Design of Fast Start-up CMOS RC Oscillator Based on Low Temperature Coefficient Current Mode Bandgap Reference

This paper presents a fully integrated 2MHz RC oscillator which is less affected by the fluctuations of power supply voltage and ambient temperature. This design consists of a current mode bandgap reference circuit and an RC oscillation circuit. Furthermore, a digital trimming circuit is used to adjust the frequency back to the ideal one, in order to obtain better accuracy. The proposed current mode bandgap reference has a very low temperature coefficient, which is only 1.66ppm/°C. This RC oscillator can work in the power supply range of l.9V to 4.6V and the ambient temperature of −40°C~+125°C, and has a very fast start-up speed. After digital trimming, the frequency can be adjusted back to the target frequency under the other four process corners, and the circuit supports complete shutdown. Spectre simulation was made based on CSMC's $0.18\mu \mathrm{m}$ CMOS technology. The final die size is $194\mu \mathrm{m}\times 87\mu \mathrm{m}$.