Flash memory reference voltage detection with tracking of cross-points of cell voltage distributions using histograms

摘要

Cross-points of flash memory cell voltage distributions are determined by reading data from a portion of the flash memory two or more times using two or more different candidate reference voltages and determining corresponding decision patterns. The frequency of occurrence of the decision patterns in the data read from the flash memory is used to conceptually construct a histogram. The histogram is used to estimate the cross-points. Employing decision patterns enables multiple cross-point voltages to be determined with a minimum of read operations.

主权项

1. A method for flash memory controller operation, comprising:
reading data from a portion of a flash memory a plurality of times using a plurality of different candidate reference voltages, each time reading data from the portion of the flash memory using a different candidate reference voltage from all other times, the plurality of different candidate reference voltages distributed over a voltage range, the voltage range 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 candidate reference voltages; counting occurrences of each of the plurality of decision patterns in the data read from the portion of the flash memory; determining one or more of the decision patterns having a minimum of occurrences; determining a cross-point voltage corresponding to a mid-point of one or more voltage regions corresponding to the one or more decision patterns determined to have a minimum of occurrences; and providing an indication of the cross-point voltage to a read data detector.