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VLSI Design
Volume 14 (2002), Issue 4, Pages 315-327

A Fast ALU Design in CMOS for Low Voltage Operation

Department of Electrical and Computer Engineering, Louisiana State University, Baton Rouge 70803-5901, LA, USA

Received 6 October 2000; Revised 25 April 2001

Copyright © 2002 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


A high-speed 4-bit ALU has been designed for 1 V operation to demonstrate the usefulness of the back-gate forward substrate bias (BGFSB) method in 1.2 μm N-well CMOS technology. The 4-bit ALU employs a ripple carry adder and is capable of performing eight operations - four arithmetic and four logical operations. The BGFSB voltage has been limited to |0.4| V. Delay time measurements are taken for all operations from the SPICE simulations with and without the back-gate forward substrate bias. A speed advantage of a factor of about 2–2.5 is obtained with BGFSB over the conventional design.