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SSM2604 excessive ADC noise

Question asked by DanielHontslager on Oct 22, 2017
Latest reply on Nov 3, 2017 by DanielHontslager

Hello,

 

I'm bringing up my first prototype with the SSM2604 connected to an LPC4330. I have everything running and I'm able to play and record audio, but there is an excessive white noise level on the ADC input.

 

My system is running at 48Khz at a master clock of 18.432Mhz and a bit clock of 3.0722Mhz, I2S transfer size is 32 bits.

 

The received noise fills about 14 of the lowest 24 bits, and the level does *not* depend on the LINVOL/RINVOL levels. Enabling LINMUTE/RINMUTE does result in completely silent output, though.

 

Apart from the noise the ADC functions properly, no other artifacts or aliasing.

 

AVDD is clean, all capacitors and ferrites are connected as described in figure 27 of the datasheet.

 

Audio playback is clean; I did not do any exact measurements yet, but playing a sine sweep sounds ok without artifacts, noise or aliasing.

 

Below is a trace of RECDAT and RECLRC with no signal applied to the LIN and RIN pins and LINVOL/RINVOL set to 0

 

Basic noise floor of SSM2604 ADC

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