Patent Publication Number: US-6909650-B2

Title: Circuit and method for transforming data input/output format in parallel bit test

Description:
This application claims priority from Korean Patent Application No. 2002-72477, filed on Nov. 20, 2002, in the Korean Intellectual Property Office, the contents of which are incorporated herein in their entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor memory device, and more particularly, to a circuit and a method for transforming a data input/output format in a parallel bit test (PBT). 
   2. Description of the Related Art 
   A parallel bit test (PBT) is used to check failures of memory cells and write/read paths by writing and reading data to and from the memory cells of a semiconductor memory device in parallel. If the number of data input/output pins (DQ) is reduced in the parallel bit test (PBT), more memory devices can be tested at the same time. For example, if 16 monitoring pins can be used in test equipment, two X 8  mode memory devices, four X 4  mode memory devices, or eight X 2  mode memory devices can be tested in the test equipment. 
   Therefore, it is advantageous in terms of time and costs to test memory devices using the PBT with a decreased number of data input/output pins DQ. In general, a circuit for transforming a data input/output format is used to reduce the number of data input/output pins (DQ) in the PBT. 
     FIG. 1  is a view of a X 4  data input/output format, and  FIG. 2  is a view of a conventional circuit for transforming a data input/output format from a X 4  mode to a X 2  mode. If the number, of memory cells (MC), e.a., MC1, MC2. MC4, MC5, connected to a column select line CSL is equal to the number of data input pins DIN 0 -DIN 3 , no problems occur. That is, all types of data patterns can be tested by writing and reading the data patterns to and from four memory cells MC1, MC2, MC4, MC5, while using four data input pins DIN 0 -DIN 3 . 
   However, in the circuit of  FIG. 2 , two memory cells are connected to one data input pin through a circuit  20  for transforming a data input/output format. That is, two memory cells MC0 and MC1 are connected to a data input pin DIN 0 , and two memory cells MC4 and MC5 are connected to a data input pin DIN 1 . As a result, the number of memory cells MC0, MC1, MC4, MC5 connected to one column selection line CSL is greater than the number of data input pins DIN 0  and DIN 1 . 
   In this case, the types of data patterns that can be written to the memory cells MC0-MC5 are limited. The following Table 1 shows types of data patterns that can be written to the memory cells MC1, MC2, MC4, MC5 in the circuit of FIG.  2 . 
   
     
       
         
             
          
             
                 
             
             
               TABLE 1 
             
          
         
         
             
             
             
          
             
               Memory cell 
               Data pattern 
                 
             
             
                 
             
          
         
         
             
             
             
             
             
          
             
               MC0 
               0 
               0 
               1 
               1 
             
             
               MC1 
               0 
               0 
               1 
               1 
             
             
               MC4 
               0 
               1 
               0 
               1 
             
             
               MC5 
               0 
               1 
               0 
               1 
             
             
                 
             
          
         
       
     
   
