Design And Application Of High-precision Clock Based On Relaxation Oscillator

Crystal oscillators cannot be integrated within the chip and take up more printed circuit board area.As integrated circuit processes and design techniques continue to advance,how to achieve high performance on-chip clocks has become a subject of much academic and industrial interest.The relaxation oscillators are increasingly used in chip design due to their compatibility with the mainstream CMOS process of integrated circuits,their small footprint,can provide clock frequencies ranging from a few Hz to several tens of MHz,which can provide clock accuracy to meet the general engineering project design requirements.This thesis presents a theoretical analysis and study of four common clock circuits.By comparing the circuit structure,design complexity,clock stability and cost,the relaxation oscillator technology is finally selected.This thesis designs relaxation oscillators for CAN and LIN bus communication clocks.The target frequency of the design is 24 MHz,the frequency accuracy is ±1%,the total current consumption of the main part of the oscillator does not exceed 1 m A,the operating temperature range is from-40°C to 125°C and the supply voltage is from 2.7 V to 3.6 V.In this thesis,the sources of the clock period and the main non-ideal characteristics of the relaxation oscillator are analysed and solutions are explored.To address the fluctuation characteristics of the relaxation oscillator system with the power supply,a low dropout regulator(LDO)is designed to provide a stable voltage source for the relaxation oscillator system to suppress power supply noise;to address the fluctuation characteristics of the clock frequency caused by process fluctuations,a resistor and capacitor trimmer array are designed to correct the clock frequency.At the same time,in the capacitor design,the matching characteristics of the capacitor and the drive capability of the driver circuit are fully considered;to address the temperature drift in the system,the design of temperature acquisition module to collect the temperature of the chip,and the dynamically adjustment of the reference voltage of the comparator help keep the clock cycle stable.The comparator section uses a hysteresis comparator with positive feedback characteristics to reduce the non-ideal characteristics of the temperature brought about by the comparator.Theoretical analysis of the relaxation oscillator is combined with the Spectre tool in Cadence software for the design and simulation of transistor-level circuits;the layout and its details are developed.Post-simulations based on the layout were carried out and the circuit and layout were optimised and verified,with the results meeting the design requirements.The final product was reviewed internally by the internship company and sent to the foundry for flow production.