Circuit to calculate square root of voltage?
Chaos Master
I am looking for a circuit to calculate the square root of a voltage,
V(out) = SQRT V(In). (e.g. I input 4V and 2V comes out, I input 3V and
~1.73V comes out).
Q: How can I do this?
[]s
--
Chaos Master®, posting from Canoas, Brazil - 29.55° S / 51.11° W
"Sing what you can't say / forget what you can't play
Hasten to drown into beautiful eyes / Walk within my poetry, this dying
music"
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[5:35]
Ken Smith
Chaos Master <c...@os.master.INVALID.INVALID> wrote:
>Hello people.
>
>I am looking for a circuit to calculate the square root of a voltage,
>V(out) = SQRT V(In). (e.g. I input 4V and 2V comes out, I input 3V and
>~1.73V comes out).
>
>Q: How can I do this?
How good does it have to be? How fast does it have to be?
You can use the exp(0.5 * ln(X) ) method. Both the exp() and ln()
functions can be done using diode drops (usually E-B diode) I'm sure
others will also suggest this one.
You can use a ADC-MICRO-DAC method. This is a one chip solution but it
does require some programming. BTW: a 32 bit in, 16 bit out sqrt() on an
8051 only takes a few milliseconds.
You can use several straight lines to sort of do the curve. If you can
stand the error this can lead to a low cost circuit that does what you
need.
There are also pulsed circuits that will do sqrt() but they respond
slowly. They are more accurate than the straight lines method though.
--
--
kens...@rahul.net forging knowledge
Spehro Pefhany
<c...@os.master.INVALID.INVALID> wrote:
>Hello people.
>
>I am looking for a circuit to calculate the square root of a voltage,
>V(out) = SQRT V(In). (e.g. I input 4V and 2V comes out, I input 3V and
>~1.73V comes out).
>
>Q: How can I do this?
1) (Easiest) Use a microcontroller (for example, a PIC). All you
need is the chip (with program) and an RC low-pass
filter/buffer on the PWM output if the micro doesn't have
a DAC output. The micro can calculate the square root
algorithmically or use a lookup table (LUT).
2) Use the relationship x^0.5 = exp(0.5*ln(x))
You can do this with a couple of quad op-amps
and some matched transistors (see AofE page 254,
for example, for a temperature-compensated type).
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
CFoley1064
>From: Chaos Master c...@os.master.INVALID.INVALID
>Date: 12/3/2004 9:35 PM Central Standard Time
>Message-id: <MPG.1c1b0d909...@News.individual.net>
>
>Hello people.
>
>I am looking for a circuit to calculate the square root of a voltage,
>V(out) = SQRT V(In). (e.g. I input 4V and 2V comes out, I input 3V and
>~1.73V comes out).
>
>Q: How can I do this?
The square root function can be implemented by placing an analog IC multiplier
in the feedback loop of an op amp.
http://www.analog.com/UploadedFiles/Data_Sheets/277093686AD633_e.pdf
I've had to do this before for a low frequency app, and this solution with this
IC worked well for me. I believe a sample circuit is in the data sheet. Also,
old issues of AD's Analogue Dialogue have more.
Good luck
Chris
Ken Smith
Spehro Pefhany <spef...@interlogDOTyou.knowwhat> wrote:
>On Sat, 4 Dec 2004 01:35:19 -0200, the renowned Chaos Master
><c...@os.master.INVALID.INVALID> wrote:
>
>>Hello people.
>>
>>I am looking for a circuit to calculate the square root of a voltage,
>>V(out) = SQRT V(In). (e.g. I input 4V and 2V comes out, I input 3V and
>>~1.73V comes out).
>>
>>Q: How can I do this?
>
>1) (Easiest) Use a microcontroller (for example, a PIC). All you
> need is the chip (with program) and an RC low-pass
> filter/buffer on the PWM output if the micro doesn't have
> a DAC output. The micro can calculate the square root
> algorithmically or use a lookup table (LUT).
>
Here's a funny idea:
If the micro has a ADC and a DAC and the DAC output can be used as the
reference for the ADC:
The ADC's number is 2^N*X/Y where X is the input and Y is the REF voltage.
All you have to do is scale the ADC number and apply it to the DAC output
and you get the sqrt() function.
John Popelish
>
> Hello people.
