Finding optimal read thresholds and related voltages for solid state memory

1. A system, comprising:

a storage read interface; and

a voltage calculator configured to:

obtain an expected value associated with stored values in solid state storage;

obtain a set of three or more points, wherein the three or more points include a voltage and a value associated with stored values;

select, from the set, two points having ratios closest to the expected value; and

determine a voltage based at least in part on the selected two points and the expected value.

2. The system of claim 1 , wherein the expected value includes one or more of the following: a ratio of ones to zeros, a ratio of zeros to ones, a number of ones, or a number of zeros.

3. The system of claim 1 , wherein the voltage calculator is configured to determine the voltage by: determining an intersection between a first line at the expected value and a second line which includes the selected two points.

4. The system of claim 1 , wherein:

the voltage calculator is configured to determine the voltage by: determining the voltage at an i th iteration; and

the voltage calculator is further configured to: determine, at a j th iteration, a voltage, including by:

selecting, from the set, a point having a ratio closest to the expected value; and

adjusting the voltage of the selected point, having the ratio closest to the expected value, by an offset.

5. The system of claim 4 , wherein the voltage calculator is configured to adjust by: adjusting in a direction that is expected to produce a ratio that is closer to the expected value.

6. The system of claim 4 , wherein:

in the event a last point in the set is one of the selected two points, the voltage calculator is configured to determine the voltage at the i th iteration; and

in the event the last point in the set is not one of the selected two points, the voltage calculator is configured to determine the voltage at the j th iteration.

7. A system, comprising:

a storage read interface; and

a voltage calculator configured to:

obtain a set of three or more points, wherein the three or more points include a voltage and a number of flipped bits associated with solid state memory;

determine a slope of a line formed by each pair of points in the set;

select, based at least in part on the determined slopes, a pair of points from the set which have the steepest line; and

determine a voltage based at least in part on the selected pair of points.

8. The system of claim 7 , wherein the number of flipped bits includes one or more of the following: a number of bits flipped from one to zero or a number of bits flipped from zero to one.

9. The system of claim 7 , wherein the voltage calculator is configured to obtain by:

reading, via the a storage read interface, the solid state memory at a first read threshold to obtain a first number of read-back values;

reading, via the a storage read interface, the solid state memory at a second read threshold to obtain a second number of read-back values; and

determining a first coordinate by taking a difference between the first number of read-back values and the second number of read-back values.

10. The system of claim 9 , wherein the voltage calculator is further configured to obtain by:

determining a second coordinate by taking an average of the first read threshold and the second read threshold.

11. The system of claim 9 , wherein the first number of read-back values includes one or more of the following: a number of zeros or a number of ones.

12. A system, comprising:

a storage read interface; and

a voltage calculator configured to:

obtain a voltage corresponding to an expected value associated with stored values;

obtain a voltage corresponding to a local minimum, between a first local maximum and a second local maximum, in a distribution of voltages; and

generate a voltage bounded by the voltage corresponding to the expected value and the voltage corresponding to the local minimum.

13. The system of claim 12 , wherein the value includes one or more of the following: a ratio of ones to zeros, a ratio of zeros to ones, a number of ones, or a number of zeros.

14. The system of claim 12 , wherein the voltage calculator is configured to generate by: determining an average of the voltage corresponding to the expected value and the voltage corresponding to the local minimum.

15. A method, comprising:

obtaining an expected value associated with stored values in solid state storage;

obtaining a set of three or more points, wherein the three or more points include a voltage and a value associated with stored values;

selecting, from the set, two points having ratios closest to the expected value; and

using a voltage calculator to determine a voltage based at least in part on the selected two points and the expected value.

16. The method of claim 15 , wherein the expected value includes one or more of the following: a ratio of ones to zeros, a ratio of zeros to ones, a number of ones, or a number of zeros.

17. The method of claim 15 , wherein using the voltage calculator to determine the voltage includes determining an intersection between a first line at the expected value and a second line which includes the selected two points.

18. The method of claim 15 , wherein:

using the voltage calculator to determine the voltage includes determining the voltage at an i th iteration; and

the method further includes determining, at a j th iteration, a voltage, including by:

selecting, from the set, a point having a ratio closest to the expected value; and

adjusting the voltage of the selected point, having the ratio closest to the expected value, by an offset.

19. The method of claim 18 , wherein adjusting includes adjusting in a direction that is expected to produce a ratio that is closer to the expected value.

20. The method of claim 18 , wherein:

in the event a last point in the set is one of the selected two points, the voltage at the i th iteration is determined; and

in the event the last point in the set is not one of the selected two points, the voltage at the j th iteration is determined.

21. A method, comprising:

obtaining a set of three or more points, wherein the three or more points include a voltage and a number of flipped bits associated with solid state memory;

determining a slope of a line formed by each pair of points in the set;

selecting, based at least in part on the determined slopes, a pair of points from the set which have the steepest line; and

using a voltage calculator to determine a voltage based at least in part on the selected pair of points.

22. The method of claim 21 , wherein the number of flipped bits includes one or more of the following: a number of bits flipped from one to zero or a number of bits flipped from zero to one.

23. The method of claim 21 , wherein obtaining includes:

reading, via the a storage read interface, the solid state memory at a first read threshold to obtain a first number of read-back values;

reading, via the a storage read interface, the solid state memory at a second read threshold to obtain a second number of read-back values; and

determining a first coordinate by taking a difference between the first number of read-back values and the second number of read-back values.

24. The method of claim 23 , wherein obtaining further includes determining a second coordinate by taking an average of the first read threshold and the second read threshold.

25. The method of claim 23 , wherein the first number of read-back values includes one or more of the following: a number of zeros or a number of ones.

26. A method, comprising:

obtaining a voltage corresponding to an expected value associated with stored values;

obtaining a voltage corresponding to a local minimum, between a first local maximum and a second local maximum, in a distribution of voltages; and

using a voltage calculator to generate a voltage bounded by the voltage corresponding to the expected value and the voltage corresponding to the local minimum.

27. The method of claim 26 , wherein the value includes one or more of the following: a ratio of ones to zeros, a ratio of zeros to ones, a number of ones, or a number of zeros.

28. The method of claim 26 , wherein using the voltage calculator to generate includes determining an average of the voltage corresponding to the expected value and the voltage corresponding to the local minimum.