Design Of An Integrated Low-noise Temperature-compensated Crystal Oscillator

The crystal oscillator utilizes the piezoelectric effect of the crystal to generate mechanical vibration,and has good physical characteristics and high stability.It is often used as a pulse signal and frequency source.It is widely used in key fields such as the electronic technology industry,communication radar,and national defense.Important devices in the field.With the emergence of artificial intelligence,5G and other technologies,various industries are transforming to intelligence and miniaturization.Nowadays,crystal oscillators are also developing in the direction of intelligence,high stability,and low power consumption.However,due to the inherent nature of the crystal itself Property,when the outside temperature changes,it will affect the output of the oscillator frequency,resulting in a deviation from the nominal frequency.In order to improve the frequency and temperature characteristics of the oscillator,the research and application of temperature compensation technology has appeared very early.At present,whether it is an analog temperature-compensated crystal oscillator or a digital temperature-compensated crystal oscillator,the voltage of the varactor diode contains the oscillator's AC voltage will deteriorate the phase noise index of the oscillator.This paper designs a new type of temperature-compensated crystal oscillator suitable for integration.The variable capacitance of the load uses a temperature coefficient capacitor and is connected in series with the crystal oscillator to form a compensation circuit.This avoids the use of varactor diodes.In this solution,the temperature and frequency curve of the crystal oscillator is approximately regarded as the connection of several straight line segments.Since a single capacitor can only be compensated within a certain temperature range,an analog switch circuit is designed to select each straight line segment according to the current temperature.Corresponding temperature coefficient capacitors realize automatic segment temperature compensation.This article first introduces the structure and related main parameters of the crystal resonator,briefly analyzes the phase noise,introduces the basic principles of temperature compensation and common compensation methods,and then the design of each hardware circuit in the program and the selection of various components The type is described in detail,and the programming ideas of the software part are also summarized.After completing the above work,software simulation simulation debugging is carried out to detect the operation of the circuit and ensure that the compensation scheme is feasible.Draw the PCB circuit diagram on the basis of the circuit schematic,and complete the work of physical welding,test and test the welded physical circuit to ensure that the design requirements can be met in the actual process.Finally,a thermostat experiment was conducted to obtain the compensated temperature-frequency curve after processing the data of the thermostat.Observe the compensation results and phase noise.In the experimental temperature range of-20?~+70?,the output frequency stability of the crystal oscillator reached ± 2ppm,and the phase noise index was-129dBc/Hz at 1KHz from the carrier.The design scheme is feasible,but due to the approximate method of frequency temperature curve,the compensation accuracy needs to be improved and improved.