I've been reading about varicaps, and I'd like to try to use one in an op-amp integrator circuit to be able to adjust the gain.
My confusion though is that every varactor diode datasheet I've read indicates that only 2 pins are used, like a normal diode. The capacitance is supposed to change with reverse voltage across the diode, but how then is the capacitor supposed to be used in useful way?
Only 2 pins used in both package types!
Doesn't make any sense to me, since obviously you can't keep the diode at a constant reverse voltage AND use it in any type of circuit where an alternating waveform is applied. I was expecting them to have a 3rd pin where an external control voltage was applied.
What am I missing?
Best Answer
Sure you can as the millions of varactor tuners produced will testify.
Of course, the AC signal must be relatively small. From Wikipedia.