Low noise parametric quartz crystal oscillator

It is well known for a long time that oscillation in a circuit can be sustained by using a parametric action instead of a conventional amplifier. In that case, the resonant circuit loss is compensated by a periodic change of an oscillation loop parameter at an appropriate frequency (pump action). The modulated parameter should be, for instance, the series capacitance of a RLC resonant circuit by using a varactor diode. In fact, this component basically operates as a noiseless reverse-biased junction expected to be a good candidate for a low noise oscillator circuit design. Parametric amplifiers widely used in the microwave domain are much less used in the RF oscillator circuits, probably because their development leads to a more involved circuitry and the lack of suitable simulation tools. The paper recalls the principle of the parametric oscillator an example of which using a quartz resonator (PXO) will be presented. Various methods used to analyse the behaviour of the PXO are described, and comparison between theory, simulation, and experimental results are discussed. Encouraging power spectral density,of phase noise fluctuations obtained so far are demonstrated.