20.3 A feedforward controlled on-chip switched-capacitor voltage regulator delivering 10W in 32nm SOI CMOS

Abstract

On-chip (or fully integrated) switched-capacitor (SC) voltage regulators (SCVR) have recently received a lot of attention due to their ease of monolithic integration. The use of deep trench capacitors can lead to SCVR implementations that simultaneously achieve high efficiency, high power density, and fast response time. For the application of granular power distribution of many-core microprocessor systems, the on-chip SCVR must maintain an output voltage above a certain minimum level Uout, min in order for the microprocessor core to meet setup time requirements. Following a transient load change, the output voltage typically exhibits a droop due to parasitic inductances and resistances in the power distribution network. Therefore, the steady-state output voltage is kept high enough to ensure VOUT >Vout, min at all times, thereby introducing an output voltage overhead that leads to increased system power consumption. The output voltage droop can be reduced by implementing fast regulation and a sufficient amount of on-chip decoupling capacitance. However, a large amount of on-chip decoupling capacitance is needed to significantly reduce the droop, and it becomes impractical to implement owing to the large chip area overhead required. This paper presents a feedforward control scheme that significantly reduces the output voltage droop in the presence of a large input voltage droop following a transient event. This in turn reduces the required output voltage overhead and may lead to significant overall system power savings.