Analysis and Optimization of Sleep Modes in Subthreshold Circuit Design


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David Blaauw

Subthreshold operation is a promising method for reducing power consumption in ultra-low power applications, such as active RFIDs and sensor networks. It was shown in previous works that operating at the Vmin supply voltage results in optimal energy operation, where Vmin typically falls below the threshold voltage. However, all previous subthreshold analyses ignore the leakage current in standby mode. Hence, for applications where operation at Vmin results in completion of the task well ahead of the required deadline, the energy consumption can be significantly under-estimated. In this work, we investigate the effect of the non-zero standby energy on the optimal energy consumption in subthreshold operation. We first analyze energy consumption both with and without a cutoff technique in standby mode. Two parameters are proposed to capture the cutoff structure’s effect on the energy consumption and delivered for the generic power gating switch (PGS) case. Second, a methodology to minimize the total energy consumption is addressed. The selection of the PGS is examined by comparing three different PGS. Then, a co-optimization method to optimize the size of the PGS concurrently with the supply voltage is proposed. In case of long duty cycle operation where most of sensor applications fall, this approach provides extremely small PGS size together with slightly higher supply voltage than the conventional Vmin as an optimum operation and results in total energy reduction by 99.2% compared to 


Analysis and Optimization of Sleep modes in Subthreshold Circut Design

Mingoo Seok, Scott Hanson, Dennis Sylvester, David Blaauw, “Analysis and Optimization of Sleep modes in Subthreshold Circut Design,” ACM/Design Automation Conference (DAC), June 2007 ©IEEE File: [PDF Document]