A 0.0043-mm(2) 0.085-mu W/MHz Relaxation Oscillator Using Charge-Prestored Asymmetric Swings R-RC Network

In this brief, a charge-prestored 21.2-MHz relaxation oscillator is proposed for ultralow-power applications. It occupies only 0.0043 mm(2) in 0.18-mu m CMOS by resistor reusing and is reference-free. The simulated temperature coefficient (TC) of the output frequency is 15.2 ppm/degrees from -30 degrees C to 125 degrees C. By generating an asymmetric capacitor charging swing, our charge-prestored technique reduces significantly the power consumed by the swing-boosting RC network during the charging phase. Also, the R-RC structure further improves the energy efficiency. The total power consumption of the oscillator core is 1.806 mu W at 0.8 V, corresponding to an energy efficiency of 0.085 mu W/MHz that compares favorably with the state of the art.