This paper describes a novel method to realize microprocessor compensated crystal oscillator (MCXO) by using the dual-mode excited AT-cut quartz crystal resonator (QXR).According to the harmonic effect

normalized beat frequency of the 3rd overtone frequency and 3 times of the fundamental frequency is almost linearly dependent on the changes of ambient temperature.By stimulating the fundamental and the 3rd overtone frequencies output simultaneously

the changes of ambient temperature was measured by the beat frequency and the temperature compensation was accomplished by the utilization of the dependence of the temperature on the beat frequency and the method of pulses deletion.This temperature measurement technique can eliminate the thermal lag due to the difference in thermal time constants of the QXR and the thermistor

and can overcome the limitation of temperature field gradient.The implementation of the means in MCXO is described.The dual-mode oscillating circuit and its block diagram are given and the practical experimental data are discussed.