Abstract:
The present invention discloses an address buffer and a semiconductor memory device having the address buffer. The address buffer comprises a first buffer for latching a signal in response to a first control signal in a normal operation mode in the semiconductor memory device and generating a buffered signal by buffering the latched signal in response to a second control signal, and a second buffer for maintaining a mode-setting signal in a reset status in the normal operation mode and for outputting the mode-setting signal by using the latched signal in response to the first control signal and a mode-setting command in a mode-setting operation mode. Accordingly, the mode-setting signal is generated only in the mode-setting operation mode, thereby reducing undesirable current consumption.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an address buffer and a semiconductor memory device having the same.  
           [0003]    2. Description of Related Art  
           [0004]    A conventional semiconductor memory device includes an address buffer comprising a normal address buffer unit for buffering addresses received from address pins in normal operation mode and a mode-setting signal buffer unit for buffering mode-setting signals received from the address pins in a mode-setting operational mode.  
           [0005]    The conventional address buffer, however, involves a problem that the logic level of the mode-setting signals is transited in response to the logic level transition of the addresses input through the address pins in the normal operational mode, which increases current consumption. That is, the mode-setting signal buffer unit is actually operated during the normal operational mode, thereby undesirably consuming current.  
           [0006]    [0006]FIG. 1 illustrates a conventional semiconductor memory device. The conventional semiconductor memory device comprises address pins  10 - 1  to  10 - n,  command pins  12 - 1  to  12 - 3 , address buffers  14 - 1  to  14 - n,  a chip selection signal (CSB) buffer  16 - 1 , a row address strobe signal (RASB) buffer  16 - 2 , a column address strobe signal (CASB) buffer  16 - 3 , an address decoder  18 , a mode-setting register  20 , a command decoder  22  and a PCLKR signal generating circuit  24 .  
           [0007]    The address pins  10 - 1  to  10 - n  receive external addresses A 1  to An. The command pins  12 - 1 ,  12 - 2  and  12 - 3  receive command signals CSB, RASB, CASB, respectively. The address buffers  14 - 1  to  14 - n  latch the external addresses A 1  to An in response to the PCLKR signal and generate buffered mode-setting signals MAB 1  to MABn. The address buffers  14 - 1  to  14 - n  buffer the external addresses A 1  to An in response to the active command ACT and generate buffered addresses AB 1  to ABn. The address decoder  18  decodes the buffered addresses AB 1  to ABn and generates decoded addresses DAB 1  to DABm. The mode-setting register  20  receives the buffered mode-setting signals MAB 1  to MABn and outputs mode-setting signals MDAB 1 -MDABk in response to the mode-setting command MRS.  
           [0008]    The CSB buffer  16 - 1  buffers the chip selection signal CSB and generates a buffered chip selection signal CSBB. The RASB buffer  16 - 2  buffers the row address strobe signal RASB and generates a buffered row address strobe signal RASBB. The CASB buffer  16 - 3  buffers a column address strobe signal CASB and generates a buffered column address strobe signal CASBB. The command decoder  22  decodes the buffered command signals CSBB, RASBB, CASBB and generates a mode-setting command MRS, an active command ACT, a pre-charge command PRE and a refresh command REF. The PCLKR signal generating circuit  24  generates the PCLKR signal in response to the buffered row address strobe signal RASBB.  
           [0009]    [0009]FIG. 2 illustrates a circuit diagram of the address buffer comprising the normal address buffer unit  30  and the mode-setting signal buffer unit  32 . The normal address buffer unit  30  comprises inverters I 1 , I 2 , I 5 , I 6  and I 7 , complementary metal oxide semiconductor (CMOS) transmission gates C 1  and C 2 , and a latch L 1  comprising inverters I 3  and I 4 . The mode-setting signal buffer unit  32  comprises an inverter I 8 , a CMOS transmission gate C 3 , a PMOS transistor P and a latch L 2  comprising inverters I 9  and I 10 .  
           [0010]    In FIG. 2, references A, AB, MAB, ACT denote an external address externally input, a buffered address, a mode-setting signal and an active command, respectively. The PCLKR signal is a clock signal generated in response to the row address strobe signal RASB of logic “low” level. A reference VCCH denotes a voltage that maintains a logic “high” level upon power-up and is then transited to a logic “low” level.  
