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FDC1004EVM: Measure resolution and data variation question

Hongyu Wang
Prodigy 20 points
Part Number: FDC1004EVM

The FDC 1004 board was used to measure the capacitance change of MEMS. The MEMS comprises four Parallel plate capacitive sensing parts which are good for 4 channel sensing. The expected resolution is below 1 fF. For the measured data, the variation is severe which should be a constant value when the structure is static. The data was attached. As it showed the variation is large than 10 fF. This makes it difficult to measure the capacitance change (less than 10 fF) when the structure is moving. It will be appreciated if you have any comments. Thanks for your help.

  • 0
    TI__Genius 10080 points

    Hello,

    Thank you for posting.

    There is a 46 fF offset deviation across temperature that is listed as a typical specification in the datasheet (section 7.5 - Electrical Characteristics). A temperature calibration will need to be performed in order to measure with a resolution below 1 fF.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    Prodigy 20 points

    Hello Nicole,

    Thanks for your answer. 

    Could you provide more detail about the temperature calibration? I took the measure in the room in which the temperature should be constant. Regarding the drastic fluctuations in data, do you think this is due to temperature offset?

    Best regards,

    Hongyu

  • +1 in reply to Hongyu Wang
    TI__Genius 10080 points

    Hello Hongyu,

    It is possible that the noise you are seeing is caused by environmental factors. It is reasonable to see a noise floor on the order of fF, but make sure that you are avoiding long cables to connect the sensors, and note that a larger sensor area has a higher chance for the sensor to be affected by noise or interference from the environment. The following Capacitive Sensing FAQ has links to various application notes that may help with sensor connection and design.

    Best regards,

    Nicole