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FDC2214 - Is there an optimal ratio of capacitance between the fixed LC capacitor and sensor?

Jay Chang16
Prodigy 60 points
Other Parts Discussed in Thread: FDC2214, FDC1004

I am working with the FDC2214 eval board.  The range of the capacitor I am trying to measure is from ~1 to 800 fF, a really small capacitance.  With the fixed capacitor being 33pF, is it too difficult to have the sensitivity to measure down to single digit fFs?  Should I try swapping out the 33pF cap for a smaller one?  

I also have your FDC1004 but would like to see if I can get better results with the FDC2214.

Thank you!

  • 0
    TI__Expert 8050 points
    Hi Jay,

    It's possible to measure down to single digit fFs with the 33pF. There is some trade-off by using a smaller cap. You can potentially get a little better resolution, but your signal is likely to drift more. The actual resolution you can get will also depend on other noise sources in your system.

    You may even try removing the 33pF. The LC tank can still oscillate because there is parasitic capacitance from the chip and the PCB. You can compare the performances with and without the 33pF to see which configuration works better with your system.

    Regards,
    Yibo