A 12.77-MHz on-chip relaxation oscillator with digital compensation for loop delay variation

This paper presents a 12.77-MHz low power, RC on-chip relaxation oscillator with self-compensation technique. A digital feedback loop is implemented to maintain the frequency stability. A replica comparator is added to generate a reference pulse width for the compensation. After compensation, the frequency is tuned by a digitally controlled delay element. The proposed design is fabricated in 0.18-μm CMOS process. The main oscillator consumes 12.8 μW at 0.9-V supply voltage. The whole system consumes 56.2 μW when the digital compensation blocks are enabled. The measured output frequency variation is less than ±0.4% across -30 to 120°C. For a supply range of 0.6 V to 1.1 V, the frequency varies less than 0.5%/V after compensation.