Tracking of optimum read voltage thresholds in nand flash devices
First Claim
1. A method for biasing read voltage for flash memory in a storage system, performed by the storage system, comprising:
- tracking bit flips in a first direction and bit flips in a second direction in data reads of the flash memory in the storage system, based on error correction of the data reads, wherein each bit flip comprises a data read of a bit read in error in a specified direction;
comparing or forming a ratio of the bit flips in the first direction to the bit flips in the second direction or the bit flips in one of the first direction or the second direction to a total number of bit flips; and
adjusting read voltage level for the flash memory in the storage system, based on the comparing or the forming the ratio.
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Abstract
A method for biasing read voltage for flash memory in a storage system, performed by the storage system, is provided. The method includes tracking bit flips in a first direction and bit flips in a second direction in data reads of the flash memory in the storage system, based on error correction of the data reads. The method includes comparing or forming a ratio of the bit flips in the first direction to the bit flips in the second direction or the bit flips in one of the first direction or the second direction to a total number of bit flips. The method includes adjusting read voltage level for the flash memory in the storage system, based on the comparing or the forming the ratio.
264 Citations
20 Claims
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1. A method for biasing read voltage for flash memory in a storage system, performed by the storage system, comprising:
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tracking bit flips in a first direction and bit flips in a second direction in data reads of the flash memory in the storage system, based on error correction of the data reads, wherein each bit flip comprises a data read of a bit read in error in a specified direction; comparing or forming a ratio of the bit flips in the first direction to the bit flips in the second direction or the bit flips in one of the first direction or the second direction to a total number of bit flips; and adjusting read voltage level for the flash memory in the storage system, based on the comparing or the forming the ratio. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A tangible, non-transitory, computer-readable media having instructions thereupon which, when executed by a processor, cause the processor to perform a method comprising:
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determining a quantity of bit flips from a logical 0 to a logical 1 or a quantity of bit flips from a logical 1 to a logical 0 in data reads of the flash memory in the storage system, based on error correction of the data reads, wherein each bit flip comprises a data read of a bit read in error in a specified direction; forming a comparison or a ratio of the quantity of the bit flips from the logical 0 to the logical 1 or the quantity of the bit flips from the logical 1 to the logical 0 to each other or to a total number of bit flips; and setting read voltage level for the flash memory in the storage system, based on the comparison or the ratio. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A storage system, comprising:
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flash memory having adjustable read voltage level; and one or more processors, configurable to; perform error correction of data reads of the flash memory; track bit flips in the data reads, based on the error correction, wherein each bit flip comprises a data read of a bit read in error in a specified direction; form a comparison or a ratio of a quantity of bit flips in a first direction or a quantity of bit flips in a second direction to each other or to a total number of bit flips; and direct a read voltage level for the flash memory, based on the comparison or the ratio. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification