Minimizing read disturb in an array flash cell
A method of reducing read disturb in NVM cells by using a first drain voltage to read the array cells and using a second, lower drain voltage, to read the reference cells. Drain voltages on global bitlines (GBLs) for both the array and the reference cells may be substantially the same as one another to maintain main path capacitance matching, while drain voltages on local bitlines (LBLs) for the reference cells may be lower than the drain voltage on local bitlines (LBLs) for the array cells to reduce second bit effect. Reducing the drain voltage of the reference cell at its drain port may be performed using a clamping device or a voltage drop device.
1. A method of sensing nonvolatile memory (“NVM”) cells comprising: applying a first drain or source (drain/source) voltage to an NVM data bearing cell and applying a second drain or source (drain/source) voltage, which is substantially always lower than the first drain/source voltage, to an NVM reference cell used to sense the NVM data bearing cell.
2. The method of claim 1 , wherein drain/source voltages on global bitlines (GBLs) for both the data bearing and the reference cell are substantially the same; and drain/source voltages on local bitlines (LBLs) for the data bearing and the reference cells are different than one another.
3. The method of claim 2 , wherein the drain/source voltage on local bitlines (LBLs) for the reference cell is lower than the drain/source voltage on local bitlines (LBLs) for the data bearing cell.
4. The method of claim 1 , further comprising using first drain or source driving circuitry to provide the first drain/source voltage; and using second drain or source (drain/source) driving circuitry to provide the second drain/source voltage.
5. The method of claim 1 , wherein a sensing path capacitance for the data bearing cell and a sensing path capacitance for the reference cell is substantially matched.
6. The method of claim 1 , further comprising reducing the drain/source voltage of the reference cell at a drain or source port.
7. The method of claim 6 , wherein reducing the drain/source voltage includes using a clamping device.
8. The method of claim 6 , wherein reducing the drain/source voltage includes using a resistor or a transistor connected as a resistor.
9. The method of claim 1 , wherein applying a different drain/source voltage to the reference is achieved by using a different trim option with the drain or source driver of the reference cell.
10. The method of claim 1 , further comprising source-side sensing to read both the data bearing cell and the reference cell.
11. The method of claim 1 , further comprising using drain-side sensing to read both the data bearing cell and the reference cell.
12. A memory device comprising non-volatile memory (NVM) cells comprising: one or more data bearing cells; one or more reference cells adapted to be used for sensing or reading data bearing cells; and one or more circuit portions adapted to substantially always apply a lower drain or source (drain/source) voltage to a reference cell being used to sense a data bearing cell than the drain or source (drain/source) voltage being applied to the cell being sensed.
13. The device according to claim 12 , wherein said one or more circuit portions are adapted to reduce a voltage between a voltage supply and a drain/source of the reference cell.
14. The device according to claim 13 , wherein said one or more circuit portions are adapted to reduce a voltage between a global bitline and a local bitline associated with the drain/source of the reference cell.
15. The device according to claim 14 , wherein said one or more circuit portions are comprised of a clamping device.
16. The device according to claim 15 , wherein said one or more circuit portions are comprised of a resistor or a transistor connected as a resistor.
17. The device according to claim 15 , wherein said one or more circuit portions are comprised of a field effect transistor (“FET”) transistor having its drain (D) connected to a given second global bitline, its source (S) connected to a given local bitline, and its gate (G) connected to a regulated voltage.