An Improved Overtone Crystal Oscillator with Microprocessor Temperature Compensation

For improving the frequency-temperature characteristic of temperature compensation overtone crystal oscillator (TCOXO), a novel 120MHz TCOXO design is described in this paper. It is different from general methods, in which a compensated 40MHz 3th overtone crystal oscillator is frequency tripled. This design utilizes a 100MHz AT-cut 5th overtone crystal oscillator mixing with a 20MHz AT-cut VCXO, then the 120MHz signal is gained through the filter. In this design, AT89S52 microprocessor is chosen to control and supply the adjusted voltage which the 20MHz VCXO needs, consequently, frequency deviations of the two crystal oscillators are compensated so that the 120MHz is the stable output frequency. As the frequency deviation of the 100MHZ overtone crystal oscillator and the 20MHz VCXO is both compensated simply by the latter, which makes frequency deviations of total system even more, the piecewise linear interpolation method is used. In this work, verified experiment results of the compensation are presented. The stability of the experimental 120MHz TCOXO with microprocessor temperature compensation achieves plusmn 2 times 10^-7 within the temperature range from -30 to +70degC. The adding inductance method in the common design is not contained, therefore, this novel design is helpful for improving frequency-temperature performances of TCOXO. Synchronously, frequency multiplication is substituted by mixing so that it is possible to reduce the phase noise of the high-frequency TCOXO with this method