VC pots

[Scott Gravenhorst]

I have seen circuits for 'voltage controlled resistors' that are really 
an MOS analog switch whose control input is driven by a pulsewidth 
modulated constant frequency oscillator.

A voltage divider circuit should just be two analog switches, with one 
common connection, where one uses the pulse output of the oscillator 
for control and the other uses the inversion of the pulse output.

Has anyone here tried to use this method to add voltage control to a 
circuit (to do what the pot does)?