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TLV320ADC3120: No audio output from piezo preamp

Kagen Aeby
Prodigy 80 points
Part Number: TLV320ADC3120


Tool/software:

Hi I am trying to get audio output from a piezo preamp. I am using a breakout board I made for the TLV320ADC. This board works when using analog input one with a condensor microphone, in differential AC coupled configuration, biased with micbias. I am trying to get audio now from a piezo contact mic with a preamp circuit, but I do not get any audio output in this configuration. I have it AC coupled single ended configuration, with 2INM connected coupled to ground through a capacitor. I have attached screenshots of my scope with analog output to the IN2P pin with a 1khz square wave, as well as I2c and I2S output from my logic analyzer. 

  • 0
    TI__Mastermind 48285 points

    Hi Kagen,

    First thing I would try is to go back to the condenser mic but with the single ended configuration. If you just leave the minus leg of the mic floating/disconnected it should still work assuming the registers are set up correctly. That would be a good way to verify the software settings.

    Your I2S stream is showing no toggling at all which indicates either the ADC is not powering up, not able to latch to the I2S bus, or is not converting. Even if there was something strange about the source, it would still be toggling. Your bitclock appears to be changing duty cycle frequently. Was it doing the same thing in the condenser mic case?

    I am concerned about your piezo source though. Your scope is showing some ringing as low as -0.7V however the absolute minimum on the pin is only -0.3V. A low pass filter might be needed to keep the input signal in the boundaries to prevent damage.

    Best regards,
    Jeff McPherson