs at that rate but I know they are not
> hard to find, especially with only 10 or 12 bits.
>

The required rate of change is only up to about 15kHz and transferring
the analog control signal to digital at 100ksps or so is a piece of
cake. Can be done with a very tiny ADC.

> The rest is easy... 1 GHz clock might be a bit tricky in one of the
> very low power FPGAs, but maybe. The dual latches used for DDR work
> might just enable this on a pretty low power device. It would be an
> interesting design task. Either way one of the conventional FPGAs could
> handle this easily I'm sure and the smaller ones don't suck so much
> power. I could poke around a bit if you are interested.
>

Maybe not just yet because I want to find out whether we can just plop
in a class-D chip. We don't have a budget for an extra FPGA design for
this phase. But that could change when this becomes a product and I'll
keep you in mind (assuming you can legally do freelance work, as in not
bound by an employer).

[rickman]

I'm not clear on your answer. To make sure you understand what I am
suggesting... You can use a slower counter clock if you dither the
pulse width. In reality you would need to use some feedback similar to
a sigma-delta circuit. The pulse width would only vary from ideal by a
fraction of a count at any one time and the error could be accumulated
and used to add a delta on the next pulse width. Another plus is that
the feedback loop can be internal to the digital circuit since the error
source is the low order bits that are being truncated.

I think John Larkin has picked up on this judging from his post. The
question is whether the small instantaneous deviations will make a
difference. Similar to sigma-delta the "noise" would be at a high
frequency.

--

Rick

[Joerg]

What this means is that my filter after the power stage would have to
roll off at lower frequencies, to combat the resulting noise. That lead
to two not so nice effects: Larger magnetics in a product where small
size is very important. Also more ringing upon rapid control signal
changes which becomes harder to mitigate the lower the ringing frequency is.

[rickman]

On 5/30/2014 3:35 PM, Joerg wrote:
> rickman wrote:
>> On 5/30/2014 3:02 PM, Joerg wrote:
>>> rickman wrote:
>>>> On 5/30/2014 12:42 PM, Joerg wrote:
>>>>> Lasse Langwadt Christensen wrote:
>>>>>> Den fredag den 30. maj 2014 17.32.27 UTC+2 skrev Reinhardt Behm:
>>>>
>>>>>>>
>>>>>>> But generating a PWM at 1MHz with a resolution of 0.1% mean you need
>>>>>>> a base
>>>>>>> frequency for your counter of 1GHz. I don't know any CPU that could
>>>>>>> do that.
>>>>>>
>>>>>> he did say the input was limited to 15KHz, so 2*15K*1000 >= 30MHz
>>>>>> plenty of cpus that can do that
>>>>>>
>>>>>
>>>>> But their timers won't run faster than MLCK and that seriously limits
>>>>> the granularity if the PWM has to pipe out at a MHz. I'd need almost a
>>>>> Giggeehoitz. Not that it can't be done but that's a really fat CPU.
>>>>
>>>> This is starting to sound like a job for FPGAman! Where's my cape?
>>>> Durn, at the cleaners after that messy SERDES job.
>>>>
>>>
>>> I bet an FPGA with some minor analog sprinkles around it could do this
>>> job nicely. But that would be like using a Porsche to go to the grocery
>>> store.
>>
>> And what is wrong with that? Porche makes a mom-mobile! ...
>
>
> For the ritzy crowd with beaucoup disposable income, yes.

Have you looked at the price of a Honda lately? There are *no* cheap cars.

>> ... FPGAs come in
>> lean, mean sizes for any budget. If you are short on board space they
>> even come in some pretty teeny-tiny packages if you don't mind very fine
>> pitch BGA type things. Otherwise they just come in small packages.
>>
>
> It is like shooting a fly with a 50mm canon. The fly will be killed dead
> for sure, as John Wayne would say, but it's overkill. We have no people
> who can program FPGA. It ain't in the budget (yet).

You can make any analogy you wish, but mostly people just don't "get"
FPGAs. You have no people with FPGA experience, so I expect you won't
be learning much more about them in the future. They really aren't so
hard.

>> Actually a digital approach would need either the comparator that you
>> seem to not like or an ADC which might be a better match. If you need
>> up to a 1 MHz pulse rate I assume you would need a 1 MHz ADC sample rate
>> which is not too hard, but it would start to use a few mA. It's been a
>> while since I've looked at ADCs at that rate but I know they are not
>> hard to find, especially with only 10 or 12 bits.
>>
>
> The required rate of change is only up to about 15kHz and transferring
> the analog control signal to digital at 100ksps or so is a piece of
> cake. Can be done with a very tiny ADC.

The requirements seem to be a bit vague. So the sample rate would only
need to be 100 ksps? So why is the pulse rate up to 1 MHz? Can the
pulse widths be dithered across 10 pulses? That can lower the clock
rate by 10x.

>> The rest is easy... 1 GHz clock might be a bit tricky in one of the
>> very low power FPGAs, but maybe. The dual latches used for DDR work
>> might just enable this on a pretty low power device. It would be an
>> interesting design task. Either way one of the conventional FPGAs could
>> handle this easily I'm sure and the smaller ones don't suck so much
>> power. I could poke around a bit if you are interested.
>>
>
> Maybe not just yet because I want to find out whether we can just plop
> in a class-D chip. We don't have a budget for an extra FPGA design for
> this phase. But that could change when this becomes a product and I'll
> keep you in mind (assuming you can legally do freelance work, as in not
> bound by an employer).

Yeah, I get that. Simpler is better and if you understand it well, that
makes it simpler.

No employer other than myself. :) Happy to help if you need it.

--

Rick

[John Larkin]

On Fri, 30 May 2014 12:35:10 -0700, Joerg <inv...@invalid.invalid>

I know a guy, if you're ever interested. We swap Visio block diagrams
to define the function, and then he codes it.

Some of the so-called CPLDs are actually small FPGAs with internal
flash, cost roughly $1.50 in low volumes. It's liberating to have all
that logic available.

[Joerg]

There are. A friend bought a new Kia Soul for around $13k. It is a
remarkably practical car. My SUV was just shy of $18k in 1997, new, and
one can probably find a similar one for maybe $3-5k more these days.

It doesn't have to be a fancy car.

>
>>> ... FPGAs come in
>>> lean, mean sizes for any budget. If you are short on board space they
>>> even come in some pretty teeny-tiny packages if you don't mind very fine
>>> pitch BGA type things. Otherwise they just come in small packages.
>>>
>>
>> It is like shooting a fly with a 50mm canon. The fly will be killed dead
>> for sure, as John Wayne would say, but it's overkill. We have no people
>> who can program FPGA. It ain't in the budget (yet).
>
> You can make any analogy you wish, but mostly people just don't "get"
> FPGAs. You have no people with FPGA experience, so I expect you won't
> be learning much more about them in the future. They really aren't so
> hard.
>

First I'll learn uC some more. I grok their HW innards but am a bit
rocky when programming. FPGA would be next in line since there is less
opportunity to use one in my field. I do get peeks into the world of
FPGA sometimes because I always work for several clients simultaneously.
Some are bigger companies who have FPGA coders.

>
>>> Actually a digital approach would need either the comparator that you
>>> seem to not like or an ADC which might be a better match. If you need
>>> up to a 1 MHz pulse rate I assume you would need a 1 MHz ADC sample rate
>>> which is not too hard, but it would start to use a few mA. It's been a
>>> while since I've looked at ADCs at that rate but I know they are not
>>> hard to find, especially with only 10 or 12 bits.
>>>
>>
>> The required rate of change is only up to about 15kHz and transferring
>> the analog control signal to digital at 100ksps or so is a piece of
>> cake. Can be done with a very tiny ADC.
>
> The requirements seem to be a bit vague. So the sample rate would only
> need to be 100 ksps? So why is the pulse rate up to 1 MHz? Can the
> pulse widths be dithered across 10 pulses? That can lower the clock
> rate by 10x.
>

In pretty much any a PWM-driven power stage the PWM frequency must be
several times higher than the highest spectral components in your
control signal. You could theoretically get away with it at the Nyquist
limit but the filter requirements would be onerous. Remember that the
filter is always in the power path so everything gets big, heavy and
expensive. Keeping the PWM frequency well north of 10x makes this job
almost infinitely easier.

