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FDC2214EVM: Values for LC-Resonator to set Fref to 10kHz

Robert Reichel
Prodigy 10 points
Part Number: FDC2214EVM
Other Parts Discussed in Thread: FDC2214

Hello!

I want to measure the capacity of a sensor, but the sensor needs to be measured at around 10kHz. The sensor has a capacity of 300 - 600 pF.

I tried changing the values of L and C to 1µF and 100µH, which should give me a resonance frequency of 15,9 kHz but the Software then tells me

that my sensor capacity is a negative number.

Which values for L and C would you recommend using to measure 300 to 600 pF at around 10 or 20 kHz? The datasheet mentions that 20 kHz can be achieved by using a 1mH coil,

but is it also possible to raise the parallel capacitance to get the desired resonance frequency?

Kind Regards,

Reichel Robert

  • 0
    TI__Genius 17440 points

    Hi Robert,

    I would recommend checking the Rp value of your sensor. If this value is too low, the FDC2214 may not be able to drive enough current to keep the sensor oscillating. You can check this with an oscilloscope by ensuring that the voltage drop from INA to ground (or INB to ground) is within the recommended range (between 1.2-1.8 V).

    May I ask why your sensor needs to have a resonant frequency close to 10 kHz? That is an especially low frequency for the FDC2214, which can drive sensors between 10 kHz and 10 MHz. The sensor frequency will affect the resolution of your capacitance measurement. The FDC2214 measures the resonant frequency of the sensor and outputs a digitized value that can be converted to a shift in capacitance. The device only has a certain amount of time to make this frequency measurement, based on the sample rate you set. A higher frequency will have significantly more sensor oscillations within the sample period, which will yield a much better measurement resolution. The minimum sensor frequency I would recommend using with the FDC2214 is 100 kHz; frequencies below this will have very poor resolution.

    Regards,