Paper Review: Duet An accurate Leakage Estimation and Optimization Tool for Dual-Vt Circuits

Abstract
We present a new approach for the estimation and optimization of standby power dissipation in large MOS digital circuits. We first introduce a new approach for accurate and efficient calculation of the average standby or leakage current in large digital circuits by introducing the concepts of “dominant leakage states” and the use of state probabilities. Combined with graph reduction techniques and simplified nonlinear simulation, our method achieves speedups of three to four orders of magnitude over exhaustive SPICE simulations while maintaining very good accuracy. The leakage current calculation is then utilized in a new leakage and performance optimization algorithm for circuits using dual Vt processes. Our approach is the first to consider the assignment of both the Vt and the width of a transistor, simultaneously. Our optimization approach uses incremental calculation of leakage and performance sensitivities and can take into account a partially defined circuit state constraint for the standby mode of the device. In tests on a variety of industrial circuits, our optimization approach was able to obtain 81–100% of the performance achievable with all low transistors, but with 1/3 to 1/6 the standby current. We also show that knowledge of the standby state of the device enhances the leakage/performance tradeoff.

Paper Location
None

Citation
[1] S. Sirichotiyakul, T. Edwards, C. Oh, R. Panda, and D. Blaauw, "Duet: An Accurate Leakage Estimation and Optimization Tool for Dual-Vt Circuits," IEEE Transactions on Very Large Scale Integration, vol. 10, 2002, pp. 79-90.

Positive

• The algorithm proposed, while limited in the paper assumes that several discrete Vt's can be used
• Clear definitions, and use of graph theory notation
• Very reasonable and clear description of the used graph reduction for DC analysis

Negative

• The methodology used assumes that the high and low Vt are fixed. This is not necessarily true.
• Also assumes that each individual transistor can be individually assigned a threshold voltage. This make not be reasonable in a real design.