Fault Tolerance in bit swapping LFSR using FPGA Architecture

The design for low power has become one of the greatest challenges in high-performance very large scale integration (VLSI) design. It has been found that the power consumed during test mode operation is often much higher than during normal mode operation. This is because most of the consumed power results from the switching activity in the nodes of the circuit under test (CUT), which is much higher during test mode than during normal mode operation. BIST is a design technique that allows a circuit to test itself. In this, the test performance achieved with the implementation of BIST is proven to be adequate to offset the disincentive of the hardware overhead produced by the additional BIST circuit. The technique can provide shorter test time compared to an externally applied test and allows the use of low-cost test equipment during all stages of production. BIST technique uses linear feedback shift register (LFSR) for generating test pattern. The proposed design, called bit-swapping LFSR (BS-LFSR), is composed of an LFSR and a 2 × 1 multiplexer. When used to generate test patterns for scan-based built-in self-tests, it reduces the number of transitions that occur at the scan-chain input during scan shift operation by 50% when compared to those patterns produced by a conventional LFSR. Hence, it reduces the overall switching activity in the circuit under test during test applications. The BS-LFSR is combined with a scan-chain-ordering algorithm that orders the cells in a way that reduces the average and peak power (scan and capture) in the test cycle or while scanning out a response to a signature analyzer. These techniques have a substantial effect on averageand peakpower reductions with negligible effect on fault coverage or test application time.