Design of Monolithic CMOS LDO Regulator With ${rm D} ^{2}$ Coupling and Adaptive Transmission Control for Adaptive Wireless Powered Bio-Implants

摘要

This paper presents a monolithic CMOS low drop-out regulator for adaptive wireless powered bio-implants. A dual-loop control scheme is proposed to enhance load/DVS transient response, without a filter capacitor. The inner loop employs a direct dynamic coupling technique to improve transient response by directly detecting voltage variations through a capacitive coupling high-pass filter. Meanwhile, the outer loop adopts an adaptive transmission control to improve the regulator's large-signal transient response. The regulator is intrinsically stabilized without frequency compensation. Both small-signal and large-signal analysis are provided as design guidelines. The proposed regulator was fabricated with a 0.35-$mu{hbox {m}}$ CMOS process, with an active die area of 0.35 $mu {hbox {m}} ^{2}$. Experimental results demonstrate a 1.6-$mu {hbox {s}}/{hbox {V}}$ down-tracking and 2.2- $mu {hbox {s}}/{hbox {V}}$ up-tracking speed for DVS reference tracking, with undershoot/overshoot voltages controlled below 90 mV. Without a filter capacitor, the output voltage of the regulator recovers within 2.0 $mu {hbox {s}}$ for 100-mA load change, with less than 90-mV variation. The current/power efficiency stays above 93/78% over the entire interested load current range, with a peak value of 99.96/91.1%, respectively.