Semiconductor memory device with multiple sub-arrays of different sizes

Abstract

A semiconductor memory device includes a memory cell array divided into a plurality of sub-arrays. The number of memory cells per bit line in at least one of the sub-arrays differs from the number of memory cells per bit line in other sub-arrays. When the sense amplifiers can accommodate a bit line loading of (2,+2,/N) memory cells per bit line, the size and bit line loading of one of more of the sub-arrays can be increased. This can provide sub-arrays of different sizes and can reduce the number of the sub-arrays and the number of the sense amplifier regions. Accordingly, the chip efficiency is improved. Maximum current for sensing during simultaneous accesses of multiple arrays can access two sub-arrays with different bit line loadings and avoid simultaneously accessing two sub-arrays having high bit-line loadings.