A Fast ALU Design in CMOS for Low Voltage Operation

Abstract

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.