A 0.4-V 0.93-nW/kHz Relaxation Oscillator Exploiting Comparator Temperature-Dependent Delay to Achieve 94-ppm/°C Stability

Abstract

This paper presents the analysis and design of a relaxation oscillator that counteracts the complementary-toabsolute-temperature (CTAT) property of the comparator delay with the proportional-to-absolute-temperature (PTAT) property of the RC core to realize temperature-stabilized operation. By using a feedback bias network to linearize the comparator CTAT delay, thus improving the overall temperature stability by 20x, this technique enables a comparator with ~20x less bandwidth and an overall oscillator with ~5x lower power than conventional approaches. In a 0.18-μm silicon on insulator CMOS process, this design consumes 1.14 nW from a 0.4-V supply operating at 1.22 kHz, with a temperature coefficient (TC) as low as 40 ppm/°C (μ = 94 ppm/°C for n = 5) achieving stateof-the-art efficiency (0.93 nW/kHz) for kilohertz-range relaxation oscillators.