Reduction of back pattern dependency effects in memory devices

A method for operating a memory that includes multiple analog memory cells, the method comprising:

• storing data in the memory by writing first storage values to the cells, so as to cause the cells to hold respective electrical charge levels;
• after storing the data, reading second storage values from at least some of the cells, including at least one interfered cell that belongs to a group of cells;
• detecting and canceling a Back Pattern Dependency (BPD) distortion caused by the electrical charge levels of one or more interfering cells in the group to at least one of the second storage values read from the at least one interfered cell;
• and
• processing the second storage values, including the at least one of the second storage values in which the BPD distortion was canceled, so as to reconstruct the data,
• wherein the cells in the group are connected in series to one another, wherein reading the second storage value from the interfered cell comprises applying a read voltage to a gate of the interfered cell, applying pass voltages to respective gates of the other cells in the group and measuring a current flowing through the cells responsively to the applied read voltage and pass voltages, and wherein canceling the BPD distortion comprises reducing at least one of the pass voltages while not violating a predefined performance criterion, and reading the second storage value from the interfered cell using the reduced pass voltages.

A data storage apparatus, comprising:

• an interface, which is operative to communicate with a memory that includes multiple analog memory cells;
• and
• a processor, which is coupled to store data in the memory by writing first storage values to the cells so as to cause the cells to hold respective electrical charge levels, to read, after storing the data, second storage values from at least some of the cells, including at least one interfered cell that belongs to a group of cells, to detect and cancel a Back Pattern Dependency (BPD) distortion caused by the electrical charge levels of one or more interfering cells in the group to at least one of the second storage values read from the at least one interfered cell, and to process the second storage values, including the at least one of the second storage values in which the BPD distortion was canceled, so as to reconstruct the data,
• wherein the processor is coupled to recursively estimate a part of the BPD distortion in a given cell in the group based on one or more other parts of the BPD distortion in one or more cells in the group that were programmed earlier than the given cell, and on the second storage values that were read from the one or more cells, and to estimate the part of the BPD distortion by measuring a total BPD distortion that is caused by the cells in the group, and estimating the part of the BPD distortion based on the total BPD distortion.

A data storage apparatus, comprising:

• an interface, which is operative to communicate with a memory that includes multiple analog memory cells;
• and
• a processor, which is coupled to store data in the memory by writing first storage values to the cells so as to cause the cells to hold respective electrical charge levels, to read, after storing the data, second storage values from at least some of the cells, including at least one interfered cell that belongs to a group of cells, to detect and cancel a Back Pattern Dependency (BPD) distortion caused by the electrical charge levels of one or more interfering cells in the group to at least one of the second storage values read from the at least one interfered cell, and to process the second storage values, including the at least one of the second storage values in which the BPD distortion was canceled, so as to reconstruct the data,
• wherein the cells in the group are connected in series to one another, wherein the processor is coupled to read the second storage value from the interfered cell by applying a read voltage to a gate of the interfered cell, applying pass voltages to respective gates of the other cells in the group and measuring a current flowing through the cells responsively to the applied read voltage and pass voltages, and to cancel the BPD distortion by reducing at least one of the pass voltages while not violating a predefined performance criterion, and reading the second storage value from the interfered cell using the reduced pass voltages.

A data storage apparatus, comprising:

• a memory, which comprises multiple analog memory cells;
• and
• a processor, which is coupled to store data in the memory by writing first storage values to the cells so as to cause the cells to hold respective electrical charge levels, to read, after storing the data, second storage values from at least some of the cells, including at least one interfered cell that belongs to a group of cells, to detect and cancel a Back Pattern Dependency (BPD) distortion caused by the electrical charge levels of one or more interfering cells in the group to at least one of the second storage values read from the at least one interfered cell, and to process the second storage values, including the at least one of the second storage values in which the BPD distortion was canceled, so as to reconstruct the data,
• wherein the processor is coupled to recursively estimate a part of the BPD distortion in a given cell in the group based on one or more other parts of the BPD distortion in one or more cells in the group that were programmed earlier than the given cell, and on the second storage values that were read from the one or more cells, and to estimate the part of the BPD distortion by measuring a total BPD distortion that is caused by the cells in the group, and estimating the part of the BPD distortion based on the total BPD distortion.