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We present a new concept and its circuit implementation for a high-speed and low-voltage associative co-processor with Hamming distance ordering. A hierarchical search architecture keeps high speed in large input number. Our circuit implementation allows unlimited data base capacity and achieves low-voltage operation under 1.0 V for SoC applications, which are difficult for the conventional analog approaches. The search logic embedded in a memory cell realizes word-parallel Hamming distance ordering for high-speed sorting/routing applications as well as near/nearest-match detection for recognition. Our fabricated 0.18 μm 64-bit 32-word associative co-processor operates at 411.5 MHz and 40.0 MHz at 1.8 V and 0.75 V respectively.