AD8304: RFI issue

Document created by analog-archivist Employee on Feb 23, 2016Last modified by analog-archivist Employee on Feb 23, 2016
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When I am using the phone just beside the AD8304, it will work abnormally. I
added shield for AD8304 and re-measure but the problem still exist. Would you
kindly give some professional suggestions on this issue?

 

This problem could be caused by a couple of things.  It’s hard for me to tell
by looking at the PCB photo, but it looks like there are no guard traces
surrounding the input line from the photodiode to the INPT pin (pin 4).  If the
guard voltage is not present, there may be currents induced into the input
traces by other parts of the circuit.  I have attached an app note that shows
how to minimize current leakage in the input circuit. The VSUM pins (pins 3 and
5) provide the guard voltage, which should be routed next to, and under the
input trace. It’s also possible that the power supply decoupling is not
sufficient.  Both the data sheet and the app note discuss how to implement
supply decoupling and bypassing to reduce any noise on the power supply traces.
It would be much easier for us to figure out what the problem is if we had your
schematic and PCB layout drawing.

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