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FDC2112: FDC2112 LSB resolution using a 4 pF sensor

Stephen Ledingham
Prodigy 10 points
Part Number: FDC2112

Hi Ti

Assuming a system noise floor of < 10fF (Ti spec for FDC2x1x is 0.3 fF):

1) What is the LSB resolution (in fF) for 4 pF sensor capacitance using a sampling rate of 100 sps ?

2) What is the LSB resolution (in fF) for 4 pF sensor capacitance using a sampling rate of 10 sps

Many thanks, Steve

  • 0
    TI__Genius 17440 points

    Hi Steve,

    The FDC2112 measures the frequency change of the sensor LC tank to determine the change in capacitance. It converts the sensor frequency into a digital value representing the ratio of the sensor frequency to the reference frequency (clock) and outputs this value. Because the device works in the frequency domain, we measure the LSB in Hz. It is possible to convert the frequency shift into a capacitance shift using equation 7 in the datasheet, but this is not necessary in most applications. The raw output data from the FDC2112 can be used to detect a target interaction.

    The LSB resolution for the FDC2112 is about 152.4Hz for both given sample rates. Both sample rates are slow enough that they will not limit the resolution. However, there are several other factors to consider when determining the resolution of the system. I highly recommend that you read this application note about resolution optimization for the LDC131x devices. Although the app note is geared toward inductive sensing, the same resolution optimization approaches apply for capacitive sensing.

    Regards,