>
> I am looking for a circuit to calculate the square root of a voltage,
> V(out) = SQRT V(In). (e.g. I input 4V and 2V comes out, I input 3V and
> ~1.73V comes out).
>
> Q: How can I do this?
data sheet)
http://www.analog.com/UploadedFiles/Data_Sheets/737468486AD538_c.pdf
so I will point you to another method that involves an analog
multiplier in a feedback loop described here:
http://www.phys.ualberta.ca/~gingrich/phys395/notes/node109.html
(figure 14 of this data sheet).
http://www.analog.com/UploadedFiles/Data_Sheets/737468486AD538_c.pdf
or page 8 of
http://www.intersil.com/data/fn/fn2477.pdf
--
John Popelish
Chaos Master
[circuit: V(OUT)=SQRT V(IN)]
> Others have described the log-antilog method (shown on page 9 of this
> data sheet)
> http://www.analog.com/UploadedFiles/Data_Sheets/737468486AD538_c.pdf
>
> so I will point you to another method that involves an analog
> multiplier in a feedback loop described here:
> http://www.phys.ualberta.ca/~gingrich/phys395/notes/node109.html
> (figure 14 of this data sheet).
> http://www.analog.com/UploadedFiles/Data_Sheets/737468486AD538_c.pdf
> or page 8 of
> http://www.intersil.com/data/fn/fn2477.pdf
Thank you and all others that replied, will put those PDF's in my
download manager' queued downloads so it downloads them and I can read
them when I have time.
[]s
--
Chaos Master®, posting from Canoas, Brazil - 29.55° S / 51.11° W
"Sing what you can't say / forget what you can't play
Hasten to drown into beautiful eyes / Walk within my poetry, this dying
music"
- My loveletter to nobody
My e-mail address is renanDOTbirckATgmailDOTcom [DOT=. AT=@].
DON'T SPAM IT. REPLY TO NEWS UNLESS I ASK YOU TO REPLY BY MAIL
Stefan Wyss
Here you got it:
http://www.edn.com/archives/1997/112097/24di_07.htm
Cu, Stefan
Nicholas O. Lindan
> I am looking for a circuit to calculate the square root of a voltage,
> V(out) = SQRT V(In). (e.g. I input 4V and 2V comes out, I input 3V and
> ~1.73V comes out).
>
> Q: How can I do this?
And don't forget the 's.e.d answer to everything': A PIC.
Do it in software... Built in A/D -> sqrt() -> D/A
--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/
Jim Thompson
<c...@os.master.INVALID.INVALID> wrote:
>Hello people.
>
>I am looking for a circuit to calculate the square root of a voltage,
>V(out) = SQRT V(In). (e.g. I input 4V and 2V comes out, I input 3V and
>~1.73V comes out).
>
>Q: How can I do this?
>
>[]s
Dig back thru OLD MC1494-95-96 data sheets. One of them showed a
multiplier in the feedback loop of an OpAmp to do square-root.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Chaos Master
> And don't forget the 's.e.d answer to everything': A PIC.
>
> Do it in software... Built in A/D -> sqrt() -> D/A
A PIC... A PIC... everything is a PIC! :)
I want to do an analog solution first... without using the
microcontroller or (A/D)/(D/A) converter.
[]s
--
Chaos Master®, posting from Canoas, Brazil - 29.55° S / 51.11° W
"Sing what you can't say / forget what you can't play
Hasten to drown into beautiful eyes / Walk within my poetry, this dying
music"
- My loveletter to nobody
My e-mail address is renanDOTbirckATgmailDOTcom [DOT=. AT=@].
DON'T SPAM IT. REPLY TO NEWS UNLESS I ASK YOU TO REPLY BY MAIL
Winfield Hill
>
> Chaos Master wrote:
>
>>
>> I am looking for a circuit to calculate the square root of a
>> voltage, V(out) = SQRT V(In). (e.g. I input 4V and 2V comes
>> out, I input 3V and ~1.73V comes out).
>
> a multiplier in the feedback loop of an OpAmp to do square-root.
Yes, MC1494 fig 25, and MC1495 fig 27. But nothing in the MC1496
data. Jim, did you design those chips? Who wrote the datasheets?
--
Thanks,
- Win
Jim Thompson
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:
The MC1495 came first, and is nothing more than your basic (Barrie)
Gilbert Cell.
