Abstract:
A memory device including a parallel test circuit can overcome a channel deficiency phenomenon of test equipment by reducing the number of input/output pads. The memory device including a parallel test circuit comprises a burst length regulating block, a parallel test block, an output block and a plurality of input/output pads. The burst length regulating block sets a second burst length at a test mode which is longer than a first burst length at a normal mode. The parallel test block compresses data and tests the compressed data by a repair unit. The output block sequentially outputs data outputted from at least two or more parallel test blocks depending on the second burst length. The plurality of input/output pads externally output data outputted from the output block.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to a memory device including a parallel test circuit, and more specifically, to a memory device including a parallel test circuit which overcomes a channel deficiency phenomenon of test equipment by reducing the number of input/output pads.  
         [0003]     2. Description of the Prior Art  
         [0004]     In general, data should exactly be read or written in a semiconductor memory device such as a dynamic RAM. For the exact read/write operation, even one defective cell should not exist on a chip. However, as the number of cells integrated in one chip increases more and more due to high integration of the semiconductor memory device, the number of defective cells may also increase in spite of improvement of the manufacture process. If the exact test is not performed on these defective cells, the reliability of the semiconductor memory device cannot be secured.  
         [0005]     Although it is important to perform a reliable test on devices, a high speed test can also be performed on a great number of cells. Specifically, since reduction of improvement period and test time of a semiconductor memory device directly affects cost of products, the reduction of test time has been the main issue manufacture companies.  
         [0006]     When one cell is tested to distinguish pass or fail of cells in a memory chip of a semiconductor memory device, the test of the highly integrated memory device takes much time and causes increase of cost.  
         [0007]     As a result, a parallel test mode is used to reduce the test time.  
         [0008]     When the same data are read after the same data are written in a plurality of cells, the parallel test determined pass or fail of the cells with an exclusive OR logic circuit. The value of the logic operation is “1” to determine pass of the cells if the same data are read, and the value of the logic operation is “0” to determine fail of the cells if the different data are read, thereby reducing the test time.  
         [0009]      FIG. 1  is a diagram illustrating a parallel test structure of a conventional memory device. Here, a parallel test of a 4×32 DRAM is exemplified.  
         [0010]     Referring to  FIG. 1 , since the fail cells are repaired in a half bank unit, a parallel test block  1  compresses data of a half bank at a parallel test mode, and outputs the compressed data to an input/output pad DQ. Here, the parallel test measures a lot of dies in one test equipment.  
         [0011]     As a result, the large number of dies can be measured when four input/output pads DQ are used to reduce the number of channels in the test equipment than when 8 input/output pads DQ are used in the test equipment. However, since data compressed in one bank unit are outputted through four input/output pads DQ, the repair operation is required to be performed simultaneously in one bank unit, thereby reducing the efficiency of the repair operation.  
       SUMMARY OF THE INVENTION  
       [0012]     It is an object of the present invention to maintain repair efficiency at a parallel test mode and to reduce the number of input/output pads DQ.  
         [0013]     In an embodiment, a memory device including a parallel test circuit comprises a burst length regulating block, a parallel test block, an output block and a plurality of input/output pads. The burst length regulating block sets a second burst length at a test mode which is longer than a first burst length at a normal mode. The parallel test block compresses data by a repaired unit and tests the compressed data. The output block sequentially outputs data outputted from at least two or more parallel test blocks depending on the second burst length. The plurality of input/output pads externally output data outputted from the output block. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Other aspects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:  
         [0015]      FIG. 1  is a diagram illustrating a parallel test structure of a conventional memory device;  
         [0016]      FIG. 2  is a diagram illustrating a parallel test structure of a memory device according to an embodiment of the present invention;  
         [0017]      FIG. 3  is a block diagram illustrating an output unit of  FIG. 2 ; and  
         [0018]      FIG. 4  is a block diagram illustrating a burst length regulating circuit of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     The present invention will be described in detail with reference to the accompanying drawings.  