   However, when data patterns of Table 1 are used, it is impossible to check failures between two adjacent input/output lines, e.g., between an input/output line connected to the memory cell MC0 and an input/output line connected to the memory cell MC1 or between an input/output line connected to the memory cell MC4 and an input/output line connected to the memory cell MC5. 
   This is because it is impossible to generate a data pattern, which can be written with different data in the memory cells MC0 and MC1 or MC4 and MC5, i.e., (0,1,0,1) or (1,0,1,0), by the conventional circuit  20  for transforming an input/output format shown in FIG.  2 . 
   SUMMARY OF THE INVENTION 
   The present invention provides a circuit for transforming a data input/output format which is capable of generating various data patterns when the number of memory cells connected to one column selection line is greater than the number of data input pins. 
   According to an aspect of the present invention, there is provided a circuit for transforming a data input/output format of a semiconductor memory device. The circuit comprises a first transmission circuit which is activated when a first test mode signal is enabled, receives n data inputs from n data input ends, and transmits the n data inputs to m memory cells, wherein n and m are natural numbers and m is greater than n. A second transmission circuit is activated when a second test mode signal is enabled, receives n data inputs from the n data input ends, and transmits the n data inputs to the m memory cells. Data that is transmitted to adjacent memory cells of the m memory cells is inputted to different input ends of the n data input ends. 
   In one embodiment, he circuit further comprises a command register which receives a command and an address from outside the semiconductor device and outputs the first test mode signal and the second test mode signal according to combinations of the command and the address. It is preferable that the command register is a mode register set (MRS). 
   In one embodiment, the first transmission circuit comprises m switches which connect the n data input ends with the m memory cells in response to the first test mode signal. 
   In one embodiment, the second transmission circuit comprises m switches which connect the n data input ends with the m memory cells in response to the second test mode signal. 
   According to another aspect of the present invention, there is provided a method for transforming a data input/output format of a semiconductor memory device. The method comprises enabling a first test mode signal, receiving n data inputs from n data input ends and transmitting the n data inputs to m memory cells while the first test mode signal is enabled, wherein n and m are natural numbers and m is greater than n, and receiving n data inputs from the n data input ends and transmitting the n data inputs to the m memory cells while the second test mode signal is enabled. Data that is transmitted to adjacent memory cells of the m memory cells is input to different input ends of the n data input ends. 
   In one embodiment, the method further comprises receiving a command and an address from outside the semiconductor memory device and generating the first test mode signal and the second test mode signal according to combinations of the command and the address. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
       FIG. 1  is a schematic diagram of X 4  data input/output format. 
       FIG. 2  is a schematic diagram of a conventional circuit for transforming data input/output format from a X 4  mode to a X 2  mode in a parallel bit test. 
       FIG. 3  is a view of a circuit for transforming data input/output format according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention now will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. 
     FIG. 3  is a view of a circuit for transforming data input/output format according to an embodiment of the present invention. 
   Referring to  FIG. 3 , a circuit  30  for transforming a data input/output format according to an embodiment of the present invention includes a first transmission circuit  31 , a second transmission circuit  32 , a mode register set (MRS)  33 , NAND gates  34  and  36 , and inverters  35  and  37 . 
   The first transmission circuit  31  is activated when a first test mode signal PBTX 2 _SS is enabled as logic high, receives two data inputs from two data input ends DIN 0  and DIN 1 , and transmits the data inputs to four memory cells (MC) MC0, MC1, MC4, and MC5. The second transmission circuit  32  is activated when a second test mode signal PBTX 2 _DS is enabled as logic high, receives two data inputs from two data input ends DIN 0  and DIN 1 , and transmits the data inputs to four memory cells MC0, MC1, MC4, and MC5. Here, a signal PCLKM is maintained as logic high. 
   In particular, data transmitted to adjacent memory cells of the memory cells MC0, MC1, MC4, and MC5 is inputted to different input ends DIN 0  or DIN 1 . 
   The mode register set (MRS)  33  receives a command COM and an address ADD from outside the semiconductor memory device and outputs the first test mode signal PBTX 2 _SS and the second test mode signal PBTX 2 _DS according to combinations of the command COM and the address ADD. 
   More specifically, the first transmission circuit  31  includes four switches T 1  through T 4  which connect two data input ends DIN 0  and DIN 1  with four memory cells MC0, MC1, MC4, and MC5 in response to the enabling of the first test mode signal PBTX 2 _SS. The four switches T 1  through T 4  are each composed of a CMOS transmission gate. 
   The switch T 1  connects the data input end DIN 0  with the memory cell MC0 in response to the enabling of the first test mode signal PBTX 2 _SS. The switch T 2  connects the data input end DIN 1  with the memory cell MC4 in response to the enabling of the first test mode signal PBTX 2 _SS. The switch T 3  connects the data input end DIN 0  with the memory cell MC1 in response to the enabling of the first test mode signal PBTX 2 _SS. The switch T 4  connects the data input end DIN 1  with the memory cell MC5 in response to the enabling of the first mode signal PBTX 2 _SS. 
   The second transmission circuit  32  includes four switches T 5  through T 8  which connect two input ends DIN 0  and DIN 1  with four memory cells MC0, MC1, MC4, and MC5 in response to the enabling of the second test mode signal PBTX 2 _DS. The switches T 5  through T 8  are each composed of a CMOS transmission gate. 
   The switch T 5  connects the data input end DIN 0  with the memory cell MC0 in response to the enabling of the second test mode signal PBTX 2 _DS. The switch T 6  connects the data input end DIN 0  with the memory cell MC4 in response to the enabling of the second test mode signal PBTX 2 _DS. The switch T 7  connects the data input end DIN 1  with the memory cell MC1 in response to enabling of the second test mode signal PBTX 2 _DS. The switch T 8  connects the data input end DIN 1  with the memory cell MC5 in response to the enabling of the second test mode signal PBTX 2 _DS. 
   The following Table 2 shows types of data patterns which can be written in memory cells MC0, MC1, MC4, and MC5 in the circuit of  FIG. 3  according to the present invention. In the circuit according to the present invention, various types of data patterns, which can be written in the memory cells MC0, MC1, MC4, and MC5, can be generated by controlling states of the first test mode signal PBTX 2 _SS and the second test mode signal PBTX 2 _DS. 
   
