100-MHz Low-Phase-Noise Microprocessor Temperature-Compensated Crystal Oscillator

Abstract

An AT-cut third-overtone 100-MHz quartz crystal resonator was used to achieve a 100-MHz low-phase-noise voltage-controlled crystal oscillator prototype. The unloaded quality factor of the used resonator is about 132 K, and the equivalent dynamic capacitance is about 1.2 fF. For the characteristic of the large equivalent dynamic capacitance of the resonator, the design method and the actual measured data of the low-phase-noise oscillator prototype are given. An explanation of why larger equivalent dynamic capacitance and higher voltage-control sensitivity can lead to bad phase noise in half-bandwidth is given. The STM32F103RCT6 MCU is used to read the real-time data of temperature sensor of the microprocessor temperature-compensated crystal oscillator (MTCXO) and the real-time control voltage loading on the MTCXO. Therefore, the real-time communication between a personal computer and an MTCXO is achieved. The control voltage $V$ achieved in this way has already considered both the effect of the actual working condition of the MTCXO circuit and the effect of the MTCXO internal reference voltage that it is not accurate enough. After temperature compensation, the measured temperature performance of the 100-MHz low-phase-noise MTCXO are better than ±0.45 ppm/−30 °C –+50 ° C, and measured phase noise results are better than −157 dBc/Hz at 1 KHz and −170 dBc/Hz at 10 KHz.