Apex HV opamp issues.

[George Herold]

Hi guys (and dolls), So if you read in JL's TI opamp thread,
I am having noise issues in our laser diode.
I turns out (I think) that the extra noise is coming
from my Piezo drive.
The original circuit used a PA141 from Apex.
(I can't find a schematic on-line, but I have a hard copy.)
Several years ago this HV opamp went away and the
recommended replacement from Apex was the PA314
https://apexanalog-public.sharepoint.com/Resources/PA341U.pdf

I basically plugged it in, it worked, and I forgot about it.
Well it's not quite the same... a few differences but the big one
is the noise... Some gawd awful 350 uV rms in a 10 k Hz BW...
(~350nV/rt Hz.) And no spec on the low freq. 1/f noise.

So I've been trying to beat the noise down in the current circuit,
but with no luck. I use it as a x10 inverting amp. Rin= 10 k ohm and
Rf= 100k ohm. I tried rolling off the gain with 100pf in parallel
with Rf, but this lead to low level oscillations.. (scratch scratch.)
I then tried adding more compensation capacitance from 10 pF to ~70 pF
but this did nothing.

Any ideas for trying to salvage this circuit?
I could live with a bandwidth of 5 kHz or so.

TIA
George H.

[Jan Panteltje]

On a sunny day (Fri, 13 Mar 2015 10:10:38 -0700 (PDT)) it happened George
Herold <ghe...@teachspin.com> wrote in
<ad164713-93a0-48f2...@googlegroups.com>:

Sometimes {tm)
------||---10k ----
| 1n |
|----------||------ |
| 100p |
10k ----- 100 k-----------------
| |
--- - |
> -----
--- +

if its oscillatiing you have some pole somewhere.
This has worked in the past (don't ask me)
but I don't know your loop bandwidth and whatever is in it.
Anyways the extra RC (could be some other place that moves) could help against oscillations.

It could work, it could not work, but.. could save time if it does.

[George Herold]

OK, I'll give it a try... I was thinking some resistance in series
with the 100pF..(?)

(I just ordered some LTC6090's from DK...)

I also noticed that the PA341 has been replaced with the PA441..
30 times less noise!

[Phil Hobbs]

How about a resistor in series with the output? Your piezo is probably
in the nanofarads.

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

[Tim Wescott]

Maybe they were getting lots of complaints! Is it pin-compatible?

--

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

[mako...@yahoo.com]

> >> >
> >> >So I've been trying to beat the noise down in the current circuit, but
> >> >with no luck.

try reading this
http://www.ti.com/lit/ml/sloa082/sloa082.pdf

especially about the different contributions of
noise voltage and noise current

Mark

[George Herold]

Yeah... more band-aids. I'm not sure it would help.
As is the piezo can only react at ~3kHz, so I've already got
a bunch of filtering.

I was looking at the noise more closely... turns out it's almost all
1/f noise.. I need DC and well another opamp is looking like my solution.

(And then some sort of mini pcb to shoe horn it in the the existing pcb.)

George H.

[George Herold]

Yup.. I order one of those too.. but only 1.. ~$50 each!

George H.

[George Herold]

Thanks Mark, (I've read plenty about noise.)
This opamp seems to have a ton of 1/f noise
with a 1/f corner freq. that looks to be >10 kHz!


George H.

[John Larkin]

Apex used to use an AT&T high-voltage CMOS analog process that was
astoundingly noisy, 140 nv/rtHz or something crazy like that. Maybe
the PA141 was one of those. There was an appnote on compounding that
dog with a good low-voltage opamp.

These days, most of their products are regular surfmount parts on PC
boards.

You could try my cheap and almost-famous optocoupler-based HV
amplifier.

https://dl.dropboxusercontent.com/u/53724080/Optos/HVamp.JPG


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

[Jim Thompson]

On Fri, 13 Mar 2015 10:10:38 -0700 (PDT), George Herold
<ghe...@teachspin.com> wrote:

How about the MP118... Spice model on my website, by yours truly ;-)

Model includes .AC and .TRAN

...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.

[Phil Hobbs]

Cheer up, I've measured pHEMTs with 1/f corners of 50 MHz. ;)
(It was the otherwise excellent SKY65050.)

[George Herold]

Thanks but I think I'll try the LTC thing first.
The Apex amp sticks out and can be cut off,
and a pcb soldered in place.

