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FDC2214: Question about active shielding setup

Part Number: FDC2214
Other Parts Discussed in Thread: FDC1004

Dear TI experts,

According to the datasheet, the buffered signal of INxA acts as the drive signal for the active shield.

But the oscilloscope shows a 180° phase difference between the signals on INxB and INxA.

For differential sensor configuration, do I need to configure the active shield as shown below?

where INxA and INxB each have their own active shield.

And is there a crosstalk issue with this configuration?

Or the buffered signal of INxA is sufficient for the sensor in differential configuration.

Best regards,

Will

  • Will,

    Your diagram looks correct as long as your goal is to actively shield your two electrodes separately. I say "conceptually" because I have not seen anyone use the device this way before. Please be sure any input impedance of your shield drivers is considered in your sensor design since input capacitance and resistance can skew the sensor frequency, Rp  and Q.

    I'm not sure about the crosstalk. Depending on your electrode & shield design & placement, its conceivable that the INxA shield could interfere with the INxB electrode. It may not be enough of an effect to create problems, but its something to keep in mind.

    Please consider using the FDC1004 as an alternative to the FDC2xxx series. The FDC1004 has built-in shield drivers, and can be easily configured for differential measurements.
    More info on the FDC1004 can be found at FDC1004 Capacitive Sensing FAQ page.
    We have found that many users have struggled with the FDC2xxx because of EMI, even with good grounding and shielding strategies. 

    regards,
    John