High precision RC-oscillator using R-2R ladder for digital calibration

This paper presents a fully integrated RC-type relaxation oscillator with high precision over supply, temperature and process calibration by trimming, achieving 50ppm/°C maximum temperature coefficient and 1% final accuracy in the operating range. The low sensitivity to 1.8V supply is achieved by ratio metric technique and generating supply proportional voltage reference and current source. The small size trimming step of 0.3% and high step linearity is achieved by current source, which use 9 bit R-2R ladder network. The circuit is manufactured at 180nm technology.