NOR-type mask ROM having dual sense current paths

摘要

A NOR-type mask ROM reduces the resistance ratio of buried diffusion layers and improves the drive capacity of bank selection transistors by utilizing sub-bit line selection transistors located near the center of a memory cell array. The sub-bit line selection transistors are connected to a pair of sub-bank selection lines that divide the memory cell array into symmetric upper and lower portions. The bank selection transistors couple alternate sub-bit lines to main bit lines at both ends of the sub-bit lines, thereby forming a dual current path between the main bit lines and the memory cells coupled to the sub-bit lines.