The MC1496 stripped off linearizing diodes... for use as an RF signal
mixer.
The MC1494 added level-shifting and various compensations, and was
done by an employee of mine, Maurice Free, as his Master's Thesis,
under my tutelage.
The data sheets were done by the Motorola Applications Department, as
were most Motorola data sheets in the '60's. So they don't always
make sense ;-)
Tim Wescott
> On 4 Dec 2004 09:11:00 -0800, Winfield Hill
> <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:
>
>
>>Jim Thompson wrote...
>>
>>>Chaos Master wrote:
>>>
>>>
>>>>I am looking for a circuit to calculate the square root of a
>>>>voltage, V(out) = SQRT V(In). (e.g. I input 4V and 2V comes
>>>>out, I input 3V and ~1.73V comes out).
>>>
>>>Dig back thru OLD MC1494-95-96 data sheets. One of them showed
>>>a multiplier in the feedback loop of an OpAmp to do square-root.
>>
>>Yes, MC1494 fig 25, and MC1495 fig 27. But nothing in the MC1496
>>data. Jim, did you design those chips? Who wrote the datasheets?
>
>
> The MC1495 came first, and is nothing more than your basic (Barrie)
> Gilbert Cell.
>
> The MC1496 stripped off linearizing diodes... for use as an RF signal
> mixer.
>
> The MC1494 added level-shifting and various compensations, and was
> done by an employee of mine, Maurice Free, as his Master's Thesis,
> under my tutelage.
>
> The data sheets were done by the Motorola Applications Department, as
> were most Motorola data sheets in the '60's. So they don't always
> make sense ;-)
>
> ...Jim Thompson
My only experience with the MC1495 in a commercial circuit was a
controller board that I used to maneuver around. It was in a hybrid
analog/digital control loop, where the processor did the "executive"
control like setting targets and commanding mode changes, and the analog
board actually closed the loops.
The multiplier took the secant of one axis angle and multiplied it by
the the angle of a second axis to control a third. The ironic thing (to
me) was that the processor was calculating the secant, all of the axis
information was available to the processor, it would have taken one
measly line of code to do the multiplication -- yet we had an analog
part in there, in a spot where the specs were critical enough that every
two years or so manufacturing engineering would have to re-spec a part
because somebody's process had been "improved".
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Fred Bartoli
"Chaos Master" <e-m...@is.INVALID> a écrit dans le message de
news:MPG.1c1be48f3...@News.individual.net...
> Nicholas O. Lindan to stdout:
>
> > And don't forget the 's.e.d answer to everything': A PIC.
> >
> > Do it in software... Built in A/D -> sqrt() -> D/A
>
> A PIC... A PIC... everything is a PIC! :)
>
> I want to do an analog solution first... without using the
> microcontroller or (A/D)/(D/A) converter.
>
How about that one ? Purely analogic but nevertheless uses a PIC.
You use the input clamp diodes to give exp/log response. The PIC give them
matched and in the same package.
The pb is that they share a common connection at the supply rail and we have
to do with this. Of course this circuit is not temperature stable and adding
some compensation will probably lead to an even more completly stupid
circuit.
But hey, we've used a PIC.
Dclamp Dclamp ___
.--|<-+->|----+-|___|-.
| | | R |
| | | |\| |
___ | |\| | '-|-\ | ___ ___
IN -|___|-+-|-\ | ___ | >--+-|___|-+-|___|-+- OUT
R | >+-|___|-+-|+/ R | R |
.-|+/ 2R | |/| | |
| |/| .-. | |
=== | | | |
GND |R| | |\| |
'-' '-|-\ |
| | >--'
+-----------------|+/
| |/|
.-.
| |
|R|
'-'
|
===
GND
(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)
--
Thanks,
Fred.
Rich Grise
Does anybody even make them any more? The 1496 was the only one of the
three that I found that wasn't stamped "OBSOLETE".
What would somebody use these days?
(Oh, right! All together now, "Use a PIC"! ;-) )
Cheers!
Rich
Frank Bemelman
<fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> schreef in
bericht news:41b21319$0$25965$626a...@news.free.fr...
[snip]
> But hey, we've used a PIC.
Excellent! ;-) No programming skills/tools needed either, this time.
--
Thanks, Frank.
