FLASH CHANNEL CALIBRATION WITH MULTIPLE LOOKUP TABLES

摘要

A system and method for generating lookup tables for use in an adaptive multiple-read system for reading flash memory. Successive different attempts are made to decode previously stored data using error correction codes, the attempts differing, for example, with respect to the combination of raw data words used for each attempt, each raw data word having been obtained by reading a code word of data using a different word line voltage. When a decoding attempt succeeds, log likelihood ratios are calculated from counts of flipped bits, i.e., bits in the raw data read from the memory having a different value than the corresponding bits in the decoded data.

主权项

1. A method for calibrating a flash memory, the method comprising:
performing a first read operation on a first plurality of flash memory cells, at a first word line voltage, to form a first raw data word; performing a second read operation on the first plurality of flash memory cells, at a second word line voltage, to form a second raw data word; executing a first error correction code decoding attempt with a first set of one or more raw data words including the first raw data word; and when the first error correction code decoding attempt succeeds:
generating,
from bit differences between
a second set of one or more raw data words andone or more corresponding decoded data words generated by the first error correction code decoding attempt,a first lookup table including:
a first log likelihood ratio corresponding to a first range of word line voltages anda second log likelihood ratio corresponding to a second range of word line voltages; andgenerating,
from bit differences between
a second set of two or more raw data words andtwo or more corresponding decoded data words generated by the first error correction code decoding attempt,a second lookup table including:
a third log likelihood ratio corresponding to a third range of word line voltages;a fourth log likelihood ratio corresponding to a fourth range of word line voltages; anda fifth log likelihood ratio corresponding to a fifth range of word line voltages.