Memory controller having state shaping engine and method of operating same
A memory controller includes a state shaping encoder that receives k-bit write data, selects a logical page with reference to state shape mapping information, and changes data of the logical page to decrease an occurrence probability of a high-order program state among program states used to program the k-bit data in multi-level memory cells.
1. A memory controller configured to control the operation of a nonvolatile memory device including memory cells, each of memory cells programmed to have one of first to fifteenth program states and an erase state, the fifteenth program state being a highest-order program state having an upper limit of threshold voltage distribution higher than that of the erase state and other program states, the memory controller comprising:
a state shaping engine configured to receive write data including first to fourth logical pages from a host, select at least one of the first to fourth logical pages based on state shaping mapping information, and perform a state shaping operation on the selected at least one logical page to generate state-shape encoded data to be programmed in the nonvolatile memory device,
wherein the fourth, fifth, eighth, ninth, and twelfth to fifteenth program states correspond to a first data value in the first logical page, the second to sixth, thirteenth, and fourteenth program states correspond to the first data value in the second logical page, the first to fourth and ninth to thirteenth program states correspond to the first data value in the third logical page, and the third to tenth program states correspond to the first data value in the fourth logical page, and
wherein the state shaping operation is performed by decreasing a number of a data value corresponding to the fifteenth program state in at least one of the first to fourth logical pages.
2. The memory controller of claim 1 , wherein
the erase state, the first to third, sixth, seventh, tenth, and eleventh program states correspond to a second data value being difference from the first data value in the first logical page,
the erase state, the first, seventh to eleventh, and fifteenth program states correspond to the second data value in the second logical page,
the erase state, the fifth to eighth, fourteenth, and fifteenth program states correspond to the second data value in the third logical page, and
the erase state, the first, second, and eleventh to fifteenth program states correspond to the second data value in the third logical page.
3. The memory controller of claim 2 , wherein the state shaping mapping information includes information on logical page to be selected such that an occurrence probability of the fifteenth program state is decreased and an occurrence probability of some of the first to fourth program states is increased by performing the state shaping operation.
4. The memory controller of claim 3 , further comprising a RAM configured to store the state shaping mapping information, and
wherein the state shaping mapping information is stored in the RAM during a manufacture of the memory controller.
5. The memory controller of claim 4 , wherein the state shaping mapping information is updated during periodic software updates for the memory controller.
6. The memory controller of claim 2 , wherein
if the first and fourth logical pages are selected as logical pages to be subjected to the state shaping operation, the state shaping engine is configured to decrease a number of the first data value in the first logical page and a number of the second data value in the fourth logical page, and
the state shaping engine is configured to increase a number of the second data value in the first logical page and a number of the first data value in the fourth logical page.
7. The memory controller of claim 6 , wherein
occurrence probabilities of the first to fourth program states are increased in the state-shape encoded data and occurrence probabilities of the twelfth to fifteenth program states are decreased in the state-shape encoded data.
8. The memory controller of claim 2 , wherein
if the first, third, and fourth logical pages are selected as logical pages to be subjected to the state shaping operation, the state shaping engine is configured to decrease a number of the first data value in the first logical page, a number of the second data value in the third logical page, and a number of the second data value in the fourth logical page, and
the state shaping engine is configured to increase a number of the second data value in the first logical page, a number of the first data value in the third logical page, and a number of the first data value in the fourth logical page.
9. The memory controller of claim 2 , wherein
if the first to fourth logical pages are selected as logical pages to be subjected to the state shaping operation, the state shaping engine is configured to decrease a number of the first data value in the first logical page, a number of the second data value in the second logical page, a number of the second data value in the third logical page, and a number of the second data value in the fourth logical page, and
the state shaping engine is configured to increase a number of the second data value in the first logical page, a number of the first data value in the second logical page, a number of the first data value in the third logical page, and a number of the first data value in the fourth logical page.
10. The memory controller of claim 9 , wherein occurrence probabilities of the second to fourth program states are increased in the state-shape encoded data, and occurrence probabilities of the eleventh to fifteenth program states are decreased in the state-shape encoded data.
11. The memory controller of claim 1 , further comprising:
an error detection/correction (ECC) engine configured to encode the state-shape encoded data from the state shaping engine using a coded modulation to generate ECC-encoded data that is programmed to the nonvolatile memory device.
12. The memory controller of claim 11 , wherein the ECC engine is configured to receive the ECC-encoded data from the nonvolatile memory device, and decode the ECC-encoded data using the coded modulation to generate the state-shape encoded data.
13. The memory controller of claim 12 , wherein the state shaping engine is configured to decode the state-shape encoded data from the ECC engine to generate the write data.