PCM1754: PCM1754 mute function

Hi Robin,

This is quite a bit of noise - is there a possibility of crosstalk between BCK and the output? Is there any output filtering in this system?

Thanks,
Paul

Hi Paul,

The most strange thing is the MUTE function could not be actived no matter what the voltage on this pin.

Is this normal?

Below is part of the layout, it seems the BCK is far away from VOUTL/R pin.

Robin

Hi Robin,

Can you look at the VCC supply and VCOM pins during the noise event? Do you see the noise on those two pins as well? If you do, then I think you have a digital crosstalk issue, as the PCM1754 does not much power supply noise rejection.

Thanks,
Paul

Hi Paul,

I am not sure whether the noise is induced by VCC & VCOM or not.

Please check the waveform as below

Hi Franco,

Could you post the schematic? If you are uncomfortable sharing it on e2e, please send it to frost@ti.com directly.

Thanks,
paul

Hi Franco,

I was able to look at this on the bench, and yes I also see some output noise during when the soft-mute is enabled. This might be due to this feature only being a 'soft mute', where the attenuation register is essentially set to it minimum value rather than a true analog mute. I did notice that the magnitude of the noise on my system was smaller than what you are experiencing, so there could be some digital crosstalk component as well.

I also saw almost no noise after the low pass filter on the output. I did not see the filter in your schematic - what are you using to filter the output of band noise?

Thanks,
Paul

Hi Paul , 

Thanks for your explanation.

it seems I should change PCM1754 to PCM1753 to minimize this noise by Soft Mute or add LPF on the PCM1754 output.

Do you have any suggestions about LPF for PCM1754 ?

Thanks.

Franco