# analog-design

Stefan Schippers

11/25/2020, 10:31 AM
@User first set the dc operating of the circuit. comment all .ac, .dc, .tran, insert just a .op, then after simulation do a 'print all' to verify your operating point. If all is ok then insert an AC signal somewhere (depending on what you want to do) basically "vxxx node1 node2 AC 1 0" and run .ac analysis. Values you see in AC analysis are small signal deviations (more precisely it's the circuit behavior linearized in the operating point), amplitude and phase w.r.t the ac source, in the frequency domain. Normally you set the ac source with amplitude 1 and phase 0 so any value you read from circuit voltages is the transfer function (Vo/Vxxx). If no ac source is set all values are zero in the circuit during AC analysis since there is no deviation w.r.t. the dc point.

Arsalan Athar

11/26/2020, 6:15 PM
@Stefan Schippers Thank you Stefan I have done this...