VC pots

Rick Jansen sscprick at
Mon Oct 23 10:22:19 CET 1995

In message <199510222138.OAA11107 at> you write:
> 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)?

You can build VC resistors with OTA's too. National Semiconductor's
data sheets for the 13600 show a circuit. Another method is to use 

Rick Jansen
rick at
S&H's a module and s&h's looking good

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