PCM2912A noise problem

Hi,

Can any TI employee Plz look in to this matter?

This is very serious matter.

Or else can any body give me PCM2912A EVM PCM designs?

Thanking in advance.

Hi,

Can any TI employee Plz look in to this matter?

This is very serious matter.

Or else can any body give me PCM2912A EVM PCB designs?

Thanking in advance.

Hi Pallav,

Here is the PCM2912A EVM's user guide:

http://www.ti.com/lit/pdf/sbau141

It has schematics and PCB layouts for proper reference.  Please let me know if you have any specific questions after referencing our design.

One area to note is that the capacitance on the Vcc pins should followed according to the EVM design.  Any variation may cause the power supply rails rails (which are generated via internal voltage regulators) to be noisy.  This can degrade overall performance.

Regards,

Nick

thanx nick for the reply,

I have gone through the guide and rechecked my designs . It matches with what ti has suggested in the guide.let me take time to describe the exact problem.

I have given a sine wave signal to the microphone input and recorded it using PCM2912.The recorded waveform shows noise at regular intervals in the waveform.The sound card of the test PC has been disabled.The same card was tested on other machines and gave similar performance.

While listening to audio using the card(PCM2912) the same noise could be heard at regular intervals.So its for sure the problem is not with the recording but with the design of the card. Can you through some light in what might be causing this noise.

Thanx

Hi Nick,

Thanks for your reply. It does work.

Actually the problem was with accuracy of crystal. As i change it to accurate value noise was gone.

Thank you for supporting me in this problem.[:)]

Regards,

Pallav

That's great news!  Glad to help.

-Nick

I have been having the same problem, and it is because I used a ceramic resonator.  I haven't replaced it yet but I will in the next couple days.

I deliberately made my board with poor grounding so I could see how well the devices worked on a board that had a poor layout.   (2 sided board routed ground and power)..

It worked fine except for the regular low frequency  noise. The frequency of the noise changed when I probed the resonator, so I'm sure this is the same problem.  I have a single channel Class D amp following the PCM2912 to give 1W out.

I used the TPA2006.  this works fine with a medium sized speaker but does not do well with the small ones.  for them it needs an output filter.

I have an output filter but am curious what would be recomended when going form the PCM2912 to a class D amp.  I think there needs to be a filter on the output  of the 2912 before feeding theat signal to another AMP.  Is an inductor helpful?  if any can comment they would be appreciated.

Stephen,

Typically an RC filter is used before the class D amp to prevent any out of band noise from folding back into the audible spectrum.  Also note the filter pins can be used to implement an LPF per page 22 of the d/s.

http://www.ti.com/lit/ds/symlink/pcm2912.pdf

thank you Patrick,

I currently have the filter pins not populated but will put the caps back on them.  The crystal did fix my problem as with the earlier post.  I confess if I had read the data sheet all the way through I would have used a crystal.    The sound is good.  

change of plan....now I need to SPI instead of USB..  I'll have to rig up a SPI codec or SPI DAC to replace PCM 2912. any suggestions for what TI part to use?  small is important, not sound quality.

for PCM2912A

Does anyone know if I can drive single 8 ohm speaker instead of the headphone output ? 

using the deferential output and dropping the HGND ?

Regards