1. Technical Field
The inventive concept relates generally to nonvolatile memory devices and, more particularly, to methods of reading data from nonvolatile memory devices, the nonvolatile memory devices, and methods of operating memory systems.
2. Description of the Related Art
The individual memory cells in a nonvolatile memory device, such as a flash memory device, can store data in accordance with a plurality of threshold voltage distributions, where each respective threshold voltage distribution is assigned to a corresponding logic state for stored data. The data stored by a memory cell may be read by determining whether the memory cell is turned ON/OFF when a predetermined read voltage is applied.
During (and/or following) the programming of a memory cell, its intended threshold voltage distribution may be undesirably shifted or broadened due to a number of events or conditions including (e.g., charge leakage, program disturbances, word and/or bit line coupling, temperature change, voltage change, etc. Once the threshold voltage distribution of a memory cell has been thus altered, it may become difficult to accurately read the logic state of the stored data. In some instances, the logic state can become indiscernible and a read fail may occur. Once a read fail occurs, conventional nonvolatile memory devices may perform a so-called “read retry” operation.
In general during the read retry, a nonvolatile memory device may iteratively perform a read operation. During each successive iteration of the read operation, the level of the applied read voltage may be sequentially increased or decreased until the read operation does not result in a read fail. However, the use of repeated read operations during a read retry operation may invariably extend the time required to successfully read data from the nonvolatile memory device.