A Variable-Length Coding Adjustable for Compressed Test Application

Test compression / decompression using variable-length coding is an efficient method for reducing the test application cost, i.e., test application time and the size of the storage of an LSI tester. However, some coding techniques impose slow test application, and consequently a large test application time is required despite the high compression. In this paper, we clarify the fact that test application time depends on the compression ratio and the length of codewords and then propose a new Huffman-based coding method for achieving small test application time in a given test environment. The proposed coding method adjusts both of the compression ratio and the minimum length of the codewords to the test environment. Experimental results show that the proposed method can achieve small test application time while keeping high compression ratio. key words: test compression, variable-length coding, test application time, ATE, Huffman code, and test environment