Design-specific path delay testing in lookup-table-based FPGAs

Due to the increased use of field-programmable gate arrays (FPGAs) in production circuits with high reliability requirements, the design-specific testing of FPGAs has become an important topic for research. Path delay testing of FPGAs is especially important since path delay faults can render an otherwise fault-free FPGA unusable for a given design layout. This paper presents a new approach for FPGA path delay testing, which partitions target paths into subsets that are tested in the same test configuration. Each path is tested for all combinations of signal inversions along the path length. Each configuration consists of a sequence generator, response analyzer, and circuitry for controlling inversions along tested paths, all of which are formed from FPGA resources not currently under test. Two algorithms are presented for target-path partitioning to determine the number of required test configurations. The test circuitry associated with these methods is also described. The results of applying the methods indicate that our path-delay-testing approach requires seconds per design to cover all paths with delay within 10% of the critical path delay. The approach has been validated using Xilinx Virtex devices.