A process and temperature compensated ring oscillator

An on-chip oscillator with small frequency variation in a digital 0.6 /spl mu/m CMOS technology is described. The oscillator utilizes a bias technique to compensate for the influences on the oscillation frequency caused by both temperature and process variations. No external components are needed in the oscillator. Simulation results show that the frequency of the proposed oscillator has a peak variation of /spl plusmn/6.8% for all process corners and a temperature range of 120/spl deg/C. The oscillator is measured to operate at a center frequency of 680 kHz and have a peak variation of /spl plusmn/4.7% over 29 sample chips in two different lots and a temperature range of 35/spl deg/C to 115/spl deg/C. As a comparison, a conventional inverter chain oscillator is made on the same chip. The frequency variation of the conventional inverter chain is /spl plusmn/14.6%.