This paper describes a variable supply-voltage (VS) scheme. From an external supply, the VS scheme automatically generates minimum internal supply voltages by feedback control of a buck converter, a speed detector, and a timing controller so that they meet the demand on its operation frequency. A 32-b RISC core processor is developed in a 0.4-μm CMOS technology which optimally controls the internal supply voltages with the VS scheme and the threshold voltages through substrate bias control. Performance in MIPS/W is improved by a factor of more than two compared with its conventional CMOS design.
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