Research On Temperature Compensation Technology Of Crystal Oscillator

Crystal oscillator has been widely used in aerospace,instrumentation,radar,communications and other fields.Temperature compensated crystal oscillator has many advantages,like low consumption,quickstart-up,and being integrated easily.Therefore,it is one of the most frequently used oscillators as well.In this paper,the equivalent transformation of a crystal resonator with series capacitor is studied firstly.The predecessors have done some research in this equivalent transformation,by using some approximations.It is found during the derivation process that four unknowns can be solved by one equation without approximations by extracting the implicit condition of the equation.The implicit condition is that the equation is applicable for any frequency.Finally,it is proved that the application range of this equivalent transformation is not related by the Q value of the resonator,or the resonant frequency,or the capacitance ratio and so on.It is suitable for all piezoelectric resonators in accordance with the Butterworth-Van Dyke(BVD)model.After that,this paper studies the method of the measurement of quartz crystal unit parameters based on the zero phase frequency.In the early days,the equivalent parameters were measured by crystal impedance meter.At present,the International Electrotechnical Commission recommends the method of the measurement of quartz crystal unit parameters by using vector network analyzer.Because of the approximations,the theoretical error of the method will increasing when the Q value of the resonator is low.In this paper,a method for measuring the equivalent parameters of the crystal resonator based on the resonant frequency,the anti-resonant frequency,the load resonant frequency and the load anti-resonant frequency is presented.There is no approximation in the derivation process,so this method not affected by the Q value,which is verified by the simulation experiments as well.After solving the frequency random walk and the inaccuracy of nominal value of load capacitance by the derivative equation of phase frequency curve,this paper measures the equivalent parameters of a 5MHz crystal resonator and a 10 MHz crystal.The test results show that the measured equivalent parameters are consistent with those of the nominal value.Since the M value and Q value of the two resonators are high,the supplier's test error would be small.Therefore,the experimental results demonstrate the effectiveness of the proposed method.Based on the measurement of frequency,the dynamic resistance R1 is measured,and frequency is one of the most accurate physical quantities,so this method is profitable to improve the accuracy of the test.At the same time,the frequency measurement method is relatively mature,so this method is convenient to operate.In this paper,the advantage of this method is been verified in theory,and the preliminary experiment verified its feasibility.Next,this paper introduced the thermal hysteresis effect which is the main factor affecting the temperature stability of the temperature compensate crystal oscillator(TCXO).After analysis,we found that the one-dimensional temperature information of the sensor could not describe the four-dimensional temperature distribution of the resonator completely.The presentation above results in the same temperature corresponding to different output frequencies.On this basis,a real-time temperature compensation method is proposed to maintain the consistency of the test environment.Then,this paper designs a 100 MHz low phase noise real-time TCXO.The experimental results show that the frequency temperature stability and phase noise of this oscillator reaches or exceeds that of the same kind of industrial products in the world.At the end of this paper,the Trim effect was analyzed.Through the analysis,it is found that the cause of the Trim effect is the nonlinearity of the voltage controlled characteristic curve of the voltage controlled crystal oscillator.And this inference is verified by a preliminary experiment.Finally,this paper analyzes the possibility that TCXO can output multiple frequencies by two-dimensional compensation technique.