Design of a high-density multiple-valued content-addressable memory based on floating-gate MOS devices

A high-density, VLSI-oriented cellular associative memory for real-time numeric and nonnumeric computation is presented. Three kinds of basic search operations, which are parallel by word and serial by digit slice, are considered. A search word and memory words are encoded to several discrete values so that the number of digits to perform comparisons while searching can be greatly reduced. A multiple-valued down literal circuit of two variables, which is the basic building block for a compact content-addressable memory (CAM), can be implemented using a floating-gate MOS transistor whose threshold voltage is controllable by the external input signal. It is demonstrated that the number of transistors, cells, and interconnections between cells in an r-valued CAM are reduced to less than 1/log₂r in comparison with the corresponding binary implementation.