Design Of Low Noise And High Precision CMOS Quartz Crystal Oscillator

With the development of information technology,especially in the field of global positioning system,measurement,communication,time and frequency measurement,the accuracy and stability of the reference frequency source are getting higher and higher requirements.To produce high-quality signal source,you must choose a good oscillation circuit,the ordinary oscillator,for example,the frequency stability of the LC oscillator is poor,which should not be used directly.Therefore,we need to join the high stability of the resonant device to improve the frequency stability,such as crystal resonators,surface acoustic wave devices,resonators and dielectric resonators,etc.Because of high value,the crystal resonator is widely used,and the crystal oscillator made with it has good frequency stability.Being based on the Nuvoton 0.35?m 5V standard CMOS process,a CMOS cross-coupled crystal oscillator with low noise and high accuracy is designed.First,using CMOS cross-coupling to produce negative resistance for compensating the energy which crystal oscillation required,at the same time increasing the common mode feedback for the crystal oscillation current to provide a stable DC operating point,and then adding the pre-suppression circuit,high-pass filter to reduce the circuit noise,In order to make the crystal oscillator operate in a more stable state,the design of a BJT-based bandgap reference voltage source to provide bias voltage and current,while designing a low dropout linear regulator for power supply of the crystal oscillator circuit.Being based on Nuvoton0.35?m5V standard CMOS technology,the circuit is simulated by Cadence Specter.The results show that the oscillation time of the oscillator is about 1.5ms at the power supply voltage of 4.5V;The peak value of the output waveform is 1.08V and the output DC level is about 801.6mV;The output signal frequency is 20MHz,and the frequency stability is 95ppm at room temperature;The frequency stability is 95ppm at room temperature,in the case of VDD = 4.05V,VDD = 4.95V,T-25?,T = 85?;The frequency stability is 92ppm?83ppm?77ppm?76ppm.The phase noise can reach-143dBc/Hz @ 1 kHz,-165dBc/Hz @ 10 kHz,-177dBc/Hz@1MHz.Being based on the NUVOTON0.35.?mCMOS process,the Laker tool is used to complete the layout design and the graph is simulated by Hspice.The results show that the oscillation time of the oscillator is about 2.5ms at the power supply voltage of 4.5V,and the output waveform-peak is 0.939V;The output frequency is about 752mV.The output signal frequency is 20MHz,and the frequency stability is 80ppm at room temperature,in the case of VDD = 4.05V,VDD = 4.95V,T =-25?,T = 85?,the frequency stability is 81 ppm,79 ppm,71 ppm,66 ppm.Phase noise can reach-132dBc/Hz @ 1 kHz,-156dBc/Hz @ 10 kHz,-169.2dBc/Hz @ 1MHz.After completing the film and test,the quartz crystal oscillator output frequency is 20MHz.