Method for precharging word and bit lines for selecting memory cells within a memory array
View Patent ↗The invention includes an apparatus and method of selecting memory cells within a memory array. The method includes receiving a memory cell address. A column address and a row address are generated from the memory cell address. Row select lines or column select lines are pre-charged. A self-timed charging circuit is initiated to provide an adequate amount of time to charge a selected row, and to initiate elimination of static current flowing to unselected rows after a self-timed delay. The other of the row select lines or the column select lines are then pre-charged. Memory cells are selected based upon the column address and the row address. One of two states of the memory cells can be based upon sensing threshold voltages of sense lines that correspond with the selected memory cells.
1. A method of selecting memory cells within a memory array, the method comprising:
receiving a memory cell address;
generating a column address and a row address from the memory cell address;
pre-charging row select lines;
initiating a delay circuit to ensure that a heaviest loaded row select line is properly charged;
pre-charging column select lines; and
selecting memory cells based upon the column address and the row address.
2. The method of selecting memory cells within a memory array of claim 1 , wherein the delay circuit comprises a self-timed select circuit.
3. The method of selecting memory cells within a memory array of claim 1 , wherein pre-charging the row select lines comprises:
charging a row charge holding device for each row select line;
dis-charging each row charge holding device if any row address lines associated with the row address is a first voltage potential.
4. The method of selecting memory cells within a memory array of claim 3 , wherein each row charge holding device is dis-charged if the row select line corresponding to the row charge holding device is not selected.
5. The method of selecting memory cells within a memory array of claim 3 , wherein the first voltage potential is below a threshold voltage potential.
6. The method of selecting memory cells within a memory array of claim 3 , wherein a charging transistor for charging the charge holding device is located on a different substrate than the memory array, and a memory array substrate that comprises the memory array includes passive circuit devices.
7. The method of selecting memory cells within a memory array of claim 1 , further comprising:
detecting one of two states of the memory cells depending upon weather a sensed voltage of each memory cell is above or below a threshold voltage.
8. The method of selecting memory cells within a memory array of claim 1 , wherein the row select lines are word lines.
9. The method of selecting memory cells within a memory array of claim 1 , wherein the column select lines are bit lines.
10. The method of selecting memory cells within a memory array of claim 1 , wherein a timing delay of the delay circuit estimates a worst case time delay associated with row select lines.
11. The method of selecting memory cells within a memory array of claim 1 , wherein initiating the delay circuit comprises:
charging a worst case delay estimate capacitor with a dummy word line select line.
12. The method of selecting memory cells within a memory array of claim 11 , wherein the dummy word line is selected upon initiation of access of the memory array.
13. The method of selecting memory cells within a memory array of claim 1 , wherein pre-charging the row select lines comprises:
charging charge holding devices corresponding to each of the row select lines;
activating a row select line as a function of charge on a corresponding charge holding device; and
dis-charging corresponding charge holding devices if any of a plurality of address lines electrically connected to the charge holding device are below a first voltage potential.
14. The method of selecting memory cells within a memory array of claim 1 , wherein pre-charging the column select lines comprises:
pre-charging charge holding devices corresponding to each of the column select lines;
activating a column select line as a function of charge on a corresponding charge holding device; and
dis-charging corresponding charge holding devices if any of a plurality of address lines electrically connected to the charge holding device are below a first voltage potential.
15. A method of selecting memory cells within a memory array, the method comprising:
receiving a memory cell address;
generating a column address and a row address from the memory cell address;
pre-charging column select lines;
initiating a delay circuit to ensure that a heaviest loaded column select line is properly charged;
pre-charging row select lines upon activation by the delay circuit; and selecting memory cells based upon the column address and the row address.