Commutating Filter (was "Stacked Power Supplies...")

Stopp,Gene gene.stopp at
Wed May 20 21:30:00 CEST 1998

The commutation filter uses multiplexed capacitors in its integrators.
In this case, there are two cascaded switched cap integrators, with
feedback to provide a state-variable configuration. Each integrator has
a one-of-eight analog mux with eight caps, and they are scanned by the
same address lines. It's like having eight sample-and-holds in each
integrator, rather than a single cap.

It was originally presented in Electronotes as a kind of "novelty"
filter - not much introduction or theory, just "hey, here's a weird
filter you may want to try". They were obviously preying on the
synthesizer builder's inability to resist a device with such strange

They got me, I built one :)

I'll post when I have it up and running again.

 - Gene

From: sasami at
To: synth-diy at
Subject: Re: Commutating Filter (was "Stacked Power Supplies...")
Date: Tuesday, May 19, 1998 8:12PM

Would you care to educate the ignorant as to the purpose of a comutating


>The switching frequency is controlled by an ultrasonic VCO (I think I
>used a 4046). I provided sweep inputs (naturally!). The analog switches
>are 4051's.
> - Gene

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