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TLV320AIC3256: AMIC gain setting

Helen Lin
Prodigy 30 points
Other Parts Discussed in Thread: TLV320AIC3256

art Number: TLV320AIC3256

Dear TI teams,

For our customer's application: We use the MCU (STM32) and codec IC (TLV320AIC3256). We found the confuse about extra gain here.

We use the label mic, and its spec about nominal sensitivity is -42dB. And we used the programmer setting in a gain of -10dB.

Theoretically, the result is around -52dB when we do the measurement. However, we got the -20dB.

It seems that some setting to make extra 32dB gain. We wonder to know where cause it. 

Is there some setting when the progress of ADC to make extra gain?

As we got the information from software is as below setting:

MIC PGA Gain Control
  • L : 20db
  • R: 0db
ADC Gain
 using -10db.Fine Gain Adjustment
  • L: 0db
  • R: 0db
ADC Phase Compensation
ADC_FS : 31.250KHz to be precise 
Rest of the config is correctMICBIAS
Voltage Source: DRVdd_HP
Output Voltage: 2.5V

Please kindly know how could do next step. Thanks.

  • 0
    TI__Expert 6440 points

    Hi Helen,

    The default gains of the PGA and ADC is 0 dB. So I don't think there is any gain in the electrical path.

    Are you testing with tones? If so could you measure the microphone's electrical output level and let us know the measured Vrms value?

    Diljith

  • 0 in reply to Diljith
    Prodigy 30 points

    Hi Diljith,

    Yes.We used the tones to check it. You mean that measure the MICBIAS waveform? Thanks.

  • 0 in reply to Helen Lin
    TI__Expert 6440 points

    You should measure at the input pins to the device where the mic is connected (e.g. IN1L/R or IN2L/R or IN3L/R).

    Are you using an EVM or a custom board? If it's a custom board, please share the schematics.

    The signal level depends on many factors - the SPL level of the test signal being played, the sensitivity of the microphone, the PGA and ADC gains.

    The electrical output level of the mic depends on the SPL level of the test signal.

    Best Regards.

  • 0 in reply to Diljith
    Prodigy 30 points

    Hi Diljith,

    We use the custom board. I've send the schematic to you by e-mail. Thanks.

    IN3L

    IN3R

  • 0 in reply to Helen Lin
    TI__Expert 6440 points

    Thank you for sending the schematics.

    I recommend that you split the tests into two parts – one to measure the sensitivity of the  microphone and the second to test the channel gain in the electrical path (i.e. from the MIC+ input to the ADC output).

    It will be difficult to test the sensitivity of the microphone in a normal environment. It will have to be done in a quiet environment.

    The tests to check the gain of the electrical path is relatively straightforward. You can play an input from a known source – from AP for example – and check the levels of the ADC output.

    I would recommend that we first measure the channel gain of the electrical path and ensure that it is proper before doing the acoustic measurements.

    Best Regards.