Design Of High Precision Temperature Compensation Circuit For Low Power Real Time Clock

The real-time clock provides an accurate time reference and has important applications in areas such as mobile communications,Internet of Things,and smart meters.The real-time clock's frequency source is a32.768kHz tuning fork quartz crystal,which produces a clock deviation of±150ppm over a temperature range of-40°C to 85°C.When two nodes is communicating,the clock accuracy of the communication device is too low to cause the receiver to lose information or reread the information,which seriously affects the performance and power consumption of the communication device.According to China's telecommunications industry standards,the clock accuracy applied to communication equipment is at least±4.6ppm.For this requirement,this paper designs a high-precision temperature compensation circuit for low-power real-time clock.This thesis describes the physical characteristics of the quartz crystal oscillator,the classification and indicators of the temperature sensor,and the current mainstream temperature compensation program.On this basis,a high-precision compensation circuit structure for low-power real-time clock is designed.The circuit mainly includes two parts:a temperature sensor and a digital compensation circuit.The temperature sensor utilizes a frequency-locked loop structure to generate a frequency signal that varies with temperature,and then the counter converts the frequency signal into a digital quantity representing the temperature.The frequency-locked loop structure uses a chopper modulation circuit to reduce the impact of 1/f noise and operational amplifier offset voltage.The digital compensation circuit calculates the frequency deviation of the quartz crystal oscillator according to the temperature output from the temperature sensor,then applies the integer frequency compensation by the suppression/injection pulse to the offset frequency value to be compensated.In order to reduce the power consumption,the high-frequency delay signal required for digital compensation can be realized by the high-frequency oscillation signal output by the temperature sensor.Based on the GF130nm process,this thesis designed the temperature compensation circuit.The layout area is0.26mm~2.The post-simulation results shows that the temperature sensor consumes 64.7?W at 1.5V,the resolution of the temperature sensor is 0.038°C and the three-point calibration accuracy is±0.46°C.Based on this temperature compensation circuit,the accuracy of the crystal oscillator is±2.5ppm,the power consumption of the temperature compensation circuit is 288nW.