ULPAnalog
|
Hello
In the first method, you are not only changing the differential input to the opamp but also the common mode, which is why I suspect the amplifier is not biased properly. Notice that in your method 2, both inverting and non-inverting input terminals of the opamp are biased at 1.65V and incremental analysis is done around this operating point. I would suggest you to try the testbench shown in the attachment, with Vin,d being a small differential voltage applied. The derivative of the output wrt to Vin,d should match with the gain obtained from AC analysis.
Thanks and regards
|