An Area‐Efficient Resistor‐less On‐Chip Frequency Reference for Ultra‐Low Power Real‐Time Clock Application

Abstract

In this paper, we propose a fully integrated and area‐efficient resistor‐less relaxation oscillator (ROSC) for ultra‐low power real‐time clock (RTC) applications. The proposed ROSC is based on a conventional current‐mode ROSC and is modified to be an area‐efficient circuit configuration without using resistors. The proposed ROSC consists of a temperature‐compensated bias current generator (BCG), proportional to absolute temperature (PTAT) voltage source, current‐mode ROSC, shunt regulator, and output logic circuit. The BCG, PTAT voltage source, and shunt regulator are used to compensate for the temperature characteristics of the ROSC. The area of our proposed ROSC was extremely small, 0.022 mm2. Simulated results demonstrated that our proposed ROSC generates a 32.5 kHz clock frequency and achieves ultra‐low power dissipation of 271 nW. The temperature and voltage dependence of the oscillation frequency were 138 ppm/°C and 13.9 ppm/mV, respectively. Monte Carlo statistical simulations showed that the mean, standard deviation, and coefficient of variation are 32.3, 0.6 kHz, and 1.9%, respectively. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A self-bias NAND gate and its application to non-overlapping clock generator for extremely low-voltage CMOS LSIs

“…Several ELV circuit design techniques have been studied. [33][34][35][36][37][38][39][40][41][42] Matsuzuka et al reported an ELV ring oscillator (ROSC) using self-bias inverters (SBINVs) as a clock generator for the cold-start operation of a PMS. 33) The ROSC operated at an extremely low supply voltage of 42 mV.…”

A 42 mV startup ring oscillator using gain-enhanced self-bias inverters for extremely low voltage energy harvesting

“…[25][26][27][28][29][30][31][32][33][34][35] As a first step in the realization of such converters, an extremely low voltage oscillator is required to start the PMS. [32][33][34][35][36][37][38][39] A ring oscillator (ROSC) consisting of CMOS inverters is widely used because it can operate at lower supply voltages. However, the voltage gain of the inverter decreases as the supply voltage decreases, and thus it is difficult to operate at a sub-100 mV supply voltage, which is the typical output voltage range of a TEG with a small temperature difference.…”