Supply-Scalable High-Speed I/O Interfaces

Improving the energy efficiency of computer communication is becoming more and more important as the world is creating a massive amount of data, while the interface has been a bottleneck due to the finite bandwidth of electrical wires. Introducing supply voltage scalability is expected to significantly improve the energy efficiency of communication input/output (I/O) interfaces as well as make the I/Os efficiently adapt to actual utilization. However, there are many challenges to be addressed to facilitate the realization of a true sense of supply-scalable I/O. This paper reviews the motivations, background theories, design considerations, and challenges of scalable I/Os from the viewpoint of computer architecture down to the transistor level. Thereafter, a survey of the state-of-the-arts fabricated designs is discussed.