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An Ultra-Low Energy Subthreshold SRAM Bitcell for Energy Constrained Biomedical Applications

The Charles L. Brown Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, VA 22904, USA
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The original of this paper had been presented in IEEE S3S Conference 2013.
J. Low Power Electron. Appl. 2014, 4(2), 119-137; https://doi.org/10.3390/jlpea4020119
Received: 1 March 2014 / Revised: 6 May 2014 / Accepted: 19 May 2014 / Published: 27 May 2014
(This article belongs to the Special Issue Selected Papers from IEEE S3S Conference 2013)
Energy consumption is a key issue in portable biomedical devices that require uninterrupted biomedical data processing. As the battery life is critical for the user, these devices impose stringent energy constraints on SRAMs and other system on chip (SoC) components. Prior work shows that operating CMOS circuits at subthreshold supply voltages minimizes energy per operation. However, at subthreshold voltages, SRAM bitcells are sensitive to device variations, and conventional 6T SRAM bitcell is highly vulnerable to readability related errors in subthreshold operation due to lower read static noise margin (RSNM) and half-select issue problems. There are many robust subthreshold bitcells proposed in the literature that have some improvements in RSNM, write static noise margin (WSNM), leakage current, dynamic energy, and other metrics. In this paper, we compare our proposed bitcell with the state of the art subthreshold bitcells across various SRAM design knobs and show their trade-offs in a column mux scenario from the energy and delay metrics and the energy per operation metric standpoint. Our 9T half-select-free subthreshold bitcell has 2.05× lower mean read energy, 1.12× lower mean write energy, and 1.28× lower mean leakage current than conventional 8T bitcells at the TT_0.4V_27C corner. Our bitcell also supports the bitline interleaving technique that can cope with soft errors. View Full-Text
Keywords: subthreshold; SRAM; half-select; half-select-free; 9T; bitcell; ultra-low-energy; biomedical; minimum energy point; energy per operation subthreshold; SRAM; half-select; half-select-free; 9T; bitcell; ultra-low-energy; biomedical; minimum energy point; energy per operation
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Banerjee, A.; Calhoun, B.H. An Ultra-Low Energy Subthreshold SRAM Bitcell for Energy Constrained Biomedical Applications. J. Low Power Electron. Appl. 2014, 4, 119-137.

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