Need to make multiplication circuit - Electronic Circuits Projects Diagrams Free

TheJokerV · 8th February 2008, 06:35 AM

I hope everyone is doing well. I need to make a circuit which multiplies two analog inputs. Essentially I have to build a circuit which takes in 2 voltages and has an output voltage equal to some constant time the two voltages multiplied together. I know how to build exponential, summation and difference circuits using opamps but I have no ide how to build a multiplication circuit. Any suggestions/ideas? Thanks guys.

Diver300 · 8th February 2008, 08:43 AM

You need a log circuit, which is basically the inverse of the exponential circuit.

Two inputs, A and B
Log them both
add them up
take the exponent.

Mathematically, log(A*B) = log(A)+log(B)

so

A*B = 10 ^ (log(A)+log(B))

(assuming a base 10 log but any base will do as long as your exponential is to the same base)

This is how log table or slide rules allowed us to do reasonably accurate multiplication or division before calculators.

There have been analog multiplication circuits that use this principal. It is now much easier to do it all digitally.

Pommie · 8th February 2008, 11:23 AM

Could you use something like the AD834. Google four quadrant multipliers for others.

Mike.

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8th February 2008, 06:35 AM	(permalink)
TheJokerV	Need to make multiplication circuit I hope everyone is doing well. I need to make a circuit which multiplies two analog inputs. Essentially I have to build a circuit which takes in 2 voltages and has an output voltage equal to some constant time the two voltages multiplied together. I know how to build exponential, summation and difference circuits using opamps but I have no ide how to build a multiplication circuit. Any suggestions/ideas? Thanks guys.

8th February 2008, 08:43 AM	(permalink)
Diver300	You need a log circuit, which is basically the inverse of the exponential circuit. Two inputs, A and B Log them both add them up take the exponent. Mathematically, log(AB) = log(A)+log(B) so AB = 10 ^ (log(A)+log(B)) (assuming a base 10 log but any base will do as long as your exponential is to the same base) This is how log table or slide rules allowed us to do reasonably accurate multiplication or division before calculators. There have been analog multiplication circuits that use this principal. It is now much easier to do it all digitally.

8th February 2008, 11:23 AM	(permalink)
Pommie	Could you use something like the AD834. Google four quadrant multipliers for others. Mike. Last edited by Pommie; 8th February 2008 at 11:25 AM.