How to measure capicitance of component at specific voltage

[uoficowboy]

Hi - I'd like to build a circuit that measures very small capacitances at specific bias voltages. My interest is in measuring the capacitance of a diode both reverse and forward biased.

Most techniques I've seen involving measuring capacitance of a capacitor involve charging up the component quite a bit - typically changing the voltage by at least a couple volts. I'd ideally like to be changing the voltage of the part no more than 50mV or so. I'm expecting capacitances of 1-50pF, so this isn't a huge charge!

Can anybody suggest any ways of doing this?

Thanks so much!!!

 

[keith1200rs]

You could measure the amplitude and/or phase of an AC signal fed to the diode through a resistor.

Keith.

 

[FvM]

Re: How to measure capicitance of component at specific volt

Most techniques I've seen involving measuring capacitance of a capacitor involve charging up the component quite a bit - typically changing the voltage by at least a couple volts.

It's not true for most quality LCR meters, that basically use small signal AC impedance measurement at selectable frequency and drive level.
They usually also have an option to supply a DC bias voltage.