MEMORY SYSTEM AND CONTROL METHOD FOR THE SAME
First Claim
1. A memory system comprising:
- a storage apparatus including a plurality of semiconductor memory cells, each cell being configured to store N-bit coded data based on 2N (N is a natural number not smaller than
2) threshold voltage distributions;
a storage section configured to store a first LLR table that consists of normal LLR data corresponding to predetermined threshold voltages and a second LLR table that consists of LLR data such that absolute values of two LLRs at each location corresponding to each location in the first LLR table at which a sign is inverted between two adjacent LLRs are different from absolute values of the respective LLRs in the first LLR table; and
a decoder configured to, when performing decoding processing through probability-based repeated calculations using an LLR calculated from the first or second LLR table and the threshold voltage,perform the decoding processing using the LLR calculated from the second LLR table and the threshold voltage if the decoding processing using the LLR calculated from the first LLR table and the threshold voltage results in an error.
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Abstract
A memory system in an embodiment having a host and a memory card, including: a plurality of semiconductor memory cells, each cell being configured to store N-bit coded data based on threshold voltage distributions; an LLR table storage section configured to store a first LLR table that consists of normal LLR data corresponding to predetermined threshold voltages and a second LLR table that consists of LLR data such that two LLRs at each location corresponding to each location in the first LLR table at which a sign is inverted between two adjacent LLRs are “0”; and a decoder configured to perform decoding processing through probability-based repeated calculations using an LLR.
144 Citations
19 Claims
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1. A memory system comprising:
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a storage apparatus including a plurality of semiconductor memory cells, each cell being configured to store N-bit coded data based on 2N (N is a natural number not smaller than
2) threshold voltage distributions;a storage section configured to store a first LLR table that consists of normal LLR data corresponding to predetermined threshold voltages and a second LLR table that consists of LLR data such that absolute values of two LLRs at each location corresponding to each location in the first LLR table at which a sign is inverted between two adjacent LLRs are different from absolute values of the respective LLRs in the first LLR table; and a decoder configured to, when performing decoding processing through probability-based repeated calculations using an LLR calculated from the first or second LLR table and the threshold voltage, perform the decoding processing using the LLR calculated from the second LLR table and the threshold voltage if the decoding processing using the LLR calculated from the first LLR table and the threshold voltage results in an error. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A control method for a memory system, comprising:
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detecting threshold voltages of semiconductor memory cells, each cell storing N-bit coded data based on 2N (N is a natural number not smaller than
2) threshold voltage distributions;calculating a first LLR from a first LLR table that consists of normal LLR data corresponding to predetermined threshold voltages and from the detected threshold voltages; performing first LDPC decoding in which decoding processing is performed based on the first LLR; calculating, if the first LDPC decoding fails, a second LLR from a second LLR table that consists of LLR data such that absolute values of two LLRs at each location corresponding to each location in the first LLR table at which a sign is inverted between two adjacent LLRs are smaller than absolute values of the respective LLRs in the first LLR table and from the detected threshold voltage; and performing second LDPC decoding in which decoding processing is performed based on the second LLR. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A memory system comprising:
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a storage apparatus including a plurality of NAND-type semiconductor memory cells, each cell being configured to store N-bit coded data based on 2N (N is a natural number not smaller than 2 but not greater than
7) threshold voltage distributions;an LLR table storage section configured to store a first LLR table that consists of normal LLR data corresponding to average threshold voltage distributions for many semiconductor memory cells and a second LLR table in which values of two LLRs at each location corresponding to each location in the first LLR table at which a sign is inverted between two adjacent LLRs are both “
0”
; anda decoder configured to, when performing LDPC decoding processing through probability-based repeated calculations using an LLR calculated from the first or second LLR table and the threshold voltage, perform the decoding processing using the LLR calculated from the second LLR table adapted for a shift of the threshold voltage distributions and from the threshold voltage if the decoding processing using the LLR calculated from the first LLR table and the threshold voltage results in an error.
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Specification