           [0011]    The inverter I 1  inverts the external address A. The CMOS transmission gate C 1  is turned on in response to the PCLKR signal of logic “low” level, thereby transmitting an output signal of the inverter I 1  to the latch L 1 . The latch L 1  latches and inverts an output signal of the CMOS transmission gate C 1 . The CMOS transmission gate C 2  is turned on in response to the active command of a logic “low” level, thereby transmitting an output signal of the latch L 1 . The inverters I 6  and I 7  buffer an output signal of the CMOS transmission gate C 2 , thereby generating the buffered address AB.  
           [0012]    The inverter I 8  inverts the output signal of the latch L 1 . The CMOS transmission gate C 3  is turned on in response to the signal PCLKR of logic “high” level, thereby transmitting an output signal of the inverter I 8 . The PMOS transistor P is turned on in response to the VCCH signal of logic “low” level after power-up and when the voltage of a node n equals the power supply voltage. The latch L 2  is reset by the PMOS transistor P, thereby generating the mode-setting signal MAB of a logic “low” level. Further, the latch L 2  generates the mode-setting signal of a logic “low” level when a signal of a logic “high” level is transmitted from the CMOS transmission gate C 3  to the latch L 2 . Conversely, latch L 2  generates the mode-setting signal of logic “high” level when a signal of logic “low” level is transmitted.  
           [0013]    Therefore, in the normal operation mode that the active command ACT, the pre-charge command PRE or the refresh command REF is applied to the semiconductor memory device, the CMOS transmission gate C 1  is turned on in response to the PCLKR signal of a logic “low” level generated in response to row address strobe signal RASB, so that the external address A is transmitted to the latch L 1  via the inverter I 1 . When the signal PCLKR of the logic “low” level is transited to the logic “high” level, the CMOS transmission gate C 3  is turned on and a signal, i.e., the address A, latched in the latch L 1 , is transmitted via the inverter I 8  and the CMOS transmission gate C 3  to the latch L 2 .  
           [0014]    Accordingly, the mode-setting signal MAB is transited from a logic “low” level to a logic “high” level along with the logic level transition of the address A during the normal operation mode, thereby causing undesired current consumption.  
           [0015]    [0015]FIG. 3 is a timing diagram illustrating operation of the address buffer in FIG. 2, wherein the address A is transited from a logic “low” level to a logic “high” level.  
           [0016]    When the row address strobe signal RASB of a logic “low” level and the address A transiting from a logic “low” level to a logic “high” level are externally input to the semiconductor memory device at rising edge of a clock signal CLK, the PCLKR signal is generated in response to the row address strobe signal RASB. The CMOS transmission gate C 1  transmits the address A to the latch L 1  in response to the PCLKR signal of a logic “low” level. The CMOS transmission gate C 3  transmits the signal output from the latch L 1  to the latch L 2  in response to the PCLKR signal of a logic “high” level. Accordingly, current is consumed by the address buffer because the mode-setting signal MAB is transited from a logic “low” level to a logic “high” level along with level transition of the address A in the normal operation mode. Further, if the active command ACT of a logic “high” level is generated, the CMOS transmission gate C 2  is turned on and generates the buffered address AB rising up from a logic “low” level to a logic “high” level.  
           [0017]    Worse, such current consumption by the mode-setting signal buffer unit increases as the number of the address buffers increases.  
         SUMMARY OF THE INVENTION  
         [0018]    To overcome the problems described above, a preferred embodiment of the present invention provides an address buffer wherein a mode-setting signal is not changed in response to logic level of an address externally input during a normal operation mode, thereby reducing current consumption, and a semiconductor memory device utilizing such an address buffer.  
           [0019]    In accordance with one aspect of the present invention, there is provided an address buffer comprising: a first buffering means for generating a buffered address upon buffering a signal externally applied in a normal operation mode; and a second buffering means for keeping a mode-setting signal in a reset status in the normal operation mode and for generating the mode-setting signal by buffering the signal externally applied in a mode-setting operation mode.  
           [0020]    The first address buffer includes: a first transmission gate for transmitting the signal by being turned on in response to a first control signal; a first latch for latching an output signal of the first transmission gate; a second transmission gate for transmitting an output signal of the first latch by being turned on in response to a second control signal; and a buffer for generating the buffered address by buffering an output signal of the second transmission gate.  
           [0021]    The second buffer includes: an ANDing circuit for ANDing the first control signal and the mode-setting command; a third transmission gate for transmitting the output signal of the first latch in response to an output signal of the ANDing circuit; and a second latch for generating the mode-setting signal by latching an output signal of the third transmission gate and resetting the mode-setting signal.  
