In my testbench, I’ve configured Cs=Cf=1 pF C s = C f = 1 pF and have included both a diffstbprobe on the differential-mode (DM) loop and an iprobe on the common-mode (CM) loop. My intention is to evaluate the loop gain under these configurations. However, I have encountered some discrepancies in the results and would like to confirm a few aspects: Simulation Setup: Is it permissible and valid to use both diffstbprobe and iprobe within the same simulation? Would the presence of both probes simultaneously affect the accuracy or interpretation of the results? Result Discrepancy: When I run STB analysis: Selecting the iprobe (e.g., /I0/IPROBE ) for the CM loop gives me a positive loop gain. The phase starts at −180° − 18 0 ° and transitions down to −360 ° . Using diffstbprobe with the analysis mode set to "common-mode" results in a negative gain . The phase instead starts at −180 ° and increases toward 0 ° . Debug for the circuit: Even in the iprobe simulation and trans simulation, the CM loop is unstable, is there a function that can plot the pole location on the schematic to figure out which location cause the unstable issue? These results diverge significantly, leading me to question whether there might be a fundamental issue in the interpretation of results or possible configuration misalignment. Could you help me understand why these settings yield different outcomes? Which method or setup is more accurate for analyzing a CMFB (Common-Mode Feedback) loop under closed-loop conditions? And also ref: https://www.eecis.udel.edu/~vsaxena/courses/ece614/Handouts/Loop%20Stability%20Analysis.pdf
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