A Low-Vt Small-Offset Gated-Preamplifier for Sub-1-V DRAM Mid-Point Sensing

Satoru AKIYAMA
Riichiro TAKEMURA
Tomonori SEKIGUCHI
Akira KOTABE
Kiyoo ITOH

Publication
IEICE TRANSACTIONS on Electronics   Vol.E95-C    No.4    pp.600-608
Publication Date: 2012/04/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E95.C.600
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Solid-State Circuit Design – Architecture, Circuit, Device and Design Methodology)
Category: 
Keyword: 
low-voltage DRAM,  gated preamplifier,  mid-point sensing,  variations in threshold voltage,  

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Summary: 
A gated sense amplifier (GSA) consisting of a low-Vt gated preamplifier (LGA) and a high-Vt sense amplifier (SA) is proposed. The gating scheme of the LGA enables quick amplification of an initial cell signal voltage (vS0) because of its low Vt and prevents the cell signal from degrading due to interference noise between data lines. As for a conventional sense amplifier (CSA), this new type of noise causes sensing error, and the noise-generation mechanism was clarified for the first time by analysis of vS0. The high-Vt SA holds the amplified signal and keeps subthreshold current low. Moreover, the gating scheme of the low-Vt MOSFETs in the LGA drives the I/O line quickly. The GSA thus simultaneously achieves fast sensing, low-leakage data holding, and fast I/O driving, even for sub-1-V mid-point sensing. The GSA is promising for future sub-1-V gigabit dynamic random-access memory (DRAM) because of reduced variations in the threshold voltage of MOSFETs; thus, the offset voltage of the LGA is reduced. The effectiveness of the GSA was verified with a 70-nm 512-Mbit DRAM chip. It demonstrated row access time (tRCD) of 16.4 ns and read access (tAA) of 14.3 ns at array voltage of 0.9 V.