Design And Implementation Of A Novel VCTCXO

Crystal oscillators are the key components of almost all kinds of electronic equipment. As the fast development and wide use of smart devices, the requirement for high frequency stability and low power consumption crystal oscillators increases rapidly. Voltage controlled crystal oscillators are adopted to construct signal generator and frequency synthesizer inside of all kinds of communication equipment, such as global position systems(GPS) tracker. Besides, frequency variation occurs in crystal resonators because of its intrinsic property, which is wanted to be eliminated in the conditions with requirement for high frequency stability. Thus, when design such crystal oscillators that could modulate frequency, good frequency temperature characteristic is a big plus. The microprocessor compensation method arouses researchers and scholars interests because of its advantages of small size, low consumption and high frequency stability.Based on the consideration above and the current status of crystal oscillators, a novel voltage controlled temperature compensated crystal oscillator(VCTCXO) is designed and implemented in this thesis. Microprocessor is adopted to realize temperature compensation and voltage control, i.e., excellent frequency stability is guaranteed as well as frequency regulation among wide temperature range. In order to assure the precision of frequency temperature characteristic our designed VCTCXO, STM32 microprocessor is adopted. Comparing with tyical 51 Single-Chip, STM32 has better performance, better compensated results could be realized based on different algorithms. At the meantime, a real time PC host system is designed to monitor the temperature compensation and the voltage control process of VCTCXO.In our designed system, compensated voltages for temperature compensation and voltage control are applying on the same variode of the crystal oscillator. This method could efficiently avoid mutual interference of two variodes, which is a problem in the traditional approach, and obtain great frequency temperature characteristic. We verify the realistic feasibility of our designed VCTCXO by trial-producing a VCTCXO prototype and a series of experiments on it.Firstly, we measured the frequency temperature characteristic of the chosen three frequencies, and obtain the compensated voltage data which compensate the frequency right to the center frequencies. After that, we did the fitting of the voltage data and applied it in to the microprocessor. Then, we perform the temperature compensation and voltage control on the voltage controlled crystal oscillator to verify our purpose. Experiment results show that our designed VCTCXO prototype possesses high frequency stability at different center frequencies, which is less than 2ppm. Thus, our expected goal is achieved.