My only problem is my HV supply is a bit high.
right now it runs off ~+155 and -12.
(LTC6090 max is 150V)
I don't need all the HV ~110-130 would be fine.
And low current, I don't know the C of my piezo stack,
but max freq is 3kHz. A few mA of current at most.
Could I just do a series (beefy) zener? ~20V.
With some RC filtering behind if needed.

George H.

[George Herold]

Woah this?
http://www.digikey.com/product-search/en?vendor=0&keywords=MP118

That even more $!

George H.

[Jim Thompson]

On Fri, 13 Mar 2015 16:29:22 -0700 (PDT), George Herold

[snip]

You can use it to launch satellites ;-)

[George Herold]

On Friday, March 13, 2015 at 6:55:40 PM UTC-4, Phil Hobbs wrote:
> On 3/13/2015 4:17 PM, George Herold wrote:
> > On Friday, March 13, 2015 at 4:04:28 PM UTC-4, mako...@yahoo.com wrote:
> >>>>>>
> >>>>>> So I've been trying to beat the noise down in the current circuit, but
> >>>>>> with no luck.
> >>
> >> try reading this
> >> http://www.ti.com/lit/ml/sloa082/sloa082.pdf
> >>
> >> especially about the different contributions of
> >> noise voltage and noise current
> >>
> >> Mark
> >
> > Thanks Mark, (I've read plenty about noise.)
> > This opamp seems to have a ton of 1/f noise
> > with a 1/f corner freq. that looks to be >10 kHz!
> >
> >
> > George H.
> >
> Cheer up, I've measured pHEMTs with 1/f corners of 50 MHz. ;)

Well it just means filtering is pointless...
(in retrospec, I should have measured the noise first)

Replacing the entire opamp with a pcb is something
that I can get (some) customers to do in the field.
(a TO-3-8 package, eight fat pins and two mounting holes)

George H.

[Tim Wescott]

Apex parts definitely make you pay for the privilege of not having to roll
your own amp. It's worth it if your volume is low and the cost of failure
is high.

[Frank Miles]

At least with some of the Apex amplifiers, they depend on high output
capacitance as part of the frequency compensation. Adding (too much)
output resistance would make these amplifiers go unstable.

Increasing the load capacitance might be part of reducing closed loop
amplifier bandwidth.

HTH-

[George Herold]

Yeah, we've been happily paying that cost for years.
Now due to their crappy opamp,
combined with my lack of due diligence...
the return shipping costs to India
will make it seem like nothing.
(at least I found it now, I think we've only shipped one to India...
and you never know we might find someone there
who can handle a soldering iron.)

George H.

[Jim Thompson]

The MP118, the one I wrote the Spice model for, uses pole-splitting
compensation, plus a lead zero... external cap.

[George Herold]

I'm not a complete idiot.. the laser's are
all tested with the SAS linewidth, ~10 MHz ideal,
and power broadened to ~20Mhz at a guess.

And this 2-4 MHz "junk" was small enough to get through my net,
and still screw up something else.
(sorry, I'll be kicking myself all weekend.)

George H.

[Tim Wescott]

See if you can get Pimpom's email addy -- he's out in the sticks
somewhere, but maybe you could ship it to him for the repair.

(or have them toss it in the dumpster and just send a new one?)

--
www.wescottdesign.com

[Jan Panteltje]

On a sunny day (Fri, 13 Mar 2015 13:45:11 -0700) it happened John Larkin
<jla...@highlandtechnology.com> wrote in
<jji6gadtd50u67np8...@4ax.com>:

>
>You could try my cheap and almost-famous optocoupler-based HV
>amplifier.
>
>https://dl.dropboxusercontent.com/u/53724080/Optos/HVamp.JPG

Thats is a keeper.

[John Larkin]

It likes capacitive loads, which become the dominant pole in the
feedback loop. With that sort of compensation, more C load just makes
it more stable.

[Tim Wescott]

Ooooh, I wish I were still working at FLIR. Our head analog engineer was
excellent, but very averse to odd topologies and to circuits that he
didn't think would simulate well. Tossing this schematic in front of him
in a meeting would be like tossing a cat into a cage full of antisocial
dogs.

--
www.wescottdesign.com

[John Larkin]

On Sat, 14 Mar 2015 13:43:41 -0500, Tim Wescott <t...@seemywebsite.com>
wrote:

If he was adverse to odd designs, how did the E45 software wind up so
weird? It's not a regular camera interface, it's a network device over
USB with a bizarre cable.

