*Article* **A 1.1 V 25 ppm/***◦***C Relaxation Oscillator with 0.045%/V Line Sensitivity for Low Power Applications**

**Yizhuo Liao and Pak Kwong Chan \***

**\*** Correspondence: epkchan@ntu.edu.sg; Tel.: +65-67904513

**Abstract:** A fully-integrated CMOS relaxation oscillator, realized in 40 nm CMOS technology, is presented. The oscillator includes a stable two-transistor based voltage reference without an operational amplifier, a simple current reference employing the temperature-compensated composite resistor, and the approximated complementary to absolute temperature (CTAT) delay-based comparators compensate for the approximated proportional to absolute temperature (PTAT) delay arising from the leakage currents in the switches. This relaxation oscillator is designed to output a square wave with a frequency of 64 kHz in a duty cycle of 50% at a 1.1 V supply. The simulation results demonstrated that the circuit can generate a square wave, with stable frequency, against temperature and supply variation, while exhibiting low current consumption. For the temperature range from −20 ◦C to 80 ◦C at a 1.1 V supply, the oscillator' output frequency achieved a temperature coefficient (T.C.) of 12.4 ppm/◦C in a typical corner in one sample simulation. For a 200-sample Monte Carlo simulation, the obtained T.C. is 25 ppm/◦C. Under typical corners and room temperatures, the simulated line sensitivity is 0.045%/V with the supply from 1.1 V to 1.6 V, and the dynamic current consumption is 552 nA. A better figure-of-merit (FoM), which equals 0.129%, is displayed when compared to the representative prior-art works.

**Keywords:** relaxation oscillator; voltage reference; composite resistor; current reference; temperature compensation; cross-coupled pair; delay drift compensation
