How to avoid distortion or clipping on the ADC inputs for the ADAU144x evaluation board

Document created by BrettG on Aug 5, 2011
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The evaluation board uses AD1938 converters. You can see in the  AD1938 datasheet that the full-scale differential ADC input is 1.9 Vrms.  However, since the evaluation board uses line inputs that are  single-ended, the input filtering is actually single-ended, and the  filter circuit artificially creates the differential signal.

 

The single-ended range on this board is actually ~2.8  Vp-p. I would suggest dropping the test input signal down a bit below  2.8 Vp-p and then inching it up until you read about -1 dBFS peak in the  DSP core.

 

You can easily monitor the input level in the DSP using these methods: http://ez.analog.com/message/7669#7669

I  would suggest using the peak method. You don’t want to be right at 0  dBFS because harmonic distortion will be a bit high. I would step it  down to -1 dBFS for the best balance of noise and distortion.

 

This FAQ was generated from the following discussion: How to avoid distortion or clipping on the ADC inputs for the ADAU144x evaluation board

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