Design Of Low Power And High Stability RC Oscillator For MCU

The clock circuit drives the entire chip and is an indispensable part of the chip.Among the commonly used clock circuit,RC oscillator is widely used for its small area,low cost and convenience for integration.However,the traditional RC oscillator's frequency tends to change with temperature and power supply voltage,failing to meet the stability requirements of the chip on the clock.Therefore,a low power and high stability RC oscillator is designed in this paper.In this thesis,the relaxation oscillator is used as the main part of the RC oscillator to provide a 16 MHz output frequency.The main work includes:(1)The oscillation frequency stability with supply voltage,reference voltage and temperature is proposed;(2)The reference current source is designed to drive the comparator and amplifier.And the combination of positive and negative temperature coefficient resistors is used to guarantee stability of the reference current with temperature;(3)In order to keep the frequency independent of the comparator delay,a voltage average feedback loop with integrator is designed to compensate the variation of the oscillator period caused by the comparator delay;(4)The reference voltage control circuit is presented by blending resistors with different temperature coefficient to provide a compensated reference voltage that changes with temperature,to compensate the frequency variation with temperature and to obtain high temperature frequency.Meantime the deviation of the oscillation frequency with the process can be corrected by adjusting the reference voltage.Based on the GF 0.13?m process,the layout and post simulation of the RC oscillator is completed.Simulation results show that the RC oscillator achieves frequency variation of 0.37% against temperature variation of-40?~85? and 0.44% against supply variation of 2.7V~3.3V.And under the TT process corner,the total current of the circuit is 1.71?A/MHz at 3V supply and 55? condition.