>
>>> The rest is easy... 1 GHz clock might be a bit tricky in one of the
>>> very low power FPGAs, but maybe. The dual latches used for DDR work
>>> might just enable this on a pretty low power device. It would be an
>>> interesting design task. Either way one of the conventional FPGAs could
>>> handle this easily I'm sure and the smaller ones don't suck so much
>>> power. I could poke around a bit if you are interested.
>>>
>>
>> Maybe not just yet because I want to find out whether we can just plop
>> in a class-D chip. We don't have a budget for an extra FPGA design for
>> this phase. But that could change when this becomes a product and I'll
>> keep you in mind (assuming you can legally do freelance work, as in not
>> bound by an employer).
>
> Yeah, I get that. Simpler is better and if you understand it well, that
> makes it simpler.
>
> No employer other than myself. :) Happy to help if you need it.
>

Good. It's similar on another project where I did everything with some
hardware and a PC last year. But if all goes well we will develop the
real product this fall and then a uC specialist will become involved
whom we could not use for cost reasons so far. Luckily he is local,
about 20 minutes via mountain bike or car (40min with a regular bicycle).

[Joerg]

John Larkin wrote:
> On Fri, 30 May 2014 12:35:10 -0700, Joerg <inv...@invalid.invalid>
> wrote:
>
>> rickman wrote:

[...]

>>> ... FPGAs come in
>>> lean, mean sizes for any budget. If you are short on board space they
>>> even come in some pretty teeny-tiny packages if you don't mind very fine
>>> pitch BGA type things. Otherwise they just come in small packages.
>>>
>> It is like shooting a fly with a 50mm canon. The fly will be killed dead
>> for sure, as John Wayne would say, but it's overkill. We have no people
>> who can program FPGA. It ain't in the budget (yet).
>
> I know a guy, if you're ever interested. We swap Visio block diagrams
> to define the function, and then he codes it.
>
> Some of the so-called CPLDs are actually small FPGAs with internal
> flash, cost roughly $1.50 in low volumes. It's liberating to have all
> that logic available.
>

Yes, they sure are tempting. In the past FPGA have always turned me off
because they were either power guzzlers or went unobtainium all the
time. The only series that I really liked was from Intel with true CMOS
behavior, meaning power went to almost zero at low clock. But then Intel
dropped the ball again. I had almost used them in a design. That could
have resulted in a serious black eye. But what I understood from what
Rick said in the past this has become better where some series will be
around for longer.

Many of my designs require 20 or 30 years of production life. That rules
out a lot of stuff that others take for granted.

[Lasse Langwadt Christensen]

so clock it at 2MHz, I still think it'll be close


-Lasse


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[Tim Wescott]

Depending on who you ask, it's not "like" a sigma-delta -- it _is_ a
sigma-delta. Just because _most_ sigma-delta converters use 1-bit D/A or
A/D conversion doesn't mean they all do.

It's exactly what I was suggesting.

[Tim Wescott]

What are you controlling that high-frequency noise matters so much?
Nearly all the plants that I encounter are intrinsically low-pass.

If you're filtering to get the bulk of the PWM out, then much of the
sigma-delta noise will be in the stopband of the filter, even if it's of
lower frequency than the PWM. Particularly if the sigma-delta modulator
uses a 2nd- or 3rd-order filter.

[Tim Wescott]

Well... Why? You have analog in, and if you're driving your own final
amp, PWM out. So you can difference the PWM and your analog command
signal, feed that to an integrator of suitable gain, and drive the
amplifier input with that plus your analog command signal.

It seems like a low component count slam-dunk to me, unless there's
something that you're doing that is outside of my assumptions.

[Lasse Langwadt Christensen]

exactly, sigma-delta is about getting from one resolution to another while shaping the quantization error towards higher frequencies

the reason for 1 bit is that then linearity comes for "free"

-Lasse

[Tim Wescott]

If I may interject -- this is the sort of FPGA project that I'd sign up
to doing, confident that I could make it work just fine. And keep in
mind -- when I do HDL I get involved in conversations with folks like
Rick that basically start out with "You're a software engineer, aren't
you?" and go downhill from there.

This ain't rocket science!

[rickman]

On 5/30/2014 4:31 PM, Tim Wescott wrote:
> If I may interject -- this is the sort of FPGA project that I'd sign up
> to doing, confident that I could make it work just fine. And keep in
> mind -- when I do HDL I get involved in conversations with folks like
> Rick that basically start out with "You're a software engineer, aren't
> you?" and go downhill from there.
>
> This ain't rocket science!

Please don't accuse me of being biased toward software people. I don't
assume they are incapable of understanding something outside their
field. I always wait for them to misunderstand something about hardware
before I correct them. I know any number of software folks who are very
capable of FPGA work just like I know hard core board level designers
who can learn FGPA work as well.

In fact someone came to the FPGA group asking for help writing a "hello
world" program in an FPGA. Several of us tried to explain how hard it
would be to write HDL as if it were software to produce the program...
he showed us wrong. We gave him a little help in the first steps of
coding, but he got it up and working very quickly and went on to
complete his project which was a technology demonstration.

He was appreciative of my help and tried to get his boss to approve a
consulting contract for training, but they didn't want to spend the
funds. Instead he talked them into sending me $500 for the pre-sales
support I had given him for free. lol So I sent him a polo shirt.

BTW, I have always maintained that FPGA work is not rocket science. It
is usually the software or board level designers who claim FPGA work is
too hard unless you "really need" it. I say it is not hard to design,
debug or maintain, just different in some ways. FPGAs are not used as
often as useful because of the lack of good understanding of their true
benefits and capabilities.

--

Rick

[rickman]

I think you have the availability issue backwards. FPGA vendors have
some of the longest lived products in the IC world. It is not at all
uncommon to design in an FPGA when it is new and not get an EOL notice
for well over 10 years. You were dealing with Intel who dabble in
secondary business areas and then close up shop when they lose interest.
I don't know that Intel has ever shipped a production FPGA so I would
hardly call them an FPGA vendor in any sense of the word.

> Many of my designs require 20 or 30 years of production life. That rules
> out a lot of stuff that others take for granted.

If you need a 20 year production life, what parts *can* you use? Does
LTI give any assurance of a 20 year product life? What MCUs or DSPs are
around after 20 years? Of these parts, I would be much less worried
about FPGAs being around in 20 years although that is likely stretching
it. If you need 30 years... I guess I don't know, I only been in the
business for 40 years and don't expect to be around myself for another
30... in the large sense. ;)

BTW, there are several device families around with "true CMOS" power
consumption. If you don't need 1 GHz there are FPGAs that are lower
power than many ARM MCUs.

--

Rick

[Tim Wescott]

On Fri, 30 May 2014 16:48:15 -0400, rickman wrote:

> On 5/30/2014 4:31 PM, Tim Wescott wrote:
>> If I may interject -- this is the sort of FPGA project that I'd sign up
>> to doing, confident that I could make it work just fine. And keep in
>> mind -- when I do HDL I get involved in conversations with folks like
>> Rick that basically start out with "You're a software engineer, aren't
>> you?" and go downhill from there.
>>
>> This ain't rocket science!
>
> Please don't accuse me of being biased toward software people.

That comment wasn't aimed at you -- I had a customer insist that I close
a control loop in an FPGA instead of on a processor. I couldn't even
talk them around to putting a MicroBlaze or whatever into their FPGA.
When I got it working and it made its way to the in-house FPGA people,
the first thing they said was "You're a software guy, aren't you?"

(It had some gawdawful 16-level multiplexer that I couldn't figure out
how to break into smaller pieces or pipeline, which was by far the source
of the most delay in the circuit, so it was a fair criticism).

[rickman]

On 5/30/2014 5:35 PM, Tim Wescott wrote:
> On Fri, 30 May 2014 16:48:15 -0400, rickman wrote:
>
>> On 5/30/2014 4:31 PM, Tim Wescott wrote:
>>> If I may interject -- this is the sort of FPGA project that I'd sign up
>>> to doing, confident that I could make it work just fine. And keep in
>>> mind -- when I do HDL I get involved in conversations with folks like
>>> Rick that basically start out with "You're a software engineer, aren't
>>> you?" and go downhill from there.
>>>
>>> This ain't rocket science!
>>
>> Please don't accuse me of being biased toward software people.
>
> That comment wasn't aimed at you --

I think my comment made it sound like I was taking it personally.
Written word vs. spoken. Sorry.

> I had a customer insist that I close
> a control loop in an FPGA instead of on a processor. I couldn't even
> talk them around to putting a MicroBlaze or whatever into their FPGA.
> When I got it working and it made its way to the in-house FPGA people,
> the first thing they said was "You're a software guy, aren't you?"
>
> (It had some gawdawful 16-level multiplexer that I couldn't figure out
> how to break into smaller pieces or pipeline, which was by far the source
> of the most delay in the circuit, so it was a fair criticism).

