Low Power 32kHz Crystal Oscillator Based On Sub-harmonic Pulse Injection

In order to reduce the average power consumption,sleep timers are widely used to synchronize wireless sensor nodes so that high-power communication modules can operate periodically.32k Hz crystal oscillators remain the most popular choice for sleep timers due to their frequency stability,simplicity,and low cost.Because sleep timers must always be on,they must consume less power than the average wireless node.The low power crystal oscillator circuit designed in this thesis adopts sub-harmonic pulse injection technology.In this thesis,the crystal oscillator is analyzed by negative resistance analysis method and energy injection method respectively from the functional requirements of the crystal oscillator,in order to explore the lowest realizable power consumption of 32k Hz crystal oscillator,and the feasibility of sub-harmonic pulse injection technology is described in detail.Then,this thesis proposes a T/4 delay slicer,which not only converts the sine wave of the crystal port into 32k Hz square wave clock,but also introduces the T/4 delay,which provides accurate time control for energy injection.In order to make the crystal oscillator work reliably under process,voltage,and temperature variations,a low power current reference source is designed to control the delay time.Finally,a frequency divider and a bootstrapping pulse generation circuit are designed in this thesis.They excite the proposed full NMOS driver at a frequency of 8k Hz to realize the sub-harmonic pulse injection at the valley and peak of the crystal oscillation waveform.In this thesis,the design of low power crystal oscillator based on TSMC40nm CMOS technology is completed.The layout area is 0.0402mm~2.Simulation results show that the crystal oscillator can operate normally in the temperature range from-25℃to 85℃.The power consumption is 4.22n W at supply voltage of 0.6V,temperature of 25℃and TT process corner.The maximum frequency deviation is 137ppm in the temperature range from-25℃to 85℃.The voltage regulation rate within the voltage range of 0.6～1V is 14.5ppm/V.