I. Introduction
Today, mobile devices are widely used, and they process various applications, for example, dealing with a video phone, playing TV programs or DVDs, and processing office files. One of the key devices in these mobile devices is the system-on-a-chip (SoC). The SoC embeds many modules, such as the processor cores, hardware accelerators, various embedded memories, and so on. Therefore, the SoC is required to have both higher operating performance to process various applications and lower power consumption to prolong the battery life. To acquire the best performance, voltage scaling along with process scaling is effective.