System optimization in flash memories
Methods of determining distributions may include performing a number of hard reads, performing a number of background reads at a frequency based on the number of hard reads, and estimating a conditional probability density of a cell voltage based on the hard reads and the background reads.
1. A method of determining distributions, comprising:
performing a number of hard reads;
performing a number of background reads at a frequency based on the number of hard reads; and
estimating a conditional probability density of a cell voltage based on the hard reads and the background reads.
2. The method of claim 1 , wherein the estimating step includes estimating the conditional probability density with a true data of 1 and estimating the conditional probability density with a true data of 0.
3. The method of claim 2 , further comprising estimating an optimal hard read threshold.
4. The method of claim 3 , wherein the optimal hard read threshold is estimated as a cross-point between the conditional probability density with a true data of 1 and the conditional probability density with a true data of 0.
5. The method of claim 3 , wherein the estimating the optimal hard read threshold is performed as a background operation.
6. The method of claim 2 , further comprising calculating a least-likelihood ratio (LLR).
7. The method of claim 6 , wherein the LLR is calculated as the logarithm of a ratio of the conditional probability density with a true data of 1 to the conditional probability density with a true data of 0.
8. The method of claim 6 , wherein the calculating the LLR is performed as a background operation.
9. A system for determining distributions, comprising:
a controller suitable for:
performing a number of hard reads;
performing a number of background reads at a frequency based on the number of hard reads; and
estimating a conditional probability density of a cell voltage based on the hard reads and the background reads.
10. The system of claim 9 , wherein the estimating includes estimating the conditional probability density with a true data of 1 and estimating the conditional probability density with a true data of 0.
11. The system of claim 10 , wherein the controller is further suitable for estimating an optimal hard read threshold.
12. The system of claim 11 , wherein the optimal hard read threshold is estimated as a cross-point between the conditional probability density with a true data of 1 and the conditional probability density with a true data of 0.
13. The system of claim 11 , wherein the controller is configured to estimate the optimal hard read threshold as a background operation.
14. The system of claim 9 , wherein the controller is further suitable for calculating a least-likelihood ratio (LLR).
15. The system of claim 14 , wherein the LLR is calculated as the logarithm of a ratio of the conditional probability density with a true data of 1 to the conditional probability density with a true data of 0.
16. The system of claim 14 , wherein the controller is configured to calculate the LLR as a background operation.