A 10T Non-precharge Two-Port SRAM Reducing Readout Power for Video Processing

Hiroki NOGUCHI  Yusuke IGUCHI  Hidehiro FUJIWARA  Shunsuke OKUMURA  Yasuhiro MORITA  Koji NII  Hiroshi KAWAGUCHI  Masahiko YOSHIMOTO  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E91-C   No.4   pp.543-552
Publication Date: 2008/04/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e91-c.4.543
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Advanced Technologies in Digital LSIs and Memories)
Category: 
Keyword: 
8T SRAM cell,  10T SRAM cell,  low-power SRAM,  non-precharge SRAM,  two-port SRAM,  video processing,  

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Summary: 
We propose a low-power non-precharge-type two-port SRAM for video processing that exploits statistical similarity in images. To minimize the charge/discharge power on a read bitline, the proposed memory cell (MC) has ten transistors (10T), comprised of the conventional 6T MC, a readout inverter and a transmission gate for a read port. In addition, to incorporate three wordlines, we propose a shared wordline structure, with which the vertical cell size of the 10T MC is fitted to the same size as the conventional 8T MC. Since the readout inverter fully charges/discharges a read bitline, there is no precharge circuit on the read bitline. Thus, power is not consumed by precharging, but is consumed only when a readout datum is changed. This feature is suitable to video processing since image data have spatial correlation and similar data are read out in consecutive cycles. As well as the power reduction, the prechargeless structure shortens a cycle time by 38% compared with the conventional SRAM, because it does not require a precharge period. This, in turn, demonstrates that the proposed SRAM operates at a lower voltage, which achieves further power reduction. Compared to the conventional 8T SRAM, the proposed SRAM reduces a charge/discharge possibility to 19% (81% saving) on the bitlines. As the measurement result, we confirmed that the proposed 64-kb video memory in a 90-nm process achieves an 85% power saving on the read bitline, when considered as an H.264 reconstructed image memory. The area overhead is 14.4%.