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Decoupling of input ports

Question asked by RMSacoustics on Mar 21, 2016
Latest reply on Mar 24, 2016 by RMSacoustics

Hi there,

 

I am struggling with noise that might be generated inside the ADAU1772.

When working with the evaluation board I get a lower output noise with the same settings as with my final PCB design

A possible cause of this could be in the way of connecting the common mode port with the reference inputs and its decoupling.

According to the ADAU datasheet these should be connected and decoupled to ground via 10 uF.

However, on the evaluation board CM is not connected to the input references but all ports incl CM are separately decoupled to ground.

The datasheet tells that the decoupling of CM is necessary as it prevents crosstalk between de DACs and ADCs.

 

Now my question is whether this also influences noise and what the best way is to connect these ports.

Further I wonder if it is necessary to connect unused input ports to CM.

 

Thanks, Rob

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