Subthreshold leakage control techniques for low power digital circuits

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Includes bibliographical references (p. 273-277).Scaling and power reduction trends in future technologies will cause subthreshold leakage currents to become an increasingly large component of total power dissipation. As a result, new techniques are needed in order to provide high performance and low power circuit operation. This dissertation develops new circuit techniques that exploit dual threshold voltages and body biasing in order to reduce subthreshold leakage currents in both standby and active modes. To address standby leakage currents, a novel sleep transistor sizing methodology for MTCMOS circuits was developed and new "imbedded" dual V1 techniques were described that could provide better performance and less area overhead by exploiting different logic styles. Work was also done to develop new MTCMOS sequential circuits, which include a completely novel way to hold state during standby modes. Body biasing circuit techniques were also explored to provide dynamic tuning of device threshold voltages to tune out parameter and temperature variations during. the active state. This not only helps reduce active leakage currents but also improves process yields as well. A final research direction explored optimal V cc/Vt tuning during the · active modes as a function of varying workloads and temperatures so that a chip can automatically be configured to operate at the lowest energy level that balances subthreshold leakage power and dynamic switching power. Through novel circuit techniques and methodologies, this work illustrates how subthreshold leakage currents can be controlled from a circuit perspective, thereby helping to enable continued aggressive scaling of semiconductor technologies.by James T. Kao.Ph.D