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Questions of FDC2212

zhao Steven
Prodigy 90 points
Other Parts Discussed in Thread: FDC2212, FDC1004

Hello,

We'd like to use FDC2212 for the people proximity detection. There are still some unclear items need to consult you. Thx.

Q1, just as the one of FDC1004, could we use the "active shielding" method onto FDC2212, in order to reduce the interference between two channels?

Adding GND to act as shielding is not so good, which would reduce the sensitivity of detection range.

Q2, for the single-end sensor solution, what if the antenna pad is connected to INxB instead of INxA? any difference between them?

Many thx.

  • 0
    TI__Expert 8050 points
    Hello Steven,

    1. FDC2212 does not have an active shield driver. Depending on your user scenarios, some proximity applications may not need a shield at all.

    2. You can connect the sensor pad to either INxA or INxB.

    Regards,
    Yibo
  • 0 in reply to Yibo Yu
    Prodigy 90 points

    Hello Yibo,

    Then, can I make an active shielding circuit (include op + copper pad), which connected to INxA, together with the approach sensing pad?

    I hope our product have better sensing directivity, and no or weak response to the unwanted input signal from side and bottom.

    Thx.

  • 0 in reply to zhao Steven
    TI__Genius 9300 points
    Can you use 2 electrodes, separated in X and Y? This way, if two sensors respond with similar signal level, you will know that a target approaches from the front. If one reacts stronger than the other, that will mean the target is either on the side or bottom.
    To achieve true directivity, you will need 3 electrodes, though.
  • 0 in reply to Evgeny Fomin
    Prodigy 90 points

    Hello Evgeny,

    Many thanks for your advice. Also, I'm very happy that more and more TI experts note our problems and difficulties now. Appreciation.

    In order to better communication, here I'd like to list our issues & questions on this sensor IC and application.

    1, we just want to trigger the sensor from the front side, and need to filter/shield the unwanted signal from side and back.

    1.1, could the active shielding method be used to FDC2212, although maybe it's made of operational amplifier circuit?

    maybe I have to put 2 channels on the front PCB (quite small, 5cm^2 around), so I must consider how to reduce the interference between channels, even the one from other functions circuits at another PCB in parallel with front PCB (<10mm distance between them).

     I used to see some articles about active shielding, and sounds quite better  compared to GND shield. So, if ok, I'd like to use it in our circuits of FDC2212.

    e2e.ti.com/.../what-are-you-sensing-a-novel-approach-for-capacitive-based-liquid-level-sensing

    2, EMC immunity test

    2.1, sensor has no response to the hand approach if the common mode noise with resonant frequency (e,g, for our EVM board 5.4MHZ) is inject from power supply line. how to solve it?

    2.2  same issue is applicable for the noise at the harmonics of resonant frequency. 

    2.3, glitch filter setting sounds not work well for high frequency common mode noise, e.g., >10MHz, although it's been set as 10MHz for glitch filter.

    Still have more questions because all are new for us, but we can firstly focus on these items above.

    Many thx.

  • 0 in reply to zhao Steven
    TI__Genius 9300 points

    Hello,

    Apologies for the delayed answer.

    1) Yes, you can design a voltage follower. Just make sure that the bandwidth is large (say >300MHz). I would, however, first try to shield the sensor using GND on the sides and see if it get it solved.

    2 channels of the same FDC will not interfere with each other - they are multiplexed.

    2) I am checking if we have EMI mitigation appnote, I will get back to you on this shortly. In short, add a common-mode choke on INA/B pins. FDC EVM even has a footprint for it.