AD9271 Output Varying by up to 10% from channel to channel

Document created by analog-archivist Employee on Feb 23, 2016
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I am seeing a variation in outputs from channel to channel when I input the
same signal on all channels. The variance is around 10%.


If the input is DC coupled into the ADC, then the channels will have different
offsets, and the offset will be change with gain. 
The offset is coming from the LNA.  It is not trimmed out, so there can be
variation channel to channel.  Since the offset is in the LNA, the VGA
amplifies it, so it will appear gain dependent.  We would recommend you use the
high-pass filter (Register 2B, bits 1:0).  This will remove the offset and gain
dependence prior to the ADC.