Nonvolatile semiconductor memory device that achieves speedup in read operation
A plurality of first sub-bit lines are each connected to a common source line via a corresponding first sub-bit line reset transistor with NMOS structure, and a plurality of second sub-bit lines are each connected to the common source line via a corresponding second sub-bit line reset transistor with NMOS structure. The plurality of first and second sub-bit line reset transistors have their respective gates receiving a sub-bit line reset signal. This sub-bit line reset signal becomes “H” for a predetermined period of time after read data is obtained during a read period.
1. A nonvolatile semiconductor memory device comprising:
a plurality of memory transistors each of which has nonvolatile storage capability by being turned on or off upon being selected;
a main bit line;
a plurality of sub-bit lines provided correspondingly to said main bit line, wherein
for each column, one side electrodes of said plurality of memory transistors are connected to one of said plurality of sub-bit lines, and
during a read period, one selected sub-bit line among said plurality of sub-bit lines and said main bit line are electrically connected and precharged to a predetermined potential, and then one memory transistor among said plurality of memory transistors having said one side electrode connected to said selected sub-bit line enters a selected state, whereby read data is obtained based on the amount of current flowing thorough said main bit line,
said nonvolatile semiconductor memory device further comprising:
resetting means resetting said main bit line and said selected sub-bit line to a standard potential after said read data is obtained during said read period,
wherein said resetting means includes:
main bit line resetting means resetting said main bit line to said standard potential; and
sub-bit line resetting means resetting said plurality of sub-bit lines to said standard potential.
2. The nonvolatile semiconductor memory device according to claim 1 , wherein
said sub-bit line resetting means resets said plurality of sub-bit lines to said standard potential at a time.
3. The nonvolatile semiconductor memory device according to claim 2 , wherein
said plurality of sub-bit lines are classified into a plurality of first and second sub-bit lines,
said sub-bit line resetting means includes first sub-bit line resetting means resetting said plurality of first sub-bit lines to said standard potential, and second sub-bit line resetting means resetting said plurality of second sub-bit lines to said standard potential, and
said first and second sub-bit line resetting means have independent driving abilities of each other.
4. The nonvolatile semiconductor memory device according to claim 1 , wherein said sub-bit line resetting means resets said sub-bit lines to the standard potential not through a main bit line.
5. The nonvolatile semiconductor memory device according to claim 1 , wherein said sub-bit line resetting means resets said sub-bit lines to the standard potential through a common source line.
6. The nonvolatile semiconductor memory device according to claim 1 , wherein said sub-bit line resetting means resets said sub-bit lines to the standard potential through a line different from a main bit line.