loose-electron wrote on Oct 26th, 2009, 11:56am:The circuit does not make sense at the level of analysis shown.
Two ideal op-amps (note the word "IDEAL" here) can not be connected together at the output.
Hi Jerry,
I mostly agree with you. However, if we starting point are two (in principle) opamps with different input referred offset, then those two opamps
have to be different (since their op point will not be the same) regardless the used topology.
Again assuming non-ideal opamps and that the output/input impedances are not very different and finite (they will due to the different internal unbalances) a first order approx will be that the overall offset will be about +15m for one of them and -15 for the other one.
If those impedances are significantly different the offset will be split according to such "voltage divider" set by the output impedances.
By my point is that from the very first moment it is stated one amp has 10m of input referred offset while the second one has 20mv, then the opamps are not ideal and
in principle they could be connected as shown.
Best
Tosei