I think that is more an issue of experience. I'm no guru of FPGAs
really. I have done my share of work with them and understand lots of
issues like the one you had. But if you are trying to optimize things
there are all sorts of tricks to use. Mostly it is better to *not*
optimize, but to design cleanly. Optimization can be expensive and
breaks easily.

Muxes in particular are one of the more awkward things to implement in
an FPGA. There is no real way to optimize them unless there are missing
pieces, for example a barrel shifter doesn't need the full N inputs to
every output bit. I have also minimized them by using an adder as part
of the mux. Most FPGAs have 4 input LUTs, a mux just has three inputs,
so the fourth can be used as an output enable. Two muxes feeding an
adder can have enables which allow the adder to be used as another mux.
Or you can use four 2 input muxes with enables to feed a 4-lut which
is just a 4-or gate. The trick is getting the tools to give you then
when you are coding in an HDL, lol.

Otherwise muxes eat LUTs for breakfast, lunch and dinner. The best way
to optimize them is to avoid them as much as possible.

--

Rick

[Joerg]

It can be done this way, although the output in the simulation isn't
very clean around the min/max values of the drive signal.

[simulation file]

Just came back from a gnarly mountain bike ride. Got a blister on the
right palm from all the handlebar wrestling. That's a pain when the
computer mouse is on the right, ouch, ouch ...

[Joerg]

That's where I can continue talking. But the plant in this case is
finicky and light, plus nasty resonances here and there.

> If you're filtering to get the bulk of the PWM out, then much of the
> sigma-delta noise will be in the stopband of the filter, even if it's of
> lower frequency than the PWM. Particularly if the sigma-delta modulator
> uses a 2nd- or 3rd-order filter.
>

Stopband is a pretty gradual thing when you can't go past 3rd order on
the output filter. This application is sensitive to noise because the
load is super fast.

[rickman]

On 5/30/2014 5:35 PM, Tim Wescott wrote:

BTW, if you are ever in that position again, feel free to email me a
question or two. I don't have to be on the clock for every little nit.

--

Rick

[Lasse Langwadt Christensen]

all deltasigmas have "issue" when you get very close to the rails, though I'd think pwm also have a similar problem

>
>
> [simulation file]
>

I just threw that together to show deltasigma, I'd expect an AD7400 to
perform better

>
>
> Just came back from a gnarly mountain bike ride. Got a blister on the
>
> right palm from all the handlebar wrestling. That's a pain when the
>
> computer mouse is on the right, ouch, ouch ...
>

I used to work with a guy that two mouses, one for each hand. He claimed it was very quick to get used to switching between them

-Lasse

[Joerg]

We also had it happen with a big medical system. Forgot which vendor but
all they could offer was to pour it into a new (more expensive) FPGA
series which would have meant a major relayout. So we poured it into our
own ASIC instead and that has no EOL issue.

>
>> Many of my designs require 20 or 30 years of production life. That rules
>> out a lot of stuff that others take for granted.
>

> If you need a 20 year production life, what parts *can* you use? ...


Tons. For example, I used CD4000 logic extensively. In the mid-90's a
Fairchild engineer told me that would be a stupid decision, they'd go
obsolete, I should use their single-package logic. Well, most of this is
still in production. Then staples such as the LM324, those are here to
stay. Also MMBT3904, BFS17, and so on. I just used a BFR92 on a new
design. The first time I used one I was in the mid-80's and even then it
wasn't exactly new.


> ... Does LTI give any assurance of a 20 year product life?


LTC? Yes, pretty much. Before they call off anything they try to contact
anyone who has ever bought it to see if it's ok.


> ... What MCUs or DSPs are
> around after 20 years? ...


8051. That's why this is one of my favorites.


> ... Of these parts, I would be much less worried

> about FPGAs being around in 20 years although that is likely stretching
> it. If you need 30 years... I guess I don't know, I only been in the
> business for 40 years and don't expect to be around myself for another
> 30... in the large sense. ;)
>

Some of my designs have already celebrated their 20th in production and
no end in sight.

> BTW, there are several device families around with "true CMOS" power
> consumption. If you don't need 1 GHz there are FPGAs that are lower
> power than many ARM MCUs.
>

That would be nice.

[Joerg]

The load is highly non-linear and very capacitive in behavior. So yeah,
you could do a feedback thing with a separate lowpass to close the loop
and call it good. But it may not be as good as going in with a clean PWM
in the first place, adds a layer of risk that can (hopefully) be avoided.

Also, it's HV stuff so will be noisy as hell.

[Joerg]

Lasse Langwadt Christensen wrote:

Not really. For example, right now I have it running on the simulator
with the LTC6992. Performs beautifully, very linear, but that chip has
quite high tolerances in the modulation factor. I could compensate for
that with demodulation plus a local loop and will probably do so if I
don't find anything better. However, that adds a lot of parts.

>>
>> [simulation file]
>>
>
> I just threw that together to show deltasigma, I'd expect an AD7400
> to perform better
>
>>
>> Just came back from a gnarly mountain bike ride. Got a blister on
>> the
>>
>> right palm from all the handlebar wrestling. That's a pain when the
>>
>>
>> computer mouse is on the right, ouch, ouch ...
>>
>
> I used to work with a guy that two mouses, one for each hand. He
> claimed it was very quick to get used to switching between them
>

I can use a mouse with either hand and before moving my office one room
down the hallway had the mouse on the left. It drove my sister crazy
when she was visiting. Now it's on the right and there is hardly space
for it on the left. Oh well, it'll heal. Problem is, I want to do
another much longer ride on the weekend.

[rickman]

On 5/30/2014 8:10 PM, Joerg wrote:
> rickman wrote:
>>

>> I think you have the availability issue backwards. FPGA vendors have
>> some of the longest lived products in the IC world. It is not at all
>> uncommon to design in an FPGA when it is new and not get an EOL notice
>> for well over 10 years. You were dealing with Intel who dabble in
>> secondary business areas and then close up shop when they lose interest.
>> I don't know that Intel has ever shipped a production FPGA so I would
>> hardly call them an FPGA vendor in any sense of the word.
>>
>
> We also had it happen with a big medical system. Forgot which vendor but
> all they could offer was to pour it into a new (more expensive) FPGA
> series which would have meant a major relayout. So we poured it into our
> own ASIC instead and that has no EOL issue.

Don't believe that for a moment! ASICs require a fab to be made. The
only FPGA I have ever had go EOL was because the fab house was closing
that fab line. FPGA makers don't build their own fabs like most chip
makers these days. ASICs are made on the same lines. When the fab
closes all the product either ends or goes to another fab which means
they have to work the process which is more NRE.

I'm curious about your story. Yes, FPGAs go EOL, but like I said not
remotely short lived. I would expect this design was either a long time
in production or they picked an FPGA that was already long in the tooth.

>> If you need a 20 year production life, what parts *can* you use? ...
>
>
> Tons. For example, I used CD4000 logic extensively. In the mid-90's a
> Fairchild engineer told me that would be a stupid decision, they'd go
> obsolete, I should use their single-package logic. Well, most of this is
> still in production. Then staples such as the LM324, those are here to
> stay. Also MMBT3904, BFS17, and so on. I just used a BFR92 on a new
> design. The first time I used one I was in the mid-80's and even then it
> wasn't exactly new.

Your example is CD4000 SSI/MSI logic? So why don't you build your
current design with those parts? lol I mean a part that is a bit more
complex. What MCUs have you used for 20 years other than the 8051?
Many MCU parts go obsolete in 10 years if not shorter. I've seen DSP
chips that lasted less than 5 years.

I read a thread the other day that mentioned a vendor who had a list of
long life products they would commit to making for 10 years or so. I
can't remember where it was. The vendor may have been Motorola.

>> ... Does LTI give any assurance of a 20 year product life?
>
>
> LTC? Yes, pretty much. Before they call off anything they try to contact
> anyone who has ever bought it to see if it's ok.

Yes, well everyone does that... although it is not a question really.
So if you tell LTI you are still using the part they will continue to
make it for you without quadrupling the price?

>> ... What MCUs or DSPs are
>> around after 20 years? ...
>
>
> 8051. That's why this is one of my favorites.

Yes, I knew you would mention that one. But that is the *only* one and
even then not all the parts are pin compatible.

So if you need some *real* processing capability, something that would
be the equivalent of a *real* MCU or FPGA, what would you use? Unless
they are making a 100 MHz 8051 I think you are pretty limited by that
choice.

>> ... Of these parts, I would be much less worried
>> about FPGAs being around in 20 years although that is likely stretching
>> it. If you need 30 years... I guess I don't know, I only been in the
>> business for 40 years and don't expect to be around myself for another
>> 30... in the large sense. ;)
>>
>
> Some of my designs have already celebrated their 20th in production and
> no end in sight.

