Efficient Test Pattern Compression Techniques Based on Complementary Huffman Coding

In this paper, complementary Huffman encoding techniques are proposed for test data compression of complex SOC designs during manufacturing testing. The correlations of blocks of bits in a test data set are exploited such that more blocks can share the same codeword. Therefore, beside the compatible blocks used in previous works, the complementary property betweens blocks can also be used. Based on this property, two methods are proposed for Huffman encoding. According to this technique, more blocks will share the same codeword and the size of the Huffman tree can be reduced. This will not only reduce the area overhead of the decoding circuitry but also substantially increase the compression ratio. In order to facilitate the proposed complementary encoding techniques, a don´t-care assignment algorithm is also proposed. According to experimental results, the area overhead of the decompression circuit is lower than that of the full Huffman coding technique. Moreover, the compression ratio is higher that that of the selective and optimal selective Huffman coding techniques.