Distributed Network of LDO Microregulators Providing Submicrosecond DVFS and IR Drop Compensation for a 24-Core Microprocessor in 14-nm SOI CMOS

Abstract

A distributed network of low-dropout (LDO) microregulators (uREGs) senses and corrects the voltages at multiple points on a power supply grid in a multi-core microprocessor to reduce errors due to IR drops. A voltage regulator controller (VREGC) compares the voltages at various points on the grid to a programmable reference and delivers a set of corrective 2-b up/down (UP/DN) codes (global feedback) to the distributed uREGs across the core. Inside each uREG, the UP/DN codes control a local charge pump that sets the reference for an asynchronous comparator that turns on and off a pMOS passgate with a sub-nanosecond response. To mitigate the self-generated ripple, hybrid fast/slow passgate control is employed, whereby a parallel pMOS passgate with a slew-rate-limited gate drive is used to supply the dc portion of the load current. The distributed regulator architecture includes a scheme for limiting the degree of load-sharing imbalances among its uREGs due to the VREGC comparator offsets. Adding a switched-capacitor (SC) accelerator to the charge pump of each uREG speeds up the output-voltage transitions by up to 17 × for greater dynamic voltage and frequency scaling (DVFS) savings. Line and load regulations are 9 mV/V and 1.1 mV/A, respectively. The regulator achieves a peak power efficiency of 95.2% and a peak current efficiency of 99.1%. It reaches a peak power density of 82.3 W/mm2.