An integrated charge-transfer relaxation oscillator without comparator

This letter presents a charge-transfer relaxation oscillator that achieves ultra-low power operation without comparator. The oscillator is implemented by charging or discharging the negative plate of the capacitor to a reference voltage through charge-transfer technique and the positive plate of the capacitor by a constant reference current, respectively. A special sawtooth waveform is generated, and a pseudo-inverter chain with delay compensation is adopted to determine the oscillation state. In the proposed structure, a conventional comparator has been eliminated to avoid comparator offset effect. The oscillator has been implemented with TSMC 0.18 \(\upmu \)m CMOS process. The circuit operates in subthreshold region and consumes a total power of 85 nW. The circuit demonstrates a frequency variation less than 0.8%/V over 1.2–1.8 V, leading to a temperature coefficient of 33 ppm/\(^{\circ }\)C over ? 40 to 80 \(^{\circ }\)C.