Analysis and design of low phase noise crystal oscillators

The methods to reduce phase noise of crystal oscillators are presented and analyzed in the paper. According to analysis of Leeson formula, phase noise has a direct relation with noise factor F, corner frequency f_c and loaded quality factor Q_L. Based on the method of reducing phase noise by improving Q_L, the formula of Q_L is derived by analysis of Pierce oscillator circuit and simulated by MATLAB. According to the simulation result, we can draw a conclusion that Q_L is explicitly related to circuit parameters. Based on this conclusion, phase noise of a Pierce crystal oscillator is simulated and analyzed by the Agilent Advanced Design System. The simulated phase noise results are reduced by adjusting circuit parameter. A design of the prototype 120 MHz Pierce crystal oscillator is presented and the experiments are carried out. The measured near carrier frequency phase noise can achieve -100 dBc/Hz@10Hz and -132 dBc/Hz@100Hz. The simulated and experimental results show that it is feasible to design low phase noise crystal oscillator based on improving Q_L.