A 40-nm 0.5-V 12.9-pJ/Access 8T SRAM Using Low-Energy Disturb Mitigation Scheme
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- YOSHIMOTO Shusuke
- Kobe University
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- TERADA Masaharu
- Kobe University
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- OKUMURA Shunsuke
- Kobe University
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- SUZUKI Toshikazu
- Semiconductor Technology Academic Research Center (STARC)
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- MIYANO Shinji
- Semiconductor Technology Academic Research Center (STARC)
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- KAWAGUCHI Hiroshi
- Kobe University
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- YOSHIMOTO Masahiko
- JST, CREST
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Abstract
This paper presents a novel disturb mitigation scheme which achieves low-energy operation for a deep sub-micron 8T SRAM macro. The classic write-back scheme with a dedicated read port overcame both half-select and read-disturb problems. Moreover, it improved the yield, particularly in the low-voltage range. The conventional scheme, however, consumed more power because of charging and discharging all write bitlines in a sub-block. Our proposed scheme reduces the power overhead of the write-back scheme using a floating write bitline technique and a low-swing bitline driver (LSBD). The floating bitline and the LSBD respectively consist of a precharge-less CMOS equalizer (transmission gate) and an nMOS write-back driver. The voltage on the floating write bitline is at an intermediate voltage between the ground and the supply voltage before a write cycle. The write target cells are written by normal CMOS drivers, whereas the write bitlines in half-selected columns are driven by the LSBDs in the write cycle, which suppresses the write bitline voltage to VDD - Vtn and therefore saves the active power in the half-selected columns (where Vtn is a threshold voltage of an nMOS). In addition, the proposed scheme reduces a leakage current from the write bitline because of the floating write bitline. The active leakage is reduced by 33% at the FF corner, 125°C. The active energy in the write operation is reduced by 37% at the FF corner. In other process corners, more writing power reduction can be expected because it depends on the Vtn in the LSBD. We fabricated a 512-Kb 8T SRAM test chip that operates at a single 0.5-V supply voltage. The test chip with the proposed scheme respectively achieves 1.52-µW/MHz writing energy and 72.8-µW leakage power, which are 59.4% and 26.0% better than those of the conventional write-back scheme. The total energy is 12.9 µW/MHz (12.9 pJ/access) at a supply voltage of 0.5V and operating frequency of 6.25MHz in a 50%-read/50%-write operation.
Journal
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- IEICE Transactions on Electronics
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IEICE Transactions on Electronics E95.C (4), 572-578, 2012
The Institute of Electronics, Information and Communication Engineers
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Keywords
Details 詳細情報について
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- CRID
- 1390001204379529856
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- NII Article ID
- 10030940790
- 120005672405
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- NII Book ID
- AA10826283
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- BIBCODE
- 2012IEITE..95..572Y
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- ISSN
- 17451353
- 09168524
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- HANDLE
- 20.500.14094/90002972
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- Text Lang
- en
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- Data Source
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- JaLC
- IRDB
- Crossref
- CiNii Articles
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- Abstract License Flag
- Disallowed