Abstract:
A circuit for generating an address of a semiconductor memory device which improves usage yield of the semiconductor memory device. The memory device includes circuitry to detect errors of various sections of a memory chip. After detecting the error-prone sections, the remainder of the memory chip can be used instead of discarding the entire memory device.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a semiconductor memory device, and more particularly, to a circuit for generating an address of a semiconductor memory device, which improves usage yield of the semiconductor memory device. 
     BACKGROUND OF THE INVENTION 
     A related art circuit for generating an address of a semiconductor memory device will be described with reference to the accompanying drawings. 
     FIG. 1 is a block diagram showing a related art circuit for generating an address of a semiconductor memory device, FIG. 2 shows a refresh counting unit of FIG. 1, and FIG. 3 shows an address switching unit of FIG.  1 . 
     As shown in FIG. 1, the related art circuit for generating an address of a semiconductor memory device includes a refresh counting unit  11  outputting an n-bit refresh address BX signals in response to a refresh enable signal REN to refresh an address; an address buffer  13  outputting an n-bit input address AX signals in response to an external address EXa; and an address switching unit  13  selecting either the BX or the AX signals and outputting bank address and internal address (BA &amp; Int) signals in response to the REN signal. 
     As shown in FIG. 2, the refresh counting unit  11  includes n refresh counters  20   0  to  20   n−1  outputting BX signals BX[ 0 ] to BX[n−1], respectively, to the address switching unit  13  when enabled by the refresh enable signal REN. The refresh counters  20   0  to  20   n−2  also output carry signals C 0  to C n−2 , where each carry signal is received by the respective higher order bit neighboring refresh counters  20   1  to  20   n−1 . 
     The address switching unit  13 , as shown in FIG. 3, includes n switches  30   0  to  30   n−1  to select either the n-bit BX or AX signals to output as internal addresses Int[ 0 ] to Int[n−1]. The selection is performed in response to the refresh enable REN signal. 
     The operation of the aforementioned related art circuit for generating an address of a semiconductor memory device will be described below. 
     When no refresh operation takes place, i.e., when the REN is disabled, the address switching unit  13  selects the AX signals from the address buffer  12  to be output as the Int signals. However, when the refresh operation does take place, i.e., when the REN is enabled, the address switching unit  13  selects the BX signals from the refresh counting unit  11 . 
     The above mentioned related art circuit for generating an address of a semiconductor memory device has at least the following problem. When there are errors in any part of the memory device, the entire device must be discarded. This is even if a majority of the sections of the device may be properly functioning. This reduces the usage yield of the semiconductor memory device since the usable sections of the memory are also discarded, and thus increases the production cost due to the unnecessary discarding of useful devices. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter. 
     Another object of the present invention is to provide a circuit for generating an address of a semiconductor memory device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     Another object of the present invention is to provide a circuit for generating an address of a semiconductor memory device, which improves yield of the semiconductor memory device. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
     To achieve at least these objects and other advantages in a whole or in part and in accordance with purposes of the present invention, as embodied and broadly described, a circuit for generating an address of a semiconductor memory device includes a half chip enable unit receiving a half chip enable signal for allowing a memory cell having a defect to be constructed by a half chip; a refresh counting unit generating a refresh address in response to an external refresh enable signal and the half chip enable signal; an address buffer receiving an external address and generating an input address; an address switching unit selectively outputting one of the refresh address and the input address as an internal address in response to the refresh enable signal and the half chip enable signal; a block fail determining unit outputting a block fail signal data indicating a poor memory cell in response to the half chip enable signal; and a bank address coding unit generating a bank address using the refresh address and performing a logic operation of an output signal of the block fail determining unit and a bank address when the half chip enable signal is enabled in a half chip operation, to output the logic operated signal to a coded bank address of the defected memory cell. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
     FIG. 1 is a block diagram showing a related art circuit for generating an address of a semiconductor memory device; 
     FIG. 2 is a detailed diagram showing a refresh counting unit of FIG. 1; 
     FIG. 3 is a detailed diagram showing an address switching unit of FIG. 1; 
     FIG. 4 is a block diagram showing a circuit for generating an address of a semiconductor memory device according to an embodiment of the present invention; 
     FIG. 5 is a detailed diagram showing a half chip enable unit; 
     FIG. 6 is a detailed diagram showing a block fail determining unit; 
     FIGS. 7A and 7B are detailed diagrams showing a first decoder and a second decoder of the bank address coding unit, respectively; 
     FIG. 8 is a detailed diagram showing a refresh counting unit of FIG. 4; 
     FIG. 9 is a detailed diagram showing an address switching unit of FIG. 4; and 
     FIG. 10 is a schematic view of a bank according to the embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings. 
     As shown in FIG. 4, a circuit for generating an address of a semiconductor memory device according to an embodiment of the present invention includes a half chip enable unit  41 , a refresh counting unit  42 , an address buffer  43 , an address switching unit  44 , a bank address coding unit  45 , and a block fail determining unit  46 . 
