An Efficient BIST Architecture for Delay Faults in the Logic Cells of Symmetrical SRAM-Based FPGAs

Abstract

The objective of this paper is to propose a BIST scheme enabling the test of delay faults in all the Look-Up Tables (LUTs) of FPGA SRAMs, in a Manufacturing context. The BIST scheme does not consume any area overhead and can be removed from the device after the test thus, allowing the use of the whole circuit by the user. The structure we propose is composed of a simple test pattern generator, an error detector and a chain of LUTs. The chain of LUTs is formed alternatively by a LUT and a flip---flop. By using such a chain, the test of all delay faults in every LUT is enabled. In this paper, we develop an experiment based on the implantation of our BIST architecture in a Virtex FPGA from Xilinx. The purpose of this experiment is to show the feasibility of our solution. As a result, one important issue from this solution is its ability to detect the "smallest" delay faults in the LUTs, i.e. the smallest delays that can be observed on a LUT output.