Method for Reading Data Stored in a Flash Memory According to a Threshold Voltage Distribution and Memory Controller and System Thereof

Abstract

A method for reading data stored in a flash memory is disclosed. The flash memory comprises a plurality of memory cells and each memory cell has a particular threshold voltage The method includes: obtaining a first threshold voltage distribution representing threshold voltages of a first group of the memory cells; obtaining a second threshold voltage distribution representing threshold voltages of a second group of the memory cells, wherein the second threshold voltage distribution is different from the first threshold voltage distribution, and the first group of the memory cells comprises at least a part of the second group of the memory cells; and controlling the flash memory to perform at least one read operation upon the first group of the memory cells according to the second threshold voltage distribution.

What is claimed is: 
     
         1 . A method for reading data stored in a flash memory, wherein the flash memory comprises a first set of memory cells and a second set of memory cells, and each memory cell corresponds to a particular threshold voltage, the method comprising:
 measuring a first voltage characteristic of the first set of the memory cells;   measuring a second voltage characteristic of the second set of the memory cells; and   reading the first set of the flash memory by using the second voltage characteristic.   
     
     
         2 . The method as claimed in  claim 1 , wherein the first voltage characteristic is different from the second voltage characteristic, and the first set of memory cells comprises at least a part of the memory cells of the second set. 
     
     
         3 . A memory controller for reading data stored in a flash memory, wherein the flash memory comprises a first set of memory cells and a second set of memory cells, and each memory cell corresponds to a particular threshold voltage, the memory controller comprising:
 a control logic, measuring a first voltage characteristic of the first set of the memory cells, measuring a second voltage characteristic of the second set of the memory cells, and reading the first set of the flash memory by using the second voltage characteristic.   
     
     
         4 . The memory controller as claimed in  claim 3 , wherein the first voltage characteristic is different from the second voltage characteristic, and the first set of memory cells comprises at least a part of the memory cells of the second set. 
     
     
         5 . A method for reading data stored in a flash memory, wherein the flash memory comprises a plurality of memory cells and each memory cell has a particular threshold voltage, the method comprising:
 reading a part of the memory cells of the flash memory by a first control gate voltage;   detecting error bits of the memory cells;   correcting the error bits of the memory cell by reading the flash memory continuously;   reading the flash memory for measuring a first voltage characteristic of the memory cells;   averaging the first voltage characteristic for obtaining a second voltage characteristic; and   reading a part of the flash memory again by using the second voltage characteristic.   
     
     
         6 . A system for reading data stored in a flash memory, wherein the flash memory comprises a plurality of memory cells and each memory cell has a particular threshold voltage, the system comprising:
 a control logic for reading a part of the memory cells of the flash memory by using a first control gate voltage;   a detector for detecting error bits of the memory cells;   a corrector for correcting the error bits of the memory cell by reading the flash memory continuously;   wherein the control logic further obtains a first voltage characteristic of the memory cells by reading the flash memory, averages the first voltage characteristic for obtaining a second voltage characteristic, and reads a part of the flash memory again by using the second voltage characteristic.