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TLV320ADC6120: Record a PDM microphone using TLV320ADCx120

V G
Prodigy 10 points
Part Number: TLV320ADC6120

Hey,

I am trying to use the TLV320ADC6120 to sample a PDM MEMS microphone.

The adc is configured via I2C and its output is read via I2S using an ESP32C6. I am using a PDM breakout board (https://learn.adafruit.com/adafruit-pdm-microphone-breakout) to generate PDM-data.

The breakout board is connected as follows:

DATA------IN2P_GPI1
CLK-------IN2M_GPO1
SELECT----GND
GND-------GND
3V--------Vin

These are the settings sent via I2C (there is no NAK) after powering up:

// wait for 1ms

h4E WR h00 h00 // select page 0
h4E WR h02 h81 // SLEEP_CFG := SLEEP_CFG_DEFAULT | SLEEP_CFG_AREG_SELECT_INTERNAL | SLEEP_CFG_SLEEP_ENZ_ACTIVE

// wait for 1ms

h4E WR h00 h00 // select page 0
h4E WR h07 h70 // ASI_CFG0 := ASI_CFG0_DEFAULT | ASI_CFG0_FORMAT_I2S
// (the breakout board has no capacitor between data and GPI1, so we need to use CH1_CFG0_DC_DC
h4E WR h3C h50 // CH1_CFG0 := CH1_CFG0_DEFAULT | CH1_CFG0_INSRC_PDM | CH2_CFG0_INSRC_PDM | CH1_CFG0_DC_DC
h4E WR h22 h41 // GPO_CFG0 := GPO_CFG0_DEFAULT | GPO_CFG0_GPO1_CFG_PDMCLK | GPO_CFG0_GPO1_DRV_ACTLOW_ACTHIGH
// actually this is not required but should not change anything
h4E WR h21 h63 // GPIO_CFG0 := GPIO_CFG0_DEFAULT | GPIO_CFG0_GPIO1_CFG_PDMCLK | GPIO_CFG0_GPIO1_DRV_ACTLOW_ACTHIGH
// CH2 shouldn't be required
h4E WR h2B h45 // GPI_CFG0 := GPI_CFG0_DEFAULT | GPI_CFG0_GPI1_CFG_PDMDIN1 | GPI_CFG0_GPI2_CFG_PDMDIN2
h4E WR h73 hF0 // IN_CH_EN := IN_CH_EN_CH1_ENABLED | IN_CH_EN_CH2_ENABLED | IN_CH_EN_CH3_ENABLED | IN_CH_EN_CH4_ENABLED
h4E WR h74 hC0 // ASI_OUT_CH_EN := ASI_OUT_CH_EN_CH1_ENABLED | ASI_OUT_CH_EN_CH2_ENABLED

// wait for 1ms

h4E WR h00 h00 // select page 0
h4E WR h75 h60 // PWR_CFG := PWR_CFG_DEFAULT | PWR_CFG_ADC_PDZ_ON | PWR_CFG_PLL_PDZ_ON

Afterwards the clock is running with about 2.8MHz on GPO1.

The problem is that Data does not seem to contain any useful data. I only receive noise but no sound. I also have to use a high gain to see any signal at all.
Interestingly, the Data-signal looks similar if the mic is not powered at all.

Loud sounds (e.g. a clapping near the microphone) are visible in the audio-signal, even if you do not recognize them when listening to the recorded audio. It rather looks like a single oscillation.

If the adc is configured to sample analog signals, it is working properly, so I guess that there is a problem with my configuration process.

Since I2C and I2S are working properly when sampling an anlog microphone, there shouldn't be a problem.

Do you have any ideas why I do not receive any useful data via I2S? Am I missing some required parameters in my configuration?

Thank you in advance

  • 0
    TI__Mastermind 23030 points

    Just to clarify..

    Are you getting 2.8Mhz on the Clock on the Mic?

    Is there Toggling on Data output?

    Does grounding the Select Line correspond to selecting the Mic on your baord ?

  • 0 in reply to Sanjay Dixit
    Prodigy 10 points

    Are you getting 2.8Mhz on the Clock on the Mic?

    Yes, 2.8MHz is the clock frequency going to the microphone.

    Is there Toggling on Data output?

    This is a screenshot of the signals (clock and data).


    Does grounding the Select Line correspond to selecting the Mic on your baord ?

    Grounding means to set the SELECT pin on the breakout board to GND. (On the ESP32 I only evaluate the left channel sent via I2S, but the results doesn't change depending on the voltage of SELECT.)

  • 0 in reply to V G
    TI__Mastermind 23030 points

    You can put a RC Low pass filter with a cutoff frequency of 100Khz on the Data line of the Mic, The output will show the analog equivalent coming out of the Mic. If a 1K signal is fed as a sound to the Mic,The voltage across C should have a sine wave on it.