Design Of Quick Start CMOS Crystal Osicillator

Most sensor nodes adopt a heavily-duty cycle working mode in order to save power consumption of the chip.So some modules in the system which include the clock circuit always need to wake up periodically.In most chip,the crystal oscillator is often used as the main clock because of its stable frequency characteristics.But it takes hundreds of microseconds for the crystal oscillator form start-up to steady.During this time,the chip is in a waiting state.And the power consumption wasted in the waiting state increases with the increase of the start-up time.A self-tracking energy injection scheme based on the constant frequency injection method is proposed in this thesis In order to reduce the injection energy loss while reducing the crystal oscillator start-up time.This method generates a constant frequency clock to inject energy without calibrating the circuit.The piezoelectric effect of the crystal is used to generate a sine wave at both ends of the crystal by connecting the two ends of the crystal to the power and ground supply respectively through the switch resistance module.The sine wave is compared with the reference voltage through a comparator to generate a clock which the frequency and phase is corresponding to the crystal.The clock can realize self-tracking energy injection,and quickly increase the motion current and there is no need for ring oscillator or voltage controlled oscillator.So it can accelerate the start-up of crystal oscillators and save a large amount of energy during energy injection.In addition,after the energy injection is completed,the three-stage amplifier is used to increase the negative resistance,breaking the limitation of the maximum value of the negative resistance in the traditional structure,further reducing the startup time and reducing the startup energy consumption.The design of fast-start crystal oscillator which frequency is 24MHz has completed based on the 40nm process whose area is 0.036mm~2 and the stable power consumption is 87.98?W.The start-up time of the crystal oscillator with 6p F load capacitance is 11.9?s and the startup power consumption is 11.3n J when the corner is TT process temperature is 20?.The max start-up time of the crystal oscillator is 13.4?s when the temperature changes from-40°C to 90°C.