If you use it one one USB port, and change ports next time, even a
different slot on a hub, the PC software forgets that it exists.

The thermal part works pretty well.

[Winfield Hill]

George Herold wrote...

>
> Hi guys (and dolls), So if you read in JL's TI opamp thread,
> I am having noise issues in our laser diode.
> I turns out (I think) that the extra noise is coming
> from my Piezo drive.
> The original circuit used a PA141 from Apex.
> (I can't find a schematic on-line, but I have a hard copy.)
> Several years ago this HV opamp went away and the
> recommended replacement from Apex was the PA314
> https://apexanalog-public.sharepoint.com/Resources/PA341U.pdf
>
> I basically plugged it in, it worked, and I forgot about it.
> Well it's not quite the same... a few differences but the big one
> is the noise... Some gawd awful 350 uV rms in a 10 k Hz BW...
> (~350nV/rt Hz.) And no spec on the low freq. 1/f noise.
>
> So I've been trying to beat the noise down in the current circuit,
> but with no luck. I use it as a x10 inverting amp. Rin= 10 k ohm and
> Rf= 100k ohm. I tried rolling off the gain with 100pf in parallel
> with Rf, but this lead to low level oscillations.. (scratch scratch.)
> I then tried adding more compensation capacitance from 10 pF to ~70 pF
> but this did nothing.
>
> Any ideas for trying to salvage this circuit?
> I could live with a bandwidth of 5 kHz or so.
>
> TIA
> George H.

Yep, most of the APEX opamps made with MOSFET input transistors
are very noisy, especially at low frequencies. For example, the
PA141 spec says 50uV rms, over a 10kHz bandwidth. By comparison
the PA341 spec is 337uV rms. Whoa!! Their JFET-input opamps
are much better, for example the PA97 specs 2uV rmw over 10kHz.
So you could change to one of those types.

Or you could make your own HV amplifier, using a low-voltage
JEFT opamp to control MOSFET power transistors. We show an
example in Figure 3.75 in AoE 2nd edition (also see Figure
6.47). These amplifiers can be even more quiet. I updated
the circuit for AoE-III, see Figure 3.111. [Note, AoE-III
is being printed and will be shipping in a week or two.]

A more advanced circuit is set for the AoE x-Chapter book
(for the time being it's Figure 4x.50 in section 4x.18),
where there's a lengthy careful analysis of the design,
and its performance into large capacitive loads, etc.

A refined version of that circuit is in development for a
freebie PCB, so y'all can easily make your own. It's my
Rowland EE Labs AMP-62A project, and here's a schematic:
https://www.dropbox.com/s/cqpoyr2toj1c7pt/AMP-62A-2_sch_r3_fast.pdf?dl=0
https://www.dropbox.com/s/0e5x0mhr5ldwjho/AMP-62A-2_pcb_r3_3D-image.JPG?dl=0




--
Thanks,
- Win

[Jim Thompson]

On 14 Mar 2015 13:32:45 -0700, Winfield Hill

The MP118 is JFET input, and noise is modeled in my Spice subcircuit.

[John Larkin]

On 14 Mar 2015 13:32:45 -0700, Winfield Hill
<hi...@rowland.harvard.edu> wrote:

I don't understand the Q8-Q10 string. Is that safe?

--

John Larkin Highland Technology, Inc

picosecond timing laser drivers and controllers

[Winfield Hill]

John Larkin wrote...

Absolutely. Avalanche is your friend, provided you keep
the power dissipation under control. If we assume about
600V avalanche, at 0.5mA that's a very relaxed 300mW.
The lowest-current series current-source avalanches first,
then the next highest, and so on. So the current-source
varies by about maybe up to 0.1mA over voltage. But hey,
that's far better than using 2W carbon pullup resistors!

Another scheme I like is the MOSFETs wired in cascode,
but this requires six series resistors to handle 1kV.
But it does let you double or triple the pullup current.


--
Thanks,
- Win

[John Larkin]

On 14 Mar 2015 14:30:24 -0700, Winfield Hill

LND150 data sheets don't mention an avalanche rating.

Looks like Microchip acquired Supertex.

[Winfield Hill]

John Larkin wrote...
> Winfield Hill wrote:
>> John Larkin wrote...

Right, when you see an official "avalanche" rating, it's
actually a thermal-mass parameter, for use with pulsed
high-power levels. It's consistent with and derivable
from the Transient Thermal Impedance plots.

