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 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
.