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 parameters. 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 factor Q(0) of about 1.05 × 10(5). 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).