US Patent 8661294 Nonvolatile memory device and related program verification circuit

A program verification circuit comprises a failed state counting unit and a failed bit counting unit. The failed state counting unit counts failed program states among a plurality of program states, and generates a first program mode signal indicating whether counting of failed bits is required. The failed bit counting unit selectively counts failed bits in response to the first program mode signal, and generates a second program mode signal indicating whether a program operation is completed.