(remove 'x' and 'invalid' when replying by email)
Spehro Pefhany
<f.bem...@xs4all.invalid.nl> wrote:
>"Fred Bartoli"
><fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> schreef in
>bericht news:41b21319$0$25965$626a...@news.free.fr...
>
>[snip]
>
>> But hey, we've used a PIC.
>
>Excellent! ;-) No programming skills/tools needed either, this time.
I'm not sure the protection networks in the PIC are very good diodes,
though. They seem to behave like resistors in series with small
diodes.
Glen Walpert
<spef...@interlogDOTyou.knowwhat> wrote:
>On Sun, 5 Dec 2004 00:27:11 +0100, the renowned "Frank Bemelman"
><f.bem...@xs4all.invalid.nl> wrote:
>
>>"Fred Bartoli"
>><fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> schreef in
>>bericht news:41b21319$0$25965$626a...@news.free.fr...
>>
>>[snip]
>>
>>> But hey, we've used a PIC.
>>
>>Excellent! ;-) No programming skills/tools needed either, this time.
>
>I'm not sure the protection networks in the PIC are very good diodes,
>though. They seem to behave like resistors in series with small
>diodes.
>
Even if they were good diodes they would make a lousy log amp (and
thus a lousy square rooter) for reasons discussed here before and no
doubt sitll findable with a google groups search on "log amp" or
"logarithmic" or perhaps "multiplier", also discussed in some detail
by Bob Pease in articles EDN articles available on the National web
site.
The suggestion to use a multiplier in the feedback path of an op-amp
IAW a number of data sheets and app notes from various mfgrs
(originally by Analog Devices) was a good one.
<OT> But I have worked on control systems which did a square root
pneumatically, and you could certainly still find examples of this in
numerous refineries and power plants, far more accurate than anything
which can be done with diodes and working reliably for decades in
conditions too harsh for most electronic components </OT>.
Regards,
Glen
Tony Williams
Chaos Master <c...@os.master.INVALID.INVALID> wrote:
> I am looking for a circuit to calculate the square root of a
> voltage, V(out) = SQRT V(In). (e.g. I input 4V and 2V comes out,
> I input 3V and ~1.73V comes out).
The data sheet for the Raytheon RC4200 multiplier
(XY/Z) has a couple of tidy looking square root
circuits. 8 resistors and 2x 8-pin DIP packages.
--
Tony Williams.
Jim Thompson
[snip]
>
>Does anybody even make them any more? The 1496 was the only one of the
>three that I found that wasn't stamped "OBSOLETE".
>
>What would somebody use these days?
>
>(Oh, right! All together now, "Use a PIC"! ;-) )
>
>Cheers!
>Rich
>
Probably there's an Analog Devices chip that has everything in it.
Max Hauser
Translinear circuits? Are there no analog experts here at all? (Those
suggesting microprocessors for getting an analog square root function have
been noted down and are permanently disbarred. :-)
Who knows if any of this shows up online, but there is plenty in print,
familiar to specialists. Try searching under "Translinear circuits" or
"Barrie Gilbert" or possibly the latter's seminal pair of papers in the
December 1968 _IEEE Journal of Solid-State Circuits_ of which the truly
relevant one is not the "Precise four-quadrant multiplier with subnanosecond
response" but rather "A new wide-band amplifier technique" which contains
the insightful and prophetic phrase "The number of circuits that can be
devised to perform functions of this kind is legion."
This is from memory, I am pressed for time. You can even do it all directly
with FETs if you really want. Klumperink and Meyer and Mack and I wrote a
broad survey paper in 96 though it does not mention square roots
specifically. Evert Seevinck wrote a good thesis on the subject in 81 or
82, I wrote something back then that touched on the FET versions, many
others did too. (Analog multipliers in feedback loops. Hmmph.)
-- Max
"Chaos Master" in news:MPG.1c1b0d909...@News.individual.net...
Winfield Hill
>
> Jeez Louise. All these replies and nobody (that I spotted anyway)
The classic translinear circuit is the Gilbert cell, which is the
prime component in most analog multipliers, which were recommended
several times in this thread. There's your mention of translinear
circuits. :>) I prefer the AD734, and have often suggested it for
tasks like this. The datasheet fig 9 shows a square root circuit.
--
Thanks,
- Win
Rick
Barry Gilbert himself freely admits in his publications that a
certain Mr H.E. Jones has prior art on the "Gilbert Cell".
