Circuit to calculate square root of voltage?

Chaos Master · Dec 4, 2004

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
--
Chaos MasterŽ, 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

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NP in foobar2000: 02. Nightwish - [Angels Fall First] Angels Fall First
[5:35]

CFoley1064 · Dec 4, 2004

Subject: Circuit to calculate square root of voltage?
From: Chaos Master ch@os.master.INVALID.INVALID
Date: 12/3/2004 9:35 PM Central Standard Time
Message-id: <MPG.1c1b0d90982267ab989734@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

Chaos Master · Dec 4, 2004

John Popelish to stdout:

[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 MasterŽ, 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
UNWANTED REPLIES = PLONK TO WHO SENT THEM.

Stefan Wyss · Dec 4, 2004

Chaos Master <ch@os.master.INVALID.INVALID> wrote in message news:<MPG.1c1b0d90982267ab989734@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?

[]s
--
Chaos MasterŽ, 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.
UNWANTED REPLIES = PLONK TO WHO SENT THEM.

NP in foobar2000: 02. Nightwish - [Angels Fall First] Angels Fall First
[5:35]

Here you got it:
http://www.edn.com/archives/1997/112097/24di_07.htm

Cu, Stefan

Nicholas O. Lindan · Dec 4, 2004

"Chaos Master" <ch@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).

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 · Dec 4, 2004

On Sat, 4 Dec 2004 01:35:19 -0200, Chaos Master
<ch@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

480)460-2350 | |
| E-mail Address at Website Fax

Winfield Hill · Dec 4, 2004

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?

--
Thanks,
- Win

Chaos Master · Dec 4, 2004

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.

[]s
--
Chaos MasterŽ, 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
UNWANTED REPLIES = PLONK TO WHO SENT THEM.

Rich Grise · Dec 4, 2004

On Sat, 04 Dec 2004 09:11:00 -0800, Winfield Hill 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?

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

Tony Williams · Dec 5, 2004

In article <MPG.1c1b0d90982267ab989734@News.individual.net>,
Chaos Master <ch@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.

Winfield Hill · Dec 21, 2004

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. :&gt

I prefer the AD734, and have often suggested it for
tasks like this. The datasheet fig 9 shows a square root circuit.

--
Thanks,
- Win

Ric · Dec 21, 2004

Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

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. :&gt I prefer the AD734, and have often suggested it for
tasks like this. The datasheet fig 9 shows a square root circuit.

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 · Dec 22, 2004

Rick wrote...

Winfield Hill wrote:
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. :&gt I prefer the AD734, and have often suggested it for
tasks like this. The datasheet fig 9 shows a square root circuit.

Barry Gilbert himself freely admits in his publications that a
certain Mr H.E. Jones has prior art on the "Gilbert Cell".

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

Tony Williams · Dec 22, 2004

In article <cq95j70c31@drn.newsguy.com>,
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 · Dec 23, 2004

In me, the Tony Williams:

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 MasterŽ, 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 · Dec 23, 2004

On 23 Dec, tonyw@ledelec.demon.co.uk wrote:

| | +---+---+ | |
| [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 · Dec 23, 2004

Tony Williams wrote...

On 23 Dec, tonyw@ledelec.demon.co.uk wrote:

| | +---+---+ | |
| [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.

Did you cancel that? Could you repost it? It didn't appear.

--
Thanks,
- Win

Tony Williams · Dec 27, 2004

In article <ofgts0t7iagfs7hromo297n7tlk74mm53f@4ax.com>,
Spehro Pefhany <speffSNIP@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 · Dec 27, 2004

Tony Williams wrote:

In article <ofgts0t7iagfs7hromo297n7tlk74mm53f@4ax.com>,
Spehro Pefhany <speffSNIP@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.

Nice. Also QPC19, Q77, Q184 and Q258.

Mike Monett

Winfield Hill · Dec 27, 2004

Nicholas O. Lindan wrote...

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

Circuit to calculate square root of voltage?

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