           [0022]    The second latch further includes a reset transistor for resetting the mode-setting signal.  
           [0023]    In accordance with another aspect of the present invention, there is provided a semiconductor memory device comprising: a plurality of pins; and a plurality of buffers for buffering signals input through the plurality of pins, wherein each of the buffers includes: a first buffering means for generating a buffered signal by buffering the signals in a normal operation mode; and a second buffering means for maintaining a mode-setting signal in a reset status in the normal operation mode and generating the mode-setting signal by buffering the signals in a mode-setting operation mode.  
           [0024]    In accordance with further another aspect of the present invention, there is provided a semiconductor memory device comprising: a plurality of pins; and a plurality of buffers for buffering signals input through the plurality of pins, wherein each of the buffer includes: a first buffering means for latching the signals in response to a first control signal in a normal operation mode of the semiconductor memory device and generating buffered signals by buffering latched signals in response to a second control signal; a second buffering means for generating a mode-setting signal using the latched signals in response to the first control signal and a mode-setting command in a mode-setting operation mode, and maintaining the mode-setting signal in reset status in the normal operation mode. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    The other features and advantages of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows when taken in conjunction with the accompanying drawings, in which like reference numerals denote like parts, and in which:  
         [0026]    [0026]FIG. 1 is a circuit diagram of a semiconductor memory device in accordance with the conventional art;  
         [0027]    [0027]FIG. 2 is a circuit diagram of an address buffer in accordance with the conventional art;  
         [0028]    [0028]FIG. 3 is a timing diagram illustrating the operation of the address buffer shown in FIG. 2;  
         [0029]    [0029]FIG. 4 is a block diagram of a semiconductor memory device in accordance with the present invention;  
         [0030]    [0030]FIG. 5 is a circuit diagram of an address buffer in accordance with the present invention; and  
         [0031]    [0031]FIGS. 6A and 6B are timing diagrams illustrating operation of the address buffer shown in FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    Reference will now be made in detail to a preferred embodiment of the present invention, example of which is illustrated in the accompanying drawings.  
         [0033]    [0033]FIG. 4 is a block diagram of a semiconductor memory device in accordance with one embodiment of the present invention. Like reference designates the like element in FIG. 1 and FIG. 4. Address buffers  40 - 1  to  40 - n  in the semiconductor memory device of FIG. 4 are different from the address buffers  14 - 1  to  14 - n  in FIG. 1 and other elements in FIG. 4 are the same as FIG. 1.  
         [0034]    The address buffers  40 - 1  to  40 - n  latch external addresses A 1  to An in response to a PCLKR signal, and then generate mode-setting signals MAB 1  to MABn in response to a buffered clock signal PCLK and to a mode-setting command MRS and buffered addresses AB 1  to ABn by buffering the latched external addresses A 1  to An in response to an active command ACT.  
         [0035]    That is, the address buffers  40 - 1  to  40 - 4  in FIG. 4 generate the buffered addresses AB 1  to ABn and the mode-setting signals MAB 1  to MABn maintain a logic “low” level in normal operation mode of the semiconductor memory device. The mode-setting signals MAB 1  to MABn are generated only when the mode-setting command MRS is generated.  
         [0036]    Accordingly, the address buffers in accordance with the present invention do not consume current in the normal operation mode even if the addresses are changed because the logic level of the mode-setting command MRS is not changed during the normal operation mode.  
         [0037]    [0037]FIG. 5 is a circuit diagram of the address buffer in accordance with the present invention. The address buffer in accordance with the present invention is configured to add a NAND gate NA and an inverter I 11  to the mode-setting signal buffer unit  32 ′ of the address buffer in FIG. 2.  
         [0038]    Comparing the address buffers in FIG. 2 with that in FIG. 5, the address buffer unit  30  in FIG. 5 is identical to that in FIG. 2 but the mode-setting signal buffer unit  32 ′ in FIG. 5 is different from the mode-setting signal buffer unit  32  in FIG. 2.  
         [0039]    The NAND gate NA NANDs the PCLKR signal and the mode-setting command MRS. The inverter I 11  inverts an output signal of the NAND gate NA.  
         [0040]    Operation of the address buffers shown in FIG. 5 will be described below. Operation of the address buffer unit  30  in FIG. 5 is identical to the operation of the address buffer unit  30  in FIG. 2. Accordingly, explanation about the operation of the address buffer unit  30  will be omitted. Operation of the mode-setting signal buffer unit  32 ′ will be described.  
