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VLSI Design
Volume 2013 (2013), Article ID 382682, 10 pages
Research Article

FPGA Fault Tolerant Arithmetic Logic: A Case Study Using Parallel-Prefix Adders

Department of Electrical Engineering, The University of Texas at Tyler, Tyler, TX 75799, USA

Received 5 August 2013; Accepted 19 September 2013

Academic Editor: Chien-Min Ou

Copyright © 2013 David H. K. Hoe et al. 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.


This paper examines fault tolerant adder designs implemented on FPGAs which are inspired by the methods of modular redundancy, roving, and gradual degradation. A parallel-prefix adder based upon the Kogge-Stone configuration is compared with the simple ripple carry adder (RCA) design. The Kogge-Stone design utilizes a sparse carry tree complemented by several smaller RCAs. Additional RCAs are inserted into the design to allow fault tolerance to be achieved using the established methods of roving and gradual degradation. A triple modular redundant ripple carry adder (TMR-RCA) is used as a point of reference. Simulation and experimental measurements on a Xilinx Spartan 3E FPGA platform are carried out. The TMR-RCA is found to have the best delay performance and most efficient resource utilization for an FPGA fault-tolerant implementation due to the simplicity of the approach and the use of the fast-carry chain. However, the superior performance of the carry-tree adder over an RCA in a VLSI implementation makes this proposed approach attractive for ASIC designs.