METHOD OF FLASH CHANNEL CALIBRATION WITH MULTIPLE LUTS FOR ADAPTIVE MULTIPLE-READ
Error Correction Codes, which are able to take soft-decision information, work much better when compared with hard-decision decoding. It can achieve much better performance. However, due to lack of direct soft-decision information for the NAND flash, multiple-reads with different voltage thresholds are used to generate the soft-decision information. Another invention disclosure describes a method to perform the multiple-read adaptively with different voltage threshold for the NAND flash in order to minimize the number of total multiple-read. The invention disclosure described here is a method of flash channel calibration, which will generate multiple LUTs for adaptive multiple-read with different voltage threshold.
1 . An SSD storage device that enables the multiple read for a same flash page by setting different threshold voltage.
2 . The SSD system of claim 1 that issues a pre-defined maximum number of multi-read commands to flash memory.
3 . The SSD system of claim 2 that consists of soft-decision and hard-decision ECC decoder, statistics information collector and NAND flash calibration control logic capable for multiple-LUT generation.
4 . The SSD system of claim 3 that tries to decode a code-word successfully using either soft-decoding or hard-decoding approach by one or more copies of raw code-words corresponding to different voltage threshold.
5 . The SSD system of claim 4 that count the flip number from zero to one and one to zero by comparing the decoded code-words with all copies of raw un-decoded code-words.
6 . The SSD system of claim 5 that is able to differentiate flip count from zero to one and one to zero at different intersection by providing low-page and/or middle page.
7 . The SSD system of claim 5 that uses one to zero and zero to one flip count to calculate the multiple-read LLR LUT.
8 . The SSD system of claim 7 that can choose any combination of voltage thresholds within the total maximum thresholds.
9 . The SSD system of claim 8 that can generate multiple-LUTs (one LUT for each voltage threshold combination) for less or equal number of M-RD in one calibration process.
10 . The SSD system of claim 6 that uses the generated multiple-LUTs to support adaptive multiple-read or non-adaptive multiple-read during normal multiple-read decoding process.