         [0041]    In the normal operation mode of the semiconductor memory device, the NAND gate NA generates a signal of a logic “high” level when the PCLKR signal of a logic “high” level and the mode-setting command MRS of a logic “low” level are applied to the semiconductor memory device and then the CMOS transmission gate C 3  is turned off in response to the signal of a logic “high” level output from the NAND gate NA. Accordingly, the latched signal latched by the latch L 1  is not transmitted to the latch L 2 . Thus, the mode-setting signal MAB maintains logic “low” level regardless of a change of the address A and the mode-setting signal buffer unit  32 ′ does not consume current in the normal operation mode.  
         [0042]    On the other hand, during the mode-setting operation, the NAND gate NA generates a signal of a logic “low” level, turning on the CMOS transmission gate C 3  when the PCLKR signal of logic “high” level and the mode-setting command MRS of a logic “high” level are applied to the semiconductor memory device. Those of skill in the art will appreciate that NAND gate NA and inverter I 11  thus effectively AND the PCLKR signal and the mode-setting command MRS. The CMOS transmission gate C 3  transmits the signal latched by the latch L 1  to the latch L 2  and the latch L 2  latches the signal transmitted from the CMOS transmission gate C 3 . At this time, the mode-setting signal MAB is changed in response to the change of the address A.  
         [0043]    [0043]FIGS. 6A and 6B are timing diagrams showing operation of the address buffer shown in FIG. 5.  
         [0044]    Operation of the address buffer in normal operation mode will be described in conjunction with FIG. 6A. At a rising edge of the clock signal CLK, when the row address strobe signal RASB of a logic “low” level is externally applied to the semiconductor memory device along with the row address A, the PCLKR signal of a logic “high” level is generated. Therefore, the CMOS transmission gate C 1  transmits the address A by being turned on and the latch L 1  latches the address A in response to the PCLKR signal of a logic “low” level. The CMOS transmission gate C 3  is turned off in response to the PCLKR signal of logic “low” level, thereby not transmitting the address A. Accordingly, the mode-setting signal MAB maintains a logic “low” level.  
         [0045]    Further, in case the PCLKR signal is transited to a logic “high” level and the mode-setting command MRS maintains a logic “low” level, the CMOS transmission gate C 3  is turned off, not transmitting the signal. Accordingly, even if the PCLKR signal is transited to a logic “high” level, the mode-setting signal MAB maintains logic “low” level, not being changed. Further, when the active command ACT of a logic “high” level is generated, the CMOS transmission gate C 2  is turned on, thereby transmitting the signal latched by the latch L 1 . That is, a buffered address AB of a logic “high” level is generated.  
         [0046]    As shown in FIG. 6A, the CMOS transmission gate forming the mode-setting signal buffer is turned off, thereby keeping the mode-setting signal MAB in a logic “low” level and preventing undesired current consumption in the address buffer.  
         [0047]    Operation of the address buffer in the mode-setting operation mode will be described in conjunction with FIG. 6B. At a rising edge of the clock signal CLK, when the row address strobe signal RASB of a logic “low” level is externally applied to the semiconductor memory device along with the row address A, the PCLKR signal of a logic “high” level is generated. The CMOS transmission gate C 1  transmits the address A by being turned on in response to the PCLKR signal of a logic “low” level and the latch L 1  latches the address A.  
         [0048]    When the mode-setting command MRS is in logic “high” level, the CMOS transmission gate C 3  is turned on and transmits the signal latched by the latch L 1  to the latch L 2 . Therefore, the mode-setting signal MAB may be transited from a logic “low” level to a logic “high” level. At this time, the CMOS transmission gate C 2  is turned off because the active command is not generated, and the signal latched in the latch L 1  is not transmitted. As a result the buffered address AB that is an output signal of the address buffer unit  30  maintains its previous logic level. That is, the logic level of the mode-setting signal MAB is transited in response to the externally applied signal during the mode-setting operation.  
         [0049]    Accordingly, in the address buffer in accordance with the present invention, the mode-setting signal maintains a logic “low” level in the normal operation mode and its logic level is changed in response to the externally applied signal only in the mode-setting operation mode, thereby reducing undesired current consumption in the normal operation mode.  
         [0050]    In the description with respect to the embodiment of the present invention, the mode-setting signal is input from the address pins in the mode-setting operation mode, but the mode-setting signal may be input through another pin. Thus, the present invention may be applied to the address buffer receiving the mode-setting signal from pins other than the address pins also.  
         [0051]    While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.