The Design And Implementation Of120MHz Low Phase Noise Crystal Oscillator

Many modern electronic systems such as radar, communications equipment, andmeasuring instruments need frequency source with high frequency stability. Crystaloscillator having high quality factor is always used as the high performance referencesource of frequency source, and provides clock signal for many electronic devices. Withthe development of electronic technology, the phase noise performance of crystaloscillator plays a decisive role in the overall performance of many electronic systems.Therefore researching the working mechanism and noise property of crystal oscillator，analyzing the practical ways to reduce the phase noise and designing low phase noisecrystal oscillator have important theoretical significance and practical value.In this thesis，the physical and electrical properties of the quartz crystal resonator isanalyzed first, then the principle of positive feedback is analyzed，presenting theamplitude and phase stability conditions, introducing three basic oscillation circuits.The noise in amplifier and resonator analyzed. Frequency domain phase noise and timedomain Allan variance characterizing frequency stability are elaborated, the calculationformula from phase noise to Allan variance is deduced, the practical conversion methodis gave. The phase noise is analyzed based on ‘Leeson model’, obtaining the method ofreducing phase noise. The rigorous formula of unloaded factor QLof Pierce oscillationcircuit is deduced，obtaining the conclusion that QLincreases as C1, which is verifiedusing ADS. The120MHz Pierce crystal oscillator is designed on the basis of theobtained conclusion. The phase noise of designed crystal oscillator is measured by theAgilent E5052B source analyzer, displaying good phase noise characteristic.‘Energytrapping’ phenomenon in the crystal resonator is analyzed; the internal modulationgenerated by ‘Energy trapping’ is one of the sources of phase noise，increasing phasenoise near carrier frequency. Finally the measured phase noise is converted to Allanvariance, millisecond Allan variance is the order of10-12, meeting the target.