Voltage-Controlled Variable Capacitor

Hi all,

This is a different idea altogether from the synth I'm building.

So I have this idea for a band-variable vocoder. Knowing how vocoders work and how to make them, I would need a variable capacitor in the nanofarad range for this to work. Now, I'm already having problems just finding a variable cap in that range, but it gets better: I want it to be voltage controlled as well.

Sure, it's always possible to make one, but I was curious as to if such devices even exist. The best thing I can think of is to use a capacitance multiplier circuit, which can of course accept a varying voltage and alter capacitance like that.

Any other ideas?

 

Similar to a multiplier, but actually seemingly more practical. It seems that making it variable could be difficult, however. I'll look into it. Thanks!