12.9 A 1.55×0.85mm<sup>2</sup> 3ppm 1.0μA 32.768kHz MEMS-based oscillator

Abstract

Mobile time-keeping applications require small form-factor, tight frequency stability, and micro-power 32.768kHz clock references. Today's 32kHz quartz resonators and oscillators are facing challenges in size reduction. Previously described MEMS-based oscillators can achieve tight accuracy but operate at high frequency with power unsuitable for mobile applications. This paper introduces a 32kHz MEMS-based oscillator. Based on a comparison table of recent oscillators shown in Fig. 12.9.6, it offers the smallest size, 1.55×0.85mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , with the best frequency stability, 100ppm (XO) and 3ppm (TCXO) over the industrial temperature range of -40 to 85°C. Supply current is 0.9 and 1.0μA for XO and TCXO, respectively, at supply voltages from 1.5 to 3.6V.