Quote:
Originally posted by Since87
It looks like the summing amplifier has an awfully high offset for some reason.
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I figured that one out already.
One the really bad parts of not knowing much is the ability to read a datasheet without spotting important stuff.
Page 12 of the opa227 pdf, input bias current cancellation - they specifically say not to use an external cancellation resistor. I did and it does make a difference. The power of re-reading.
Also, I do need to switch to a ground plane on the back of the board. The trace feeding the former external cancellation resistor is very thin and shared with one of the diff-amps. Ground float perhaps? Grounding through vias should also allow tightening up the layout.
I'm still using three difference amps feeding into a summing amp. I'll draw a schematic when I wake up this evening.