Frank Wiedmann wrote on Oct 18th, 2009, 12:51am:A transient simulation of the step response is the most reliable way of determining stability. It should always be done to verify the stability of the circuit, even if the circuit was designed with small-signal analyses. The disadvantage of the transient simulation is that it usually takes much longer than a small-signal analysis and that it is more difficult to extract a number like the phase margin from the results.
Thanks for your suggestion. I still have some question about the stability judging by the transient simulation. For opamp simulation, input is a square wave using vpulse source in spectreRF, and if no ring in the rise time at the output. It is ok! For RF circuit, usually, there is an input match network including capacity for match and dc separation in amplifier and with an output match network after it. In this case, should I still use vpulse source in series with a 50 resistance(vpulse source has no output resistance), and add the vpulse in the input match and see the wave after the output match? If there is no ring, it is ok?
Another question is about the stability at the time of power on, should I simulation it to confirm the stability? If I should simulation the state of power on, what input signals source should I choose?