"How to design RF circuits"-oscillators

Readily available harmonic balance simulators can be used to accurately predict the frequency, output power and harmonic content of RF and microwave oscillators. Phase noise can also be simulated, although values are highly dependent on the flicker noise parameters within the non-linear model. In the absence of a non-linear simulator, a relatively cheap small-signal simulator can still be used to predict frequency. Output power can be estimated by assuming 10-20% DC-to-RF efficiency. In reality, the small-signal simulation is vital to ensure that adequate negative resistance is available for start-up of oscillation. As a rule of thumb a negative resistance some 20% greater than the sum of the total positive resistances should be created. The small-signal simulation also illustrates the potential for unwanted or spurious frequencies of oscillation, at which the presence of negative resistance must be avoided.