Analog Signal Calculator/ A+B and A-B

Opamps can perform arithmetic addition and arithmetic subtraction at

Opamps can do more complicated things.

A - B How about Y = ------- A + B

What would be your approach? :)

BTW this function is quite common in the analog surround sound processors.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

LVDT?

John

Something like this?

Martin

On a sunny day (Tue, 06 Nov 2007 15:50:30 -0000) it happened " snipped-for-privacy@googlemail.com" wrote in :

• A ----------|\ 2*A | >--------------------- --|/ | | | - | | |-- 2R -- | | R R R | | | /// |--- A+B |--- A-B | | R R | | | --- R ----| + | | | B ---|\ 2*B | | - | | >------------- R ----|\ -2*B | --|/ | | >----- | - | --|/ |-- 2R -- | + R /// | ///

Here is a nice audio experiment that uses summing and substracting:

The obvious thing is to put a multiplier in the feedback path. The log/anti-log method is available too. If the problem is 2-quadrant, then the variable transconductance method can be used.

See the Analog Devices _Nonlinear Circuits Handbook_, pp.271-326. No doubt there must be something available on the Analog Devices website too.

On Tue, 06 Nov 2007 15:50:30 -0000 in sci.electronics.design, " snipped-for-privacy@googlemail.com" wrote,

Aren't adding and subtracting examples 1 and 2 in the op-amp app note?

On Nov 6, 7:50 am, " snipped-for-privacy@googlemail.com" wrote: \\

If you have power supplies and amplifiers, the solution is trivial (in the sense that a summing junction or inverting amplifier is a trivial item to build from op amps).

If there's no power, the best solution might be a center-tapped coupling transformer: drive B into the primary of the transformer, connect the secondary center tap to A, and the branches of the secondary will now have A+B and A-B signals.

The transformer has to be wound in 1:2 ratio or you will get a pair of signals A + kB and A -kB instead... if you wind your own transformer, a trifilar winding would be suitable.