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DC offset of the AD9276 output

Question asked by udomchai on Mar 28, 2013
Latest reply on Apr 5, 2013 by udomchai



I have two questions.


I use AD9276-80 KIT to capture ultrasound echo signals and notice different DC offsets on each channel. These DC offsets also vary with the TGC gain. I try to remove these DC offsets by setting the AAF bandpass filter between 3.72-11.56 MHz (by setting registers 0F and 2B) but they still remain on the outputs. The DC offset voltage are around 17-51 micro Volt when the TGC is set to the maximum while our echo signals are around 102 micro Vpp.


1) What should I do to remove this offset? Since it varies with the TGC, if the TGC varies with time, therefore, removing the mean from the signal does not totally clean up the offset.


2) I notice the registers flex_offset 0x10 (hex) and bias_current 0x12 (hex) controlling LNA force offset correction and LNA bias current adjustment. I am not sure that they would be related to my problem. However, I cannot find the information about how to use these registers on the AD9276 data sheet. Could you please forward us the information?