Research On Temperature Compensated Crystal Resonator Based On Force-frequency Characteristics

With the development of the Internet of things technology,the world has gradually entered the era of Internet of Everything,and various types of intelligent terminal products have emerged one after another.As the"heart"of artificial intelligence terminal products,crystal oscillators have been put forward more stringent requirements.It must not only have the basic requirements of high stability,but also have additional requirements for small size.The traditional high-stability crystal oscillator improves the temperature-frequency stability index by adopting the external compensation network method,which uses the compensation voltage generated by the compensation network to feedback and adjust the output frequency of the crystal oscillator.However,the extra compensation network means extra volume,which makes the traditional high-stability crystal oscillators usually large in size and difficult to apply to portable terminals that are used.In this context,this paper designs a small volume crystal resonator that uses force-frequency characteristics to compensate for its own temperature-frequency characteristics.This topic comes from the National Natural Science–Basic research high-performance TCXO with Overtone Crystal Based on Stress-frequency Relation of Crystal.1.Analyze the influence of coating direction,coating thickness and coating shape on the frequency of the crystal resonator.In order to explore the influence of different coating methods on the frequency pull of crystal resonators,the finite element simulation analysis of three coated crystal resonators is carried out.Firstly,the thermal-structural coupling field analysis of three coated crystal resonators is carried out by ANSYS finite element analysis software.Through the post-processing results,it is found that the stress compensation films at different temperatures have different forms and directions of applying thermal stress to the crystal.The simulation results provide a visual guidance for the stress application problem of the stress compensation crystal resonator compensation film.Subsequently,the modal analysis of the crystal resonator model under pre-stress is carried out.Among them,the pre-stress is the thermal stress of the film generated by the thermal-structural coupling field analysis.The temperature-frequency characteristic of the natural frequency before and after compensation is obtained by measuring the natural frequency of the crystal resonator before and after coating at different temperatures.The simulation experiment verified that the coating treatment has a compensation effect on the frequency of the crystal resonator.2.Through the experimental verification,the actual effect of the coating on the frequency of the crystal resonator can be obtained,and the optimal coating scheme can be determined.In this paper,by comparing the temperature-frequency stability characteristics of three kinds of stress-compensation film crystal resonators,it is determined that the x-axis direction of the crystal piece is the optimal coating direction of the stress-compensation film,and the semi-annular stress-compensation film is the best coating shape.By comparing the temperature and frequency stability characteristics of different thickness stress-compensation film crystal resonators,it is determined that the 0.5 times center electrode thickness is the optimum coating thickness of the semi-annular stress-compensated film.Experiment show that the temperature frequency stability of the crystal resonator can reach10^-6 orders of magnitude only under the stress-compensation.Compared with traditional temperature compensated crystal oscillators,the stress-compensated crystal resonator has the advantages of low cost,low power consumption and small volume,and ensures high temperature and frequency stability requirements.This provides a new idea for the development of new temperature compensated crystal oscillators.