[time-nuts] Simulation tools for oscillators

[Tim Shoppa]

Are there any useful, free or near-free tools for simulating
high-performance oscillators? I'm thinking particularly about
making at least a little bit quantatitive statments
about phase noise through simulation.

SPICE will simulate an oscillator starting up, doesn't do a
particularly good job when the nonlinearities of a simple
oscillator kick in to limit the amplitude but most of the
active device models can be tweaked to mimic the real world
near saturation.

If the active devices never go into saturation but there's
an actual AGC loop then things can be done somewhat
realistically without tweaking.

But I have no idea how to properly model phase noise in even
the most cartoon-like way with SPICE.

Setting the time step to something ridiculously small and
then FFTing to the frequency domain is almost completely
hopeless due to all the numerical noise.

SPICE old-timers will laugh at me because I even tried to
simulate an oscillator in it, I'm sure :-). Hey, I actually
started on a 11/780 with 50 users too!

What do the pros use? I know there are goals (maximize
power, minimize noise, at the same time minimize heating)
and SPICE can vaguely help with them
but common sense and cut-and-try seem to be the best tools
I know of!

Tim.