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 for memory self-calibration, the method comprising:
programming a voltage on a selected memory cell of a memory array;
programming a voltage on a memory cell adjacent to the selected memory cell; and
determining an effect on the selected memory cell in response to programming the voltage on the memory cells adjacent to the selected memory cell by:
reading the selected memory cell to determine a voltage stored on the selected memory cell;
determining a difference between the voltage programmed on the selected memory cell and the voltage read from the selected memory cell; and
generating an offset voltage determined by the effect.
2. The method of claim 1 wherein the self-calibration is performed at power-up of a memory device that includes the memory array.
3. The method of claim 1 and further including storing an indication of the effect.
4. The method of claim 1 and further comprising:
programming a voltage to another memory cell that is adjacent to the selected memory cell;
determining an effect on the selected memory cell in response to programming the voltage on the memory cell adjacent to the selected memory cell; and
averaging the effects to determine another offset voltage.
5. The method of claim 1 and further comprising:
generating a programming offset for different areas of the memory array; and
storing the programming offsets in a table in the memory array.
6. The method of claim 5 wherein the self-calibration updates the table, comprising a plurality of offset voltages, at power-up.
7. A method for removing systemic offsets in a memory device, the method comprising:
determining an offset voltage in response to systemic influences in the memory device;
reading a voltage representative of a bit pattern from a memory cell;
adjusting the voltage with the offset voltage to generate an adjusted voltage; and
determining the bit pattern in response to the adjusted voltage.
8. The method of claim 7 wherein the systemic influences comprise temperature induced systemic influences.
9. The method of claim 8 and further including performing a read path adjustment of the memory device by:
determining a temperature of the memory device;
determining a voltage offset associated with the temperature;
adjusting the voltage read from the memory cell in response to the voltage offset; and
an analog-to-digital conversion process using the adjusted voltage to determine the bit pattern.
10. The method of claim 9 wherein adjusting the voltage read from the memory cell comprises one of either adding or subtracting the voltage offset from the voltage read from the memory cell.
11. The method of claim 9 wherein determining the voltage offset comprises one of reading the voltage offset from a table with the associated temperature or interpolating between two temperatures and associated voltage offsets in the table.
12. A memory system comprising:
an array of memory cells; and
control circuitry for the array of memory cells wherein the control circuitry is configured to program a first voltage on a selected memory cell, program a voltage on at least one memory cell adjacent to the selected memory cell, and determine an average offset voltage of the selected cell in response to the programming of the at least one memory cell adjacent to the selected memory cell.
13. The memory device of claim 12 wherein the control circuitry is further configured to generate an offset table in the memory array that stores an average offset voltage for each of a plurality of areas of the memory array.
14. The memory device of claim 13 wherein the control circuitry is further configured to receive a bit pattern to be programmed into an addressed memory cell, submit the bit pattern to a read/write channel for conversion to a representative voltage, adjust the representative voltage to an adjusted voltage in response to the offset table, and program the adjusted voltage into the addressed memory cell.
15. The memory system of claim 14 wherein the read/write channel is configured to perform both analog-to-digital conversion and digital-to-analog conversion.
16. The memory system of claim 12 wherein the average offset is applied to voltages to be programmed to particular areas of the memory array.
17. The memory system of claim 16 wherein the particular of areas of the memory array comprise one of: each memory block, corners of the memory array, periodic intervals of memory cells, or a center of the memory array.
18. The memory system of claim 12 wherein the array of memory cells is coupled to the control circuitry over a read/write channel.
19. The memory system of claim 18 wherein the read/write channel is configured to couple a plurality of arrays of memory cells to the control circuitry.
20. The memory system of claim 12 wherein the array of memory cells are configured to be programmed to a multiple bit state.