Yes, if you are using stuff like 2N2222 transistors, sure. But I am
talking about something of similar complexity to an FPGA, DSP or modern
MCU. Otherwise just keep using the stuff you have been using.

>> BTW, there are several device families around with "true CMOS" power
>> consumption. If you don't need 1 GHz there are FPGAs that are lower
>> power than many ARM MCUs.
>>
>
> That would be nice.

--

Rick

[josephkk]

On Thu, 29 May 2014 14:20:26 -0700, Joerg <inv...@invalid.invalid> wrote:

>Folks,
>
>Does anyone know an IC that can turn a control voltage into PWM and can
>handle PWM frequencies in the 50-1000kHz range? Similar to a class D
>driver but has to go down to DC. The changes in control would be
>restricted to the audio spectrum below 15kHz.
>
>The LTC6992 does this nicely but isn't precise enough. Same with
>555-style timers or switcher chips. I am looking for better 1% and
>ideally a lot better, including nonlinearity, drift, warts and all. A uC
>is not suitable either because it should be simple and I need very fine
>control granularity, down to around 0.1%.
>
>Can't use short-lived consumer chips for radios and TV sets and such.

The only things that i have seen that are even close were V to F
converters. And they did DC to a few hundred Hz on the input spectrum.
Maybe some audiophool Class D amplifier IC.

?-)

[josephkk]

On Fri, 30 May 2014 09:57:30 -0700, Joerg <inv...@invalid.invalid> wrote:

>whit3rd wrote:

>> On Thursday, May 29, 2014 6:07:45 PM UTC-7, Joerg wrote:
>>> John Larkin wrote:
>>

>>>> How about a sawtooth or triangle waveform and a comparator. Close a
>>>> feedback loop around that, with a PWM to DC converter; the PWM-DC part
>>>> can be made very linear.
>>
>>> That's what I wanted to avoid for real estate reasons.
>>

>> It's only a dual comparator and a transistor! The first comparator is set
>> up as a Schmitt trigger with thresholds at +Vs and -Vs; its output drives
>> a resistor to the base, capacitor from collector to base, emitter to V-.
>> That makes a triangle wave. The second comparator takes signal in
>> on one input, and triangle wave on the other, and you're done.
>
>
>Sure, I know how to do it analog. But it's not quite as simple as it
>looks. Offsets, drift, regulators for super-stable rails et cetera. I
>thought there's got to be a solution-in-a-can because of all the class D
>amps these days. But the problem seems to be DC because audio doesn't
>need that. So maybe there isn't a suitable IC.

Well you can band split it, a bit messier but it works. Put the crossover
at about 30 Hz and do the LF yourself.

?-)

[josephkk]

On Fri, 30 May 2014 09:47:56 -0700, Joerg <inv...@invalid.invalid> wrote:

>Tim Wescott wrote:

>> On Thu, 29 May 2014 14:20:26 -0700, Joerg wrote:
>>
>>> Folks,
>>>
>>> Does anyone know an IC that can turn a control voltage into PWM and can
>>> handle PWM frequencies in the 50-1000kHz range? Similar to a class D
>>> driver but has to go down to DC. The changes in control would be
>>> restricted to the audio spectrum below 15kHz.
>>>
>>> The LTC6992 does this nicely but isn't precise enough. Same with
>>> 555-style timers or switcher chips. I am looking for better 1% and
>>> ideally a lot better, including nonlinearity, drift, warts and all. A uC
>>> is not suitable either because it should be simple and I need very fine
>>> control granularity, down to around 0.1%.
>>>
>>> Can't use short-lived consumer chips for radios and TV sets and such.
>>

>> A 555 or other teeny thing wrapped with integrating feedback, to hold the
>> average at precisely what you want? It kinda violates your "one chip"
>> desire, but at least it can be done with a minimum of small parts.
>>
>
>I am going to do something like that (but probably not with a 555) if
>nothing single-chip comes up. That's the reason for this thread, to see
>if there isn't anything out there. I mean, every class-D amp must have a
>super-linear PWM generator. It's just that most have the power stages
>built in (would be ok, can be left idle) and have lousy or no DC
>performance (would not be ok).

Ok a weird question: Does the response need to be 0.1% for any step size
at 15 kHz? Can it be "slew rate limited" a bit to get to 0.1% for a large
step; to like 900 Hz?

?-)

[rickman]

On 5/30/2014 7:59 PM, Joerg wrote:
>
> Stopband is a pretty gradual thing when you can't go past 3rd order on
> the output filter. This application is sensitive to noise because the
> load is super fast.

I guess I'm not really following all this. You have a control circuit
that is not easy to do with analog chips and yet you don't want to use a
digital control. From the bits and pieces I am seeing I believe a
classic ADC-DSP-DAC would suit this problem very well. Forget the silly
PWM thing and all the goofy filtering problems. I only call it silly
because in this design it doesn't seem to fit very well. With a pretty
basic digital path you could do the whole thing in one chip even. I
believe ADI makes some devices intended for exactly this although I've
never used them.

Or maybe I'm still not following what you are trying to do.

I could recommend a chip that could handle this *very* easily, but if
you think an FPGA is hard to program, this would blow your mind!

--

Rick

[Joerg]

rickman wrote:
> On 5/30/2014 8:10 PM, Joerg wrote:
>> rickman wrote:
>>>
>>> I think you have the availability issue backwards. FPGA vendors have
>>> some of the longest lived products in the IC world. It is not at all
>>> uncommon to design in an FPGA when it is new and not get an EOL notice
>>> for well over 10 years. You were dealing with Intel who dabble in
>>> secondary business areas and then close up shop when they lose interest.
>>> I don't know that Intel has ever shipped a production FPGA so I would
>>> hardly call them an FPGA vendor in any sense of the word.
>>>
>>
>> We also had it happen with a big medical system. Forgot which vendor but
>> all they could offer was to pour it into a new (more expensive) FPGA
>> series which would have meant a major relayout. So we poured it into our
>> own ASIC instead and that has no EOL issue.
>
> Don't believe that for a moment! ASICs require a fab to be made. The
> only FPGA I have ever had go EOL was because the fab house was closing
> that fab line. FPGA makers don't build their own fabs like most chip
> makers these days. ASICs are made on the same lines. When the fab
> closes all the product either ends or goes to another fab which means
> they have to work the process which is more NRE.
>
> I'm curious about your story. Yes, FPGAs go EOL, but like I said not
> remotely short lived. I would expect this design was either a long time
> in production or they picked an FPGA that was already long in the tooth.
>

It was a cutting-edge FPGA in the mid 90's. With ASICs you can get much
more design security. The trick is to pick a foundry you trust and a
run-of-the-mills process that is used for tons of other products. By
going directly to the foundry you are cutting out one middleman (the
FPGA vendor) and thus reduce the overall risk.

An example for the longevity of semiconductor processes: We just started
something on a 4" wafer. Those date back almost to the days of
Methusaleh yet it's no problem. If a process is also used to make mil
stuff, chances are it'll survive both of us.

>
>>> If you need a 20 year production life, what parts *can* you use? ...
>>
>>
>> Tons. For example, I used CD4000 logic extensively. In the mid-90's a
>> Fairchild engineer told me that would be a stupid decision, they'd go
>> obsolete, I should use their single-package logic. Well, most of this is
>> still in production. Then staples such as the LM324, those are here to
>> stay. Also MMBT3904, BFS17, and so on. I just used a BFR92 on a new
>> design. The first time I used one I was in the mid-80's and even then it
>> wasn't exactly new.
>
> Your example is CD4000 SSI/MSI logic? So why don't you build your
> current design with those parts? lol

And I might. Plus opamps/comparators.


> ... I mean a part that is a bit more

> complex. What MCUs have you used for 20 years other than the 8051? Many
> MCU parts go obsolete in 10 years if not shorter. I've seen DSP chips
> that lasted less than 5 years.
>

I pretty much only used the 8051 when I was allowed to decide. Clients
have used Atmels and also PICs that have lasted a long time but I don't
have production data for those products.

> I read a thread the other day that mentioned a vendor who had a list of
> long life products they would commit to making for 10 years or so. I
> can't remember where it was. The vendor may have been Motorola.
>

There is one other method but it requires you to be an important enough
customer: Negotiate a deal where, in case the product is ever obsoleted
in the first half of this century, you retain the right to have it made
at a foundry of your choice. For that, all the GDSII data goes into
escrow at some law office. It'll never come out of there if they stick
to their promise. But if they don't or if they go belly-up, it does.

