Compensation for voltage drifts in analog memory cells
First Claim
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1. A method for data storage, comprising:
- storing data in a group of analog memory cells of a memory by writing into the memory cells respective first storage values that are above a minimum readable value that can be sensed by the memory;
after storing the data, reading respective second storage values from the memory cells;
identifying a subset of the memory cells in which the respective second storage values have drifted from the respective first storage values that were above the minimum readable value and have decreased to below the minimum readable value;
operating on the memory cells in the identified subset so as to cause the second storage values of at least one of the memory cells in the subset to again exceed the minimum readable value; and
re-reading at least the modified second storage values so as to reconstruct the stored data.
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Abstract
A method for data storage includes storing data in a group of analog memory cells by writing respective first storage values into the memory cells. After storing the data, respective second storage values are read from the memory cells. A subset of the memory cells, in which the respective second storage values have drifted below a minimum readable value, is identified. The memory cells in the subset are operated on, so as to cause the second storage values of at least one of the memory cells in the subset to exceed the minimum readable value. At least the modified second storage values are re-read so as to reconstruct the stored data.
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Citations
28 Claims
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1. A method for data storage, comprising:
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storing data in a group of analog memory cells of a memory by writing into the memory cells respective first storage values that are above a minimum readable value that can be sensed by the memory; after storing the data, reading respective second storage values from the memory cells; identifying a subset of the memory cells in which the respective second storage values have drifted from the respective first storage values that were above the minimum readable value and have decreased to below the minimum readable value; operating on the memory cells in the identified subset so as to cause the second storage values of at least one of the memory cells in the subset to again exceed the minimum readable value; and re-reading at least the modified second storage values so as to reconstruct the stored data. - View Dependent Claims (2, 3, 5, 6, 7, 8, 9, 10, 11, 27)
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4. A method for data storage, comprising:
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storing data in a group of analog memory cells by writing respective first storage values into the memory cells; after storing the data, reading respective second storage values from the memory cells; identifying a subset of the memory cells in which the respective second storage values have drifted below a minimum readable value; operating on the memory cells in the subset so as to cause the second storage values of at least one of the memory cells in the subset to exceed the minimum readable value; and re-reading at least the modified second storage values so as to reconstruct the stored data, wherein operating on the memory cells in the subset comprises re-reading multiple instances of the second storage values from the memory cells in the subset, selecting one or more of the memory cells in the subset in which at least one of the re-read instances of the second storage values was raised above the minimum readable value due to reading noise, and associating the selected memory cells with a programming level corresponding to the first storage values that are directly above the minimum readable value.
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12. A method for data storage, comprising:
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storing data in a group of analog memory cells by writing respective first storage values into the memory cells; after storing the data, reading respective second storage values from the memory cells; identifying a subset of the memory cells in which the respective second storage values have drifted below a minimum readable value; writing third storage values into one or more of the memory cells that neighbor the memory cells in the subset, wherein the third storage values are selected so as to cause the second storage values of at least one of the memory cells in the subset to exceed the minimum readable value; and re-reading at least the modified second storage values so as to reconstruct the stored data.
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13. Apparatus for data storage, comprising:
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an interface, which is operative to communicate with a memory that includes a plurality of analog memory cells; and a processor, which is coupled to store data in a group of the analog memory cells by writing into the memory cells respective first storage values that are above a minimum readable value that can be sensed by the memory, to read respective second storage values from the memory cells after storing the data, to identify a subset of the memory cells in which the respective second storage values have drifted from the respective first storage values that were above the minimum readable value and have decreased to below a the minimum readable value, to operate on the memory cells in the identified subset so as to cause the second storage values of at least one of the memory cells in the subset to again exceed the minimum readable value, and to re-read at least the modified second storage values so as to reconstruct the stored data. - View Dependent Claims (14, 15, 17, 18, 19, 20, 21, 22, 23, 28)
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16. Apparatus for data storage, comprising:
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an interface, which is operative to communicate with a memory that includes a plurality of analog memory cells; and a processor, which is coupled to store data in a group of the analog memory cells by writing respective first storage values into the memory cells, to read respective second storage values from the memory cells after storing the data, to identify a subset of the memory cells in which the respective second storage values have drifted below a minimum readable value, to operate on the memory cells in the subset so as to cause the second storage values of at least one of the memory cells in the subset to exceed the minimum readable value, and to re-read at least the modified second storage values so as to reconstruct the stored data, wherein the processor is coupled to re-read multiple instances of the second storage values from the memory cells in the subset, to select one or more of the memory cells in the subset in which at least one of the re-read instances of the second storage values was raised above the minimum readable value due to reading noise, and to associate the selected memory cells with a programming level corresponding to the first storage values that are directly above the minimum readable value.
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24. Apparatus for data storage, comprising:
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an interface, which is operative to communicate with a memory that includes a plurality of analog memory cells; and a processor, which is coupled to store data in a group of the analog memory cells by writing respective first storage values into the memory cells, to read respective second storage values from the memory cells after storing the data, to identify a subset of the memory cells in which the respective second storage values have drifted below a minimum readable value, to write third storage values into one or more of the memory cells that neighbor the memory cells in the subset, wherein the third storage values are selected so as to cause the second storage values of at least one of the memory cells in the subset to exceed the minimum readable value, and to re-read at least the modified second storage values so as to reconstruct the stored data.
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25. Apparatus for data storage, comprising:
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a memory, which comprises a plurality of analog memory cells; and a processor, which is coupled to store data in a group of the analog memory cells by writing into the memory cells respective first storage values that are above a minimum readable value that can be sensed by the memory, to read respective second storage values from the memory cells after storing the data, to identify a subset of the memory cells in which the respective second storage values have drifted from the respective first storage values that were above the minimum readable value and have decreased to below the minimum readable value, to operate on the memory cells in the identified subset so as to cause the second storage values of at least one of the memory cells in the subset to again exceed the minimum readable value, and to re-read at least the modified second storage values so as to reconstruct the stored data.
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26. Apparatus for data storage, comprising:
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a memory, which comprises a plurality of analog memory cells; and a processor, which is coupled to store data in a group of the analog memory cells by writing respective first storage values into the memory cells, to read respective second storage values from the memory cells after storing the data, to identify a subset of the memory cells in which the respective second storage values have drifted below a minimum readable value, to write third storage values into one or more of the memory cells that neighbor the memory cells in the subset, wherein the third storage values are selected so as to cause the second storage values of at least one of the memory cells in the subset to exceed the minimum readable value, and to re-read at least the modified second storage values so as to reconstruct the stored data.
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Specification