Temperature-compensated crystal oscillator using a two-port crystal resonator

Abstract

In general, the oscillation frequency of a quartz crystal oscillator is shifted by varying the load capacitance of the quartz crystal resonator. Since the relation between load capacitance and oscillation frequency of the crystal resonator is nonlinear, the rate of change of frequency is slightly different from the load capacitance before and after the frequency shift. When the variation of oscillation frequency due to aging is compensated using the temperature-compensated crystal oscillator (TCXO) or the voltage-controlled temperature-compensated crystal oscillator (VCTCXO) or the oscillation frequency is shifted, the frequency compensation amount set by the temperature compensation circuit is different before and after the compensation. Thus, the frequency versus temperature characteristics vary. To solve this problem, the author has developed a special quartz crystal resonator with two-port electrodes. Since this crystal resonator has two load capacitances, the compensation of the temperature characteristics and the shift of oscillation frequency can be conducted independently. Thus, the problem of the changes in the temperature characteristics due to the oscillation frequency shift of a TCXO has been solved. This problem could not be solved using the conventional quartz crystal oscillator having only one capacitance. In this paper, measurement is made under the condition that the oscillation frequency of the TCXO using a two-port crystal resonator is shifted by ± 15 ppm and the performance is compared with that of TCXO using a conventional crystal resonator. the measurement has revealed that the change of frequency versus temperature characteristics is extremely small when the oscillation frequency of the TCXO using a two-port crystal resonator is shifted.