we are using ADR550BRTZ as reference in our AD system. currently we meet a weird phenomenon in 8 PCBA among 50 PCBA total. the output value does not meet spec, sometimes it fluctuates at a rough 1mv range, sometimes it not only fluctuate, but also keep decrease. i attach some picture to show the abnormal output, and i also attach the relevant schematics. we have suspect the design, so i cut the trace which connects post-stage circuit, but the problem is still there.
when we resolder these defect chip, the problem would disappeare for a while or permenantly on different PCBA (we have 8 defect PCBA total). and when we use cleaning agents to clean the PCBA, it would also make the problem disappeare for a while or permenantly on different PCA.
we have a similiar design on the same PCBA using the same ADR550BRTZ, but in layout it's in other place. but the problem never happened at there.
sometimes i found some chip would self-recover to normal without i do something to it, but it would go back to abnormal after some time, and the situation could happen repeatly.
could someone give me some suggestion? you can find the weird output waveform and design schematics in attachment.