A Comparative Study Between Static and Dynamic Sleep Signal Generation Techniques for Leakage Tolerant Designs

Power gating techniques are rapidly gaining popularity assisting the management of leakage power consumption for deep submicrometer microprocessors´ functional units. Power gating is based on an input sleep signal to set the functional unit into a low leakage mode. However, power gating techniques in general inherently lack information about the utilization profile of the functional units they manage. This limitation is usually handled either statically by using a fixed length counter that generates the sleep signal when the functional unit is idle for a specified number of cycles or dynamically by changing the number of cycles before the sleep signal is generated depending on the previous history of operation. In this paper, a comparative study between the static and dynamic approaches regarding the power-performance tradeoff will be presented. It will be shown that the dynamic sleep signal generator is capable of tracking the operation of the functional units while achieving accuracies up to 90% compared to an average of 40%-60% for the static sleep signal generator (SSSG). Additionally it saves up to 80% more leakage versus the SSSG. This study is very important in assisting circuit designers choose between both techniques depending on the power gated circuit.