[sdiy] Simple circuit challenge: |a-b|

Rutger Vlek rutgervlek at gmail.com
Thu Mar 21 20:50:44 CET 2024

Dear list,

while hobbying on an experimental design, I'm looking for a simple analog
circuit to give me the absolute value of the difference between two signals
(mathematically written as |a-b|).

I already have a working circuit, but it's rather big for my needs. It uses
an inverting opamp to invert signal A, followed by a bog-standard full wave
precision rectifier circuit where -A and B are summed together and being
rectified. The total is 3 opamps, 2 diodes and 9 resistors. As I need to
repeat the circuit many times in the final application, I'm wondering: is
there anything simpler that can do this?

- working across full audio range
- distortion as consequence of diode drops is no problem (might even be

Many thanks for any suggestions!


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