         [0020]      FIG. 2  is a diagram illustrating a parallel test structure of a memory device according to an embodiment of the present invention.  
         [0021]     Referring to  FIG. 2 , since a repair operation is performed in a half bank unit at a parallel test mode, a parallel test block  1  compresses data of a half bank, and outputs the compressed data. Here, two data outputted from one bank, that is, a pair of half banks HALF-A and HALF-B are sequentially outputted through one input/output pad DQ. Here, an output unit  2  having a pipe latch scheme sequentially outputs two data outputted from one bank to the input/output pad DQ.  
         [0022]     Here, a burst length (hereinafter, referred to as “BL”) twice longer than a BL at a normal mode is required to be set at the parallel test mode.  
         [0023]     As a result, since one bank, that is a pair of half banks, can be tested through one input/output pad DQ, the number of input/output pads DQ can be reduced without reducing the repair efficiency. Therefore, the number of dies which the test equipment can test simultaneously can be increased.  
         [0024]     Meanwhile, if the structure according to an embodiment of the present invention is applied while the number of input/output pads DQ used at the test mode is maintained, the repair efficiency can be increased twice. That is, the repair operation can be performed in a quarter bank unit.  
         [0025]      FIG. 3  is a block diagram illustrating the output unit  2  of  FIG. 2 . Here, the output unit  2  has a pipe latch scheme.  
         [0026]     The output unit  2  comprises two register chains  4 , two transmission switches  6  and an data output buffer  8 .  
         [0027]     The register chain  4  comprises a plurality of registers  5   a ,  5   b , and  5   c  connected serially. One data HB 0 A of half banks HALF-A is inputted in one first register  5   a  of the two register chains, and the other data HB 0 B of HALF-B is inputted in the other first register  5   a.    
         [0028]     The transmission switch  6  sequentially transmits data from the final register  5   c  to an data output buffer  8 . That is, data HB 0 A and HB 0 B are alternately transmitted at a rising edge of the clock signal CLK.  
         [0029]      FIG. 4  is a block diagram illustrating a burst length regulating circuit. Here, the BL regulating circuit regulates a BL at a test mode to be twice longer than a BL used at a normal mode.  
         [0030]     A first BL regulating unit  10  comprises an inverter IV 1  and a NOR gate NR 1 . The NOR gate NR 1  performs a NOR operation on a test mode signal TM and a signal obtained by inverting a first normal BL control signal BL 1  in the inverter IV 1 , and generates a first test BL control signal BLT 1 . Here, the first normal BL control signal BL 1  sets a BL as “1” at the normal mode.  
         [0031]     As a result, at the normal mode, if the first normal BL control signal BL 1  is activated to a high level to set the BL as “1”, the first test BL control signal BLT 1  is activated to a high level to set the BL as “1”. Since the test mode signal TM is activated to a high level at the test mode, the first test BL control signal BLT 1  is inactivated to a low level regardless of the first normal BL control signal BL 1 .  
         [0032]     A second BL regulating unit  12  comprises an inverter IV 2 , and NAND gates ND 1 ˜ND 3 . The first NAND gate ND 1  performs a NAND operation on a second normal BL control signal BL 2  for setting the BL as “2” at the normal mode and a signal obtained by inverting the test mode signal TM in the inverter IV 2 . The second NAND gate ND 2  performs a NAND operation on the test mode signal TM and the first normal BL control signal BL 1 . The third NAND gate ND 3  performs a NAND operation on output signals from the NAND gates ND 1  and ND 2 , and generates a second test BL control signal BLT 2 .  
         [0033]     As a result, at the normal mode, the first test BL control signal BLT 1  is activated by the first BL regulating unit  10  to set the BL as “1” if the first normal BL control signal BL 1  is activated, and the second test BL control signal BLT 2  is activated to set the BL as “2” if the second normal BL control signal BL 2 .  