--
Rick
Winfield Hill
Barry is a quiet type of guy. He explained, improved, promolgated
and popularized this circuit, so we insisted on naming it after him.
He doesn't (didn't back then) use the name Gilbert Cell, hence his
proposed name (IIRC), translinear. We liked Gilbert Cell better.
--
Thanks,
- Win
Max Hauser
> Max Hauser wrote...
> >
> > Jeez Louise. All these replies and nobody (that I spotted anyway)
> > mentioned Translinear circuits? Are there no analog experts here?
>
> The classic translinear circuit is the Gilbert cell, which is the
> prime component in most analog multipliers, which were
> recommended several times in this thread. There's your
> mention of translinear circuits. :>)
Come ON. (A "textbook" explanation, facile, unrelated to the established
art that I referred to, and just what I was complaining about.)
I'll explain. Here are some things that emerge when you delve into
translinear circuits, or even just their literature. This includes an
explanation of them. (The following is supported in much more depth than I
cite here.)
(a) The prototype translinear circuit, if the subject is viewed from a long
focus, is the bipolar-transistor current mirror. (It's useful also in
explaining.) It is both the simplest embodiment of the principle, and also
is very obviously a current-input current-output function, underscoring the
point that translinear circuits basically perform arithmetic operations on
currents.
(b) In the current mirror, two junction devices (BJTs) share the same Vbe
voltage. At the same time, these devices each have a nonlinear relation of
Vbe to collector current (Ic) that is (to remarkable potential accuracy)
exponential [1]. The connection of their Vbe voltages, and the exponential
large-signal Vbe-Ic law, lead to a relation between the two collector
currents, which prevails as long as the two transistors are happy (i.e.,
forward-active). In this very simple case, the two collector currents will
tend to track, whatever else is happening, and this is useful. Notably, the
two collector currents stay equal regardless of transistor construction (the
notorious Js current-density parameter) or temperature (which shows up in
kT/q, and even more so, implicitly, in Js). Of course, you must use matched
(or deliberately area-ratioed) devices -- these designs are most often
monolithic. Commercial monolithic dual or quad transistors or monolithic
"kit parts" serve this need in a discrete design.
(c) Generalizing, if you put four Vbe voltages into a loop (two in series,
equaling the voltage across another two in series), these voltages will sum
algebraically to zero (KVL) and this again will impose a relation among
collector currents. Depending on what you do with the collector currents,
you can get explicit algebraic relationships among these currents, such as
I1 I2 = I3 I4
-- which, if I1and I2 are arranged to be identical and to equal the output
current, and I3 is a fixed current and I4 an input current, will give a DC,
large-signal, fundamentally accurate square-root relation between input and
output currents. (Embed it with an op amp and resistors and you can get and
give voltages.) Various simple, four-transistor square-root-law circuit
cores pervade the "translinear" literature. Broader versions of the
principle apply to general voltage loops of BJTs. Obvious further
generalizations apply to other semiconductor devices (even with
generalizations beyond voltage loops).
(d) The chief origin and exploration of these circuits in print is, as I
already cited in the earlier posting, Barrie Gilbert's December-1968 JSSC
"Amplifier" paper, not the companion "Multiplier" paper, which employed
some of the results. I _strongly_ recommend reading them, they disabuse
some notions cultivated elsewhere in print. The first is where the "legion"
remark appeared. In 1975, BG coined the nickname "translinear" (because
they rely on exponential I-V devices, which have TRANSconductance LINEAR in
collector current) for this pervasive class of circuits [2]. Note well
that --
(e) -- one of the basic four-junction translinear blocks is often called a
"gain cell," focus of the 1968 "Amplifier" paper, and pretty clearly
associated with Gilbert. I am using the language here carefully, read on.
This cell contains two transistors at one DC current level, whose Vbe
difference is then imposed easily onto a second pair at another DC current
level. Current differences within the two pairs are input and output
signals, and can have either polarity. Changing the relative DC currents,
or "tail" currents, controls the _current_ gain in the signal path. If then
you take two different output pairs and a single input pair, and drive the
input pair with one differential current, and the "tail" currents of the two
output pairs with a second differential current, you achieve an accurate
four-quadrant (either polarity on either input) multiplication ("with
subnanosecond response" even in 1967). Note carefully that the accurate
relation is among currents (as always with classic translinear circuits).