>
>>> ... Does LTI give any assurance of a 20 year product life?
>>
>>
>> LTC? Yes, pretty much. Before they call off anything they try to contact
>> anyone who has ever bought it to see if it's ok.
>
> Yes, well everyone does that... although it is not a question really. So
> if you tell LTI you are still using the part they will continue to make
> it for you without quadrupling the price?
>

I am pretty sure they will supply. They told me so and they've never
lied to me. Their prices are on the high side anyhow and I don't think
they would jack up the price on customers.

>
>>> ... What MCUs or DSPs are
>>> around after 20 years? ...
>>
>>
>> 8051. That's why this is one of my favorites.
>
> Yes, I knew you would mention that one. But that is the *only* one and
> even then not all the parts are pin compatible.
>

Got to stay with multi-sorce packages like 44 QFP.

> So if you need some *real* processing capability, something that would
> be the equivalent of a *real* MCU or FPGA, what would you use? Unless
> they are making a 100 MHz 8051 I think you are pretty limited by that
> choice.
>

They _are_ making 100MHz 8051. No kidding. If it ain't got enough horses
use a 2nd one :-)

>
>>> ... Of these parts, I would be much less worried
>>> about FPGAs being around in 20 years although that is likely stretching
>>> it. If you need 30 years... I guess I don't know, I only been in the
>>> business for 40 years and don't expect to be around myself for another
>>> 30... in the large sense. ;)
>>>
>>
>> Some of my designs have already celebrated their 20th in production and
>> no end in sight.
>
> Yes, if you are using stuff like 2N2222 transistors, sure. But I am
> talking about something of similar complexity to an FPGA, DSP or modern
> MCU. Otherwise just keep using the stuff you have been using.
>

This is one reason why I try to keep things simple. Many jobs that are
done with a DSP can be done without. But not all of them, of course. Of
course, for me that's easier to say than probably for you because I do
mostly analog stuff. Sometimes it's the whole architecture though and
then one of my fuirst questions to the client is about parts sourcuiing
and longevity.

[...]

[Joerg]

rickman wrote:
> On 5/30/2014 7:59 PM, Joerg wrote:
>>
>> Stopband is a pretty gradual thing when you can't go past 3rd order on
>> the output filter. This application is sensitive to noise because the
>> load is super fast.
>
> I guess I'm not really following all this. You have a control circuit
> that is not easy to do with analog chips and yet you don't want to use a
> digital control. From the bits and pieces I am seeing I believe a

> classic ADC-DSP-DAC would suit this problem very well. ...


Generating a PWM stream with down to 1nsec granularity that way would be
increadibly power intense and expensive.


> ... Forget the silly

> PWM thing and all the goofy filtering problems. I only call it silly
> because in this design it doesn't seem to fit very well. With a pretty
> basic digital path you could do the whole thing in one chip even. I
> believe ADI makes some devices intended for exactly this although I've
> never used them.
>

I haven't found any, only delta-sigma which doesn't fit too well here.

> Or maybe I'm still not following what you are trying to do.
>
> I could recommend a chip that could handle this *very* easily, but if
> you think an FPGA is hard to program, this would blow your mind!
>

I am pretty sure there are FPGA that can do this but not alone, they
must have an ADC up front because the control is analog (not my choice,
it's a requirement).

It isn't a problem at all doing this analog. I can use any old PWM chip
or one of those TimerBlox from LTC, hang an error compensation loop
around it and call it a day. Two ICs and a sprinkling of discretes. And
I will do that if there aren't any suitable single-chip class-D audio
solutions.

[Joerg]

> at 15 kHz? ...


Nope :-(


> ... Can it be "slew rate limited" a bit to get to 0.1% for a large

> step; to like 900 Hz?
>

Unfortunately that would put a serious crimp into the versatility of the
product.

[Joerg]

Yup, I've used them but they aren't precise enough. Also, they don't
work well for PWM, just for V/F anf F/V.

> Maybe some audiophool Class D amplifier IC.
>

T'is exactly what I am looking for and why I posted here :-)

[k...@attt.bizz]

On Sat, 31 May 2014 07:16:11 -0700, Joerg <inv...@invalid.invalid>
wrote:

If you think that money (and time) invested has nothing to do with
"risk", perhaps. That's a rather Democratic view of economics,
though.

>An example for the longevity of semiconductor processes: We just started
>something on a 4" wafer. Those date back almost to the days of
>Methusaleh yet it's no problem. If a process is also used to make mil
>stuff, chances are it'll survive both of us.

Crap! That must have been 1960. ;-)

>>>> If you need a 20 year production life, what parts *can* you use? ...
>>>
>>>
>>> Tons. For example, I used CD4000 logic extensively. In the mid-90's a
>>> Fairchild engineer told me that would be a stupid decision, they'd go
>>> obsolete, I should use their single-package logic. Well, most of this is
>>> still in production. Then staples such as the LM324, those are here to
>>> stay. Also MMBT3904, BFS17, and so on. I just used a BFR92 on a new
>>> design. The first time I used one I was in the mid-80's and even then it
>>> wasn't exactly new.
>>
>> Your example is CD4000 SSI/MSI logic? So why don't you build your
>> current design with those parts? lol
>
>
>And I might. Plus opamps/comparators.
>
>
>> ... I mean a part that is a bit more
>> complex. What MCUs have you used for 20 years other than the 8051? Many
>> MCU parts go obsolete in 10 years if not shorter. I've seen DSP chips
>> that lasted less than 5 years.
>>
>
>I pretty much only used the 8051 when I was allowed to decide. Clients
>have used Atmels and also PICs that have lasted a long time but I don't
>have production data for those products.

The 8051s of today aren't your grandfather's 8051s, either. I'm
trying to push the ARM-Mn as the microcontroller for the future. We
just switched to AVRs but there are a lot more choices in ARMs. If
the code is written properly, porting to a new processor isn't a big
deal.

>> I read a thread the other day that mentioned a vendor who had a list of
>> long life products they would commit to making for 10 years or so. I
>> can't remember where it was. The vendor may have been Motorola.
>>
>
>There is one other method but it requires you to be an important enough
>customer: Negotiate a deal where, in case the product is ever obsoleted
>in the first half of this century, you retain the right to have it made
>at a foundry of your choice. For that, all the GDSII data goes into
>escrow at some law office. It'll never come out of there if they stick
>to their promise. But if they don't or if they go belly-up, it does.

Use Automotive parts. They're committed to making them for at least a
decade. Of course that assumes you don't pick one that's already been
around two. ;-)

>>
>>>> ... Does LTI give any assurance of a 20 year product life?
>>>
>>>
>>> LTC? Yes, pretty much. Before they call off anything they try to contact
>>> anyone who has ever bought it to see if it's ok.
>>
>> Yes, well everyone does that... although it is not a question really. So
>> if you tell LTI you are still using the part they will continue to make
>> it for you without quadrupling the price?
>>
>
>I am pretty sure they will supply. They told me so and they've never
>lied to me. Their prices are on the high side anyhow and I don't think
>they would jack up the price on customers.

ADI hasn't stung us either. On the other end of the spectrum, I
wouldn't touch Maxim with Barak Obama's pole. Others do, and like
them. they do have some interesting parts but I *have* been bitten.

<...>

[Joerg]

Huh? Going ASIC took a lot of risk out of this process. Instead of
depending on an FPGA manufacturer who is depending on a foundry we were
then only depending on a foundry.

>> An example for the longevity of semiconductor processes: We just started
>> something on a 4" wafer. Those date back almost to the days of
>> Methusaleh yet it's no problem. If a process is also used to make mil
>> stuff, chances are it'll survive both of us.
>
> Crap! That must have been 1960. ;-)
>

Yeah, I was surprised myself. But all the places we are using for the
various fab steps consider that standard fare.

>>>>> If you need a 20 year production life, what parts *can* you use? ...
>>>>
>>>> Tons. For example, I used CD4000 logic extensively. In the mid-90's a
>>>> Fairchild engineer told me that would be a stupid decision, they'd go
>>>> obsolete, I should use their single-package logic. Well, most of this is
>>>> still in production. Then staples such as the LM324, those are here to
>>>> stay. Also MMBT3904, BFS17, and so on. I just used a BFR92 on a new
>>>> design. The first time I used one I was in the mid-80's and even then it
>>>> wasn't exactly new.
>>> Your example is CD4000 SSI/MSI logic? So why don't you build your
>>> current design with those parts? lol
>>
>> And I might. Plus opamps/comparators.
>>
>>
>>> ... I mean a part that is a bit more
>>> complex. What MCUs have you used for 20 years other than the 8051? Many
>>> MCU parts go obsolete in 10 years if not shorter. I've seen DSP chips
>>> that lasted less than 5 years.
>>>
>> I pretty much only used the 8051 when I was allowed to decide. Clients
>> have used Atmels and also PICs that have lasted a long time but I don't
>> have production data for those products.
>
> The 8051s of today aren't your grandfather's 8051s, either. I'm
> trying to push the ARM-Mn as the microcontroller for the future. We
> just switched to AVRs but there are a lot more choices in ARMs. If
> the code is written properly, porting to a new processor isn't a big
> deal.
>

Yes, but it's a re-layout and in many regulated environments you must go
through the whole big validation process again.

