A 1.7nW PLL-assisted current injected 32KHz crystal oscillator for IoT

Abstract

This paper presents a PLL-assisted crystal oscillator using a current switching phase detector (PD) with intrinsic 90° phase offset for IoT applications. The PLL provides accurate pulse injection timing into the XO, sustaining its oscillation at only 100mV amplitude and ensuring robustness operation across PVT. This technique achieves high energy injection efficiency and avoids the use of power hungry amplifiers. Measured power is 1.7nW at room temperature and operation is demonstrated from −20–80°C and across 3 corner wafers.