     The half chip enable unit  41  receives an external half chip enable signal HCE and outputs an internal half chip enable signal HEN. As shown in FIG. 5, the half chip enable unit includes two inverters INV 81  and INV 82 . Inverter INV 81  is connected to inverter INV 82  such that the input of inverter INV 81  is coupled to the output of INV 82  and the input of inverter INV 82  is coupled to the output of inverter INV 81 . During operation, the half chip enable unit  41  latches an external half chip enable signal HCE to be output to an internal half chip enable signal. 
     The refresh counting unit  42  generates n-bit refresh address signals BX in response to a refresh enable signal REN to refresh an address. The address buffer  43  receives an external address EXa and outputs n-bit input address signals AX. 
     The block fail determining unit  46  stores errors, for example when an error occurs during a chip test, and outputs a block fail signal BFI when the internal half chip enable signal HEN is enabled. As shown in FIG. 6, the block fail determining unit  46  includes inverters INV 91 , INV 92  and INV 93 , fuse FS, PMOSFET PM, NMOSFETs NM 91 , NM 92  and NM 93 . The half chip enable signal HEN is received by inverter INV 91 . The output of the inverter INV 91  is connected to the PMOSFET PM and the NMOSFET  91 . The drain of PMOSFET PM is connected to an input voltage VDD and the source is connected to fuse FS. NMOSFETs NM 91 , NM 92  and NM 93  are connected in series with NMOSFET NM 91  connected to NMOSFET NM 92  and NMOSFET NM 92  connected to NMOSFET NM 93 . The source of NMOSFET NM 93  is connected to a ground GND. Additionally, an input voltage VDD is connected to the substrate of NMOSFETs NM 92  and NM 93 . Inverter INV 92  is connected to the output of fuse FS and drain of NMOSFET NM 91 . Inverter INV 92  is connected in series with Inverter INV 93 . 
     During operation, the block fail determining unit  46  stores defect data of a block within each bank in fuse FS and outputs the defect data as a bank fail signal BFI when the half chip enable unit  41  is enabled. 
     Since the block fail signal BFI represents fail data of a block within each bank, the block fail signal outputs four bits BFI[ 0 ] to BFI[ 3 ], as shown in FIG. 9, each corresponding to a bank if one memory cell is divided into four banks. Accordingly, if a memory cell is divided into four or more banks, the bit number of the block fail signal increases by the number of increased banks. Also, the bit number of coded bank addresses BA of the bank address coding unit  46  increases. 
     The bank address coding unit  45  codes the BFI signal and either the BX signal or the AX signal to output the coded signal as a bank address signal BA. The bank address coding unit is composed of a first decoder unit, as shown in FIG. 7A, and a second decoder unit, as shown in FIG.  7 B. The first decoder unit includes an inverter INV 101 , which receives refresh enable signal and has an output connected to first gates NAND 105 , NAND 106 , NAND 107  and NAND 108 . The first decoder also has four second gates NAND 101 , NAND 102 , NAND 103  and NAND 104 , which each receive two addresses of AX signals such as AXBK[ 0 ], AXBK[ 1 ]. However, the AX signal associated with address AXBX[ 0 ] passes through inverter INV 103  prior to being received by gate NAND 104  and the AX signal associated with address AX BK[ 1 ] passes through an inverter prior to being received by gates NAND 102  and NAND 104 . The output of each of the second gates NAND 101 , NAND 102 , NAND 103  and NAND 104  is connected to a first gate NAND  105 , NAND  106 , NAND 107  and NAND 108 , respectively, so that one first gate is connected to one second gate. Each first gate NAND 105 , NAND 106 , NAND 107  and NAND 108  outputs a bank address such as BK[ 0 ] to BK[ 3 ], respectively. 
     As shown in FIG. 7B, the second decoder has two first transmission gates TS 1  and TS 2 ; two second transmission gates TS 3  and TS 4 ; inverters INV 105 , INV 106 , INV 107 , INV 108  and INV 109 ; and two gates NAND 109 , NAND 110 . The first transmission gates TS 1  and TS 2  are connected to the refresh enable signal REN, inverter INV 105  and Int signals Int[ 0 ] and BX signal BXD[ 0 ]. The outputs of transmission gates TS 1  and TS 2  are connected to second transmission gates TS 3  and TS 4 , which are also connected to the half chip enable signal and block fail signal BFI[ 0 ]. Additionally, inverter INV 106  is connected between transmission gates TS 3  and TS 4 . Gates NAND 109  and NAND 110  receive input from transmission gates TS 3  and TS 4 , but inverter INV 108  inverts the signal prior to gate NAND 110 . Gates NAND 109  and NAND 110  also receive bank address BK[ 0 ] from the first decoder shown in FIG.  7 A. Inverters INV 107  and INV 109  invert the signal output by gates NAND 109  and NAND 110 , and output decoded bank addresses BA[ 0 ] and BA[ 0 ]B. 
     During half chip operation, the second decoder decodes the bank fail signal BFI and the bank address BK, and outputs a decoded bank address BA. During normal and refresh operations, the second decoder decodes the AX signals and the bank address BK with a full chip, to output a decoded bank address BA. 
