A circuit includes a word line driver for driving a world line and a tracking word line driver for driving a tracking word line. The pulse width of a world line signal on the world line is driven to be larger than that of a tracking world line signal on the tracking world line to assist writing under difficult conditions. Because the tracking word line signal is activated later than the word line signal being activated but is deactivated at the same time with the word line, the pulse width of the word line signal is larger.