Padding of LFSR Seeds for Reduced Input Test Data Volume

In a commonly used test data compression method, the on-chip decompression logic is based on a linear-feedback shift-register ( LFSR), and compressed tests consist of seeds for the LFSR. A seed can be modified and used for applying several different tests. This reduces the input test data volume further than the basic test data compression method. In this context, this article introduces a new approach for applying several different tests based on every seed. The new approach pads a seed in different ways to obtain new seeds for LFSRs with more bits, all of which can be implemented by a single programmable LFSR. The advantage of using LFSRs with more bits is that they are effective in detecting more target faults, thus supporting test compaction together with a reduction in the input test data volume. The experimental results for benchmark circuits demonstrate these points.