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

[Roman Sowa]

What a brilliant idea!
Obvious solution was to substract first and then rectify, but doing it 
the other way around makes it simpler, not to mention the beauty of 
using Graetz bridge.
It looks like it was designed by Japanese engineer from the old synth days.
Oh wait...
Nevermind

Roman

W dniu 2024-03-28 o 03:43, houshu--- via Synth-diy pisze:
> Hello Rutger and List,
> 
> 
> Here is my solution.
> 
> 
> |a-b| = Max(a,b) - min(a,b).
> 
> 
> If output offset is acceptable, we can omit D5, D6, and R7.
> 
> Impedance of inputs should be low. When one of inputs is open, output is 
> a little distorted.
> 
> 
> Sam HOSHUYAMA
> 
> Kawasaki, Japan.
> 
> 
> 
> 
>     ------ Original Message ------
>     差出人: "Rutger Vlek via Synth-diy" <synth-diy at synth-diy.org>
>     To: "SDIY List" <Synth-diy at synth-diy.org>
>     送信済み: 金曜日, 2024/3/22 04:50
>     件名: [sdiy] Simple circuit challenge: |a-b|
> 
>     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?
> 
>     Requirements:
>     - working across full audio range
>     - distortion as consequence of diode drops is no problem (might even
>     be beneficial!)
> 
>     Many thanks for any suggestions!
> 
>     Regards,
> 
>     Rutger
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