>>> I read a thread the other day that mentioned a vendor who had a list of
>>> long life products they would commit to making for 10 years or so. I
>>> can't remember where it was. The vendor may have been Motorola.
>>>
>> There is one other method but it requires you to be an important enough
>> customer: Negotiate a deal where, in case the product is ever obsoleted
>> in the first half of this century, you retain the right to have it made
>> at a foundry of your choice. For that, all the GDSII data goes into
>> escrow at some law office. It'll never come out of there if they stick
>> to their promise. But if they don't or if they go belly-up, it does.
>
> Use Automotive parts. They're committed to making them for at least a
> decade. Of course that assumes you don't pick one that's already been
> around two. ;-)
>

Or was specifically made for a car series that then gets discontinued in
two years. That is a problem with parts for consumer electronics sucha s
TV sets. I never use them anymore.

>
>>>>> ... Does LTI give any assurance of a 20 year product life?
>>>>
>>>> LTC? Yes, pretty much. Before they call off anything they try to contact
>>>> anyone who has ever bought it to see if it's ok.
>>> Yes, well everyone does that... although it is not a question really. So
>>> if you tell LTI you are still using the part they will continue to make
>>> it for you without quadrupling the price?
>>>
>> I am pretty sure they will supply. They told me so and they've never
>> lied to me. Their prices are on the high side anyhow and I don't think
>> they would jack up the price on customers.
>
> ADI hasn't stung us either. On the other end of the spectrum, I
> wouldn't touch Maxim with Barak Obama's pole. Others do, and like
> them. they do have some interesting parts but I *have* been bitten.
>

Oh yeah, some clients have been stung, big time. OTOH that has brought
me several "design-out" assignments that then turned into longterm
client relationships. One lasted all the way until the company owner died.

[k...@attt.bizz]

On Sat, 31 May 2014 12:36:07 -0700, Joerg <inv...@invalid.invalid>
wrote:

You don't think significant NRE *ADDED* risk? You have a real funny
CFO.

>
>>> An example for the longevity of semiconductor processes: We just started
>>> something on a 4" wafer. Those date back almost to the days of
>>> Methusaleh yet it's no problem. If a process is also used to make mil
>>> stuff, chances are it'll survive both of us.
>>
>> Crap! That must have been 1960. ;-)
>>
>
>Yeah, I was surprised myself. But all the places we are using for the
>various fab steps consider that standard fare.

Seriously, I thought everyone had gone to at least 6" wafers decades
back. It's been over a decade since the digital guys went to 12"
(300mm). Of course, 8" are still common for jelly beans.

Not just layout but does anyone make a 12-clock, 12MHz 8051 anymore?
ARM *is* the way forward.

>>>> I read a thread the other day that mentioned a vendor who had a list of
>>>> long life products they would commit to making for 10 years or so. I
>>>> can't remember where it was. The vendor may have been Motorola.
>>>>
>>> There is one other method but it requires you to be an important enough
>>> customer: Negotiate a deal where, in case the product is ever obsoleted
>>> in the first half of this century, you retain the right to have it made
>>> at a foundry of your choice. For that, all the GDSII data goes into
>>> escrow at some law office. It'll never come out of there if they stick
>>> to their promise. But if they don't or if they go belly-up, it does.
>>
>> Use Automotive parts. They're committed to making them for at least a
>> decade. Of course that assumes you don't pick one that's already been
>> around two. ;-)
>>
>
>Or was specifically made for a car series that then gets discontinued in
>two years. That is a problem with parts for consumer electronics sucha s
>TV sets. I never use them anymore.

Name one (an ASSP, not an ASIC). Even if it's only in one car series,
it'll have at least a 10yr life, though if you only want one don't
count on any part being available in a decade.

>>
>>>>>> ... Does LTI give any assurance of a 20 year product life?
>>>>>
>>>>> LTC? Yes, pretty much. Before they call off anything they try to contact
>>>>> anyone who has ever bought it to see if it's ok.
>>>> Yes, well everyone does that... although it is not a question really. So
>>>> if you tell LTI you are still using the part they will continue to make
>>>> it for you without quadrupling the price?
>>>>
>>> I am pretty sure they will supply. They told me so and they've never
>>> lied to me. Their prices are on the high side anyhow and I don't think
>>> they would jack up the price on customers.
>>
>> ADI hasn't stung us either. On the other end of the spectrum, I
>> wouldn't touch Maxim with Barak Obama's pole. Others do, and like
>> them. they do have some interesting parts but I *have* been bitten.
>>
>
>Oh yeah, some clients have been stung, big time. OTOH that has brought
>me several "design-out" assignments that then turned into longterm
>client relationships. One lasted all the way until the company owner died.

The company died with him? Of course the federal government wants
that to happen but it is still pretty poor planning.

[Joerg]

Pouring it into an ASIC was not very onerous in terms of NRE. Plus we
could easily amortize it. It paid for itself in a jiffy anyhow because
the ASICs were much less expensive.

>>>> An example for the longevity of semiconductor processes: We just started
>>>> something on a 4" wafer. Those date back almost to the days of
>>>> Methusaleh yet it's no problem. If a process is also used to make mil
>>>> stuff, chances are it'll survive both of us.
>>> Crap! That must have been 1960. ;-)
>>>
>> Yeah, I was surprised myself. But all the places we are using for the
>> various fab steps consider that standard fare.
>
> Seriously, I thought everyone had gone to at least 6" wafers decades
> back. It's been over a decade since the digital guys went to 12"
> (300mm). Of course, 8" are still common for jelly beans.
>

That's what I thought as well. Until the end of last year. To me that
was like going to a car dealer and finding brand new 1956 Bel Airs.

You can but there is no law against using a 25MHz or whatever version
with a 12MHz clock.

> ARM *is* the way forward.
>

I might use my first one this year. Pondering which one to pick, one
that has good audio connectivity. Still got lots of time, maybe it'll be
the M4F series from TI. I was eyeing an AD Sharc but after a sobering
awakening with their seemingly outsourced "support" I decided not to.

>>>>> I read a thread the other day that mentioned a vendor who had a list of
>>>>> long life products they would commit to making for 10 years or so. I
>>>>> can't remember where it was. The vendor may have been Motorola.
>>>>>
>>>> There is one other method but it requires you to be an important enough
>>>> customer: Negotiate a deal where, in case the product is ever obsoleted
>>>> in the first half of this century, you retain the right to have it made
>>>> at a foundry of your choice. For that, all the GDSII data goes into
>>>> escrow at some law office. It'll never come out of there if they stick
>>>> to their promise. But if they don't or if they go belly-up, it does.
>>> Use Automotive parts. They're committed to making them for at least a
>>> decade. Of course that assumes you don't pick one that's already been
>>> around two. ;-)
>>>
>> Or was specifically made for a car series that then gets discontinued in
>> two years. That is a problem with parts for consumer electronics sucha s
>> TV sets. I never use them anymore.
>
> Name one (an ASSP, not an ASIC). Even if it's only in one car series,
> it'll have at least a 10yr life, though if you only want one don't
> count on any part being available in a decade.
>

I don't remember, too long ago. Mostly TAA, TBA and TCA series chips. I
haven't used them but clients have and then got burned.

>>>>>>> ... Does LTI give any assurance of a 20 year product life?
>>>>>> LTC? Yes, pretty much. Before they call off anything they try to contact
>>>>>> anyone who has ever bought it to see if it's ok.
>>>>> Yes, well everyone does that... although it is not a question really. So
>>>>> if you tell LTI you are still using the part they will continue to make
>>>>> it for you without quadrupling the price?
>>>>>
>>>> I am pretty sure they will supply. They told me so and they've never
>>>> lied to me. Their prices are on the high side anyhow and I don't think
>>>> they would jack up the price on customers.
>>> ADI hasn't stung us either. On the other end of the spectrum, I
>>> wouldn't touch Maxim with Barak Obama's pole. Others do, and like
>>> them. they do have some interesting parts but I *have* been bitten.
>>>
>> Oh yeah, some clients have been stung, big time. OTOH that has brought
>> me several "design-out" assignments that then turned into longterm
>> client relationships. One lasted all the way until the company owner died.
>

> The company died with him? ...


