Semiconductor storage device
View Patent ↗A semiconductor storage device in accordance with an exemplary aspect of the present invention includes a plurality of memory cells arranged in a matrix pattern, a plurality of word lines each provided so as to correspond to each line of the memory cells, a plurality of bit lines each connected to respective one of the memory cells, and a row selection circuit that, in a read operation, drives the word line to a set potential at a drive speed slower than a discharge speed of the bit line exhibited when the word line is raised roughly vertically to VDD.
1. A semiconductor storage device comprising:
a plurality of memory cells arranged in a matrix pattern;
a plurality of word lines provided to correspond to the respective rows of the memory cells;
a plurality of bit lines connected to a plurality of memory cells in respective columns of the memory cells; and
a row selection circuit that, in a read operation, drives the word line to a set potential at a drive speed slower than a discharge speed of the bit line exhibited when the word line is raised roughly vertically to the set potential.
2. The semiconductor storage device according to claim 1 , wherein the word line is driven such that an amount of voltage change of data retained in the memory cell exhibited when the word line is driven at the drive speed becomes smaller than an amount of voltage change of data retained in the memory cell exhibited when the word line is raised roughly vertically.
3. The semiconductor storage device according to claim 1 , wherein the row selection circuit comprises:
a PMOS transistor and an NMOS transistor constituting an inverter,
wherein a driving capability of the PMOS transistor is smaller than a driving capability of the NMOS transistor.
4. The semiconductor storage device according to claim 1 , wherein the row selection circuit comprises:
a PMOS transistor and an NMOS transistor constituting an inverter,
a PMOS transistor for adjusting drive speed connected to a source of the PMOS transistor; and
a voltage generation circuit connected to a gate of the PMOS transistor for adjusting drive speed.
5. The semiconductor storage device according to claim 1 , wherein the row selection circuit drives the word line to the set potential at a speed slower than the discharge speed and faster than the drive speed according to an input test signal.
6. The semiconductor storage device according to claim 1 , wherein
the memory cell comprises an access transistor, a gate of the access transistor being connected to the word line, and a source of the access transistor being connected to the bit line, and
the row selection circuit, in a read operation, first raises the word line roughly vertically to a threshold voltage of the access transistor, and then drives to the set potential.
7. The semiconductor storage device according to claim 1 , wherein
the row selection circuit further comprises a bit-line discharge signal generation circuit that generates a bit-line discharge signal, and
the word line is raised roughly vertically to the set potential after the bit line is discharged according to the bit-line discharge signal.
8. The semiconductor storage device according to claim 1 , wherein
the plurality of memory cells are divided into a plurality of memory-cell blocks, and
the bit line is provided for each of the plurality of memory-cell blocks.