This is the true six-transistor multiplier core or "six-pack" as it was
often called in the 1970s by IC designers. It and other variations are the
upshots of the 1968 "Multiplier" paper that I cited.
(f) Some later authors, despite this black-and-white origin, took to calling
a different set of six transistors (the two output pairs above, and the
differential tail current source that drives them) a "Gilbert six-transistor
multiplier" even though it is neither Gilbert's, nor a multiplier. The
original "six-pack" is a true self-contained, current-mode four-quadrant
analog multiplier and is the core of many monolithic bipolar-transistor
multiplier products.
(g) Though the translinear idea was first explored in depth in Gilbert's
1968 "Amplifier" paper, analog circuits embodying the principle can be found
earlier, even beyond the trivial example of a current mirror and its
variations. Grasselli and Stefanelli's 1966 BJT current-gain cell is
"almost" translinear. Certain JFET circuits falling outside Gilbert's
original definition embodied useful generalizations of the idea as early as
1965, I've cited them in print in the past.
(h) Some of the oldest cases of what are called generalizations of
translinearity (early to middle 1960s) employ the "square-law" relationships
found in FET devices. An aspect of translinearity that carries over to its
generalizations is that unpredictable device parameters can be cancelled out
inherently. Temperature- and manufacturing-independent square-root
functions have been designed using FETs cleverly, though the FET square laws
have not the fundamental accuracy of the BJT exponential.
(i) Please note finally that translinear circuits are _not_ "log-antilog"
analog circuits as found in classic analog-computer texts of Jackson or Korn
and Korn or in the App Notes of makers of temperature-compensated log
amplifiers (or classic discrete log-amp app circuits with Tel-Labs Q81
thermistors). They are compact, specialized circuits that directly
implement large-signal, temperature-independent linear or nonlinear
input-output relations, such as square roots.
I did not mean to claim that one of the simple four-transistor dedicated BJT
square-rooting circuits, or the various FET square-rooting circuits, was
always the best or simplest solution, but rather that they should be
suggested, and considered, for this task.
Your servant -- MH
[1] Gibbons and Horn popularized this point in an ISSCC 1963 paper, still
cited, demonstrating ten decades of current range, with attention to
second-order effects.
[2] _Electronics Letters_ vol. 11 no. 1 pp. 14-16, January 1975.
Tony Williams
Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:
[snip]
> .........I prefer the AD734, and have often suggested it for
> tasks like this. The datasheet fig 9 shows a square root
> circuit.
For powers and roots I used to be a fan of a circuit
taken from an Analog Devices publication, called the
Multifunction Circuit. Two pairs of transistors and
a few opamps.
That was in the days when packaged multiplier/dividers
were a fearsome price........
--
Tony Williams.
Chaos Master
> For powers and roots I used to be a fan of a circuit
> taken from an Analog Devices publication, called the
> Multifunction Circuit. Two pairs of transistors and
> a few opamps.
Do you have the schematic of this circuit? I wish to see it.
[]s
--
Chaos Master®, posting from Canoas, Brazil - 29.55° S / 51.11° W
"Now: the 2-bit processor, with instructions:
1. NOP - does nothing, increase PC.
2. HLT - does nothing, doesn't increase PC
3. MMX - enter Pentium(r) emulation mode; increase PC
4. LCK - before MMX: NOP ; after MMX: executes F0 0F C7 C8 "
Tony Williams
Chaos Master <e-m...@is.INVALID> wrote:
> Do you have the schematic of this circuit? I wish to see it.
Analog Devices Model 433. It was essentially a log-antilog
multiplier/divider with a 4-element resistor bridge between
the log-antilog sections. It would take powers/roots over an
exponent range of 5/1 to 1/5. I used the circuit extensively
after realising the curves of many of the exotic thermocouples
could be simply described just by raising to a specific power.
Copied below, all opamps were inverters with their +ve inputs
connected to 0v.
