VLSI Implementation of a fast rank order filtering algorithm

A useful class of digital filters is the rank order filter, of which the median filter is the most popular. This paper details the NMOS IC design of a 6-bit rank order filter based upon the approach of Fitch, Coyle, and Gallagher. The chip provides for programmable window lengths of 3, 5, 7, and 9; the selection of any element in the rank order; operation in the nonrecursive or recursive modes; and the ability to function in a "ganged" mode so that two or more identical chips can accommodate samples of length seven or eight bits.