Simultaneous state, Vt and Tox assignment for total standby power minimization

Abstract

Standby leakage current minimization is a pressing concern for mobile applications that rely on standby modes to extend battery life. Also, gate oxide leakage current (I/sub gate/) has become comparable to subthreshold leakage (I/sub sub/) in 90 nm technologies. In this paper, we propose a new method that uses a combined approach of sleep-state, threshold voltage (V/sub t/ and gate oxide thickness (T/sub ox/) assignments in a dual-V/sub t/ and dual-T/sub ox/ process to minimize both I/sub sub/ and I/sub gate/. Using this method, total leakage current can be dramatically reduced since in a known state in standby mode, only certain transistors are responsible for leakage current and need to be considered for high-V/sub t/ or thick-T/sub ox/ assignment. We formulate the optimization problem for simultaneous state, V/sub t/ and T/sub ox/ assignments under delay constraints and propose two practical heuristics. We implemented and tested the proposed methods on a set of synthesized benchmark circuits. Results show an average leakage current reduction of 5a-6X and 2-3X compared to previous approaches that only use state or state+V/sub t/ assignment, respectively, with small delay penalties.