Methods, circuits and systems for reading non-volatile memory cells
The present invention includes methods, circuits and systems for reading non-volatile memory (“NVM”) cells, including multi-level NVM cells. According to some embodiments of the present invention, there may be provided a NVM cell threshold voltage detection circuit adapted to detect an approximate threshold voltage associated with a charge storage region of a NVM cell, where the NVM cell may be a single or a multi-charge storage region cell. A decoder circuit may be adapted to decode and/or indicate the logical state of a NVM cell charge storage region by mapping or converting a detected approximate threshold voltage of the charge storage region into a logical state value.
1. A non-volatile memory (“NVM”) cell charge storage region reading circuit comprising:
a threshold voltage detection circuit to determine an approximate threshold voltage of a first NVM cell charge storage region to be decoded; and
a multifactor function of a decoder circuit to determine, when said approximate threshold voltage is within an overlapping logical state threshold voltage distribution, the logical state of said first charge storage region from the threshold voltage of a second charge storage region adjacent to said first charge storage region.
2. A non-volatile memory (“NVM”) cell charge storage region reading circuit comprising:
a threshold voltage detection circuit to determine an approximate threshold voltage of a first NVM cell charge storage region to be decoded; and
a multifactor function of a decoder circuit to use, when said approximate threshold voltage is within an overlapping logical state threshold voltage distribution, an approximate threshold voltage of an adjacent charge storage region as a differentiator to determine the logical state of said first storage region.
3. The circuit according to claim 1 and wherein said decoder circuit comprises a charge decoder to decode the threshold voltage of said first charge storage region as a lower logical value if the approximate threshold voltage of said second charge storage region is above a defined value and as a higher logical value if the approximate threshold voltage of said second charge storage region is below a defined value.
4. The reading circuit according to either claim 1 or 2 , further comprising a buffer adapted to store values correlated with approximate threshold voltage values associated with substantially each of a set of charge storage regions.
5. The reading circuit according to claim 4 , wherein said threshold voltage detection circuit is adapted to use approximate threshold voltage values stored in said buffer when determining a logical state of a given charge storage region.
6. The reading circuit according to claim 1 or 2 , wherein the first and second charge storage regions reside on a common NVM cell.
7. The reading circuit according to claim 1 or 2 , wherein the first and second charge storage regions reside on adjacent NVM cells.
8. The reading circuit according to claim 1 or 2 , wherein said threshold voltage detection circuit is adapted to determine whether the approximate threshold voltage value of the first charge storage region is associated with a first lower logical state or with a second adjacent higher logical state based on the approximate threshold voltage value of the second charge storage region.
9. The reading circuit according to claim 1 or 2 , wherein said threshold voltage detection circuit is adapted to associate the approximate threshold voltage value of the first charge storage region with the first lower logical state when the approximate threshold voltage value of the second charge storage region is above a defined value.
10. The reading circuit according to claim 1 or 2 , wherein said threshold voltage detection circuit is adapted to associate the approximate threshold voltage value of the first charge storage region with the second higher logical state when the approximate threshold voltage value of the second charge storage region is below a defined value.