PCM4204 noisy bits in ouput data line

cml

Other Parts Discussed in Thread: PCM4201, PCM4204, PCM4104

Hi everyone,

I have designed a commercial board with an ADAU DSP, a pcm4201 and a pcm4204.

I am getting a backgroung noise in the ouput data line (TDM4 channels @48KHz) from the pcm4204 to the dsp. I mean the noise is implicit in the digital signal, I don't mean there is noise in the line but lot of LSB noisy bits even with no audio input signal is injected.

But this behaviour is randon, about 50% of the times I get a clean low noise signal, 50% noisy signal. I have tried many many configurations and power changes.

What I have realised is that....if the signal is noisy, when I unconnect the 5V power from the AD, the signal becomes CLEAN (100% of tries), but if after that if I force an external reset (in the reset pin), 100% of the times the signal becomes noisy again. So, what actually this 5V disconnection does to the pcm4204?

The ad is configured in standalone mode but the reset generated by a uC... of course i wait a prudential amount of time to generate a reset after power up to get the power stable.

Any idea?? Thanks!!

Carlos

over 8 years ago

0 Justin Bohr over 8 years ago

TI__Mastermind 27910 points

Hi Carlos,

Is it possible to post the schematic for the PCM4204 and its input circuitry in you design? Is the noise in every channel or just one channel? What is the input to the system, and are you able to measure the noise with audio measurement tools?

Justin

0 cml over 8 years ago in reply to Justin Bohr

Prodigy 70 points

Edited since info was finally not relevant to solve the issue.

0 cml over 8 years ago in reply to cml

Prodigy 70 points

Of course I get the same behaviour in 4 different boards.

0 cml over 8 years ago in reply to cml

Prodigy 70 points

This measurements are with no input connected.
If there is no noise, the system sound really clean thru the pcm4104 converter. Of course with noise, the audio pcm4104 output is audible noisy in those channels. pcm4104 and ADAU work flawless 100% of the time.

0 cml over 8 years ago in reply to cml

Prodigy 70 points

These measurements are with no XLR input connected.
If there is no noise, the system sounds really clean thru the pcm4104 converter. Of course with noise, the audio pcm4104 output is audible noisy in those channels. pcm4104 and ADAU work flawless 100% of the time.

0 cml over 8 years ago in reply to cml

Prodigy 70 points

SOLVED, reset & cloking issue.

0 Justin Bohr over 8 years ago in reply to cml

TI__Mastermind 27910 points

Hi Carlos,

So was this an issue with the source of the clocks not producing a correct clock?

Justin

0 cml over 8 years ago in reply to Justin Bohr

Prodigy 70 points

AD needs to be started once the masterclock is completely stable if it is slaved.

Can you tell me how the AD is internally affected when I un&power the 5V analog reference (once both -5v&3.3v- are power on) while keeping the 3.3V powered?

Is there any internal mechanism which affects the digital syncronization by doing this??does it act as a reset??I though it should only affect the analog reference, not to the digital part.

Regards

Carlos

Audio

Audio forum

PCM4204 noisy bits in ouput data line