Rate-0.96 LDPC Decoding VLSI for Soft-Decision Error Correction of NAND Flash Memory

Abstract

The reliability of data stored in high-density Flash memory devices tends to decrease rapidly because of the reduced cell size and multilevel cell technology. Soft-decision error correction algorithms that use multiple-precision sensing for reading memory can solve this problem; however, they require very complex hardware for high-throughput decoding. In this paper, we present a rate-0.96 (68254, 65536) shortened Euclidean geometry low-density parity-check code and its VLSI implementation for high-throughput NAND Flash memory systems. The design employs the normalized a posteriori probability (APP)-based algorithm, serial schedule, and conditional update, which lead to simple functional units, halved decoding iterations, and low-power consumption, respectively. A pipelined-parallel architecture is adopted for high-throughput decoding, and memory-reduction techniques are employed to minimize the chip size. The proposed decoder is implemented in 0.13-μm CMOS technology, and the chip size and energy consumption of the decoder are compared with those of a BCH (Bose-Chaudhuri-Hocquenghem) decoding circuit showing comparable error-correcting performance and throughput.