“EChO” Reconfigurable Power Management Unit for Energy Reduction in Sleep-Active Transitions

Abstract

A novel recon figurable switched-capacitor “EChO” Power Management Unit is introduced for ultra-low power duty- cycled integrated systems (e.g., sensor nodes for critical event mon- itoring). “EChO” reduces the energ y cost associated with sleep-to- active and active-to sleep transitions by 64% with an area overhead less than 1% and no impact on act ive mode operation. Analysis shows that approximately the sam e energy reduction is achieved over a very wide range of operating conditions and design con- straints (e.g., ratio between flying and decoupling capacitances, granularity of the capacitor array). Measurements show 25–30% system power saving for a 65-nm testchip implementation of the “EChO” PMU powering a 16-kgate processing unit and a 2-kbit SRAM at 0.55-V voltage in active mode, assuming a 1-s wakeup cycle, 6.25–12.5% activity and a pr ocessing task of 250 cycles. The technique can be synergistically employed with traditional recon- figuration techniques that focus on ef ficiency in active mode (ig- noring active-sleep transitions) to sum up the bene fits.