A Compact CMOS Ring Oscillator with Temperature and Supply Compensation for Sensor Applications

This paper presents a 1MHz ring oscillator with simple temperature compensation circuit dedicated to MEMS sensor applications. A closed-loop PTAT voltage source follower coupled with an open-loop replica-biased source follower driving structure is proposed to power the CMOS ring oscillator and counteract its temperature-dependent effect. In conjunction with a pseudo-resistor based low-pass filter to lower the circuit noise, it significantly improves the jitter performance. The circuit is realized using 0.35μm CMOS technology at a 5V supply. The frequency variation of the compensated oscillator over the temperature range of - 40°C to +90°C is - 0.1% to +0.19% (22.3ppm/°C) with respect to the uncompensated frequency variation of -- 12.1% to +21.6% (2592ppm/°C) at typical process. For worst case process, the frequency deviates from - 1.5% to +1.9% for the stated temperature span and it deviates from - 1.2% to +1.2% at ±10% supply variation under 1 MHz oscillation frequency. The proposed ring oscillator is insensitive to the PVT variations. The simulated cycle-to-cycle RMS jitter value due to both the intrinsic circuit noise and the 200mV peak-to-peak power supply noise is only 64ps, which is about 50 times smaller than that of the standard ring oscillators under identical process technology and design conditions.