Tham khảo tài liệu 'adaptive techniques for dynamic processor optimization_theory and practice episode 1 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 26 Maurice Meijer José Pineda de Gyvez reducing all dimensions by a factor k enabling higher integration density 1 . In the constant-field scaling scenario the circuit speed increases theoretically with the amount of scaling k. Constant-field scaling has known benefits such as lower power per circuit constant power density and power-delay product that increases by k3. However for CMOS technology over the last 10 years it has been impossible to scale power supply voltage VDD while maintaining speed because of the constraints on the threshold voltage Vth 2 . Due to increasing leakage current in scaled devices Vth is not lowered to avoid significant static power consumption. Therefore the electrical field is rising in proportion to k resulting now in almost constant circuit power despite scaling increased power density by k2 and power-delay product improvement by a factor of k only. In essence the limits of a scaling process are caused by physical effects that do not scale properly among them are quantum-mechanical tunneling discrete carrier doping and other voltage-related effects such as the subthreshold swing and built-in voltage and minimum voltage swings. Figure Power trends as a function of the supply voltage. Besides technology scaling one of the most effective ways to reduce active power consumption is by lowering VDD. Ideally quadratic power savings are observed as displayed in Figure . VDD reduction can be applied to a complete chip but it is most effective when it is applied to local voltage domains with own performance requirements. A common approach is to perform dynamic supply scaling which exploits the temporal domain to optimize VDD at run-time. This technique dynamically varies both operating frequency and supply voltage in response to workload demands. In this way a processing unit always operates at the desired performance level while consuming the minimal amount of power. Two basic flavors exist namely dynamic voltage scaling DVS and .
