| With the rapid development of the Internet of Things technology,various IoT electronic devices have put forward higher requirements for the accuracy and power consumption of the internal real-time clock in the system.Although oscillators based on quartz crystals and various piezoelectric micro-electro-mechanical resonators can provide high-quality clock signals,the temperature stability of the output frequency still cannot meet the requirements due to the temperature characteristics of the resonator itself,so it is necessary to compensate for the temperature characteristics of the resonator at the circuit level.This dissertation proposes a low-power and high-precision temperature-compensated real-time clock circuit based on a quartz crystal.The entire system includes three sub-circuit modules:clock generation circuit,digital temperature sensing circuit,and digital temperature compensation circuit.In the clock generation circuit,a pulse-injection oscillator is designed and implemented to reduce the power consumption.By using a delay-locked loop to align the injection time of the pulse with the peak and valley of the oscillation signal,energy is injected into the resonator to maintain oscillation.In the digital temperature sensing circuit,a ring oscillator controlled by a switched-capacitor proportional to absolute temperature current source is designed and implemented,and low-power digital temperature conversion is achieved through frequency counting.Finally,this dissertation proposes a multi-phase digital temperature compensation method.According to the compensation data stored in an on-chip lookup table,the multiple delayed output signals of the delay-locked loop are dynamically selected to compensate for timing errors caused by temperature changes.The circuit design of this dissertation is based on a 65 nm low-power CMOS process,using a quartz crystal model NX3215SE from NDK company.And the supply voltage is 0.6 V.The simulation results show that the digital temperature sensor designed in this dissertation can provide a worst-case temperature sensing accuracy of ±0.61℃ in the temperature range of-25～85℃,so that the temperature compensation circuit designed in this dissertation can achieve a temperature compensation accuracy of ±2.9 ppm.The entire system consumes only 12.35 nW of power under room temperature.Compared with the state-of-the-art relevant research,the system can still provide good temperature compensation accuracy while significantly reducing power consumption,which provides the possibility of achieving ultra-low-power IoT nodes. |
