Method for storing information in a coded manner in non-volatile memory cells, decoding method and non-volatile memory
The present disclosure is directed to a method for storing information in a coded manner in non-volatile memory cells. The method includes providing a group of non-volatile memory cells of non volatile memory. The memory cell is of the type in which a stored logic state, which can be logic high or logic low, can be changed through application of a current to the cell and the state in the memory cell is read by reading a current provided by the cell. The group of non-volatile memory cells include a determined number of non-volatile memory cells which is greater than two. The group of non-volatile memory cells store a codeword formed by the values of said stored states of the cells of the group taken according to a given order. Given a set of codewords obtainable by the stored values in the determined number of non-volatile memory cells in a group, the method includes storing the information in at least two subsets of said set of codewords comprising each at least a codeword. Each codeword in a same subset has a same Hamming weight. Each codeword belonging to one subset has a Hamming distance equal or greater than two with respect to each codeword belonging to another subset.
1. A method, comprising:
providing a group of non-volatile memory cells of non-volatile memory,
stored logic states in the group of non-volatile memory cells configured to change through application of currents to the group of non-volatile memory cells, and configured to be read by reading currents provided by the group of non-volatile memory cells,
the group of non-volatile memory cells including a determined number of non-volatile memory cells that is greater than two,
the group of non-volatile memory cells configured to store codewords formed by values of the stored logic states of memory cells of the group of non-volatile memory cells taken according to a given order; and
storing information in at least two subsets of a set of codewords,
the set of codewords obtainable by the values of the stored logic states, each codeword in a same subset having a same Hamming weight,
each codeword belonging to a first subset of the at least two subsets having a Hamming distance equal or greater than two with respect to each codeword belonging to a second subset of the at least two subsets,
each codeword belonging to the first subset having a number of ones and a number of zeroes equal to the number of ones.
2. The method of claim 1 , wherein the determined number of non-volatile memory cells is an even number.
3. The method of claim 1 , wherein the determined number of non-volatile memory cells is four.
4. The method of claim 1 , wherein the at least two subsets include a subset with a codeword having all zero values, and a subset with a codeword having all one values.
5. The method of claim 1 , wherein the at least two subsets include a subset with codewords having the same first Hamming weight, and a subset with codewords having the same second Hamming weight that is different from the first Hamming weight by a value of two.
6. The method of claim 1 , further comprising:
reading the values of the stored logic states;
performing a comparison operation on the read values of the stored logic states;
obtaining a corresponding codeword by processing results of the comparison operation; and
decoding the corresponding codeword to supply a corresponding decoded symbol.
7. The method of claim 1 , wherein the reading of the values includes reading currents of the memory cells of the group of non-volatile memory cells.
8. The method of claim 6 , wherein the performing of the comparison operation includes comparing each read value from a memory cell in the group once with each other read value from remaining memory cells in the group.
9. The method of claim 4 , wherein the first subset is between the subset with the codeword having all zero values and the subset with the codeword having all one values in a bitmap.
10. A method, comprising:
reading values of stored logic states in memory cells of a group of non-volatile memory cells,
the stored logic states configured to change through application of currents to the group of non-volatile memory cells, and configured to be read by reading currents provided by the group of non-volatile memory cells,
the group of non-volatile memory cells including a determined number of non-volatile memory cells that is greater than two,
the group of non-volatile memory cells storing a codeword formed by the values of the stored logic states taken according to a given order,
information being stored in at least two subsets of a set of codewords,
the set of codewords obtainable by the values of the stored logic states, each codeword in a same subset having a same Hamming weight,
each codeword belonging to a subset of the at least two subsets having a Hamming distance equal or greater than two with respect to each codeword belonging to another subset of the at least two subsets;
performing a comparison operation on the read values of the stored logic states, the performing of the comparison operation including:
comparing each read value from a memory cell in the group once with each other read value from remaining memory cells in the group to obtain pairwise comparison results;
summing the read values of the stored logic states to obtain a sum value; and
comparing the sum value to one or more thresholds to obtain a value indicating a subset to which the read values belong;
obtaining a corresponding codeword by processing results of comparison operation, the processing of the results of the comparison operation including:
processing the pairwise comparison results separately for each subset including more than one codeword to obtain corresponding codewords; and
selecting among the corresponding codewords and codewords of subsets including one codeword based on the value indicating the subset to which the read values belong; and
decoding the corresponding codeword to supply a corresponding decoded symbol.
11. The method of claim 10 , wherein the reading of the values includes reading currents of the memory cells of the group of non-volatile memory cells.
12. The method of claim 10 , further comprising:
computing the one or more thresholds based on Probability Density Function curves or Cumulative Distribution Function curves of a sum of values of memory cells arranged in manner corresponding to each of the at least two subsets.
13. The method of claim 12 , further comprising:
selecting one or more intersections of the Probability Density Function curves as the one or more thresholds.
14. The method of claim 12 , further comprising:
computing the one or more thresholds numerically by minimizing an error probability between states associated to the one or more thresholds.
15. The method of claim 10 , wherein the determined number of non-volatile memory cells is an even number.
16. A memory, comprising:
a group of non-volatile memory cells,
stored logic states in the group of non-volatile memory cells configured to change through application of currents to the group of non-volatile memory cells, and configured to be read by reading currents provided by the group of non-volatile memory cells,
the group of non-volatile memory cells including a determined number of non-volatile memory cells that is greater than two,
the group of non-volatile memory cells configured to store codewords formed by values of the stored logic states of memory cells of the group of non-volatile memory cells taken according to a given order; and
an encoder configured to store information in at least two subsets of a set of codewords,
the set of codewords obtainable by the values of the stored logic states, each codeword in a same subset having a same Hamming weight,
each codeword belonging to a first subset of the at least two subsets having a Hamming distance equal or greater than two with respect to each codeword belonging to a second subset of the at least two subsets,
each codeword belonging to the first subset having a number of ones and a number of zeroes equal to the number of ones.
17. The memory of claim 16 , wherein the determined number of non-volatile memory cells is an even number.
18. The memory of claim 16 , wherein the at least two subsets include a first subset with a codeword having all zero values, and a subset with a codeword having all one values.
19. The memory of claim 16 , wherein the at least two subsets include a subset with codewords having the same first Hamming weight, and a subset with codewords having the same second Hamming weight that is different from the first Hamming weight by a value of two.
20. The memory of claim 16 , further comprising:
a decoder configured to read the values of the stored logic states, perform a comparison operation on the read values of the stored logic states, obtain a corresponding codeword by processing results of the comparison operation, and decode the corresponding codeword to supply a corresponding decoded symbol.