Kind of. His widow ran it for another year or two. It is good not to
make any drastic asset changes right after a spouse passed away but
eventually she sold the company. It was a smart move on her part.


> ... Of course the federal government wants

> that to happen but it is still pretty poor planning.
>

You can't always avoid it. Sam's Town was a local Western style
entertainment city right in our village (Cameron Park). Mostly for kids
and many Bay Area folks fondly remember that from trips to Lake Tahoe,
when dad pointed his Studebaker towards the off ramp. Death taxes killed
it, along with over 150 well paying jobs. Those jobs never came back and
the place was bulldozed. Dems do not understand this stuff.

[k...@attt.bizz]

On Sat, 31 May 2014 13:24:16 -0700, Joerg <inv...@invalid.invalid>

It had to have been a trivial part. ASICs are unaffordable for all
but a few applications. Really, they're only interesting when there
is no other choice (rather the same for FPGAs but on a whole different
level).

>>>>> An example for the longevity of semiconductor processes: We just started
>>>>> something on a 4" wafer. Those date back almost to the days of
>>>>> Methusaleh yet it's no problem. If a process is also used to make mil
>>>>> stuff, chances are it'll survive both of us.
>>>> Crap! That must have been 1960. ;-)
>>>>
>>> Yeah, I was surprised myself. But all the places we are using for the
>>> various fab steps consider that standard fare.
>>
>> Seriously, I thought everyone had gone to at least 6" wafers decades
>> back. It's been over a decade since the digital guys went to 12"
>> (300mm). Of course, 8" are still common for jelly beans.
>>
>
>That's what I thought as well. Until the end of last year. To me that
>was like going to a car dealer and finding brand new 1956 Bel Airs.

OK, now it's clear that you're been working in Cuba. ;-)

Well, then it's not a 12MHz clock. ;-) The greater issue is the
12-cycle (serial ALU). If you're insisting on a drop in, either will
screw all of your "agency approvals".

>
>> ARM *is* the way forward.
>>
>
>I might use my first one this year. Pondering which one to pick, one
>that has good audio connectivity. Still got lots of time, maybe it'll be
>the M4F series from TI. I was eyeing an AD Sharc but after a sobering
>awakening with their seemingly outsourced "support" I decided not to.

We're in pretty deep with Atmel on their M0 and M4(ish) products.
Sharc is a DSP and isn't really much good as a controller. Very
expensive. We use a lot of them, in fact I'm using a 41279 and 41269
on a board I'm doing right now. For a cheaper DSP, the Sigma is
pretty good series (using one of them on another board that I've just
sorta wrapped up the schematic). Each board also has one of the Atmel
ARM Mn processors for the mundane stuff.

>>>>>> I read a thread the other day that mentioned a vendor who had a list of
>>>>>> long life products they would commit to making for 10 years or so. I
>>>>>> can't remember where it was. The vendor may have been Motorola.
>>>>>>
>>>>> There is one other method but it requires you to be an important enough
>>>>> customer: Negotiate a deal where, in case the product is ever obsoleted
>>>>> in the first half of this century, you retain the right to have it made
>>>>> at a foundry of your choice. For that, all the GDSII data goes into
>>>>> escrow at some law office. It'll never come out of there if they stick
>>>>> to their promise. But if they don't or if they go belly-up, it does.
>>>> Use Automotive parts. They're committed to making them for at least a
>>>> decade. Of course that assumes you don't pick one that's already been
>>>> around two. ;-)
>>>>
>>> Or was specifically made for a car series that then gets discontinued in
>>> two years. That is a problem with parts for consumer electronics sucha s
>>> TV sets. I never use them anymore.
>>
>> Name one (an ASSP, not an ASIC). Even if it's only in one car series,
>> it'll have at least a 10yr life, though if you only want one don't
>> count on any part being available in a decade.
>>
>
>I don't remember, too long ago. Mostly TAA, TBA and TCA series chips. I
>haven't used them but clients have and then got burned.

More information?

>>>>>>>> ... Does LTI give any assurance of a 20 year product life?
>>>>>>> LTC? Yes, pretty much. Before they call off anything they try to contact
>>>>>>> anyone who has ever bought it to see if it's ok.
>>>>>> Yes, well everyone does that... although it is not a question really. So
>>>>>> if you tell LTI you are still using the part they will continue to make
>>>>>> it for you without quadrupling the price?
>>>>>>
>>>>> I am pretty sure they will supply. They told me so and they've never
>>>>> lied to me. Their prices are on the high side anyhow and I don't think
>>>>> they would jack up the price on customers.
>>>> ADI hasn't stung us either. On the other end of the spectrum, I
>>>> wouldn't touch Maxim with Barak Obama's pole. Others do, and like
>>>> them. they do have some interesting parts but I *have* been bitten.
>>>>
>>> Oh yeah, some clients have been stung, big time. OTOH that has brought
>>> me several "design-out" assignments that then turned into longterm
>>> client relationships. One lasted all the way until the company owner died.
>>
>> The company died with him? ...
>
>
>Kind of. His widow ran it for another year or two. It is good not to
>make any drastic asset changes right after a spouse passed away but
>eventually she sold the company. It was a smart move on her part.

Probably a good idea but that still shouldn't kill the company.

>> ... Of course the federal government wants
>> that to happen but it is still pretty poor planning.
>>
>
>You can't always avoid it. Sam's Town was a local Western style
>entertainment city right in our village (Cameron Park). Mostly for kids
>and many Bay Area folks fondly remember that from trips to Lake Tahoe,
>when dad pointed his Studebaker towards the off ramp. Death taxes killed
>it, along with over 150 well paying jobs. Those jobs never came back and
>the place was bulldozed. Dems do not understand this stuff.

Death taxes have to be covered by insurance. But, that's what the
lefties in government want. They have to kill wealth. "It's only
fair."

[John Larkin]

ADI just killed ADG465. It wasn't an especially old part... they just didn't
make enough money off it. Damned nuisance.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

[Joerg]

Absolutamente no. It does screaming fast image processing. No competitor
ever managed to rival it and they tried hard.


> ... ASICs are unaffordable for all

> but a few applications. Really, they're only interesting when there
> is no other choice (rather the same for FPGAs but on a whole different
> level).
>

I have to disagree because I've been involved in a few ASIC projects. If
it's just pouring existing FPGA logic into an ASIC that can be done in
the high five digits. An ASIC from scratch is around half a million
after it's all said and done, depending on design complexity. Peanuts
compared to the savings or other upsides it provides.

>>>>>> An example for the longevity of semiconductor processes: We just started
>>>>>> something on a 4" wafer. Those date back almost to the days of
>>>>>> Methusaleh yet it's no problem. If a process is also used to make mil
>>>>>> stuff, chances are it'll survive both of us.
>>>>> Crap! That must have been 1960. ;-)
>>>>>
>>>> Yeah, I was surprised myself. But all the places we are using for the
>>>> various fab steps consider that standard fare.
>>> Seriously, I thought everyone had gone to at least 6" wafers decades
>>> back. It's been over a decade since the digital guys went to 12"
>>> (300mm). Of course, 8" are still common for jelly beans.
>>>
>> That's what I thought as well. Until the end of last year. To me that
>> was like going to a car dealer and finding brand new 1956 Bel Airs.
>
> OK, now it's clear that you're been working in Cuba. ;-)
>

:-)

Are they still making them?

Not all of them. Software regression testing, yes. EMC approvals usually
not. But if you are plopping in a Testarossa-series modern MCU then you
get to do the whole enchilada, again.

Those were projects back in Europe, last century. Most of that is gone.
One of the TCA-sumpthins was for electric drill speed control and I
believe then the drill series was discontinued. But really, it's too
long ago to say for sure. Lots of audio and RF/IF chips as well. They
suddenly became unobtanium.

