Memory controller self-calibration for removing systemic influence
Self-calibration for a memory controller is performed by writing a voltage to a selected cell. Adjacent cells around the selected cell are programmed. After each of the adjacent programming operations, the voltage on the selected cell is read to determine any change in voltage caused by systemic offsets such as, for example, floating gate-to-floating gate coupling. These changes are averaged and stored in a table as an offset for use in adjusting a programming voltage or a read voltage in a particular area of memory represented by the offset. Self calibration method for temperature is determined by writing cells at different temperatures and reading at different temperatures to generate temperature offset tables for the write path and read path. These offset tables are used to adjust for systematic temperature related offsets during programming and during read.
1. A method comprising:
determining a programming offset responsive to a coupling effect in a particular area of a memory array;
storing the programming offset; and
using the programming offset for programming in the particular area of the memory array.
2. A controller configured to:
determine a programming offset responsive to a coupling effect in a particular area of a memory array;
store the programming offset; and
use the programming offset for programming in the particular area of the memory array.
3. A method comprising:
programming a selected memory cell;
programming an adjacent memory cell, wherein the adjacent memory cell is adjacent to the selected memory cell;
determining an effect of programming the adjacent memory cell on the selected memory cell; and
storing an indication of the effect in a table.
4. The method of claim 3 , further comprising:
reading the selected memory cell after programming the selected memory cell and before programming the adjacent memory cell; and
reading the selected memory cell after programming the adjacent memory cell,
wherein the effect of programming the adjacent memory cell on the selected memory cell comprises a difference between the readings.
5. The method of claim 3 , wherein the effect comprises a change in threshold voltage of the selected memory cell.
6. The method of claim 3 , wherein programming an adjacent memory cell comprises programming a plurality of adjacent memory cells and wherein determining an effect of programming the adjacent memory cell on the selected memory cell comprises determining an effect of programming the plurality of adjacent memory cells on the selected memory cell.
7. The method of claim 6 , wherein the plurality of adjacent memory cells are programmed with a same voltage.
8. The method of claim 3 , wherein programming an adjacent memory cell comprises programming the adjacent memory cell to a voltage, the method further comprising varying the voltage of the adjacent memory cell and determining an effect of varying the voltage of the adjacent memory cell on the selected memory cell.
9. The method of claim 3 , wherein the indication of the effect stored in the table comprises an offset indicating an average threshold voltage change of the selected memory cell in response to a change in the threshold voltage of the adjacent memory cell.
10. The method of claim 3 , wherein the indication of the effect stored in the table comprises a greatest voltage change that occurred on the selected memory cell in response to programming the adjacent memory cell.
11. The method of claim 3 , further comprising:
programming another selected memory cell in a different area of a memory array than an area of the memory array including the selected memory cell;
after programming the other selected memory cell, programming another adjacent memory cell, wherein the other adjacent memory cell is adjacent to the other selected memory cell;
determining an effect of programming the other adjacent memory cell on the other selected memory cell; and
storing an indication of the effect of programming the other adjacent memory cell on the other selected memory cell in a table.
12. The method of claim 3 , wherein storing an indication of the effect in a table comprises updating the table.
13. The method of claim 3 , further comprising using the indication of the effect when programming memory cells in an area of a memory array including the selected memory cell.
14. A method comprising:
writing a write voltage to a memory cell in a particular area of a memory array;
determining a read voltage of the memory cell;
determining a difference between the write voltage and the read voltage; and
storing the difference as an offset for the particular area.
15. A method comprising:
determining an offset for an area of a memory array in which a memory cell is located;
applying the offset to a target voltage to be programmed in the memory cell; and
programming an adjusted voltage into the memory cell, wherein the adjusted voltage comprises a voltage resulting from applying the offset to the target voltage.
16. The method of claim 15 , wherein determining an offset comprises reading a stored offset for the area from a table.
17. A method for performing a write path adjustment, the method comprising:
determining a temperature of a memory device;
determining an offset associated with the determined temperature;
applying the offset to a target voltage for a memory cell of the memory device; and
programming an adjusted voltage into the memory cell, wherein the adjusted voltage comprises a voltage resulting from applying the offset to the target voltage.
18. The method of claim 17 , wherein determining an offset associated with the determined temperature comprises accessing a calibration table to determine the offset.
19. The method of claim 18 , wherein determining an offset for the determined temperature further comprises interpolating between two temperatures and associated offsets in the calibration table to determine the offset associated with the determined temperature.
20. A method for performing a read path adjustment, the method comprising:
determining a temperature of a memory device;
determining an offset associated with the determined temperature; and
applying the offset to a voltage read from a memory cell of the memory device.
21. The method of claim 20 , wherein determining an offset associated with the determined temperature comprises accessing a calibration table to determine the offset.
22. The method of claim 21 , wherein determining an offset associated with the determined temperature further comprises interpolating between two temperatures and associated offsets in the calibration table to determine the offset associated with the determined temperature.