Abstract:
There is provided a semiconductor memory device which does not require an additional input pad to apply a signal for discriminating between a normal cell and a redundant cell. The semicodnuctor memory device has (claim 1). Therefore, the normal cell array or the redundant cell array is sequentially selected and tested by using the same input pad to which the bank select bit is input, without an additional pad.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor memory device, and more particularly, to a semiconductor memory device that does not require an additional pad for discriminating between normal cells and redundant cells during testing. 
     Generally, a memory cell array. in a memory device comprises a normal cell array and a redundant cell array. In testing a memory device according to the prior art, only the normal cell is initially tested. If a repairable failure is found, the cell is repaired. The cell is then retested, and memory device assembled if it passes the test. 
     However, there are some cases where a redundant cell is susceptible to a failure despite a repair. Thus, efforts have recently been made to reduce the possibility of a post-repair failure by repairing only redundant cells that pass initial tests. 
     FIG. 1 is a schematic block diagram of a conventional memory device for enabling redundant cell testing. The conventional memory device has a memory cell array 24, address input pads 10 (PAO-PA13), a row address buffer 12, row decoding means 14, redundancy decoding means 16, a column address buffer 18, column decoding means 20, and redundancy column decoding means 22. 
     The memory cell array 24 is divided into a normal cell array defined by RA13B and CA13B and a redundant cell array defined by RA13 and CA 13. Address input pads PA0-PA12 are connected to external pins that are applied during a package process. Address input pad PA13 is only used during testing. The row address buffer 12 buffers row address signals input via the address input pads PA0-PA13. The row decoding means 14 and the redundancy row decoding means 16 decode the row addresses. The row decoding means 14 decodes addresses for the normal cell array and the redundancy row decoding means 16 decodes addresses for the redundant cell array. The column address buffer 18 buffers column addresses on the address input pads PA0-PA13. The column decoding means 20 decodes addresses for the normal cell array and the redundancy column decoding means 22 decodes addresses for the redundant cell array. 
     In conventional memory devices, addresses needed for normal addressing are applied to the pads PA0-PA12. However, to test both the normal and redundant cell arrays, an additional signal is required to discriminate between the normal cell array and the redundant cell array. The signal is applied on pad PA13. That is, to test the normal cell array, defined by RA13B and CA13B, and the redundant cell array, defined by RA13 and CA13, a signal is either asserted or deasserted on the address input pad PA13. The normal cell array is selected when the most significant bit (MSB) of the address input on input pad PA13 is logic &#34;0&#34;. If the MSB is logic &#34;1&#34;, the redundant cell array is selected. 
     When an address is received on the address input pads 10 (PA0-PA13), the row address buffer 12 and the column address buffer 18 buffer the address. If the address selects the normal cell, that is, if the MSB of the address is logic &#34;0&#34;, a row predecoder 14a and a column predecoder 20a are activated. The row decoder 14a and column decoder 20b receive and decode the outputs of the row predecoder 14a and the column predecoder 20a selecting the normal cell defined by RAI3B and CA13B. 
     If the signal applied to the address input pad PA13 is logic &#34;1&#34;, that is, if the redundant cell is to be tested, a redundancy row fuse box 16a and a redundancy column fuse box 22a are activated. The redundancy row decoder 16b and the redundancy column decoder 22b receive and decode the outputs of the redundancy row fuse box 16a and the redundancy column fuse box 22b, respectively, selecting the redundant cell, defined by RA13 and CA13. 
     Thus, the semiconductor memory device shown in FIG. 1 needs an additional address input pad for applying a signal that switches between normal cells and redundant cells in a test mode, in addition to the address input pads used in the normal operating mode. A probe card used for testing the semiconductor device must include an additional input pin that corresponds to the additional address input pad PA 13. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a semiconductor memory device that does not require an additional address pad for accessing both normal cells and redundant cells during testing. 
     A semiconductor memory device includes a plurality of banks each having normal and redundant cell arrays. One of the banks is selected in response to an external input bank select bit. A test mode determining means receives an external address and generates a test mode signal in response to external control signals. A redundant cell test controller selects one of the normal and redundant cell arrays of the selected bank in response to the bank select bit and the test mode signal. 