>>>>>>>>> ... Does LTI give any assurance of a 20 year product life?
>>>>>>>> LTC? Yes, pretty much. Before they call off anything they try to contact
>>>>>>>> anyone who has ever bought it to see if it's ok.
>>>>>>> Yes, well everyone does that... although it is not a question really. So
>>>>>>> if you tell LTI you are still using the part they will continue to make
>>>>>>> it for you without quadrupling the price?
>>>>>>>
>>>>>> I am pretty sure they will supply. They told me so and they've never
>>>>>> lied to me. Their prices are on the high side anyhow and I don't think
>>>>>> they would jack up the price on customers.
>>>>> ADI hasn't stung us either. On the other end of the spectrum, I
>>>>> wouldn't touch Maxim with Barak Obama's pole. Others do, and like
>>>>> them. they do have some interesting parts but I *have* been bitten.
>>>>>
>>>> Oh yeah, some clients have been stung, big time. OTOH that has brought
>>>> me several "design-out" assignments that then turned into longterm
>>>> client relationships. One lasted all the way until the company owner died.
>>> The company died with him? ...
>>
>> Kind of. His widow ran it for another year or two. It is good not to
>> make any drastic asset changes right after a spouse passed away but
>> eventually she sold the company. It was a smart move on her part.
>
> Probably a good idea but that still shouldn't kill the company.
>

Oh, it hasn't. But the new owners haven't used me (yet). AFAICT they
still produce my designs.

>>> ... Of course the federal government wants
>>> that to happen but it is still pretty poor planning.
>>>
>> You can't always avoid it. Sam's Town was a local Western style
>> entertainment city right in our village (Cameron Park). Mostly for kids
>> and many Bay Area folks fondly remember that from trips to Lake Tahoe,
>> when dad pointed his Studebaker towards the off ramp. Death taxes killed
>> it, along with over 150 well paying jobs. Those jobs never came back and
>> the place was bulldozed. Dems do not understand this stuff.
>
> Death taxes have to be covered by insurance.

What?


> ... But, that's what the

> lefties in government want. They have to kill wealth. "It's only
> fair."
>

Yep, and then they kill scores of jobs like here in California. Seems
they don't even do exit interviews which could reveal so much. Well,
maybe they want to hide how much damage they are doing.

[Joerg]

John Larkin wrote:
> On Sat, 31 May 2014 15:17:06 -0400, k...@attt.bizz wrote:
>
>> On Sat, 31 May 2014 07:16:11 -0700, Joerg <inv...@invalid.invalid>
>> wrote:
>>
>>> rickman wrote:
>>>> On 5/30/2014 8:10 PM, Joerg wrote:

[...]

>>>>> LTC? Yes, pretty much. Before they call off anything they try to contact
>>>>> anyone who has ever bought it to see if it's ok.
>>>> Yes, well everyone does that... although it is not a question really. So
>>>> if you tell LTI you are still using the part they will continue to make
>>>> it for you without quadrupling the price?
>>>>
>>> I am pretty sure they will supply. They told me so and they've never
>>> lied to me. Their prices are on the high side anyhow and I don't think
>>> they would jack up the price on customers.
>> ADI hasn't stung us either. On the other end of the spectrum, I
>> wouldn't touch Maxim with Barak Obama's pole. Others do, and like
>> them. they do have some interesting parts but I *have* been bitten.
>>
>> <...>
>
>
> ADI just killed ADG465. It wasn't an especially old part... they just didn't
> make enough money off it. Damned nuisance.
>

Arrow and Newark still have some. Farnell has stock in Europe and Asia
but often Newark stock seems to be physically the same as Farnell
Europe. Mouser has a few thousand as well. So at least there's
opportunity to stockpile.

[Lasse Langwadt Christensen]

Den lørdag den 31. maj 2014 16.21.47 UTC+2 skrev Joerg:
> rickman wrote:
>
> > On 5/30/2014 7:59 PM, Joerg wrote:
>
> >>
>
> >> Stopband is a pretty gradual thing when you can't go past 3rd order on
>
> >> the output filter. This application is sensitive to noise because the
>
> >> load is super fast.
>
> >
>
> > I guess I'm not really following all this. You have a control circuit
>
> > that is not easy to do with analog chips and yet you don't want to use a
>
> > digital control. From the bits and pieces I am seeing I believe a
>
> > classic ADC-DSP-DAC would suit this problem very well. ...
>
>
>
>
>
> Generating a PWM stream with down to 1nsec granularity that way would be
>
> increadibly power intense and expensive.
>

the dsPIC33 has ~1ns resolution PWM and a 10 bit 2Msps ADC, $1.69 if you buy 1000


-Lasse

[Joerg]

Lasse Langwadt Christensen wrote:

How does it do that when the on-chip VCO for system frequency is spec'd
between 100MHz and 200MHz?

Silicon delay wouldn't be so nice.

[Lasse Langwadt Christensen]

never used it so I don't know, look like you have to set it for 120Mhz to get 1.04ns resolution

>
>
> Silicon delay wouldn't be so nice.
>

why not?

120MHz clock does the coarse duty cycle, a string 8 delays of nominal
1.04ns, servo the delays to make up exactly one cycle and you have 8
phases to do the fine setting duty cycle

I guess if the VCO is done with ring oscillator there is already a
string you can tap to get the extra phases for free

I believe Xilinx does something similar servoing of delays for their
IO delays

-Lasse

[Chris Jones]

On 30/05/2014 07:20, Joerg wrote:
> Folks,
>
> Does anyone know an IC that can turn a control voltage into PWM and can
> handle PWM frequencies in the 50-1000kHz range? Similar to a class D
> driver but has to go down to DC. The changes in control would be
> restricted to the audio spectrum below 15kHz.
>
> The LTC6992 does this nicely but isn't precise enough. Same with
> 555-style timers or switcher chips. I am looking for better 1% and
> ideally a lot better, including nonlinearity, drift, warts and all. A uC
> is not suitable either because it should be simple and I need very fine
> control granularity, down to around 0.1%.
>
> Can't use short-lived consumer chips for radios and TV sets and such.
>

Maybe you don't strictly need PWM, but would be able to use sigma-delta
a modulated bitstream instead. In that case you could perhaps use this
one, though it comes with galvanic isolation that you might not need:
http://www.analog.com/static/imported-files/data_sheets/AD7401A.pdf
Perhaps there is something similar and cheaper without the isolation.

Otherwise if you really need PWM, what if you wrap feedback around the
LTC6992, i.e. invert and square up its output by putting the PWM through
a CMOS inverter running from a very stable power supply, and then use
resistors to add the inverted PWM waveform to the incoming input
voltage, and call the sum the "error voltage". Theoretically the average
of this "error voltage" will be exactly mid-rail. Use an op-amp to
integrate any deviations from mid-rail and feed that into the LTC6992,
to correct it. Perhaps two op-amps would be needed as integrating
circuits tend to invert, which you might not want here.

Chris

[josephkk]

On Sat, 31 May 2014 07:23:14 -0700, Joerg <inv...@invalid.invalid> wrote:

>
>>> I am going to do something like that (but probably not with a 555) if
>>> nothing single-chip comes up. That's the reason for this thread, to see
>>> if there isn't anything out there. I mean, every class-D amp must have a
>>> super-linear PWM generator. It's just that most have the power stages
>>> built in (would be ok, can be left idle) and have lousy or no DC
>>> performance (would not be ok).
>>
>>
>> Ok a weird question: Does the response need to be 0.1% for any step size
>> at 15 kHz? ...
>
>
>Nope :-(
>
>
>> ... Can it be "slew rate limited" a bit to get to 0.1% for a large
>> step; to like 900 Hz?
>>
>
>Unfortunately that would put a serious crimp into the versatility of the
>product.

OK. Instead of a strict linearity perspective can we look at it from a
settling time perspective for various portions of step size from minimal
to full scale?

?-)

[josephkk]

On Sat, 31 May 2014 07:25:08 -0700, Joerg <inv...@invalid.invalid> wrote:

>josephkk wrote:
>> On Thu, 29 May 2014 14:20:26 -0700, Joerg <inv...@invalid.invalid> wrote:
>>
>>> Folks,
>>>
>>> Does anyone know an IC that can turn a control voltage into PWM and can
>>> handle PWM frequencies in the 50-1000kHz range? Similar to a class D
>>> driver but has to go down to DC. The changes in control would be
>>> restricted to the audio spectrum below 15kHz.
>>>
>>> The LTC6992 does this nicely but isn't precise enough. Same with
>>> 555-style timers or switcher chips. I am looking for better 1% and
>>> ideally a lot better, including nonlinearity, drift, warts and all. A uC
>>> is not suitable either because it should be simple and I need very fine
>>> control granularity, down to around 0.1%.
>>>
>>> Can't use short-lived consumer chips for radios and TV sets and such.
>>
>> The only things that i have seen that are even close were V to F
>> converters. And they did DC to a few hundred Hz on the input spectrum.
>
>
>Yup, I've used them but they aren't precise enough. Also, they don't
>work well for PWM, just for V/F anf F/V.
>

Does it HAVE to be PWM? Can't PFM do the job?

>
>> Maybe some audiophool Class D amplifier IC.
>>
>
>T'is exactly what I am looking for and why I posted here :-)

I had noticed.