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Measuring small (less than 1 pF) capacitance

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Hello,

This is a corollary thread from the previous one I made.

I am making a small (mm scale) capacitive encoder, and capacitance will likely be less than 1 pF. I would like to measure with at least 0.1 pF resolution (ideally, something like 0.05pF). This will be all embedded on a very small robot, so resource is limited.

Any suggestsion? One obvious way is to use RC, while the other one is to use sine wave input and measure the phase (which I am not too sure how to do).

Best Regards.
 

The digital capacitance sensor from Analog had already been mentioned, a lot of different analog or C-to-time converters can be imagined. The best solution depends on intended resolution, supply voltage, required interface for results. Generally a RC or LC oscillator with sensitive frequency measurement promises low part count and high resolution. A RC oscillator (e. g. from HC14 single gate) should allow direct uP interface.
 

    M

    MathGeek

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Thanks for your help.
The Analog products look promising.

Please let me know if there are other suggestions.
 

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