Low-power word-parallel nearest-Hamming-distance search circuit based on frequency mapping

Distance-frequency mapping with ring oscillators, adjustable in discrete steps, enables fast word-parallel nearest-Hamming-distance search with low power consumption. High robustness against fabrication-related variations of the MOSFET characteristics is achieved in addition. A test chip in 180 nm CMOS technology with 64 words, each consisting of 256 bits, consumes less than 36.5 mW and 307 μW at supply voltages of 1.8 and 0.7 V, respectively. In comparison to previous digital designs, power dissipation is 5 times smaller, while search speed from 50ns to 245ns for Hamming distances from 0 to 256 is approximately equal.