Research On Wide Compensation Method Of Temperature Compensated Crystal Oscillator

As a high-precision frequency source,crystal oscillators are widely used in communication,measurement,aerospace,instrumentation and other fields.Temperature compensated crystal oscillator is one of the most commonly used crystal oscillators due to its low power consumption and easy integration.The traditional temperature compensation method is to control the output frequency of the crystal oscillator to ensure the stability of the crystal oscillator output frequency and achieve the effect of temperature compensation.The structure of this compensation method is relatively complicated,and it will be disturbed by the temperature hysteresis during the compensation process,so that the temperature-frequency characteristic curves in the process of heating and cooling are inconsistent,which will introduce a certain temperature error.Aiming at the use of temperature-compensated crystal oscillators in frequency measurement instruments,this paper proposes a new open-loop software-compensated microcomputer-compensated crystal oscillator?MCXO?,which aims to improve the accuracy of frequency measurement and simplify the structure of MCXO.When the output frequency of the MCXO is used as the reference signal in the frequency measurement system,this paper does not control the output frequency of the MCXO from the hardware,but achieves the effect of temperature compensation in the form of software compensation in the process of frequency measurement.Firstly,the frequency deviation of the crystal oscillator at different temperatures needs to be obtained in advance through temperature experiments.Then,in the data processing of frequency measurement,this error is corrected,that is,the frequency nominal value in the measurement process is continuously corrected in the form of data.The value is always guaranteed to be calculated and processed based on its exact frequency,so as to achieve the purpose of temperature compensation for MCXO applied to frequency measurement.In order to suppress the temperature hysteresis effect,this paper chooses the SC-cut dual-mode crystal oscillator for experimental design.With its special temperature characteristics,The difference frequency signal of the Baseband signal and the 3^rd overtone have a linear relationship with the temperature,and the difference frequency signal can be used as the temperature sensing signal to reflect the temperature change of the crystal oscillator itself,thereby maximally suppressing the temperature effect.to improve the accuracy of the measurement.Because of the particularity of the MCXO compensated by this open-loop software,its performance specifications need to be tested together with the measurement system it constitutes.The accuracy of the system will be affected by the software algorithm.Therefore,in order to further improve the measurement accuracy,this paper uses a high-precision digital measurement scheme combined with the MCXO to verify its index.The data processing part can share one MCU,further simplify the structure of the entire system.Finally,it is proved by experiments that the MCXO compensated by this open-loop software is applied to the frequency standard of the frequency measurement system.Under the same circumstances,the structure is simpler and can obtain higher accuracy.In a wide temperature range,the measurement error can be reached5×10^-8.