Patent ID: 6914824

Claim:
A nonvolatile semiconductor memory based on a virtual ground method, the memory comprising: a plurality of memory cells arranged like a matrix; a plurality of bit lines each connected to sources or drains of memory cells arranged in a column direction; a plurality of word lines each intersecting the plurality of bit lines and each connected to gates of memory cells arranged in a row direction; a current supply circuit configured to be continuously connected to a first bit line of the plurality of bit lines during a read time, wherein the first bit line is shared by a selected memory cell of the plurality of memory cells and a first non-selected memory cell of the plurality of memory cells, and the first bit line is connected to a drain of the selected memory cell, and wherein the current supply circuit is configured to supply an electric current to the first bit line during the read time; a charge circuit unit for selectively charging a second bit line of the plurality of bit lines, wherein the charge circuit unit is configured to be selectively connected to the second bit line during the read time, and the second bit line is shared by the first non-selected memory cell and a second non-selected memory cell of the plurality of memory cells, and wherein the second bit line is connected to the charge circuit unit only for a certain portion of the read time, and the second bit line is in a floating state for a remaining portion of the read time; and a precharge circuit configured to be continuously connected to a third bit line of the plurality of bit lines during the read time, wherein the third bit line is shared by the second non-selected memory cell and a third non-selected memory cell of the plurality of memory cells, and the precharge circuit is configured to charge the third bit line during the read time.