| 摘要 |
<p>Methods (figure 4) and apparatus 6 for determining level thresholds for q-level memory cells, or multi level cells (MLC). A plurality of the memory cells are read to obtain respective read signal components (20, figure 4). The read signal components are processed by means of a vector generator 10 in dependence on signal level to produce a signal level vector, comprising a series of elements, indicative of the distribution of read signal components in order of signal level. Signal level binning of the read signal components may also be carried out. The signal level vector is scanned 11 with a sliding window of length greater than the spacing of successive window positions in the scan. At each window position, a metric Mi is calculated in dependence on the elements of the signal level vector in the window. A level-threshold for successive memory cell levels is then determined in a threshold identifier 12, in dependence on the variation of the metric, over the scan. At each window position a reference may be determined based on the average or mean of the elements. The metric may then be calculated from the difference between each element value and the reference value (24 figure 4). The system may comprise phase change memory cells or flash memory cells. The level thresholds are determined from the largest local maxima in the metric variation over the scan (figure 5). The memory cells may be encoded so as to store qary symbols of N-symbol codewords.</p> |
