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FDC2212: Waveforms

Filippo Piccardi
Prodigy 40 points
Part Number: FDC2212


Hi,

I'm using FDC2212 in single ended mode driving an LC tank composed by 22 pF capacitor and 1.8 uH Inductor with a current of 0.747 mA.

If I look at the waveforms on IN0A and IN0B (respect to ground) I see two half sine-waves with an amplitude of 3,3 V (see picture 1).
For this reason, I expect the voltage on the LC tank (V on IN0A - V on IN0B) to be a sine wave with an amplitude on 3,3 V.
However I find the waveform on picture 2.
Why is the sine wave truncated in the negative part? Is the effect of an internal clampig diode?
Why is the amplitude less than 3,3 V?
This waveform is normal or am I doing something wrong?

The datasheet recommends to set CH0_IDRIVE current in order to obtain a sensor oscillation amplitude between 1,2 V and 1,8 V but what voltage have I to consider?
The voltage on IN0A respect to ground (picture 1) or the voltage on IN0A respect to IN0B (picture 2)?

  • 0
    TI__Expert 7599 points

    Hello

    FDC2212 driving waveform is as expected. However the negative driving is not something that is typical. This indicates that the probes that are used to measure may not be properly grounded. If the ground leads has extra inductance it will end up showing as a spikes. 

    The recommended sensor voltage is between 1.2V pk 1.8V pk for best optimized results. Your plot 2 does indicate that the sensor amplitude is within 1.8V pk. Our datasheet indicates a guidance of LC sensor choice of 18uH and 33pF your choice is 1.8uH and 22pF. Have you tried to increase the inductance to 18uH?

    As we are on a break here our experts will get back to you with further questions. Meanwhile I highly recommend that you take a look at our datasheet section 10 for some guidance on setup and register settings for optimization.