     A first control signal comprises an external row address strobe signal. A second control signal is a logical combination of an external chip select signal, column address strobe signal, and write enable signal. 
     The test mode determining means includes a first transferring means for transferring the address in response to the first control signal. A first latch stores the address transferred from the first transferring means. A first inverter inverts the output of the first latch. A second transferring means transfers an output signal from the first inverter in response to the second control signal. A second latch stores a signal transferred by the second transferring means. A second inverter inverts an output signal from the second latch and outputs the test mode signal. A first precharge circuit precharges an input of the first latch. A second precharge circuit precharges an input of the second latch. 
     The test mode determining means and redundant cell test controlling means reduce the number of address pads required for testing redundant memory cells. 
     The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention which proceeds with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a conventional memory device for enabling redundant cell testing. 
     FIG. 2 is a block diagram of a memory device that enables redundant cell testing according to the present invention. 
     FIG. 3 is a block diagram showing memory cell addressing for the memory device shown in FIG. 2. 
     FIG. 4 is a detailed circuit diagram of a test mode determining means for the memory device shown FIG. 2. 
     FIG. 5 is a timing diagram for testing a memory cell array for the semiconductor memory device shown in FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 2, a semiconductor memory device according to the present invention includes a memory cell array 44 having a normal cell array defined by RA13B and CA13B and a redundant cell array defined by RA13 and CA13. Address input pads 30 (PA0-PA13) receive externally applied addresses. A row address buffer 32 buffers a row address for the address input on the address input pads 30 (PA0-PA13). Either row decoding means 34 or redundancy row decoding means 36 are activated in response to a redundancy control signal RED. The row decoding means 34 address row lines for the normal cell array of the RA13B and CA13B areas. The redundant row decoding means 36 address the row lines for the redundant cell array of the RA13 and CA13 areas. 
     A column address buffer 38 buffers a column address among the addresses input on the address input pads 30 (PA0-PA13). Column decoding means 40 address column lines of the normal cell array RA13B and CA13B and the redundancy column decoding means 42 address the column lines of the redundant cell array RA13 and CA13. A test mode determining means 46 receives an address or a combination of addresses and generates a test mode signal PRCT indicating the initiation of a test mode. The PRCT signal is generated in response to control signals PRP1D, WCBRSET, and PVCCH. A redundant cell test controlling means 48 generates the redundancy control signal RED in response to a bank select bit B of the address and the test mode signal PRCT. 
     The memory cell array 44 has a plurality of banks, one of which is selected in response to the bank select bit B of the address. The row decoding means 34 includes a row predecoder 34a for predecoding a row address from the row address buffer 32. A row decoder 34b is activated in response to the redundancy control signal RED, redecodes an output signal of the row predecoder 34a, and addresses a row of the normal cell array RA13B and CA13B. The redundancy row decoding means 36 includes a row fuse box 36a which is activated when the row address is selected for the redundant cell. A redundancy row decoder 36b is activated in response to the redundancy control signal RED, redecodes an output signal of the redundancy row fuse box 36a, and addresses a row line of the redundant cell array of RA13 and CA13. 
     The column decoding means 40 includes a column predecoder 40a that predecodes a column address input from the column address buffer 38. A column decoder 40b is activated in response to the redundancy control signal RED, redecodes an output signal from the column predecoder 40a, and addresses a column line of the normal cell array of RA13B and CA13B. The redundancy column decoding means 42 includes a redundancy column fuse box 42a which is activated when the column address selects the redundant cell. A redundancy column decoder 42b is activated in response to the redundancy control signal RED, re-decoding an output signal of the redundancy column fuse box 42a, and addressing a column line of the redundant cells RA13 and CA13. 
     The first control signal PRP1D is a pulse signal which is enabled by an external input row address strobe signal RAS ,the second control signal WCBRSET is a combination signal of a chip select signal cs , a column address strobe signal  CAS , and a write enable signal  WE . The third control signal PVCCH is a precharge signal. 
