I´d like to do a pz simulation of a circuit to see the pole movement under different operating conditions.
To do so I did a stb analysis first.
Then I compared the location of the poles from stb analysis to the ones gotten by the pz analysis.
And unfortunatelly they are totally different.
What could be the reason for this?
I assume that the operating conditons are the same.
Oh I forgot. I´m using Cadence 6.1.5
stb analysis is looking at the loop gain of a specific loop (that you point at) - not producing poles and zeros. The pz analysis is analyzing the poles and zeros of the entire circuit, not just one loop. So it's an apples and pears comparison.
meanwhile I got how I have to do the comparison.
I have to compare the poles and zeros I get from the pz analysis with the pase and magnitude response of the closed-loop systems.
The poles and zeros should match there.
Stb is just open loop as you say.
Actually stb is not open loop. It's the loop gain of a specified loop (and that loop is closed). But it's different from the transfer function from the input of the circuit to the output, which is what you mean by "closed loop", I guess. The loop gain will usually be significantly higher than the transfer function of your entire closed loop system.