VC pots

[Rick Jansen]

In message <199510222138.OAA11107 at ix4.ix.netcom.com> 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 
a JFET.

Rick Jansen
__
rick at sara.nl   http://www.sara.nl/Rick.Jansen
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