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Hi Team,
We found the RMS level vs frequency curve is weird at 0.707Vrms_1kHz input. It is not like 0.308Vrms_1kHz input.
We expect the RMS level would drop at about 20kHz, but it drop at about 10kHz when 0.707Vrms_1kHz input.
Is the curve make sense? How to improve the behavior?
Thanks
AP setting (0.308Vrms_1kHz input)
RMS level vs frequency curve (0.308Vrms_1kHz input)
RMS level vs frequency curve (0.707Vrms_1kHz input)
Schematic
Hi, Daniel,
I looked at the initial captures sent and noticed that the full-scale output of the ADC with a 0.707Vrms input is not 0dBFS, it is around +2.1dBFS, which indicates that the ADC is outputting saturated data.
By analyzing the register dump, I wanted to see if you are applying a gain on the input PGA, however it seems that even the PGA is muted, which does not makes sense as the expected output would be mute. Also, the ADCs are powered down in the code, which suggests that the dump is performed before initializing the device.
Can you please double check if the provided register dump is taken when the device is in operational mode?.
Best Regards,
-Diego Meléndez López
Audio Applications Engineer
Hi, Daniel,
Thanks for the additional information. I noticed that a 20dB gain is being applied on the ADC volume registers (P0_R83 and P0_R84), along with an additional 16 dB of gain on the device PGA (P1_R59 and P1_R60). This seems like a high gain for me, and may be the cause of the saturation on the ADC signal path. I would recommend you to keep the applied gain of the audio signal path as 0dB and retake the measurement with 0.707Vrms input, which is the full-scale input voltage for the ADC3101.
Best Regards,
-Diego Meléndez López
Audio Applications Engineer
