Ldpc decoder, semiconductor memory system, and operating method thereof

Abstract

A semiconductor memory system includes: a semiconductor memory device to store a codeword; and a low-density parity check (LDPC) decoder to decode the codeword, based on a parity check matrix, to generate a decoded codeword, wherein the LDPC decoder includes: a selector to select one or more sub-matrices that share the same layer index of the parity check matrix, and select variable nodes corresponding to columns included in the selected one or more sub-matrices based on a threshold value and a number of unsatisfied check nodes (UCNs) connected to the selected variable nodes; a variable node updater to update decision values of variable nodes corresponding to all columns included in the parity check matrix; a syndrome checker to determine whether decoding the codeword has been performed successfully or not; and a check node updater to update a backup syndrome, the threshold value, and a size of a processing unit.