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Conductive interference immunity test on FDC2214EVM

zhao Steven
Prodigy 90 points
Other Parts Discussed in Thread: FDC2214

Hello,

We performed some EMC immunity tests on our FDC2214 EVM, and got some interesting phenomena, which could not be understood by us. Could you give some comments? Thx.

Phenomena:

1, As shown in GUI, there are big variation of raw data, if the injected interference frequency is at the resonant frequency and its 3, 5, 7, 9, 11 times frequency. Our resonant frequency is around 5.47MHZ, then it's would more than 10MHZ at 3 times resonant frequency. Then, why could our sensor still detect it since the max active frequency is 10MHZ mentioned in the datasheet?

2, Also, the variation, on these frequency point, is not always toward one direction but positive change at certain frequency and negative change at other frequency.  Why is ti?

  • 0
    TI__Expert 8050 points

    Hello Steven,

    1. The 10 MHz is not a strict cut-off frequency for the LC resonator. Harmonics of the resonant frequency can still inject noise into the system even if it's above 10 MHz. However, the device may have anomalous behavior at such a high frequency.

    2. This is due to the random nature of noise.

    Regards,
    Yibo

  • 0 in reply to Yibo Yu
    Prodigy 90 points
    Hello Yibo,
    If what you said is true, it would totally overthrow our thought & expectation on the FDC2214 sensor.
    Per its datasheet, the principle of sensing is based on LC narrow pass resonator. So, we think that there is only problem at resonant frequency around during EMI test. But now, based on you said and our test result, same problem would occurred to various harmonics of resonant frequency. What's more worse, it shows that, from our tests, raw data also has quite variation even at other non-harmonic frequency----only difference is that variation is not so big.
    From this point of view, it seems that FDC has no any advantage compared to other traditional sensor with the technique of charging/discharging capacitor. In the past, the reason we give up the latter is that any frequency noise could charge/discharge the cap, which result in the wrong measurement.
  • 0 in reply to zhao Steven
    TI__Expert 8050 points
    Hello Steven,

    By definition, harmonics are multiples of the fundamental frequency. So they can still be seen by the LC tank.

    We do not claim that the LC narrow band is a noiseless system. However, it is much more immune to wide band noise compared to the traditional charge-based approach.

    Regards,
    Yibo