Efficient Leakage Power Saving by Sleep Depth Controlling for Multi-mode Power Gating

Seidai Takeda1,  Shinobu Miwa1,  Kimiyoshi Usami2,  Hiroshi Nakamura1
1The University of Tokyo, 2Shibaura Institute of Technology


Power Gating (PG) and Body Biasing (BB) are effective schemes to save leakage power in standby-time. However, in run-time, their large overheads prevent the circuit from sav-ing power in short idle times. To achieve leakage saving in short idle time, advanced PG and BB using shallow sleep mode are studied. Since the overheads of shallow sleep are smaller than those of conventional deep sleep, those circuits can achieve leakage saving even in short idle time. Depth of shallow sleep has trade-offs between the overheads and the amount of saved leakage power; hence, making decision of depth in shallow sleep is an important issue to maximize total leakage saving. However, the depth which achieves best leakage saving depends heavily on run time factors, e. g. idle time distribution and temperature. Thus, conventional circuit has multiple shallow sleep modes and chooses an adequate mode in run time. However, it causes large overhead power because of additional voltage generators. In this paper, we propose a scheme named Opt-static to control sleep depth at run-time. Our scheme uses only one shallow sleep mode, but its depth is reconfigurable. It successfully achieves leakage saving by adopting its depth with run-time factors. In addi-tion, our scheme needs only one active voltage generator; hence overhead power associated with voltage generators is smaller than the conventional circuit which has multiple shallow sleep modes. Experimental result shows that the Multi-mode PG applying our scheme achieves higher lea-kage saving than the conventional Multi-mode PG which has two shallow sleep modes, although it does not take into ac-count for overhead power of voltage generators.