[sdiy] Sallen-Key Filter & 4069

[Scott Gravenhorst]

In the spirit of really simple, I started looking at
filter topologies and noticed that the Sallen-Key
filter is really simple.  It's a second order filter
that uses just one opamp.  I also noticed that the
2 resistors responsible for tuning are connected
in series.  If a 4069 is used in the voltage controlled
resistor mode, might two of the gates be substituted 
for the tuning resistors to make it a voltage controlled
Sallen-Key?  I think this is possible, I just don't
know exactly how to do it.

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