Design And Implementation Of An Analog Temperature Compensation Crystal Oscillator

Crystal oscillator is an important frequency source,modern electronic system,often used crystal oscillator as a clock circuit.The crystal oscillator will also encounter some problems during use,one of which is the oscillation frequency drift caused by the temperature,which is caused by the physical properties of the crystal resonator.In some high-precision devices,the crystal oscillator is required to always maintain extremely high precision,and various solutions that solve this temperature result in frequency offset have occurred.One of the solutions is to fine-tune the oscillation frequency of the crystal oscillator when the temperature changes to compensate for the frequency offset caused by the temperature change.There are many different schemes for temperature compensation,thesis will introduce one of the temperature compensation programs.The temperature compensation of crystal oscillator is generally divided into analog and digital.This design uses analog temperature compensation.The common analog compensation method is to use thermistor compensation network as compensation circuit,and this design uses the temperature compensation voltage generation circuit composed of operational circuit to replace thermistor compensation network.The temperature compensation voltage generation circuit will calculate the temperature-dependent voltage and generate a suitable compensation voltage to compensate the oscillation frequency variation of the VCXO.In order to adjust the operation mode of temperature compensation voltage generation circuit according to the actual demand,based on the derivation and analysis of the circuit,a scheme to adjust the operation mode of the circuit is given,and the feasibility of the adjustment scheme is verified by the simulation test.Offset voltage need to reference the specific change law of VCXO vibration frequency of temperature characteristic set,the design process,first determine the VCXO vibration compensating voltage required by the compensation voltage curve fitting,combined with the fitting coefficient and the computing formula of temperature compensation voltage generating circuit,the parameters of the circuit size determines the temperature compensation voltage.On the other hand,the voltage frequency ratio of the voltage controlled crystal oscillator is measured and the allowable compensating voltage error is calculated.Experiments were carried out on the temperature compensation crystal oscillator,including testing the frequency and temperature characteristics of the VCXO under different base compensation voltages and the operation effects of the third and fifth order temperature compensation voltage generation circuits.Then adjust circuit parameters to verify the effect of temperature compensation.The experiment results show that,the temperature compensated crystal oscillator is in the range of-30??80?,and the frequency stability is within ±1.5ppm.