Effect of Parametric Instability on Phase Noise Degradation in a Varactor Frequency Multiplier

Varactor frequency multipliers often show parametric instability with increasing RF input power. Examination of the added phase noise of the varactor frequency multipliers show that, if parametric oscillations are present in the circuit, output phase noise degrades remarkably in some specific driving levels. Phase noise analysis is done by the conversion matrix method. The conversion method predicts the phase noise degradation precisely because it encounters the noise conversion by large driving levels. The added phase noise of a varactor frequency doubler with subharmonic oscillation is calculated and the simulation results are compared with measurement results. Both simulation and measurement show a relation between excessive phase noise degradation and the onset of subharmonic oscillation.