But in this circuit we're not subjecting the part to
any transient high-power dissipation.

> Looks like Microchip acquired Supertex.

Oops, we'll see what happens next. Fingers crossed.

You may have noticed (lower left corner of the schematic)
my enthusiasm for Infineon BSS126, instead of "my favorite"
LND150. It's a higher-current, higher-voltage part. BTW,
these SOT-23 MOSFETs have different pinouts. Just saying.


--
Thanks,
- Win

[Tim Wescott]

On Sat, 14 Mar 2015 12:19:06 -0700, John Larkin wrote:

> On Sat, 14 Mar 2015 13:43:41 -0500, Tim Wescott <t...@seemywebsite.com>
> wrote:
>
>>On Sat, 14 Mar 2015 09:11:16 +0000, Jan Panteltje wrote:
>>
>>> On a sunny day (Fri, 13 Mar 2015 13:45:11 -0700) it happened John
>>> Larkin <jla...@highlandtechnology.com> wrote in
>>> <jji6gadtd50u67np8...@4ax.com>:
>>>>
>>>>You could try my cheap and almost-famous optocoupler-based HV
>>>>amplifier.
>>>>
>>>>https://dl.dropboxusercontent.com/u/53724080/Optos/HVamp.JPG
>>>
>>> Thats is a keeper.
>>
>>Ooooh, I wish I were still working at FLIR. Our head analog engineer
>>was excellent, but very averse to odd topologies and to circuits that he
>>didn't think would simulate well. Tossing this schematic in front of
>>him in a meeting would be like tossing a cat into a cage full of
>>antisocial dogs.
>
> If he was adverse to odd designs, how did the E45 software wind up so
> weird? It's not a regular camera interface, it's a network device over
> USB with a bizarre cable.
>
> If you use it one one USB port, and change ports next time, even a
> different slot on a hub, the PC software forgets that it exists.
>
> The thermal part works pretty well.

I'm pretty sure that the handheld stuff is still all done in Sweden.

I worked on the high-dollar airborne imaging stuff. While we did make
some profoundly stupid products from time to time (usually heralded by a
company officer getting all of us into a room and telling us how smart he
was to kick off the project), more often than not we made good chit.

When I started there, a mechanical drawing had to be checked by two
people in addition to the engineer who designed the part. A circuit had
to be checked by one, other than the engineer. Software had to be
checked not at all -- you just gave them a floppy with a hex file and
signed on the dotted line. I took that to mean that software was
considered to be magic, not engineering (other aspects of engineering
management's behavior kind of confirmed that).

--
www.wescottdesign.com

[George Herold]

Wow! thanks, That's much more HV amp than I can afford to
get my head around. (at the moment)
(I'm glad JL ask about Q8-10)

I'm going to try the LTC6090.
My only issue for a retro fit is throwing
away about 20-30 V of HV supply (@ 10 mA max.)

A silly resistor divider takes too much power.
I was thinking of a series Zener (1 Watt)
I then wondered if I could run a
three terminal voltage regulator (LM317)
With the adjust pin driven from the input side?

Which lead me to the voltage divider cap multiplier.

Vin---+---+----|<|---+----+---+
| | | | |
R \ />-----+ R C
1 --+-- l l
| | o o
+-----+ a a
| | d d
R C | |
2 1 | |
gnd--+-----+-------------+---+

About 1mA flowing through R1/R2.

George H.










>
>
>
> --
> Thanks,
> - Win

[George Herold]

On Friday, March 13, 2015 at 1:10:42 PM UTC-4, George Herold wrote:
> Hi guys (and dolls), So if you read in JL's TI opamp thread,
> I am having noise issues in our laser diode.
> I turns out (I think) that the extra noise is coming
> from my Piezo drive.
> The original circuit used a PA141 from Apex.
> (I can't find a schematic on-line, but I have a hard copy.)
> Several years ago this HV opamp went away and the
> recommended replacement from Apex was the PA314
> https://apexanalog-public.sharepoint.com/Resources/PA341U.pdf
>
> I basically plugged it in, it worked, and I forgot about it.
> Well it's not quite the same... a few differences but the big one
> is the noise... Some gawd awful 350 uV rms in a 10 k Hz BW...
> (~350nV/rt Hz.) And no spec on the low freq. 1/f noise.
>
> So I've been trying to beat the noise down in the current circuit,
> but with no luck. I use it as a x10 inverting amp. Rin= 10 k ohm and
> Rf= 100k ohm. I tried rolling off the gain with 100pf in parallel
> with Rf, but this lead to low level oscillations.. (scratch scratch.)
> I then tried adding more compensation capacitance from 10 pF to ~70 pF
> but this did nothing.
>
> Any ideas for trying to salvage this circuit?
> I could live with a bandwidth of 5 kHz or so.
>
> TIA
> George H.

