Research On Adaptive Body Bias Technique

With technology scaling down, leakage power in standby mode plays an increasingly important role in total power consumption and becomes the dominant issue in low power logic design. As feature size scaled down to nanoscale, the short channel effect becomes more serious, which results in more complicated leakage mechanisms. Furthermore, leakage power becomes more susceptible to process and temperature fluctuations. As a result, the performance of traditional low power techniques is limited. Applying adaptive body bias technique, body bias can be adjusted to its optimal value under process and temperature variations, leading to considerable reduction of leakage power and effective compensation of process and temperature fluctuations. Therefore, the technique has great research value and is widely investigated.Considering the variation of each leakage component under process and temperature fluctuations, this paper deduces the theory of optimal body bias determination and proposes the implementation scheme of adaptive body bias technique. The proposed circuit consists of current difference generator, current comparator and body bias regulator. The optimal value of body bias is determined by comparing the drain leakage currents of two identical off-state replica clusters applied two slight different body bias voltages respectively. The technique will adaptively adjust the body bias according to the current comparative results and achieve the optimal body bias immediately under process and temperature variations.The proposed circuit was implemented using 90nm CMOS technology and applied on ISCAS85 benchmark circuits to validate its efficiency in different process corners (slow, typical and fast process) and operating temperatures (ranging from -40℃and 85℃). Experimental results indicate that the maximum standby leakage power reduction percentage is 93.94% and the standby leakage becomes less sensitive to process and temperature fluctuations. The proposed circuit can adaptively adjust the body bias to its optimal value during the whole standby period, which results in considerable reduction of leakage power and effective compensation of process and temperature variations.