Bit-serial realizations of a class of nonlinear filters based on positive Boolean functions

It is shown that the function of a stack filter can be realized in k-step recursive use of one binary processing circuit. The time-area complexity of the proposed filter is O(k) as compared with O(2^k) for stack filters. The proposed digital realizations are simple and modular in structure, and suitable for VLSI implementation. Analog/digital (A/D) hybrid realizations have the advantage that there is no need for an A/D converter array when the original signals come from an integrated sensor array. An experimental digital rank-order filter with a window size of three and arbitrary number of input bits is designed and implemented in a 3-μm double-metal polysilicon gate CMOS process. The chip has been fabricated and measurement results are correct with a clock frequency of up to 110 MHz