Bad column handling in flash memory
First Claim
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1. A method of operating a memory array that includes at least one bad column, comprising:
- determining location information for the at least one bad column;
compressing the location information;
providing the compressed location information to a soft-input ECC decoder as a first soft data indicating low likelihood for hard data obtained from the at least one bad column; and
decoding hard data in combination with the soft data indicating low likelihood for the hard data obtained from the at least one bad column.
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Abstract
In a flash memory, redundant columns are used alternatively as replacement columns for replacing bad columns or to provide additional redundancy for ECC encoding. Locations of bad columns are indicated to a soft-input ECC decoder so that data bits from bad columns are treated as having a lower reliability than data bits from other columns.
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Citations
15 Claims
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1. A method of operating a memory array that includes at least one bad column, comprising:
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determining location information for the at least one bad column; compressing the location information; providing the compressed location information to a soft-input ECC decoder as a first soft data indicating low likelihood for hard data obtained from the at least one bad column; and decoding hard data in combination with the soft data indicating low likelihood for the hard data obtained from the at least one bad column. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of operating a memory array comprising:
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identifying a number of columns of the memory array as bad columns; ranking the identified bad columns; replacing high-ranked bad columns with redundant columns; recording low-ranked bad columns in a record; subsequently, storing data in the memory array including in the low-ranked bad columns; subsequently, reading the data from the memory array including from the low-ranked bad columns; identifying data from the low-ranked bad columns from the record; and performing soft-input Error Correction Code (ECC) decoding of the data, where data from the low-ranked bad columns is treated as having low likelihood in response to identifying the data as coming from the low-ranked bad columns. - View Dependent Claims (12, 13, 14, 15)
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Specification