Generating soft decoding information for flash memory error correction using hard decision patterns

摘要

A flash memory controller having soft-decoding error correcting code (ECC) logic generates log likelihood ratio or similar ECC decoder soft input information from decision patterns obtained from reading data from the same portion of flash memory two or more times. Each decision pattern corresponds to a voltage region bordering one of the reference voltages. Each decision pattern represents a combination of flash memory bit value decisions for a cell voltage within the voltage region corresponding to the decision pattern when a corresponding combination of the reference voltages are used to read the cell. Numerical values are then computed in response to combinations of the flash memory bit value decisions represented by the decision patterns. The numerical values are provided to the soft-decoding ECC logic to serve as soft input information.

主权项

1. A method for operation of a flash memory controller having soft-decoding error correcting code logic, comprising:
reading data from a portion of a flash memory in a plurality of instances using a plurality of different reference voltages, in each instance reading data from the portion of the flash memory using a different reference voltage from all other instances, the plurality of different reference voltages distributed over a voltage range, the voltage range substantially centered on an estimated mid-point between a pair of adjacent target cell voltages; determining a plurality of decision patterns, each decision pattern corresponding to a voltage region bordering one of the reference voltages, each decision pattern representing a combination of flash memory decision values for a cell voltage within the voltage region corresponding to the decision pattern when a corresponding combination of the reference voltages are used to read the cell; generating a plurality of numerical values, each numerical value computed in response to the combination of the flash memory decision values represented by each decision pattern; and inputting the plurality of numerical values to the soft-decoding error correcting code logic.