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

mskala at northcoastsynthesis.com mskala at northcoastsynthesis.com
Thu Mar 21 21:12:37 CET 2024

On Thu, 21 Mar 2024, Rutger Vlek via Synth-diy wrote:
> 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?

I'm not sure it's really going to make an important difference, but you
could use a single op amp full-wave rectifier to bring the component count
for "absolute value of difference" down to two op amps, with associated
reduction in support components.  I used it in my Coiler VCF, and the
circuit is described on page 35 of the manual here:

I've seen it in a few places online, usually attributed to "Tompkins,
W.J., and J.G. Webster (eds.), Interfacing Sensors to the IBM PC.
Prentice-Hall, 1988," but I haven't actually seen the original print

Matthew Skala
North Coast Synthesis Ltd.

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