A low power trimming-free relaxation oscillator with process and temperature compensation

A low power trimming-free relaxation oscillator with process and temperature compensation is presented. It adopts a current reference based on transistors working in strong-inversion region and another subthreshold MOSFET current reference to generate the reference voltages for the comparator stage and the charging/discharging current for the oscillator core, respectively. The instability of the time constant RC induced by process and temperature variations are compensated by this scheme. The circuit is designed using TSMC 0.18 mu m standard CMOS process and simulated with Spectre. Simulations results show that the worst-case variation of the oscillation frequency is +/- 4.5% from -20 to 80 degrees C in live different process corners. The power for the proposed oscillator is only 253 nW at 27 degrees C.