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TLV320AIC3111: Electret mic configuration for input

Lolo Pidi
Prodigy 40 points
Part Number: TLV320AIC3111

I am trying to configure TLV320AIC3111 as an input only mode. I am able to get the audio samples but have one issue now. While there is no audio, there is some sound heard which I think is because of some misconfiguration of registers.

Following is the configuration I want to achieve.

Sampling Freq: 8000Hz

Clock source: Codec

Microphone: Single ended electret microphone

Following are the registers configuration:

//  Select Page 0
0, 0x00
// S/W Reset
1, 0x01
//  PLL_clkin = MCLK = 2.048MHz, codec_clkin = MCLK
4, 0x00
//  PLL Power down,  P = 1, R = 1
5, 0x11
//  J = 4
6, 0x04
//  D = 0000, D(13:8) = 0
7, 0x00
//  D(7:0) = 0
8, 0x00
//  Mode is I2S, wordlength is 16
27, 0x0C
//  NDAC is powered up and set to 1
11, 0x81
//  MDAC is powered up and set to 2
12, 0x82
//  NADC is powered up and set to 1
18, 0x81
//  MADC is powered up and set to 2
19, 0x82
//  AOSR = 128
20, 0x80
//  IADC = 384
21, 0x80
//  BCLK N-divider, BCLK divider N = 4
30, 0x84
//  Select Page 1
0, 0x01
//  MIC BIAS = AVDD
46, 0x0B
// MICPGA P = MIC 20k
48, 0x80
// MICPGA M - CM 20k
49, 0x20
// Select Page 0
0, 0x00
// POWERUP ADC channel
81, 0x80
// ADC digital volume control coarse 0dB (12dB - 20dB)
83, 0x00
// UNMUTE ADC channel
82, 0x00

If I change MIC bias from AVDD to 2V. sound is better but some prrr kind of sound is heard.

How to select proper mic bias and remove the prrr kind of constant noise in background. Does it has to do something with MIC PGA feed-forward resistance? How to select its value?

  • 0
    TI__Mastermind 24255 points

    Hello Lolo,

    Thank you for reaching out and the detailed explanation of your problem. For optimal performance, TI recommends using decoupling capacitors on all supply pins. The decoupling capacitors will help improve noise performance and normal operation. Please refer to Figure 5-1 for the recommended decoupling capacitor location and values. You can also try to adjust the value of R1 to 2.2k as per Figure 5-1, as it will decrease the current on the microphone input. 

    To select a feed forward resistance, pick the value closest to the output impedance of the microphone.

    Please let me know each change and the results. I hope this helps.

    Best,
    Andrew

  • 0 in reply to Andrew J
    Prodigy 40 points

    Thank you for the quick response. I will modify the decoupling capacitors, feed forward resistance and check the output.

    Can you also share appropriate MICBIAS and its selection? I can hear the difference in audio after changing MIC BIAS.

  • 0 in reply to Lolo Pidi
    TI__Mastermind 24255 points

    Lolo,

    Sorry for not including this in my original response. MICBIAS usually specified in the microphone datasheet as "Standard Operating Voltage" or +Vs. Select the MICBIAS setting that is closest to its value. The R1 value is also sometimes specified in the microphone datasheets as RL as well. 

    Also, here is a related app note on Common Noise Issues in Audio Codecs (ti.com). Section 2.3 Power Supplies Noise Level may be helpful in explaining the importance of conditioning the power supplies and using decoupling capacitors. "If the AVDD is not regulated properly, all the noise effects will be coupled into the MICBIAS1 pin. If a microphone is connected to the MICBIAS1 pin, the microphone signal will directly see this noise contribution at the converter input."

    Best,
    Andrew

  • 0 in reply to Andrew J
    Prodigy 40 points

    Thanks Andrew, we made the changes like you suggested and now the audio is better.

  • 0 in reply to Lolo Pidi
    TI__Mastermind 24255 points

    Hello Lolo,

    I am glad this helped solve your issue and thank you for letting me know. I will go ahead and close this thread. Please feel free to open a new thread if you have questions in the future. 

    Best,
    Andrew