     As shown in FIG. 8, the refresh counting unit  42  includes n refresh counters  60   0  to  60   n−1  and an OR gate  62 . The refresh counters output n-bit BX signals (BX[ 0 ] to BX[n−1]) to the address switching unit  44  and the bank address coding unit  45  when enabled by the refresh enable signal REN. All refresh counters are enabled and disabled simultaneously. 
     The first refresh counter  60   0  also outputs a carry signal C 0  and fed to an input of the OR gate  62 . The OR gate  62  also takes as input the half chip enable signal HEN and outputs the result of OR&#39;ing the C 0  and HEN signals. The output of the OR gate  62  is fed to the second refresh counter  60   1 . The refresh counters  60   1  to  60   n−2  also generate carry signals C 1  to C n−2  that are fed to the respective higher order refresh counters  60   2  to  60   n−1 . 
     The address switching unit  44  selects either the BX signals or the AX signals in response to the refresh enable signal REN, and outputs the selected signal as n-bit internal address Int signals. As shown in FIG. 9, the address switching unit  44 , includes an inverter  71 , an AND gate  72 , and n switches  70   0  to  70   n−1 . The switches output the n-bit Int signals (Int[ 0 ] to Int[n−1]) by selecting either the BX or the AX signals in response to an enabling signal. The enabling signal for the first switch  70   0  is the output of the AND gate  72  and the enabling signal for the remaining switches  70   1  to  70   n−1  is the REN signal. 
     The inverter  71  inverts the internal half chip enable signal HEN and the AND gate  72  performs an AND operation of the refresh enable signal REN and the inverted half chip enable signal. The output of the AND gate  72  is used to select either the BX[ 0 ] signal or the AX[ 0 ] signal by the first switch  70   0 . 
     The remaining switches  70   1  to  70   n−1  output the remaining BX or AX signals as Int[[1]−Int[n−1], respectively, in response to the refresh enable signal. 
     The operation of the circuit for generating an address of a semiconductor memory device according to the embodiment of the present invention will now be described. 
     When no errors occur in the chip, such as during a test operation, the internal half chip enable signal HEN is disabled, and thus the block fail determining unit  46  does not generate the block fail signal BFI. At this time, if the refresh enable signal REN is enabled, the address switching unit  44  selects BX signals to be outputted as the Int signals. Also, the bank address coding unit  45  codes the BX signals to output the bank address BA. 
     On the other hand, if the refresh enable signal REN is disabled when the block fail signal BFI is not generated, the address switching unit  44  selects the AX signals to be outputted as the Int signals, and the bank address coding unit  45  codes the AX signals to output the bank address BA. 
     When an error occurs on the chip, the half chip enable unit  41  outputs the internal half chip enable signal HEN in response to the external half chip enable signal HCE. Subsequently, the internal half chip enable signal HEN enables the block fail determining unit  46 . The block fail determining unit  46  codes the failure, such as errors that occur while testing the chip, and outputs the coded data as the block fail signal BFI. 
     The length of the block fail signal BFI varies depends on how many blocks a bank is divided into in the memory. If the bank is divided into two blocks as shown in FIG. 10, the block fail signal BFI would be 4 bits long. As the number of blocks increase, the number of bits of the block fail signal BFI also increases. 
     To select one of blocks A and B in a bank as shown in FIG. 10, the bank address coding unit  45  codes the block fail signal BFI  10  and the BX signals or the AX signals to output the bank address signal BA. 
     Referring to FIG. 8, if the internal half chip enable signal HEN goes high, the output of the OR gate  62 , and thus the input to the second refresh counter  60   1 , goes high as well. A coefficient value of the BX[ 0 ] signal is fixed at this juncture, and the BX[1] signal becomes the lowest address bit. As such, a half chip operation is being conducted, since the range of values outputted is reduced by half. A normal half chip operation is performed in response to the refresh enable signal REN by reducing one of the refresh counters. 
     Referring to FIG. 9, while in half chip operation, i.e. the internal half chip enable signal HEN is high, the output of the AND gate  72  goes low. Accordingly, the first switch  70   0  always selects the AX[ 0 ] while in half chip operation. 
     Also during the half chip operation, if the refresh is not carried out, i.e. the REN signal is not enabled, the remaining switches  70   1  to  70   n−1  also selects AX[ 1 ]-AX[n−1] from the address buffer  43 , and the bank address coding unit codes the entire AX signal and the block fail signal BFI to output the bank address BA. 
     On the other hand, if the refresh is performed during the half chip operation, the address switching unit  44  outputs the AX[ 0 ] signal from the address buffer  43  and the BX[ 1 ] to BX[n−1] signals from the refresh counting unit  42 . The bank address coding unit  45  codes the block fail signal BFI, AX[ 0 ], and BX[ 1 ]-BX[n−1] to output the bank address BA. 
     As mentioned above, the circuit for generating an address of a semiconductor memory device according to the present invention has at least the following advantage. The circuit enables detection of errors of various parts of a chip. When the error prone parts are detected, they can be isolated and the non-error parts can be used without discarding the whole chip. This improves the usage yield of the semiconductor memory device and results in production savings. 
     The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.