Method and memory system using a priori probability information to read stored data
A memory system comprises a non-volatile memory device that stores user data and state information regarding the user data. In a read operation of the non-volatile memory device, a memory controller calculates a priori probabilities for the user data based on the state information, calculates a posteriori probabilities based on the a priori probabilities, and performs a soft-decision operation to determine values of the user data based on the a posteriori probabilities.
1. A method of processing data in a non-volatile memory device, comprising:
receiving data and state information regarding the data from the non-volatile memory device, wherein the data and state information are stored in a same page of the non-volatile memory device;
calculating a priori probabilities for at least one bit of the data according to the state information;
calculating a posteriori probabilities for the at least one bit of the data according to the a priori probabilities; and
determining respective values for each one of the at least one bit of data according to the a posteriori probabilities.
2. The method of claim 1 , wherein the state information is stored in a meta-data area of the page.
3. The method of claim 1 , wherein the state information indicates a number of bits among the at least one bit of data that have been programmed to each one of a plurality of logical states.
4. The method of claim 1 , further comprising:
programming the data and the state information to the same page in the non-volatile memory device.
5. The method of claim 1 , wherein the a priori probabilities are multiplied by conditional probabilities to calculate the a posteriori probabilities.
6. The method of claim 5 , wherein a first one of the conditional probabilities is a probability that a bit among the at least one bit of data is read as a first logical state, given that the bit was programmed as the first logical state, and a second one of the conditional probabilities is a probability that the bit is read as the first logical state, given that the bit was programmed as the second logical state.
7. The method of claim 6 , wherein the first and second logical states are respective logical states among the plurality of logical states.
8. The method of claim 1 , wherein receiving the data and state information from the non-volatile memory device comprises operating a memory interface of a memory controller to communicate with the non-volatile memory.
9. The method of claim 1 , wherein the non-volatile memory device is a NAND flash memory device.