Autonomous Harmonic Balance

Up to here, only forced circuits were dealt with. That is, the above-mentioned methods can analyse circuits that are driven by signal sources, but do not create a signal by themselves. The typical examples are amplifiers and mixers. However, harmonic balance techniques are also capable of simulating autonomous circuits like oscillators.
This is mostly done in the following way:

1. The user enters an approximate frequency, where the oscillation is expected. (An ac simulation can be performed to get an idea about that.)
2. The user enters a frequency interval. Somewhere within this interval the oscillation must appear.
3. The user specifies a circuit node where the oscillation voltage can best be measured.
4. The simulator performs several harmonic balance analyses with different fundamental frequencies in search for the oscillation.