FLASH MEMORY REFERENCE VOLTAGE DETECTION WITH TRACKING OF CROSS-POINTS OF CELL VOLTAGE DISTRIBUTIONS USING HISTOGRAMS
First Claim
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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.
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Abstract
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.
7 Citations
20 Claims
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1. A method for flash memory controller operation, comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A flash memory controller, comprising:
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a buffer memory; a processing system comprising; read logic for reading data into the buffer memory 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; decision pattern logic for determining a plurality of decision patterns, each decision pattern corresponding to a voltage region bordering one of the candidate reference voltages; histogram logic for counting occurrences of each of the plurality of decision patterns in the data read from the portion of the flash memory, the decision pattern logic further determining one or more decision patterns having a minimum of occurrences; cross-point estimation logic for 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 read data detection logic for receiving from the cross-point estimation logic an indication of the cross-point voltage. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A computer program product for flash memory control, the computer program product comprising a computer-readable medium having stored therein in computer-executable non-transitory form instructions that, when executed on a processing system of a flash memory controller, cause the processing system to effect a method comprising:
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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 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. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification