Phase jitter minimization in UHF band VCXO

Discusses how a nonlinearity of oscillating stage affects phase noise performance of a UHF band voltage controlled crystal oscillator (VCXO). The developed oscillator is based on Colpitts circuit and on quartz crystal resonator with 100-160 MHz frequency of fundamental mode. The nonlinearity is an unavoidable part of any oscillator. So, in order to obtain UHF band signal, we have chosen a method of already existing harmonic selection (in that oscillating stage). This approach allows one to achieve phase jitter not exceeding 1.0 ps RMS for output signal in UHF band. Phase noise spectral density and signal spectral purity have been taken into consideration as the main parameters of the oscillator quality. The main question of research was how the increase of power level of one harmonic will affect a level of the phase noise. The obtained experimental results show that in certain conditions if fundamental oscillation and desired harmonic at any rate do not counter interact with each other then low phase jitter is achieved.