Just the final update on apex opamps...
(I'm still waiting on DK, but I had to leave early today.)
It turns out that I'd forgotten the first apex update,
where the PA141 went to the PA241... so here a noise plot
(noise density is uncalibrated.. though I have the gain settings.)

https://www.dropbox.com/s/1vguffiuj4noghz/Graph1.BMP?dl=0
(The black line has a slope of 1)

Turns out the opamp got progressively worse...
What's weird is that the "1/f" noise
is not 1/f, but f^-2/3.

Well since I don't understand 1/f, (1/f)^2/3 is no weirder.

George H.

[George Herold]

Oh, I should add that the x-axis "bandwidth"
is the low pass filter setting,
and the signal was AC coupled with a 10 Hz HP.

[Winfield Hill]

George Herold wrote...

>
> Just the final update on apex opamps...
> (I'm still waiting on DK, but I had to leave early today.)
> It turns out that I'd forgotten the first apex update,
> where the PA141 went to the PA241... so here a noise plot
> (noise density is uncalibrated.. though I have the gain settings.)
>
> https://www.dropbox.com/s/1vguffiuj4noghz/Graph1.BMP?dl=0
> (The black line has a slope of 1)
>
> Turns out the opamp got progressively worse...
> What's weird is that the "1/f" noise
> is not 1/f, but f^-2/3.
>
> Well since I don't understand 1/f, (1/f)^2/3 is no weirder.

We discuss in detail how this can happen in our lengthy
Chapter 8 in Art of Electronics 3rd edition, 40 tons of
which is shipping now from the printer. It's largely
due to offset shifts (i.e., popcorn-noise style) as
well as large thermal offset-voltage drifts.

A good solution is a "composite" amplifier, where
the poor amplifier is wrapped with a good opamp.


--
Thanks,
- Win

[Spehro Pefhany]

On 18 Mar 2015 20:10:37 -0700, the renowned Winfield Hill

<hi...@rowland.harvard.edu> wrote:

>George Herold wrote...
>>
>> Just the final update on apex opamps...
>> (I'm still waiting on DK, but I had to leave early today.)
>> It turns out that I'd forgotten the first apex update,
>> where the PA141 went to the PA241... so here a noise plot
>> (noise density is uncalibrated.. though I have the gain settings.)
>>
>> https://www.dropbox.com/s/1vguffiuj4noghz/Graph1.BMP?dl=0
>> (The black line has a slope of 1)
>>
>> Turns out the opamp got progressively worse...
>> What's weird is that the "1/f" noise
>> is not 1/f, but f^-2/3.
>>
>> Well since I don't understand 1/f, (1/f)^2/3 is no weirder.
>
> We discuss in detail how this can happen in our lengthy
> Chapter 8 in Art of Electronics 3rd edition, 40 tons of
> which is shipping now from the printer.

Excellent. As a send-off we need a re-write of Flanders and Swan's 20
Tons:
https://www.youtube.com/watch?v=48waPFTXJvY

Come the ghostly Magi bearing.. 40 tons of AoE..

>It's largely
> due to offset shifts (i.e., popcorn-noise style) as
> well as large thermal offset-voltage drifts.
>
> A good solution is a "composite" amplifier, where
> the poor amplifier is wrapped with a good opamp.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

[George Herold]

On Wednesday, March 18, 2015 at 11:10:45 PM UTC-4, Winfield Hill wrote:
> George Herold wrote...
> >
> > Just the final update on apex opamps...
> > (I'm still waiting on DK, but I had to leave early today.)
> > It turns out that I'd forgotten the first apex update,
> > where the PA141 went to the PA241... so here a noise plot
> > (noise density is uncalibrated.. though I have the gain settings.)
> >
> > https://www.dropbox.com/s/1vguffiuj4noghz/Graph1.BMP?dl=0
> > (The black line has a slope of 1)
> >
> > Turns out the opamp got progressively worse...
> > What's weird is that the "1/f" noise
> > is not 1/f, but f^-2/3.
> >
> > Well since I don't understand 1/f, (1/f)^2/3 is no weirder.
>
> We discuss in detail how this can happen in our lengthy
> Chapter 8 in Art of Electronics 3rd edition, 40 tons of
> which is shipping now from the printer. It's largely
> due to offset shifts (i.e., popcorn-noise style) as
> well as large thermal offset-voltage drifts.

