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

A flash memory controller, comprising:

• 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.

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:

• 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.