Simplest Possible Analog Divider

[Bret Cahill]

Some circuits use transistors or diodes to take logs, subtract and
then exponentiate to divide two signals.

The simplest mechanical divider that linear at least over a certain
range is a lever were the denominator is the distance the fulcrum is
moved away from where the numerator [force] is applied.

What's the most primitive / basic circuit that divides 2 impedances or
voltages?


Bret Cahill

 

[John Larkin]

On Sun, 4 Oct 2009 17:32:00 -0700 (PDT), Bret Cahill
<BretCahill@peoplepc.com> wrote:

Some circuits use transistors or diodes to take logs, subtract and
then exponentiate to divide two signals.

The simplest mechanical divider that linear at least over a certain
range is a lever were the denominator is the distance the fulcrum is
moved away from where the numerator [force] is applied.

What's the most primitive / basic circuit that divides 2 impedances or
voltages?


Bret Cahill

uP with 2-channel ADC, divide firmware, dac.

John

 

[John Larkin]

On Mon, 5 Oct 2009 07:13:11 -0700 (PDT), Bret Cahill
<BretCahill@aol.com> wrote:

Some circuits use transistors or diodes to take logs, subtract and
then exponentiate to divide two signals.

The simplest mechanical divider that linear at least over a certain
range is a lever were the denominator is the distance the fulcrum is
moved away from where the numerator [force] is applied.

What's the most primitive / basic circuit that divides 2 impedances or
voltages?

Bret Cahill

uP with 2-channel ADC, divide firmware, dac.

That may be the real world solution but an idealized analogy might be
interesting, maybe a variable capacitor where the distance between
plates increases with the denominator signal.

There's probably a comprehensive list of analogues between every
kinematic mechanism and its corresponding electronic circuit. It
wouldn't be a bad idea to torture some of these as much as possible.


Bret Cahill

A few classic electronic ways to do it are...

Gilbert-cell multiplier in a feedback loop

PWM multiplier in a feedback loop. Slow but very precise

Motor-driven dual 10-turn pot and a few tube opamps, like they used to
do in olden days.

An MDAC can be made to divide, too.


http://www.analog.com/en/other-products/analog-multipliersdividers/products/index.html


John

 

[Bret Cahill]

Some circuits use transistors or diodes to take logs, subtract and
then exponentiate to divide two signals.

The simplest mechanical divider that linear at least over a certain
range is a lever were the denominator is the distance the fulcrum is
moved away from where the numerator [force] is applied.

What's the most primitive / basic circuit that divides 2 impedances or
voltages?

Bret Cahill

uP with 2-channel ADC, divide firmware, dac.

That may be the real world solution but an idealized analogy might be
interesting, maybe a variable capacitor where the distance between
plates increases with the denominator signal.

There's probably a comprehensive list of analogues between every
kinematic mechanism and its corresponding electronic circuit. It
wouldn't be a bad idea to torture some of these as much as possible.


Bret Cahill

 

[Rich Grise]

On Sun, 04 Oct 2009 17:32:00 -0700, Bret Cahill wrote:

Some circuits use transistors or diodes to take logs, subtract and then
exponentiate to divide two signals.

The simplest mechanical divider that linear at least over a certain range
is a lever were the denominator is the distance the fulcrum is moved away
from where the numerator [force] is applied.

What's the most primitive / basic circuit that divides 2 impedances or
voltages?

Analog multiplier wired as a divider.

Unless you mean a simple voltage divider, two resistors in series.

Hope This Helps!
Rich

 

[whit3rd]

On Oct 4, 5:32 pm, Bret Cahill <BretCah...@peoplepc.com> wrote:

What's the most primitive / basic circuit that divides 2 impedances or
voltages?

Well, a noninverting op amp amplifier, with feedback resistor Rf and
(-) to GND
resistor Rs has output

Vo = Vin * Rs/Rf

so division of impedances is a cakewalk. One amplifier, one fixed
voltage source.

Since division blows up at divide-by-zero, only high-gain solutions
need
apply, I suspect a single op amp is the minimum circuit element that
can provide that.

 

[whit3rd]

On Oct 4, 5:32 pm, Bret Cahill <BretCah...@peoplepc.com> wrote:

What's the most primitive / basic circuit that divides 2 impedances or
voltages?

The normal op amp connected as an inverting amplifier, feedback
resistor Rf (output to (-)) and Rs (input to (-)) with (+) grounded,

Vout = - Vin * Rf/Rs

The solution has to properly blow up with zero in the divisor, so only
a high-gain amplifier can do that; one op amp and two resistors
is the most basic workable scheme. I think.