     FIG. 3 is a block diagram that shows memory cells for the semiconductor memory device in FIG.2. The memory cells 44 of FIG. 2 have two banks. The MSB of the address input from the input pad A13 is used as a bank select bit. A normal cell 50 for a first bank 50 in the memory cell array is selected when the MSB of the address is at a &#34;low&#34; level (A13B). Row and column redundant cells 52 and 54 for the first bank are selected when the MSB of the address is at a &#34;high&#34; level (A13). 
     A normal cell 56 for a second bank is selected when the MSB of the address is at a &#34;high&#34; level (A13). Row and column redundant cells 60 and 58 for the second bank are selected when the MSB of the address is at a &#34;low&#34; level (A13B). 
     FIG. 4 is a detailed circuit diagram of the test mode determining means for the semiconductor memory device of the present invention shown in FIG. 2. A transfer means TM1 transfers an address or address combination signal Ai in response to the first control signal PRP1D. A latch 62 stores a signal transferred by the transferring means TM1. Inverting means I4 inverts an output signal of the latch 62. Transfer means TM2 transfers an output signal of the inverting means 14 in response to the second control signal WCBRSET. A latch 64 stores the signal transferred by the transferring means TM2. Inverting means 17 inverts an output signal of the latch 64 and outputs a test mode signal PRCT that sets a test mode. 
     Precharge means MP1 precharges an input terminal of the latch 62 in response to the third control signal PVCCH. Precharge means MP2 precharges an input terminal of the latch 64. The transfer means TM1 comprises a transmission gate and is activated when control signal PRP1D is logic &#34;high&#34; . The transferring means TM2 comprises a transmission gate activated when control signal WCBRSET is logic &#34;high&#34;. The latch 62 comprises two inverters I2 and I3 and the latch 64 comprises two inverters I5 and I6. The inverting means I4 and I7 each comprise inverters. The precharge means MP1 and MP2 each comprise PMOS transistors. 
     FIG. 5 is a timing diagram showing how the memory cell array of the semiconductor memory device shown in FIG. 2 is tested. The chip selecting signal CS , the row address strobe signal RAS , the column address strobe signal  CAS , the write enable signal WE , and the clock signal CLK are all input at &#34;low&#34; levels to the memory device of FIG. 2. In a mode register set (MRS) cycle, the first and second control signals PRP1D and WCBRSET of FIG. 4 are driven &#34;high&#34;. The test mode signal PRCT is activated by an address or address combination Ai (FIG. 4). If a bank select bit B, which is the MSB (A13) of an address input during the MRS cycle, is high, the first bank of FIG. 3 is selected. When the bank select bit B is &#34;low&#34;, the second bank of FIG. 3 is selected. 
     After the MRS cycle, when the chip select signal cs  and the row address strobe signal  RAS  are driven to low levels, and the column address strobe signal CAS  and the write enable signal WE  are driven to &#34;high&#34; levels, an active cycle is set. 
     When the first bank is selected during the MRS cycle and the bank select bit B input during the active cycle is &#34;low&#34;, the row and column decoding means 34 and 40 of FIG. 2 are activated by the redundancy control signal RED. Thus, the normal cell 50 of the first bank is selected. When the first bank is selected during the MRS cycle and the bank select bit B input during the active cycle is &#34;high&#34;, the redundancy row and redundancy column decoding means 36 and 42 are activated by the redundant control signal RED. Thus, the redundant cells 52 and 54 of the first bank are selected. 
     When the second bank is selected during the MRS cycle and the bank select bit B input during the active cycle is &#34;low&#34;, the redundancy row and redundancy column decoding means 36 and 42 are activated. Thus, the redundant cells 58 and 60 of the second bank are selected. When the second bank is selected during the MRS cycle and the bank select bit B input during the active cycle is &#34;high&#34;, the row and column decoding means 34 and 40 are activated by the redundancy control signal RED. Thus, the normal cell 56 of the second bank is selected. 
     Therefore, the semiconductor memory device of the present invention has an advantage in that the normal or redundant cells are sequentially selected by using the same input pad A13 used for bank selection. 
     It should be understood that the present invention is not limited to the particular embodiment disclosed herein as the best mode contemplated for carrying out the present invention, but rather that the present invention is not limited to the specific embodiments described in this specification except as defined in the appended claims.