Design Of Low Power Crystal Oscillator For Real Time Clock

In recent years,with the rapid development of wearable devices and Internet of things technology,the application of wireless transmission node chip is more and more extensive.This kind of node is generally powered by batteries and the battery storage capacity is limited.In order to ensure long-term operation,the node chip's power consumption has been put forward very high requirements.In order to save energy,the typical working mode of the wireless sensor node consists of a short activation operation and a long idle state.The real time clock is operating in the idle state which is used to wake up the system,the system scheduling and synchronize sensor nodes.Because of its high frequency stability,quartz crystal oscillators are widely used in real time clock circuits.It is an important source of power consumption for real time clock circuits.Wireless transmission nodes generally use 3V battery.The low voltage can't be provided directly to the crystal oscillator.In order to reduce the power consumption of real time clock,a low power crystal oscillator is designed.This thesis systematically describes the basic principle and implementation method of a low-power crystal oscillator based on self-charging method.Starting from the quartz crystal model,some key technologies in the characteristics of quartz crystal,Pierce oscillator and self-charging method are introduced in detail.A switch pulse crystal oscillator model is established to verify the feasibility of the self-charging method;To be able to operate at a regular voltage,a reference current source is designed to drive the Pierce oscillator and use a differential amplifier instead of the bias resistor,which greatly reduces the layout area.The reference current source is designed to driver amplifier,which makes it easy to adjust the working current of the oscillator;In order to solve the contradiction between the power and the starting time,the design of the starting circuit makes the crystal oscillator to quickly start up and then shut down the starting circuit to save energy.Finally,in order to further reduce power consumption,a clock signal from the crystal oscillator is used to generate a pulse signal to control the on/off of the amplifier and a test circuit is designed to measure the growth time and decay time of the oscillation to find the optimum value of the pulse signal period and duty cycle.Based on the circuit principle analysis and sub-circuit design,this design is based on the GF130nm process and completes the design and verification of the schematics and layouts of the key sub-modules and the overall circuit of the low-power crystal oscillator circuit in the Cadence integrated environment.The layout area is 0.014mm~2.The results show that crystal oscillator can work normally in the temperature range of-20~85?.The working current of the circuit under the TT process corner and at the temperature of 25? was 9.72nA@3V.The frequency deviation within the temperature range of-20~85? was-3.62~-175.98ppm.The power supply sensitivity is 52.45ppm/V with voltage range of 2.9V~3.1V...