Hi there,
I have experienced a PSS convergence issue and needed some advice.
My circuit is a PLL that requires a certain time to settle, and I wanted to simulate the close-loop performance of the PLL.
I do PSS simulation, with "Run Transient" set to "Yes". Then I specify the proper time for the PLL to settle and I also saved the transient results.
The problem comes with the stop time setting. I know that the circuit will settle within 3us, verified by transient simulation, and I specify the stop time to be longer than that, for instance 4us.
What I noticed is that as I change the stop time, althoughalways longer than setting time, sometimes PSS converges and sometimes it does not.
For instance, I set 4us stop time, simulator converges and simulation finishes with expected results. Now I increase the stop time a bit longer to 4.1 us, then pss fails to converge. If I increase the stop time to 4.3us, it converges, and with 4.5us, it fails again.
The circuit is already settled at 4us, pss converges, and the results are as expected. What I don't understand is why the simulator can't converge at 4.1us.
What I noticed is that when it converges, it converges pretty fast, with just a few tries. when it fails, it also fails very fast, within a few iterations, "Conv norm" goes to very large number.
I wonder what could I do to improve this situation. I used default PSS convergence and accuracy settings, and I am using ic213_isr22
Thanks!