TLV320AIC3204: DC offset shiift occurs when audio signal clipping occurs at ADC front end

FYI, Here is a  screen shot of the  the clipping / offset shift I was describing earlier

Jim

Hi, Jim,

The  behavior you are describing effectively suggests a saturation on the PGA of the AIC3204. What is the input voltage provided to the codec when the phenomenon occurs?, this part accepts a full-scale input of 0.5Vrms, any voltage above it will cause clipping.

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Diego,

Yes, the input signal voltage can meet / exceed the voltage limit you mentioned at the higher amplitude levels shown in the screen shot.

Based on this info, it sounds like the the offset shift is not unusual in the presence of front end clipping - is this correct?

Thanks for the quick response,

Jim

Diego,

I have a follow-up question:

In order to solve the clipping issue and eliminate the offset shift, I have enabled the Automatic Gain Control function configured to limit the input signal and thereby reduce clipping. For the most part this is working, however, there is still a strong over shoot on fast transitioning higher amplitude signals where the clipping can still occur (see screen shot below). I have tried various parameter adjustments like changing the Target level and Attack time but that doesn't seem to help with the overshoot that much. The attack time seems to only adjust what I think of as the release time (or the time it takes to reach the threshold), but doesn't really slow down the initial attack response.

The only way I have been able to eliminate the clipping completely is to set the Max AGC gain to a value lower that the PGA gain was initially set to when the device was calibrated (which is not that desirable for me).

Let me know if you have any suggestions in this regard.

Thanks,

Jim

Hi, Jim,

Correct, exceeding the recommended operating conditions could cause device malfunction, which in this case results in the behavior you are seeing.

Implementing a workaround inside the device, like the AGC approach could help, but the issues may continue if the input signal is still above the recommended input voltage as the PGA could be saturated. Is it possible to adjust your input source to meet the recommended input voltage for the ADC?. 

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Diego,

I can adjust the input source somewhat but I am concerned that it may cause some additional issues for us. So far the AGC approach s helping quite a bit with reducing the clipping and it may more desirable to put up  with a small percentage of clipping even if I can't eliminate it all together. I am still adjusting a few AGC parameters to see if I can Improve the performance a little bit more.

Anyway, let me know if you have any additional thoughts.

Thanks again,

Jim

Thanks Diego!