Hi team
The schematic of the fully differential amplifier is in the attached pictures. I want to simulate the differential gain/stb and common mode feedback loop stb
Fig1 fully differential amplifier circuit testbench
Fig 2 Inside the fully differential opamp is my core fully differential amplifier and CMFB amp
Fig 3 My core amplifier and I put the CMDMprobe here
My question is that I did transient and stb simulation with cmdm probe. in the plot below, the transient plot is on the left. Red is the input the green is the output, which suggests a stable amplifier with a positive gain. But the stb simulation with CMDM=-1 suggests the plot on the right--the gain is negative.
Can you please let me know what I did was wrong? Or what other info do you need to help me diagnose?
Thanks
MD