Patent ID: 11961553
Assignee: SAMSUNG ELECTRONICS CO., LTD.
Field: Computer technology (Electrical engineering)
Classification: CPC G | IPC G

Claim 19:
20. A method of searching a read voltage of a nonvolatile memory device that includes a plurality of memory cells that have a first state and a second state that differ from each other, the method comprising:
determining a number n that represents a number of times a data read operation is performed, wherein n is an integer greater than or equal to two;
selecting a first read voltage level to an n-th read voltage level of the read voltage wherein a number of read voltage levels is equal to the number of times the data read operation is performed, wherein the first to n-th read voltage levels differ from each other;
generating a first cell count value to an n-th cell count value by performing a first data read operation to an n-th data read operation on the plurality of memory cells using all of the first to n-th read voltage levels;
obtaining a first variable to an (n−1)-th variable based on the first to n-th read voltage levels and the first to n-th cell count values, wherein each of the first to (n−1)-th variables includes an averaged read voltage level and a cell count change value;
obtaining a first function by performing a regression analysis based on a first-order polynomial using the first to (n−1)-th variables, wherein the first function is estimated as a first-order polynomial; and
calculating an optimal read voltage level of the read voltage based on the first function,
wherein the optimal read voltage level of the read voltage is obtained based on Equation 1, Equation 2 and Equation 3, as follows:, -
       
        b
        a
       
      
      =
      
       
        
         ∑
         
          
           X
           i
           2
          
          ⁢
          
           ∑
           
            Y
            i
           
          
         
        
        -
        
         ∑
         
          
           X
           i
          
          ⁢
          
           ∑
           
            
             X
             i
            
            ⁢
            
             Y
             i
            
           
          
         
        
       
       
        
         ∑
         
          
           X
           i
          
          ⁢
          
           ∑
           
            Y
            i
           
          
         
        
        -
        
         n
         ⁢
         
          ∑
          
           
            X
            i
           
           ⁢
           
            Y
            i
           
          
         
        
       
      
     
     ;
    
   
   
    
     Equation
     ⁢
        
     1
    
   
  
 

 
  
   
    
     
      
       X
       i
      
      =
      
       
        (
        
         
          x
          i
         
         +
         
          x
          
           i
           +
           1
          
         
        
        )
       
       /
       2
      
     
     ;
    
   
   
    
     Equation
     ⁢
        
     2
    
   
  
 

 
  
   
    
     
      
       Y
       i
      
      =
      
       
        y
        
         i
         +
         1
        
       
       -
       
        y
        i
       
      
     
     ,
    
   
   
    
     Equation
     ⁢
        
     3
    
   
  
 

wherein, in Equation 2, Xi denotes an (i+1)-th averaged read voltage level, i is an integer greater than or equal to zero and less than or equal to (n−2), and xi and xi+i denote an (i+1)-th read voltage level and an (i+2)-th read voltage level, respectively, and in Equation 3, Y1 denotes an (i+1)-th cell count change value, and yi and yi+1 denote an (i+1)-th cell count value and an (i+2)-th cell count value, respectively,
wherein the read voltage distinguishes the first state and the second state.