+---||--+ +----[R3]--+-Vout
| |\ | | |\ |
Vx--[R1]-+--|->--+---[R?]----+ +--|->-----+
| |/ | | |/
| | |
+----+ | |
| +---+---+ |
+----|---+ | B | | +----+
| | | [Ra] [Rc] | | |
| |/ \| | | |/ \| |
0v---|--| Q1a/b |----+A C+----| Q2a/b |--|---0v
| |\e e/| | | |\e e/| |
| | | [Rb] [Rb] | | |
| +-+-+ | | +-+-+ |
| | +---+---+ | |
| [Rt1] | [Rt2] |
| | -+-0v | |
+---||-+ +-||---+
| |\ | | /| |
Vz--[R2]-+--|->-+ +-<-|--+-[R4]--Vy
|/ \|
m
R3 ( Vx ) Rb + Ra
Vout= --.Vy.( -- ) where m = -------
R4 ( Vz ) Rb + Rc
For raising to a power (m= >1), B-C would be shorted and
m = (Rb + Ra)/Rb.
For roots, B-A would be shorted and m = Rb/(Rb +Rc).
For a straightforward XY/Z multiplier/divider, short ABC.
The Model 433 had an internal 9v Vref and in manufacture
the ratio R4/R3 was adjusted to equal the value of Vref/10.
--
Tony Williams.
Tony Williams
> | | +---+---+ | |
> | [Rt1] | [Rt2] |
> | | -+-0v | |
About 100mS after upload you see the typo, ambiguity,
whatever.
Rt1/2 are not temperature senstive resistors. They are
simply Rtail-1 and Rtail-2 (of the long-tailed pairs).
AFAIR I ran I-tail at about 125uA full scale using the
RCA 5-transistor array.
--
Tony Williams.
Winfield Hill
Did you cancel that? Could you repost it? It didn't appear.
--
Thanks,
- Win
Tony Williams
Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:
> Did you cancel that? Could you repost it? It didn't appear.
No I didn't cancel it and it did appear back here.
Text of the original article reposted below........
Stephan Goldstein
This circuit is described at some length (about 9 pages as I recall)
in the Nonlinear Circuits Handbook, published by Analog Devices
and edited by Dan Sheingold. There's a lot of old-time circuits
wisdom contained therein. I don't know if it's still in print, or available
on the web - I keep a copy on my desk. Tony's quick description
appears to cover most of the important bits.
Steve
Tony Williams
Stephan Goldstein <sg0ld...@yahoo.com> wrote:
> This circuit is described at some length (about 9 pages as I
> recall) in the Nonlinear Circuits Handbook, published by Analog
> Devices and edited by Dan Sheingold. There's a lot of old-time
> circuits wisdom contained therein. I don't know if it's still in
> print, or available on the web - I keep a copy on my desk.
A totally valuable book to analogue designers. I lost mine
for about 15 years but recovered it earlier this year (from
a customer's bookshelf of all places). The spine is broken
and there appears to be a chunk missing, but what is left
is still worth keeping for reference. Those 9 pages of
the Multifunction Converter are still there and the posted
sketch was copied directly from them.
> Tony's quick description appears to cover most of the
> important bits.
> > +---||--+ +----[R3]--+-Vout
> > | |\ | | |\ |
> > Vx--[R1]-+--|->--+---[R?]----+ +--|->-----+
> > | |/ | | |/
Resistor [R?] was not in the A-D circuit. It is neccessary
to avoid oscillations in the log-ratio circuit and to limit
the voltage excursions on the Q1,Q2 bases. I arbitrarily
sized [R?] so that, at full opamp output swing, the voltage
at point B did not exceed about 1V.
--
Tony Williams.
Chaos Master
> > Do you have the schematic of this circuit? I wish to see it.
>
> Analog Devices Model 433. It was essentially a log-antilog
> multiplier/divider with a 4-element resistor bridge between
> the log-antilog sections. It would take powers/roots over an
> exponent range of 5/1 to 1/5. I used the circuit extensively
> after realising the curves of many of the exotic thermocouples
> could be simply described just by raising to a specific power.
>
> Copied below, all opamps were inverters with their +ve inputs
> connected to 0v.
Good! Thanks, I will check this circuit and maybe simulate it.
Tony Williams
Chaos Master <e-m...@is.INVALID> wrote:
> Tony Williams wrote:
> > Analog Devices Model 433.
> Good! Thanks, I will check this circuit and maybe simulate it.
When m=1 the 433 circuit does Vout= X*Y/Z. If Z is
connected back to Vout then X*Y = Vout-squared.
If X is the input and Y is a fixed Vref then it
functions as a square rooter.
