A 0.0043-mm2 0.085-μW/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-
$\mu \text{m}$
CMOS by resistor reusing and is reference-free. The simulated temperature coefficient (TC) of the output frequency is 15.2 ppm/° from −30 °C to 125 °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
$1.806 \mu \text{W}$
at 0.8 V, corresponding to an energy efficiency of
$0.085 \mu \text{W}$
/MHz that compares favorably with the state of the art.