For running return ratios (CM and DM) in fully diff fb ckts: First, read the info on running return ratio (RR) for single-ended circuits, and try that test case. To set up for fully differntial sims, copy to a Linux directory the files: /home/hurst/212/rr_diff/run_rr_cm.sh , /home/hurst/212/rr_diff/rrv_cm.in , /home/hurst/212/rr_diff/rri_cm.in , /home/hurst/212/rr_diff/rr_cm2.sh , /home/hurst/212/rr_diff/run_rr_dm.sh , /home/hurst/212/rr_diff/rrv_dm.in , /home/hurst/212/rr_diff/rri_dm.in , and /home/hurst/212/rr_diff/rr_dm2.sh . Do 'chmod 0755 *.sh' to make the '.sh' shell scripts executable. For a test run, also copy /home/hurst/212/rr_diff/fbckt_for_rr and /home/hurst/212/rr_diff/MOS_models_0.4um_approx and then run 'run_rr_cm.sh' and 'run_rr_dm.sh' to run the DM and CM return ratios for the 2-stage op amp in the file 'fbckt_for_rr'. Each command should generate a plot showing RR mag and phase versus frequency. Then do the following: 0 - Find symmetric break points for the fully differential ckt that break all CM and DM feedback loops. Break the loops there. 1 - Name break points drivep, driven, measurep, measuren (either by modifying netlist, or by using 0V voltage sources). The 'drive' nodes should be on the side of the break where you would connect an independent test source for a return-ratio analysis. Don't include any independent sources in your file; they are included in the HSPICE files *.in that will '.include' your 'fbckt_for_rr' file. 2 - The HSPICE input files are called rri_cm.in and rrv_cm.in for CM return-ratio simulations. The circuit netlist is assumed to be named 'fbckt_for_rr', which is .included by these input files. (NOTE: This is a different file name that for the single-ended sims.) 3 - The command for running the cm rr simulation is: run_rr_cm.sh which runs: hspice rrv_cm.in > rrv_cm.out hspice rri_cm.in > rri_cm.out rr_cm2.sh The output file is rr_cm.out.rr 4 - The HSPICE input files are called rri_dm.in and rrv_dm.in for DM return-ratio simulations. The netlist is assumed to be named 'fbckt_for_rr', which is .included by these input files. 5 - The command for running the dm rr simulation is: run_rr_dm.sh which runs: hspice rrv_dm.in > rrv_dm.out hspice rri_dm.in > rri_dm.out rr_dm2.sh The output file is rr_dm.out.rr