         [0034]     At the test mode, if the first normal BL control signal BL 1  is activated, the second test BL control signal BLT 2  is activated to set the BL as “2”.  
         [0035]     A third BL regulating unit  14  comprises an inverter IV 3 , and NAND gates ND 4 ˜ND 6 . The fourth NAND gate ND 4  performs a NAND operation on a third normal BL control signal BL 4  for setting the BL as “4” at the normal mode and a signal obtained by inverting the test mode signal TM in the inverter IV 3 . The fifth NAND gate ND 5  performs a NAND operation on the test mode signal TM and the second normal BL control signal BL 2 . The sixth NAND gate ND 6  performs a NAND operation on output signals from the NAND gates ND 4  and ND 5 , and generates a third test BL control signal BLT 4 .  
         [0036]     As a result, at the normal mode, the second test BL control signal BLT 2  is activated by the second BL regulating unit  12  to set the BL as “2” if the second normal BL control signal BL 2  is activated, and the third test BL control signal BLT 4  is activated to set the BL as “4” if the third normal BL control signal BL 4  is activated.  
         [0037]     At the test mode, if the second normal BL control signal BL 2  is activated, the third test BL control signal BLT 4  is activated to set the BL as “4”.  
         [0038]     A fourth BL regulating unit  16  comprises an inverter IV 4 , and NAND gates ND 7 ˜ND 9 . The seventh NAND gate ND 7  performs a NAND operation on a fourth normal BL control signal BL 8  for setting the BL as “8” at the normal mode and a signal obtained by inverting the test mode signal TM in the inverter IV 4 . The eighth NAND gate ND 8  performs a NAND operation on the test mode signal TM and the third normal BL control signal BL 4 . The ninth NAND gate ND 9  performs a NAND operation on output signals from the NAND gates ND 7  and ND 8 , and generates a fourth test BL control signal BLT 8 .  
         [0039]     As a result, at the normal mode, the third test BL control signal BLT 4  is activated by the third BL regulating unit  16  to set the BL as “4” if the third normal BL control signal BL 4  is activated, and the fourth test BL control signal BLT 8  is activated to set the BL as “8” if the fourth normal BL control signal BL 8 .  
         [0040]     At the test mode, if the third normal BL control signal BL 4  is activated, the fourth test BL control signal BLT 8  is activated to set the BL as “8”.  
         [0041]     A fifth BL regulating unit  18  comprises an inverter IV 5 , and NAND gates ND 10 ˜ND 12 . The tenth NAND gate ND 10  performs a NAND operation on a fifth normal BL control signal BL 16  for setting the BL of the normal mode as “16” and a signal obtained by inverting the test mode signal TM in the inverter IV 5 . The eleventh NAND gate ND 11  performs a NAND operation on the test mode signal TM and the fourth normal BL control signal BL 8 . The twelfth NAND gate ND 12  performs a NAND operation on output signals from the NAND gates ND 10  and ND 11 , and generates a fifth test BL control signal BLT 16 .  
         [0042]     As a result, at the normal mode, the fourth test BL control signal BLT 2  is activated by the fourth BL regulating unit  16  to set the BL as “8” if the fourth normal BL control signal BL 8  is activated, and the fifth test BL control signal BLT 16  is activated to set the BL as “16” if the fifth normal BL control signal BL 16 .  
         [0043]     At the test mode, if the fourth normal BL control signal BL 8  is activated, the fifth test BL control signal BLT 16  is activated to set the BL as “16”.  
         [0044]     As discussed earlier, in a memory device including a parallel test circuit according to an embodiment of the present invention, since the number of channels in each die of the test equipment can be reduced, the test time is also reduced.  
         [0045]     Additionally, the repair efficiency can be increased when the number of input/output pads is maintained at a parallel test mode.  
         [0046]     While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and described in detail herein. However, it should be understood that the invention is not limited to the particular forms disclosed. Rather, the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined in the appended claims.