High Quality Quartz Crystal Oscillators: Frequency Domain and Time Domain Stability

Abstract

There are several aspects of electronic circuit design which must be carefully considered in order to achieve high short-term frequency stabil i ty in quartz crystal osci l la tors . W e report an advance of more than ten decibels in the state-of-the-art for high quali ty rs 5 MHz quar tz c rys ta l osc i l la tors in the no ise frequency range of 1 to 100 Hz. The most important design fac tors were A) measurement and selection of transistors for the lowest possible f l icker of phase noise' (oscillating loop and buffer stages), B) measurement and selection of transistors and diodes for the lowest possible DC flicker noise (voltage regulators, automatic gain control) , C) massive negative feedback (DC and RF) in the RF c i rcu i t ry to s tab i l ize the RF ga in and to reduce the f l icker of phase noise of the transistors ' (automatic gain control [AGC ] amplifier, buffer amplifiers, oscil lating loop amplifier) . Because more negative feedback is used in the ACC amplifier and in the buffer amplifiers than can be used in the oscil lating loop amplifier, the resultant f l icker of phase noise performance of the osci l la tor is determined by the flicker of phase noise of the t rans is tor in the oscillating loop.