A varactor model including avalanche noise source for VCOs phase noise simulation

This work studies an important area of oscillator operation VCO biased at varactor breakdown. In this operation, the oscillator´s phase noise is primarily determined by avalanche noise generated in the varactor, i.e., the phase noise can be modulated by the incremental shot noise generated at varactor breakdown. A simple experimental diode model was optimized for modeling varactor-breakdown current and an empirical shot noise model based on Hine´s theory presents good agreement with noise power measurements of varactors. The developed varactor noise-model has successfully been used to simulate the phase noise of a single-ended Colpitts InGaP HBT VCO over and beyond the varactor´s breakdown voltage. The VCO presents a phase noise below -lOOdBc/Hz for varactor voltages lower than breakdown voltage. Beyond the breakdown the phase noise gradually increases to -60 dBc/Hz@100kHz with a centre frequency deviating less than 0.6% from a 7.38GHz carrier.