Design and Analysis of Monolithic Step-Down SC Power Converter With Subthreshold DPWM Control for Self-Powered Wireless Sensors

Abstract

This paper presents a fully integrated switched-capacitor power converter for self-powered wireless sensor nodes. The design features an efficient step-down charge-pump power stage and a frequency-programmable digital feedback controller. The subthreshold-region design significantly reduces the power dissipation in the controller. Meanwhile, the programmable switching-frequency digital-pulsewidth-modulation control keeps the converter stay at high efficiency, without causing a random noise spectrum. Monolithic implementation effectively suppresses noise and glitches caused by parasitic components due to bonding, packaging, and PCB wiring. Design strategy, system modeling, optimization, and circuit implementation are addressed. An IC prototype was fabricated with a standard 0.35-¿m digital CMOS n-well process. It precisely provides a dynamic-voltage-scaling-compatible adjustable power output from 0.8 to 1.5 V and from 400 ¿W to 7.5 mW. The switching frequency is programmable from 200 kHz to 1 MHz. It achieves 66.7% efficiency with a controller power dissipation of only 147.5 ¿W.