Hi Win, I assume you are talking about 1/f noise ...(and not the 2/3rds power dependence.) I've read some stuff on 1/f. (Van-der-Ziel for one.)
I guess the classic 1/f noise is from the old carbon comp. resistors.
Here's a plot.... well it's a bit busy, I found a tiny hint of 1/f noise in (cheap, Xicon) metal film resistors.
https://www.dropbox.com/s/y1jv60eawkj9oxd/1_OVER_F.BMP?dl=0

George H.

[Phil Hobbs]

IIRC most MF resistors are specified at 1E-7V/V per decade of frequency.
I measured some as a voltage divider with a 9V alkaline, battery, and
they were nowhere near that bad.

[John Larkin]

High-value (like, 100M) thickfilms seem to have excess noise. Metal
films are hard to find at those values, but are much quieter.

--

John Larkin Highland Technology, Inc

picosecond timing precision measurement

[George Herold]

I don't really like that noise plot for the metal films...
I did it a while ago. (Maybe I'll repeat it some day.)

But now you are making me think. 1E-7 V/V per decade,
So with ten volts of bias and let's say a 1 Hz to 1 kHz bandwidth,
that would be 3E-6 V(rms)(?) and a noise density (at 1 kHz) of
~1E-7V/rtHz... that seems huge! (even it I did loose a factor
of pi in there somewhere.)

George H.

[Phil Hobbs]

> But now you are making me think.  1E-7 V/V per decade,  
>So with ten volts of bias and let's say a 1 Hz to 1 kHz bandwidth,
>that would be 3E-6 V(rms)(?) and a noise density (at 1 kHz) of
>~1E-7V/rtHz... that seems huge! (even it I did loose a factor
>of pi in there somewhere.)

By my few measurements, the real number is at least 30 dB lower than that.

Cheers

Phil Hobbs

[Winfield Hill]

John Larkin wrote...

>
> High-value (like, 100M) thickfilms seem to have excess noise. Metal
> films are hard to find at those values, but are much quieter.

Yes. The "excess noise" I've observed is usually highly voltage dependent,
proportional to voltage, etc. It may be non-existent at low voltages, like
under 10V, but severe above 50 to 100V to 1kV. And it can vary dramatically
from part to part. E.e., made some +/-2KV amplifiers, with sub 1ppm noise
levels, and 20% of the 10kV feedback resistors were very noisy and had to be
replaced.

But troublesome FET transistor noise may not have classic 1/f characteristics at
all, e.g., "telegraph noise" and "popcorn noise" are not strictly 1/f. Let's
talk after you've digested our measurements and the discussion in Chapter 8.
The book is being shipped as we speak. My order is in.


--
Thanks,
- Win

[George Herold]

Excellent! I look forward to the discussion once
my piece of the 40 tons arrives.
I wonder if the voltage dependence is a surface
thing. (could be the outer surface or some
layer underneath.)

George H.

[Jan Panteltje]

On a sunny day (Thu, 19 Mar 2015 19:45:19 -0700 (PDT)) it happened George
Herold <ghe...@teachspin.com> wrote in
<4527cdae-051b-4973...@googlegroups.com>:

>I wonder if the voltage dependence is a surface
>thing. (could be the outer surface or some
>layer underneath.)

Yes, probably above some voltage you may get arcing over minuscule 'islands' of resisytro material.

[John Larkin]

All resistors have the same Johnson noise at zero volts. Some, not
metal films, have shot noise with current flowing, which is simple
electron arrival statistics.

I conjecture that some nonmetallic resistors, like cermets, may have
shot noise when biased. They also have excess, 1/f ish, noise, maybe
from their polycrystaline confused nature. Tiny temperature variations
must play heck with a grainy cermet-like structure.

I've done a little testing on high-ohm resistors, but just enough to
get me through a project. I needed 100 Mohms and wound up using two
Dale custom-ordered 50M axials in series in mid-air, hopping over some
surface-mount parts. Cermets were awful. This is fairly difficult
stuff to measure, but would be a good student project or something.

