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ADAU1361 crosstalk

We are using an ADAU1361 with 2 single-ended microphone inputs, and have observed significant crosstalk between the channels. We connected the microphones to the LINP & RINP pins rather than the LINN/RINN pins as is suggested in the datasheet, and LINN/RINN are connected to CM.  Could this be the cause of the crosstalk problem?

  • Hello allanh,

    Yes, you need to connect the microphones to the LINN/RINN pins and then ground the LINP/RINP pins through a capacitor.

    Dave T

  • Thanks for getting back to me. The problem with the LINN/RINN pins is that their input impedance changes significantly with PGA gain (from 2K to 84K, if I read the datasheet right), which means we need to use external buffers.  When you say “ground the LINP/RINP pins through a capacitor” that is different to the advice in the datasheet which says to connect these to CM (figure 33). Is grounding them through a capacitor preferable?

  • Hello allanh,

    Yes, figure 33 looks like this:

    The CM pin is tied to the LINP and RINP.

    However, look carefully at figure 32. Yes it is for differential mics but it is actually wired as a pseudo-differential configuration. I personally think this is the better way to do it for crosstalk reasons.

    So you can see the "P" input pins are tied to ground through a capacitor.

    The way that it is draw it does not quite stand out.

    You are correct about the impedance changing. It only gets really low at really high gains but it does change a lot.

    Dave T