Beat frequency in SpectreRF PSS simulation

In a driven system, the beat frequency would be the greatest common divisor of all the input tones in the circuit (or the divided down frequencies if there are dividers in the circuit). PSS needs to solve a periodic waveform - and so you need to have an integer number of cycles of all the frequencies in the circuit.

In an autonomous system (e.g. an oscillator), you turn on the "oscillator" checkbox, and the beat frequency is then the estimated frequency, which gives PSS a starting point to solve for the oscillator frequency. It's important when in oscillator mode to select the outputs of the circuit, which include any subharmonics. In other words, if you have an oscillator followed by a divider, point at the divider output, and give the estimated divided frequency as the beat frequency. Again, this is because you need to solve an
integer number of cycles of all the frequencies in the circuit. Note, don't use oscillator mode for circuits which aren't oscillators, since you're then trying to get the simulator to solve for an unknown which is not unknown, which may lead to convergence problems.

So in your specific case, enter 384M, and turn on the oscillator checkbox, and point at the output of the oscillator.

Regards,

Andrew.

Thanks Andrews for the detailed explanation.