[George Herold]

I've never seen excess shot noise in resistors..
(excess noise that is white in frequency.)
but I haven't looked hard either.
According to Landauer a resistor should reduce the shot noise
as 1/N, where N is the number of scattering events
as a "single electron pulse" travels the length of the resistor.

I'm not sure how to think about "scattering events"
and 10 ns pulses.

>
> I've done a little testing on high-ohm resistors, but just enough to
> get me through a project. I needed 100 Mohms and wound up using two
> Dale custom-ordered 50M axials in series in mid-air, hopping over some
> surface-mount parts. Cermets were awful. This is fairly difficult
> stuff to measure, but would be a good student project or something.

I wired up my LTC6090 HV opamps today. Fired it up on the test bench.
no smoke, but all I saw noise-wise, was first the room lights, and then
60Hz, with cross-over spikies from the linear supply.... I wanted to
go watch the UB bulls play in the "big dance".* So I'll have,
to put it in the box tomorrow...(Monday) Measuring noise can be hard.
I sometime wonder how I ever made things work in the past....

George H.

*UB lost, we trailed the entire game, tied it up with ~3:00 to go,
and then lost. Still it was a great emotional ride for me.
+1, I hope Bobby Hurley stays and we go back.
(intellectually sports makes no sense at all,
for me, it's all about the emotion.)

[John Larkin]

On Fri, 20 Mar 2015 16:04:17 -0700 (PDT), George Herold

10 ns is still pretty slow.

>>
>> I've done a little testing on high-ohm resistors, but just enough to
>> get me through a project. I needed 100 Mohms and wound up using two
>> Dale custom-ordered 50M axials in series in mid-air, hopping over some
>> surface-mount parts. Cermets were awful. This is fairly difficult
>> stuff to measure, but would be a good student project or something.
>
>I wired up my LTC6090 HV opamps today. Fired it up on the test bench.
>no smoke, but all I saw noise-wise, was first the room lights, and then
>60Hz, with cross-over spikies from the linear supply.... I wanted to
>go watch the UB bulls play in the "big dance".* So I'll have,
>to put it in the box tomorrow...(Monday) Measuring noise can be hard.
>I sometime wonder how I ever made things work in the past....
>
>George H.
>
> *UB lost, we trailed the entire game, tied it up with ~3:00 to go,
>and then lost. Still it was a great emotional ride for me.
>+1, I hope Bobby Hurley stays and we go back.
>(intellectually sports makes no sense at all,
>for me, it's all about the emotion.)
>

Was that basketball? I never understood that game. It seems to be a
bunch of guys with endocrine problems, running back and forth all
night. Looks chaotic to me.

[George Herold]

Well just a number out of the air... well typical PMT pulse width,
that's more than one electron of course.

>
>
> >>
> >> I've done a little testing on high-ohm resistors, but just enough to
> >> get me through a project. I needed 100 Mohms and wound up using two
> >> Dale custom-ordered 50M axials in series in mid-air, hopping over some
> >> surface-mount parts. Cermets were awful. This is fairly difficult
> >> stuff to measure, but would be a good student project or something.
> >
> >I wired up my LTC6090 HV opamps today. Fired it up on the test bench.
> >no smoke, but all I saw noise-wise, was first the room lights, and then
> >60Hz, with cross-over spikies from the linear supply.... I wanted to
> >go watch the UB bulls play in the "big dance".* So I'll have,
> >to put it in the box tomorrow...(Monday) Measuring noise can be hard.
> >I sometime wonder how I ever made things work in the past....
> >
> >George H.
> >
> > *UB lost, we trailed the entire game, tied it up with ~3:00 to go,
> >and then lost. Still it was a great emotional ride for me.
> >+1, I hope Bobby Hurley stays and we go back.
> >(intellectually sports makes no sense at all,
> >for me, it's all about the emotion.)
> >
>
> Was that basketball? I never understood that game. It seems to be a
> bunch of guys with endocrine problems, running back and forth all
> night. Looks chaotic to me.

Yeah, I played it a lot when younger, which helps..
Team sports are fun.
I wish I still had good knees,
I hate running, but running after some ball is different.
(I'm trying to win!)

Basketball, soccer, tennis, volleyball...
I still play ping-pong, a pretty small ball,
and not much running.

George H.

[Phil Hobbs]

Cermets and high value carbon comp resistors rely on the spreading
resistance of minute contacts between grains--IOW the effective length
of the resistor is much shorter than its physical length.