Current Sense Amplifiers for Low-Voltage Memories

Nobutaro SHIBATA

IEICE TRANSACTIONS on Electronics   Vol.E79-C    No.8    pp.1120-1130
Publication Date: 1996/08/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Integrated Electronics
SRAM,  ROM,  current sensing,  amplifier,  low voltage,  

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The principles and design of current sense amplifiers for low-voltage MOS memories are described. The low input impedance of current sense amplifiers is explained using a simple model consisting of negative and positive resistance. A description of the model realized by a common-gate MOS amplifier employing transconductance enhancing techniques is also given. Some current sensing schemes for low-voltage ROM's and/or SRAM's are shown. For SRAM application, a current sensing scheme employing large-gain inverter-type amplifiers is proposed. A test chip including SRAM macrocells was designed and fabricated with 3.3-V 0.5-µm CMOS technology. An SRAM using current sense amplifiers was able to demonstrate that current sensing suppressed bitline delay to half that in conventional current-mirror types. The current sense amplifier had the same operating limit as the current-mirror type for low supply voltages. The measured operating limit of the STSM in this work was 1.3-V for threshold voltages of 0.55-V(n-channel) and -0.65-V(p-channel).