PCM3008: PCM3008: DOUT data is not always 0x0000 for Vin = 0V

Hi,

Just to make sure, you have set it in analog bypass mode (ADC direct out of DAC)? Is this click with no input to the ADC? I will check this next week with an EVM.

Best,
Mir

Hi, I just discovered that nothing is wrong with the Codec or circuit since the codec data is signed. Why is this taken for granted in CODECs? 

In any case, I have checked the ADC and DAC buffers and despite the data looks good, I still hear the click and I cannot explain why. 

Hi,

Yes, all of our digital audio is in two's complement signed format. Sorry it is not specified in the datasheet, but this is the standard for TI audio devices.  

Is the 0xFFFF value only during the click? Or were you experiencing it all the time? Are you experiencing this click only when there is no input connected to the ADC? Could you attach a scope view of the click or the click's period?

Also, your system clock should be 12.288MHz for a sampling rate of 48kHz, there is a chance a click could occur due to incorrect clocks. If your clock speed changing doesn't fix your issue please send me the answers to my questions above so I can better assist.

Best,
Mir

Hi Mir,

I measured the clock and found it was running at 12.7MHz. I adjusted it down to 12.3MHz, but the clicks persisted. I then set the sampling frequency to 32kHz, which corresponds to a system clock of 8.2MHz, but even in this case, the clicks didn't disappear.

Below are some captures of the clicks. Their frequency varies—they occur constantly but not at a fixed interval, with an average of about one click every 0.5 seconds. Sometimes, multiple clicks are generated simultaneously, as shown in the captures.

To isolate the problem, I have removed the loop ADC - DAC and sent a simple sawtooth waveform to the DAC. No clicks in this case. Additionally, I have noticed some sporadic unexpected values at the ADC output, most likely corresponding to the clicks. We can assume that the issue must be located on the ADC side. 

Hi Matteo,

Interesting. This is most likely an analog problem, not just ADC. If you are in analog bypass mode, you should be able to turn off/disable the ADC and DAC and still see your analog input at the analog output. Try doing that. If there is still no change in the clicks, there is a chance this is a power supply issue. Try a different power supply with a cleaner signal out.

Let me know if it persists after turning off the ADC and DAC and trying different power supplies.

Best,
Mir

thanks for the support Mir