Overcoming the power wall: Connecting voltage domains in series

This paper analyzes an alternative for system-level power configuration of digital circuits. To overcome the "power wall" and enable low supply voltages for digital circuits, the voltage domains of microprocessors or other digital circuit elements are connected in series. This enhances overall system efficiency and performance by allowing both the digital circuits and the power delivery circuits to operate in their region of highest efficiency. Power consumption is dramatically reduced because multiple, independent voltage levels enable each processor to operate at its local minimum energy point. A comparative analysis of series and parallel voltage domains concludes that series voltage domains consume less power. Various voltage regulations schemes ranging from software, firmware, and hardware are presented. Some of the challenges and opportunities of series circuits are discussed.