Soft Information for LDPC Decoding in Flash: Mutual-Information Optimized Quantization
High-capacity NAND flash memory can achieve high density storage by using Multi-Level Cells (MLC) to store more than one bit per cell. Although this larger storage capacity is certainly beneficial, the increased density also increases the raw Bit Error Rate (BER), making powerful error correction coding necessary. Traditional flash memories employ simple algebraic codes, such as BCH codes, that can correct a fixed, specified number of errors. This paper investigates the application of Low-Density Parity-Check (LDPC) codes which are well known for their ability to approach capacity in the AWGN channel. The authors obtain soft information for the LDPC decoder by performing multiple cell reads with distinct word-line voltages.