Estimation of level-thresholds for memory cells
First Claim
1. A level-threshold determination method for q-level memory cells, the method comprising:
- reading a plurality of the memory cells to obtain respective read signal components;
processing the read signal components in dependence on signal level to produce a signal level vector, comprising a series of elements, indicative of a distribution of the read signal components in order of signal level;
scanning the signal level vector with a sliding window of length greater than a spacing of successive window positions in the scan;
at each window position, calculating a metric dependent on the elements of the signal level vector in the window and determining a reference value for the elements in the window, wherein the metric is dependent on absolute difference between each element in the window and said reference value; and
determining a level-threshold for successive memory cell levels in dependence on variation of said metric over the scan and determining said level-threshold in dependence on location of a local maximum corresponding to that threshold in a variation of the metric over the scan, wherein a scan is performed using a scanner comprising a register configured for storing an input signal level vector and scan logic configured for calculating a measurement quantity.
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Abstract
Methods and apparatus are provided for determining level-thresholds for q-level memory cells. A plurality of the memory cells are read to obtain respective read signal components. The read signal components are processed 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. The signal level vector is scanned 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 dependence on variation of the metric over the scan.
23 Citations
20 Claims
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1. A level-threshold determination method for q-level memory cells, the method comprising:
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reading a plurality of the memory cells to obtain respective read signal components; processing the read signal components in dependence on signal level to produce a signal level vector, comprising a series of elements, indicative of a distribution of the read signal components in order of signal level; scanning the signal level vector with a sliding window of length greater than a spacing of successive window positions in the scan; at each window position, calculating a metric dependent on the elements of the signal level vector in the window and determining a reference value for the elements in the window, wherein the metric is dependent on absolute difference between each element in the window and said reference value; and determining a level-threshold for successive memory cell levels in dependence on variation of said metric over the scan and determining said level-threshold in dependence on location of a local maximum corresponding to that threshold in a variation of the metric over the scan, wherein a scan is performed using a scanner comprising a register configured for storing an input signal level vector and scan logic configured for calculating a measurement quantity. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for detecting codewords each having N symbols which are stored in respective q-level memory cells, the method comprising:
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reading a plurality of the memory cells to obtain respective read signal components, the memory cells storing respective symbols of N-symbol codewords of a predefined set of valid codewords; processing the read signal components in dependence on signal level to produce a signal level vector, comprising a series of elements, indicative of a distribution of read signal components in order of signal level; scanning the signal level vector with a sliding window of length greater than a spacing of successive window positions in the scan; at each window position, calculating a metric dependent on the elements of the signal level vector in the window; detecting a codeword corresponding to each said read signal in dependence on the or each level-threshold so determined; and determining a level-threshold for successive memory cell levels in dependence on variation of said metric over the scan and determining said level-threshold in dependence on location of a local maximum corresponding to that threshold in a variation of the metric over the scan, wherein a scan is performed using a scanner comprising a register configured for storing an input signal level vector and scan logic configured for calculating a measurement quantity. - View Dependent Claims (12, 13, 14)
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15. An apparatus for level-threshold determination on readout of q-level memory cells, the apparatus comprising:
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a vector generator for receiving a plurality of read signal components, obtained by reading respective memory cells, and processing the read signal components in dependence on signal level to produce a signal level vector, comprising a series of elements, indicative of a distribution of read signal components in order of signal level; a sliding-window scanner for scanning the signal level vector with a sliding window of length greater than a spacing of successive window positions in the scan, and, at each window position, calculating a metric dependent on the elements of the signal level vector in the window and determining a reference value for the elements in the window, wherein the metric is dependent on absolute difference between each element in the window and said reference value; and a threshold identifier for determining a level-threshold for successive memory cell levels in dependence on variation of said metric over the scan, wherein a scan is performed using a scanner comprising a register configured for storing an input signal level vector and scan logic configured for calculating a measurement quantity. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification