Non-volatile storage system with read calibration
AssigneeWestern Digital Technologies, Inc.
InventorsDavid Avraham, Eran Sharon, Ran Zamir, Alexander Bazarsky
Life of this patent
Estimating the term…
Abstract
Read reference levels are used to distinguish different data states for information stored in non-volatile memory. A storage system recalibrates its read reference levels, to maintain accuracy of the read process, by sensing samples of data for different test read reference levels and using those samples to determine an improved set of read reference levels. At least a subset of the test read reference levels used for the samples are dynamically and adaptively chosen based on indications of error for previous samples.
Claims20
An apparatus, comprising:
- a plurality of non-volatile memory cells;
- and
- one or more control circuits connected to the memory cells, the one or more control circuits configured to read data from the memory cells using a read reference level, the one or more control circuits configured to update the read reference level by:
- performing initial sensing of the memory cells using a predetermined test read reference level,
- calculating indications of error for the initial sensing,
- dynamically choosing additional test read reference levels based on the indications of error for the initial sensing,
- performing additional sensing of the memory cells using the dynamically chosen additional test read reference levels,
- calculating indications of error for the additional sensing, and
- choosing an updated read reference level based on the indications of error for the initial sensing and the indications of error for the additional sensing.
An apparatus, comprising:
- a plurality of non-volatile memory cells;
- and
- one or more control circuits connected to the memory cells, the one or more control circuits configured to perform initial sensing of the memory cells using test read reference levels and calculate indications of error for the initial sensing, the one or more control circuits configured to choose additional test read reference levels based on the indications of error for the initial sensing and perform additional sensing of the memory cells using the additional test read reference levels, the one or more control circuits configured to determine updated read reference levels based on the initial sensing and the additional sensing;
- the one or more control circuits configured to choose the additional read reference levels based on the indications of error for the initial sensing by comparing an indication of error for a sample with a lowest test read reference level to an indication of error for a sample with a highest test read reference level, choosing a new test read reference level that is lower than the lowest test read reference level if the indication of error for the sample with the lowest test read reference level is lower than the indication of error for the sample with the highest test read reference level and choosing a new test read reference level that is higher than the highest test read reference level if the indication of error for the sample with the highest test read reference level is lower than the indication of error for the sample with the lowest test read reference level.
A method for determining updated read reference levels, comprising:
- sensing initial samples for non-volatile memory cells using initial sets of read reference levels;
- determining syndrome weights for the initial samples;
- choosing additional sets of read reference levels based on syndrome weights determined for previous samples and sensing additional samples using the additional sets of read reference levels until a minimum syndrome weight is identified between two higher syndrome weights;
- determining the updated read reference levels based on the initial samples and the additional samples;
- and
- reading the non-volatile memory cells using the updated read reference levels.
(canceled)
(canceled)
Dependencies are inferred from the claim text.