AM-to-PM conversion in varactor-tuned oscillators

This brief deals with AM-to-PM noise conversion due to varactors and nonlinear capacitances. The effect increases the sensitivity of oscillators to substrate and power supply noise and sets a serious limitation to the phase noise performance of these stages when they are embedded in complete transceivers. A rigorous approach to the quantitative estimate of the conversion factor and a closed-form expression are derived. The conversion due to typical varactor structures available in integrated technology is discussed.