Hello!

I have to analyse a rather complex oscillator circuit for phase noise.  The core is build as a colpitts type oscillator. The output buffer is build as an inverter chain for creating a rectangular output signal for driving digital logic.

Using SpectreRF PSS simulation convergence could be achieved. But when I switch to ADS HB analysis I can't get any convergence. (Comparing both simulator's results to each other is a key issue of my task).

It seems, that the quasi-digital output buffer is the main source of trouble, because I don't have any problems if i remove the output stage.
As setting I use 20 harmonics and 4 times oversampling. Tolerances are set to weak. I use the transient assisted HB. Observing the transient results, it seems that a near-steady-state is reached (although the simulator doesnt recognize one...).
Has anyone suggestions what I can try for solving my problems?

Regards
Christoph

Yes with PSS I mean the shooting PSS algorithm. The oscillator converges using this method, but each simulation is taking a very long time.

The ADS version used is 2006a. I tried both kind of oscillator simulations (node select and oscprobe). The result is practically the same. As long as I abandon the output stages simulation takes it's time but converges. After adding them to simulation again, I can't get any results.

You could also try to use more harmonics, 20 might not be enough for your type of output circuit. In general, shooting (time-domain) pss is probably much better suited for this kind of circuit than harmonic balance.