Hi all,

In trying not break the loop for analyzing stability for a diff-diff opamp I tried to use the stb analysis, but found it does not allow to use more than one port or voltage source for reference (in a single-ended feedback loop one reference is enough). Consequently I found I could not use it.
Is there something I´m missing? If in fact stb cannot be used for differential circuits, is the only option (apart from breaking the loop to measure the RR) to directly measure the loop gain (a×f)?

Your comments are welcome.
Thanks

tosei

Alternatively, you can use two ideal baluns (as decribed in http://www.designers-guide.org/Analysis/diff.pdf) connected back to back and put probes in the connections between them. Page 198 of http://eeclass.stanford.edu/cgi-bin/handouts.cgi?s=&t=1185524820&cc=ee214&action... shows how to perform an analysis of the differential mode loop gain in this way. For the common mode loop gain, put an additional probe into the Vcm branch and specify this probe in the stb analysis.