University of Electronic Science and Technology of China, Chengdu, P R China.
IEEE Trans Ultrason Ferroelectr Freq Control. 2011 Jul;58(7):1302-6. doi: 10.1109/TUFFC.2011.1950.
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).
环路半带宽内的相位噪声与负载品质因数 Q(L)密切相关。本文分析了负载品质因数 Q(L)的重要性以及基于提高 Q(L)降低相位噪声的方法。通过对 Pierce 振荡器电路的分析，推导出了 Q(L)的公式，并使用商业数值分析软件进行了计算。根据结果可以得出结论，Q(L)与电路参数有明显的关系。基于这一结论，提出了一种原型 120MHz 晶体振荡器的设计，并进行了实验。所使用的晶体谐振器为 SC 切 5 次泛音晶体谐振器，空载品质因数 Q(0)约为 1.05×10(5)。调整电路参数值以使 Q(L)合理提高，同时保持输出幅度为 2 到 3dBm。在载波附近的频率相位噪声测量结果为 10Hz 时为-104dBc/Hz，100Hz 时为-134dBc/Hz。实验结果表明，基于提高 Q(L)设计低相位噪声晶体振荡器是可行的。
