An on-chip relaxation oscillator circuit with positive temperature compensation is presented. The capacitors in the oscillator circuit are PIP (Poly-Insulator-Poly) in CMOS process, it’s capacitance value has positive temperature characteristics. Positive temperature coefficient bias circuit and temperature compensation circuit are adopted to counteract the capacitor's positive temperature characteristics by temperature-compensating the charge/discharge currents, thereby ensuring precise output clock frequency. The circuit is designed with CSMC 0.35um CMOS process, the Post-Simulation results show that the maximum variation of output frequency is 0.087% and the frequency drift is 5.3ppm/°C with 5V supply voltage and within the temperature range of −40°C to 125°C.
Jiang et al. (Mon,) studied this question.