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24th March 2010, 11:48 PM  #1 
diyAudio Member
Join Date: Sep 2005

Analog computing question  how to implement X^Y=Z
An attempt at a thought provoking question for the analog computing types:
In the world of analog circuits, how would one implement the function X ^ Y = Vout? That is, a circuit block with two inputs, X and Y (inputs can be voltage or current). The output voltage (or current) is equal to the input X, raised to the power of Y (Y is also an input). One way I can think of doing it is: X ^ Y = exp(y * ln(x)) This uses a logarithmic amplifier, exponential amplifier, and one multiplier. Are there other ways/circuits to implement this function? 
25th March 2010, 12:04 AM  #2 
diyAudio Member
Join Date: Oct 2006
Location: Charlotte, NC

They do make analog multipliers in integrated circuit form. On Semi used to, at least.

25th March 2010, 01:08 AM  #3 
diyAudio Member
Join Date: Feb 2003
Location: ..

Analog Devices is a big player in analog function blocks:
Analog Multipliers/Dividers  Other Products  Analog Devices also look for log amps but today single chip flash uC with ADC and DAC can give good results for applcations that fit the resolution and speed of the digital implementation Last edited by jcx; 25th March 2010 at 01:12 AM. 
25th March 2010, 01:43 AM  #4 
diyAudio Member
Join Date: Jan 2008
Location: Virginia

One log amp for the X signal (X needs to be positive).
The result feed into a multiplier with Y. The third result fed to a good OpAmp that has in the feedback network another log amplifier (to result the exp function). 
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