Hello,

I've currently got a telescopic amplifier with a differential-difference amplifier for the commno-mode feedback (basically an amp which compares the average of the outputs to a common mode level).

I am having trouble plotting the a.c. response of the common-mode part of the circuit. I want to see the gain and phase from the outputs of the amp to the input off the DDA which feed back to the amp and then to the output.... the system is unstable and I cannot simulate the a.c. to see the poles & zeros.

I have tried placing a large RC low-pass from the outputs of the amp to the input of the DDA, but no luck.

Thanks for any help,

Thomas

You might want to search this forum for "stb analysis".