Research And Design Of On-chip RC Oscillator For MCU

As an on-chip clock source,the RC oscillator is widely used in MCU in the fields of electronic navigation,biological medical treatment and smart wearable devices.Its power consumption and stability will directly affect the performance of MCU.The MCU usually has two working modes: low-power consumption and high-speed operation,and the two working modes have different requirements for clock circuit,so it is difficult for a single RC oscillator to meet their requirements.Therefore,according to the different needs of the two working modes of MCU for the clock circuit,designing RC oscillators to meet their needs has certain research significance and practical value.The traditional RC oscillator is susceptible to temperature and power supply voltage and other factors,and the output frequency stability is low,which can not meet the requirements of MCU for clock stability.Aiming at the above shortcomings,this paper designs two RC oscillators with different structures,which are applied to MCU high-speed operation and low-power consumption.(1)According to the clock demand of MCU high-speed operation mode,a high-stability RC oscillator with output frequency of 16 mhz is designed.The oscillator utilizes a voltage averaging feedback circuit to reduce the impact of the comparator's delay on the output frequency,and the temperature compensation technology was employed to compensate the temperature influence on the output frequency so as to achieve high-stability output.A frequency selection network is designed to realize high-precision output in a wide frequency range,and meet the requirements of multi-frequency clock in full speed working mode of MCU.The layout design and post-layout simulation of high stability RC oscillator are completed in SMIC 110 nm CMOS process.The results show that the temperature characteristic is±0.13%@-30?120?,the power supply voltage characteristic is ±0.13%@1?1.4V,and the dynamic power consumption is 47?W.(2)According to the clock demand of MCU low-power mode,a low-power RC oscillator with output frequency of 32 k Hz is designed.The oscillator utilizes a split capacitor technology to reduce the impact of the comparator's delay on the output frequency,and the pre voltage stabilization technology was employed to compensate the power supply voltage influence on the output frequency so as to achieve high-stability output.At the same time,the working state of MOSFET in RC oscillator is set to sub-threshold region,which reduces its power consumption.The layout design and post-layout simulation of high stability RC oscillator are completed in SMIC 110 nm CMOS process.The results show that the dynamic power consumption is 0.55?W of RC oscillator,and in the power supply voltage range from 1 to 1.4V,the output frequency of RC oscillator changes within ±0.13%,when the temperature changes from-30 to 120°C,the output frequency of the RC oscillator changes within ±0.25%.The simulation results show that the two RC oscillators designed in this paper not only ensure low power consumption,but also achieve high stable output,which can meet the normal requirements of MCU low power consumption and high-speed operation mode,and have a certain application prospect.