Switched Capacitor Phase Shifters

[Grant Richter]

I've been looking for a simple phase shifter network.

I have a PAIA Shepard function generator kit laying around with two of the six channel VCA cards.
I thought I'd build a barber pole phaser but needed a simple phase shifter I could
reproduce eight times.

I think I found it while doing a patent search on switched capacitor filters.

The classic phase shift element uses one op-amp, three resistors, one cap and a
variable resister per stage. The various designs I've looked at use FET's or Vactec
LDR's for the variable resistor. The patent search turned up a circuit using an
electronic switch (like a CD4066) with pulse width modulation for the variable
resister.

Boy is that simple, four per package and you only need one 41khz sawtooth for the
whole array. So, one audio quad op-amp, a CD4066, one LM339 section per four
poles. Makes a four feature phase shifter section. Cheap and low parts count.

Grant