Ultra Low Power Low Frequency On-chip Oscillator for Elapsed Time Counter

Abstract

This paper presents a design of CMOS current starved inverter based oscillator which is used to drive the counters that act as a component in the elapsed time counter. A low power temperature independent biasing circuit is designed to enhance the performance meeting the frequency variations. The architecture includes usage of trim bits to shift the frequency at different process corners. Since the oscillator will run on a battery supply, variations in the performance of the oscillator across supply have been compromised. A 32.768 KHz oscillator is implemented in UMC180 CMOS technology, occupying a silicon area of 0.003064 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The oscillator consumes as little as 250 nW at room temperature, from 1.8 V power supply. A temperature stability of 454 ppm/°C from 0°C to 125°C and variation of ±12 % with supply voltage from 1.7 V to 1.9 V is achieved.