However, (AFAIR) Win's suggested AD734 (and say the
B-B MPY600) can function as a direct square-rooter,
without the need for an extra Vref.
This is because this type of multiplier has a high
gain internal opamp, which has X*Y on one input and
Z on the other. Connections are always made so the
the negative feedback forces (X*Y - Z) = 0.
If Z is made the input and Vout connected back to both
X and Y then circuit is forced to do Vout= sq-rt(Z).
No Vref needed.
--
Tony Williams.
Spehro Pefhany
Speaking of square root circuits and design methodology (another
thread), here's an interesting paper:
http://www.genetic-programming.com/jkpdf/icec1997.pdf
Tony Williams
Spehro Pefhany <spef...@interlogDOTyou.knowwhat> wrote:
> Speaking of square root circuits and design methodology (another
> thread), here's an interesting paper:
> http://www.genetic-programming.com/jkpdf/icec1997.pdf
Page 6, Figure 8. Q123 looks a little suspicious.
--
Tony Williams.
Mike Monett
Nice. Also QPC19, Q77, Q184 and Q258.
Mike Monett
Jim Thompson
What weed were those guys smoking ?:-)
Mike Monett
[...]
> What weed were those guys smoking ?:-)
>
> ...Jim Thompson
> --
> | James E.Thompson, P.E. | mens |
> | Analog Innovations, Inc. | et |
> | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
> | Phoenix, Arizona Voice:(480)460-2350 | |
> | E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
> | http://www.analog-innovations.com | 1962 |
>
> I love to cook with wine. Sometimes I even put it in the food.
Perhaps they never had to fix an autorouted board:)
Although it should be possible add more checking to the software to
prevent those errors. For example, don't connect the collector to the
emitter:)
Mike Monett
Spehro Pefhany
Humans have vestigial components too.
John Popelish
>
> Jim Thompson wrote:
> > What weed were those guys smoking ?:-)
> Perhaps they never had to fix an autorouted board:)
>
> Although it should be possible add more checking to the software to
> prevent those errors. For example, don't connect the collector to the
> emitter:)
In genetic design, any connection that is possible and not expressly
forbidden (the forbidden cases, in this case probably involve
excessive currents) are allowed. The apparently pointless parts and
connections often provide the tricks that make the circuit do
something useful but not obvious to a goal oriented observer.
--
John Popelish
Nicholas O. Lindan
> >
> > > Speaking of square root circuits and design methodology (another
> > > thread), here's an interesting paper:
> >
> > > http://www.genetic-programming.com/jkpdf/icec1997.pdf
> > Page 6, Figure 8. Q123 looks a little suspicious.
A square root circuit design by genetic algorithm.
Packed with vestigial organs and junk DNA.
Apart from all that, it works rather well.
Darwin rules. Well, God rules, Darwin interprets.
--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/
Winfield Hill
> Mike Monett wrote
>> Tony Williams wrote:
>>> Spehro Pefhany wrote:
>>>
>>>> Speaking of square root circuits and design methodology
>>>> (another thread), here's an interesting paper:
>>>>
>>>> http://www.genetic-programming.com/jkpdf/icec1997.pdf
>>> Page 6, Figure 8. Q123 looks a little suspicious.
>> Nice. Also QPC19, Q77, Q184 and Q258.
>
> A square root circuit design by genetic algorithm.
>
> Packed with vestigial organs and junk DNA.
> Apart from all that, it works rather well.
> Darwin rules. Well, God rules, Darwin interprets.
Works well? It has 0.1% accuracy over three input decades,
with 10% supply-voltage and 50C temperature effects < 0.1%?
Works over the usual production variations in BJT parms, and
doesn't require a certain beta value or leakage current, etc.?
--
Thanks,
- Win
Mike Monett
[...]
> Humans have vestigial components too.
> Best regards,
> Spehro Pefhany
Not if I designed 'em. Everyone would have exactly the right number of
parts, correctly proportioned to work in perfect harmony, like this:
http://www3.sympatico.ca/add.automation/misc/perfect.jpg
Not that I'd expect any thanks or recognition. You ungrateful wretches
would probably do away with Santa if you had a chance:
http://www3.sympatico.ca/add.automation/misc/santa.jpg
(Images courtesy of J.Thompson, I think:)
Mike Monett