The design and implementation of a 120-MHz pierce low-phase-noise crystal oscillator

The phase noise within the half-bandwidth of the loop is closely related to the loaded quality factor Q_L. The importance of loaded quality factor Q_L and the method of reducing phase noise on the basis of improving Q_L are analyzed in this paper. Formulation of Q_L is derived from analysis of the Pierce oscillator circuit, and calculated with commercial numerical analysis software. According to the results, we can draw a conclusion that Q_L is explicitly related to circuit pa rameters. Based on this conclusion, a design of the prototype 120-MHz crystal oscillator is presented and the experiments are carried out. The crystal resonator utilized is an SC-cut 5th-overtone crystal resonator with an unloaded quality fac tor Q₀ of about 1.05 × 10⁵. The circuit parameter values are adjusted to make Q_L reasonably higher, while maintaining an output amplitude of 2 to 3 dBm. The measurement results of near carrier frequency phase noise are -104 dBc/Hz at 10 Hz and -134 dBc/Hz at 100 Hz. Experimental results show that it is feasible to design a low-phase-noise crystal oscillator based on improving Q_L.