A CMOS Relaxation Oscillator with Process and Temperature Variation Compensation

In this paper, a CMOS relaxation oscillator with trimming and temperature compensation is presented for the on-chip multi-sensor systems which need MHz level frequency source. The proposed scheme uses a single current branch to charge the capacitor to generate the oscillation with voltage average feedback (VAF) circuit. Binary-weight current trimming array is adopted to reduce the frequency variation caused by the process variation under different process corners. A compensation calibration resistor array with Kelvin connection is utilized to improve the frequency variation with temperature. With the help of VAF, the frequency spread caused by the comparator delay is suppressed. This relaxation oscillator with a typical frequency of 13.4 MHz is implemented in a standard 180 nm CMOS process. Simulation results show that it achieves a frequency temperature coefficient of 28.3 ppm/degrees C from-40 degrees C to 125 degrees C and a 0.074%/0.1 V frequency variation when supply voltage changes from 2.9 to 3.7 V.