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TLV320AIC3120: AGC and digital volume control

Kazuki Itoh
Genius 10165 points
Part Number: TLV320AIC3120

Hi team,

My customer found that the digital volume control (page0 register 83 (0x53)) is not functional when AGC is enabled.

From the functional block diagram, it looks like independent functions.

From the signal chain diagram below, it looks like either digital volume control or AGC is selected.

Is it able to make digital volume control working while AGC is working?

If yes, could you please let me know how to do that?

Regards,

Itoh

  • 0
    TI__Mastermind 23030 points

    An option may be to try adjusting register 86 D6-D4 to change AGC Target level. With the output can be adjusted to -5.5db  to -24 db with respect to a full scale signal. This can give a perception similar to a volume control

  • 0 in reply to Sanjay Dixit
    TI__Genius 10165 points

    Hi Sanjay,

    Thank you for your response.

    My customer modified the target level from -20dB to -5.5dB , but the output level didn't change.

    When the maximum PGA applicable is increased, the output level got larger.

    From the above, my customer thinks the digital volume control is not functional when AGC is enabled. Do you think this is correct?

    In the functional block diagram in section 7.2, the digital volume control block is inserted in the AGC loop. So, it looks like the block diagram implies the digital volume control keeps active when AGC is enabled.

    However, in Figure 7-18, it looks like the AGC gain and digital volume control go to MUX and either one is selected.

    This is a little confusing, and my customer wants to make it clear.

    Best regards,

    Itoh

  • +1 in reply to Kazuki Itoh
    TI__Mastermind 23030 points

    Hi Itoh-san,

    It looks to me that the customer is correct.

    I also feel that the loop involving AGC the gain control is done by the PGA. only.

    The maximum signal that the ADC accepts as full scale is 0.7v rms. So if we sat a target level of AGC  at -10db , this would mean that the signal after AGC would be limited at 0.22v. Lets assume that the input signal is 50 mv rms. To be able to make 0.22vrms at the output, the PGA would have to adapt its gain to 0.22/50mv or 4.4 . As long as the Maximum AGC Gain setting is greater then 4.4 the output would be 0.22v rms.

    If we now make target level at 0 db or 0.7v. The gain of the PGA should go up to 0.7/50 mv. As long as the Maximum AGC gain setting is greater then 14 the output level should increase to 0.7v

    I would suggest that the customer tries with a 50mv signal  and chooses a Rin=20k and chooses a max AGG gain of 25 dB.  Also set R83,Page 0 to 0x00

    If this is true, increasing the target gain increases output level .

    However it is possible to make a volume control in the DSP functionality which may be an optimum location for a volume control