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Spurious frequency in AD7177-2

Question asked by AleGS on Jul 13, 2016
Latest reply on Jul 22, 2016 by jcolao


I'm using the high performance AD7177-2 adc in the evaluation board EVAL-AD7177-2SDZ because we need to achieve the highest possible resolution (in terms of dynamic range). I'm evaluating the rms noise when the inputs are shortcut (or shorted to GND); using the SINC3 filter (which has better performance) there are a spurious frequency at 57Hz  while it disappear when SINC1+5 filter is used. I've used different power supplies (I've tried even a battery) and the board is inside a metal box (grounded) to exclude that the noise is coming from outside.

The set up is the following:

  • Split supply (regulated) - as described in the User Guide (UG-849)
  • Ch0 enabled (AIN-=Ain1, AIN+=Ain0 or AIN-=Ain3, AIN+=Ain2) all the other channels are disabled
  • All buffers disabled, external reference, external crystal (same results persist with internal reference and internal clock)


Do you have any suggestion how to avoid, or at least reduce, this behavior?

Many thanks