A word-parallel digital associative engine with wide search range based on Manhattan distance

A word-parallel digital associative engine with accurate and wide-range Manhattan-distance computation is presented. It performs a continuous search operation to detect not only the nearest-match data but also all data in the sorted order of the exact Manhattan distance. The word-parallel digital implementation using a hierarchical search path provides a high-speed search operation with faultless precision, a low-voltage operation mode, and a potential capability of unlimited data capacity. Word-parallel distance calculation circuits autonomously count the Manhattan distance using a weighted search clock to detect the nearest-match data. An associative engine, with 64 words of 8 bit×32 element, has been fabricated using a 0.18 μm CMOS process and successfully tested. The worst-case search time of all data sorting takes 5.85 μs at a supply voltage of 1.8 V.