     
       
         
             
          
             
                 
             
             
               TABLE 2 
             
          
         
         
             
             
             
          
             
                 
               DIN0/DIN1 (PBTX2_SS = 1, 
               DIN0/DIN1 (PBTX2_SS = 0, 
             
             
               Memory 
               PBTX2_DS = 0) 
               PBTX2_DS = 1) 
             
          
         
         
             
             
             
             
             
             
             
             
             
          
             
               cell 
               0/0 
               0/1 
               1/0 
               1/1 
               0/0 
               0/1 
               1/0 
               1/1 
             
             
                 
             
             
               MC0 
               0 
               0 
               1 
               1 
               0 
               0 
               1 
               1 
             
             
               MC1 
               0 
               0 
               1 
               1 
               0 
               1 
               0 
               1 
             
             
               MC4 
               0 
               1 
               0 
               1 
               0 
               0 
               1 
               1 
             
             
               MC5 
               0 
               1 
               0 
               1 
               0 
               1 
               0 
               1 
             
             
                 
             
          
         
       
     
   
   For example, when PBTX 2 _SS is logic “1” and PBTX 2 _DS is logic “0”, the switches T 1  through T 4  of the first transmission circuit  31  are turned on, and the switches T 5  through T 8  of the second transmission circuit  32  are turned off. Thus, the data input end DIN 0  and the memory cell MC0 are connected with each other, the data input end DIN 1  and the memory cell MC4 are connected with each other, the data input end DIN 0  and the memory cell MC1 are connected with each other, and the data input end DIN 1  and the memory cell MC5 are connected with each other. Therefore, four types of data patterns, i.e., (0,0,0,0), (0,0,1,1,), (1,1,0,0), and (1,1,1,1), can be generated according to the four cases where data input ends DIN 0  and DIN 1  are connected with the memory cells MC0, MC1, MC4, and MC5. 
   When PBTX 2 _SS is logic “0” and PBTX 2 _DS is logic “1”, the switches T 1  through T 4  of the first transmission circuit  31  are turned off, and the switches T 5  through T 8  of the second transmission circuit  32  are turned on. Thus, the data input end DIN 0  and the memory cell MC0 are connected with each other, the data input end DIN 0  and the memory cell MC4 are connected with each other, the data input end DIN 1  and the memory cell MC1 are connected with each other, and the data input end DIN 1  and the memory cell MC5 are connected with each other. Therefore, four types of data patterns, i.e., (0,0,0,0), (0,1,0,1,), (1,0,1,0), and (1,1,1,1), can be generated according to the four cases where data input ends DIN 0  and DIN 1  are connected with the memory cells MC0, MC1, MC4, and MC5. 
   As described above, in the circuit for transforming a data input/output format according to the present invention, various types of data patterns can be generated. In particular, it is possible to generate data patterns that can be written with different data in the memory cells MC4 and MC5, i.e., (0,1,0,1) or (1,0,1,0), which is contrary to the conventional circuit  20  for transforming an input/output format shown in FIG.  2 . 
   Therefore, it is possible to check failures between two input/output lines, e.g., between the input/output line connected to the memory cell MC0 and the input/output line connected to the memory cell MC1 or between the input/output line connected to the memory cell MC4 and the input/output line connected to the memory cell MC5. 
   According to a circuit for transforming a data input/output format according to the present invention, it is possible to generate various types of data patterns when the number of memory cells connected to one column selection line is greater than the number of data input pins. Therefore, various failures can be checked by the circuit for transforming a data input/output format according to the present invention. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.