Power supply circuits for ultralow-power subthreshold CMOS smart sensor LSIs

A low-voltage power supply circuit was developed for micropower CMOS LS1 applications, with microwatt smart-sensor LSIs being the specific focus. The circuit consists of a switched-capacitor voltage converter and a series regulator. The switched converter lowers battery voltage by 1.5-3 V to a low voltage of 0.5-0.7 V that drives the series regulator, and the series regulator provides LS1 logic gates with a power voltage of 0.4-0.6 V such that the logic gates operate at a subthreshold region. The switched converter lowered the -voltage of a 1.5-V battery to 0.68 V in a sample circuit designed to produce a supply voltage of 0.6 V, and the series regulator lowered it further to 0.6 V. The power efficiency of the switched converter is 83 %, and the total efficiency is 73 % with a 13-mu A output current.