Read operation for non-volatile storage that includes compensation for coupling
View Patent ↗Shifts in the apparent charge stored on a floating gate (or other charge storing element) of a non-volatile memory cell can occur because of the coupling of an electric field based on the charge stored in adjacent floating gates (or other adjacent charge storing elements). The problem occurs most pronouncedly between sets of adjacent memory cells that have been programmed at different times. To compensate for this coupling, the read process for a given memory cell will take into account the programmed state of an adjacent memory cell.
1. A method for reading data from a first set of non-volatile storage elements, comprising:
reading a flag associated with a second set of non-volatile storage elements, said second set of non-volatile storage elements are adjacent to said first set of non-volatile storage elements, said second set of non-volatile storage elements store multiple groupings of data, said flag indicates whether said one of said groupings has been programmed;
reading said data from said first set of non-volatile storage elements without compensating for a coupling between said first set of non-volatile storage elements and said second set of non-volatile storage elements if said flag indicates that said one of said groupings has not been programmed for said second set of non-volatile storage elements; and
reading said data from said first set of non-volatile storage elements with compensation for coupling between said first set of non-volatile storage elements and said second set of non-volatile storage elements if said flag indicates that said one of said groupings has been programmed.
2. A method according to claim 1 , wherein:
said reading a flag includes reading a group of non-volatile storage elements and determining whether any of said group of non-volatile storage elements has data in a most programmed data state.
3. A method according to claim 1 , further comprising: communicating said data for said first set of non-volatile storage elements while reading additional data for additional non-volatile storage elements.
4. A method according to claim 1 , wherein:
said multiple groupings of data include a first page and a second page; and
said flag indicates whether said second page has been programmed for said second set of non-volatile storage elements.
5. A method according to claim 4 , wherein said reading said data from said first set of non-volatile storage elements with compensation comprises:
applying a first voltage to control gates for said first set of non-volatile storage elements;
sensing conduction of said first set of non-volatile storage elements;
applying said first voltage plus an offset to said control gates for said first non-volatile storage elements;
sensing conduction of said first set of non-volatile storage elements; and
storing an appropriate result of said two sensing steps.
6. A method according to claim 4 , wherein
said first set of non-volatile storage elements are capable of storing data in four data states including a first data state, a second data state, a third data state and a fourth data state; and
said reading said data from said first set of non-volatile storage elements with compensation comprises using a first reference, a first reference plus offset, a second reference, a second reference plus offset, a third reference, and a third reference plus offset.
7. A method according to claim 1 , wherein:
said first set of non-volatile storage elements include a second grouping of data programmed subsequent to writing to adjacent non-volatile storage elements for a first grouping of data.