A Study of Temperature Compensated Crystal Oscillator Based on Stress Processing

The most temperature compensated crystal oscillators must use compensation circuits and always based on fundamental crystals. We combine the different characteristics of quartz crystal including frequency-temperature characteristics and frequency-stress characteristics, with the influence of stress on the frequency of crystal blank to compensate the temperature influence on the frequency of crystal. A lot of experiments have been done to prove that with stress processing the frequency - temperature performance of overtone crystals can be improved obviously. With this way, the new crystal oscillators can show a good frequency -temperature performance, lower power consumption, lower cost, lower phase noise and better short term stability. Now the frequency -temperature stability of the oscillator samples can be better than +3 ppm from -30 to +85 deg. C temperature range. Based on the samples and with a simple circuit compensation it is easy to obtain plusmn0.5 ppm stability. To generate the suitable stress, we use the double plating electrode. It is a double metal temperature sensor, and when temperature changes there is a possibility for the shape of sensor to be changed also. Therefore, the electrode can apply the stress to the blank of the crystal. We choose overtone crystal and it can show better stability and aging than those of fundamental crystal, and higher frequency -stress sensitivity. Generally, the stress on the crystal will influence the aging of crystal and oscillator. Choosing suitable double-metal electrode materials and with the overtone crystal, the aging of the crystal oscillators can still show the same specification as conventional ones.