Semiconductor memory device
View Patent ↗With the objective of providing a semiconductor memory device which is made identical in usability to a static RAM by use of dynamic memory cells and realizes a high-speed memory cycle time, there is provided a pseudo static RAM having a time multiplex mode which, when instructions for a memory operation for reading memory information from each of memory cells each requiring a refresh operation for periodically holding the memory information, or writing the same therein is issued, carries out an addressing-based autonomous refresh operation different from the memory operation before or after the memory operation. The pseudo static RAM includes address signal transition detectors for a row and a column, and a page mode which independently performs a column address selecting operation according to an address signal transition detect signal of the second address signal transition detector.
1. A semiconductor memory device comprising:
a plurality of word lines;
a plurality of bit lines;
a plurality of memory cells coupled to the plurality of word lines and the plurality of bit lines so that one memory cell is coupled to one word line and one bit lines, wherein the plurality of memory cells stores information therein and each of which needs a first operation to hold the information stored therein;
a row address decoder which receives row address signals and which selects one of plurality of word lines in accordance with the row address signals;
a row address transition detector which receives the row address signals to detect a transition of the row address signals;
a column address decoder which receives column address signals (and which selects one of the plurality of bit lines in accordance with the column address signals;
a column address transition detector which receives the column address signals to detect a transition of the column address signals; and
a timer which instructs the first operation to the plurality of memory cells in accordance with information holding capability of the plurality of memory cells,
wherein the column address transition detector instructs a second operation which selects bit lines continuously to the column address decoder when the row address signals are constant and the column address signals are changed, and
wherein the first operation is executed autonomously before or after a memory operation which is a reading operation for outputting the information from the memory cells or a writing operation for inputting the information to the memory cells each of which are different from the first operation.
2. The semiconductor memory device according to claim 1 ,
wherein the semiconductor memory device is a pseudo static random access memory, and
wherein the memory cells are dynamic memory cells.
3. The semiconductor memory device according to claim 2 ,
wherein the first operation is a refresh operation, and
wherein the second operation is a page mode operation.
4. The semiconductor memory device according to claim 1 , further comprising:
a judgment circuit which detects an earlier one between a request signal for a memory operation which includes reading operation and the writing operation and a request signal for the first operation,
wherein the judgment circuit arbitrates the memory operation and the first operation so as not to overlap on a time base according to a judgment output of the judgment circuit.
5. The semiconductor memory device according to claim 4 ,
wherein a preliminary operation for word line selecting under a subsequently-executed operation of the memory operation and the first operation is executed in parallel during the previously-executed operation thereof.
6. The semiconductor memory device according to claim 4 ,
wherein a rising of a word line under the subsequently-executed operation between the memory operation and the first operation is set after a word line reset operation and a bit line precharging operation under the previously-executed operation thereof are completed.