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/ $^{\circ}$ from $-$ 30 $^{\circ}$ C to 125 $^{\circ}$ 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.