Leakage Power Optimization Techniques for Ultra Deep Sub-Micron Multi-Level Caches

On-chip L1 and L2 caches represent a sizeable fraction of the total power consumption of microprocessors. In deep sub-micron technology, the subthreshold leakage power is becoming the dominant fraction of the total power consumption of those caches. In this paper, we present optimization techniques to reduce the leakage power of on-chip caches assuming that there are multiple threshold voltages, VTH's, available. First, we show a cache leakage optimization technique that examines the trade-off between access time and leakage power by assigning distinct VTH's to each of the four main cache components - address bus drivers, data bus drivers, decoders, and SRAM cell arrays with sense-amps. Second, we show optimization techniques to reduce the leakage power of L1 and L2 on-chip caches without affecting the average memory access time. The key results are: 1) 2 VTH's are enough to minimize leakage in a single cache; 2) if L1 size is fixed, increasing the L2 size can result in much lower leakage without reducing average memory access time; 3) if L2 size is fixed, reducing L1 size can result in lower leakage without loss of the average memory access time; and 4) smaller L1 and larger L2 caches than are typical in today's processors result in significant leakage and dynamic power reduction without affecting the average memory access time.