Abstract:
Disclosed is a data output buffer having a preset structure. The data output buffer comprises a plurality of groups, each group having two data output buffers, a preset driver for precharging or discharging any one output of two output buffers in each group, a control circuit for generating a control signal to drive the preset driver when outputs of the two output buffers in each group are same, and a set circuit connected between the outputs of the two data output buffers in each group, for making the outputs of the two data output buffer in each group the same level. Therefore, a data output speed of the data output buffer could be improved and the peak current could be also reduced.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a data output buffer for semiconductor devices, and more particularly, to a data output buffer having a present structure. 
     2. Background of the Related Art 
     FIG. 1 is a block diagram for generating a control signal for use in semiconductor devices. 
     An address transition detecting unit  10  senses when an inputted address is shifted to generate an address transition detection signal atd. An equalization signal generating circuit  20  generates an equalization signal peq according to the address transition detection signal atd. A control and delay circuit  30  generates various control signals and delay signals (peqdly, poe . . . ) according to the inputted equalization signal peq. 
     FIG. 2 is a detailed circuit diagram of a conventional data output buffer. The operation of the data output buffer will be described by reference to FIG.  3 . In FIG. 3, an address Add, a chip select signal/CS, an output enable signal/OE and a write enable signal/WE are signals used for the operation of the common semiconductor memory devices. 
     FIG. 2 has a structure in which in a given period of time after transition of an address is detected in a read operation and a read cycle then begins, a data sodin from a sense amplifier (not shown) reaches a data output buffer and at once a pulse output enable signal poe operates the data output buffer, which then outputs a data. This will be described in detail below. 
     If the read operation begins, the output signal sodin of the sense amplifier reaches the data output buffer. As the pulse output enable signal poe through inverters I 1  and I 2  is at a LOW level, that is, the outputs of NAND gates ND 1  and ND 2  are at HIGH levels in a standby mode, PMOS and NMOS transistors P 1  and N 1  are turned off. Thus, the output dout is changed to a HIGH impedance level by an external termination circuit  40 . Thereafter, if the pulse output enable signal poe becomes HIGH, the output sodin of the sense amplifier is transferred to the output dout. If the output sodin of the sense amplifier is HIGH, the output of the NAND gate ND 1  becomes LOW. The signal of the LOW level is applied to the gate terminal of the PMOS transistor P 1  via the inverters I 3  and I 4 . Accordingly, the PMOS transistor P 1  is turned on, so that the output dout becomes HIGH. 
     On the contrary, the output of the NAND gate ND 2  becomes HIGH. The signal of the HIGH level is inverted by the inverter  16  and is then applied to the gate terminal of the NMOS transistor N 1 . Therefore, the NMOS transistor N 1  is turned off. 
     This type of the data output buffer has an external load and a rapid read cycle. Furthermore, if this data output buffer has to output data opposite to data of the previous cycle, the output dout must largely swing from  0 V to Vcc. Therefore, there is a possibility that noise may occur due to delayed speed and increased peak current. In particular, if the data output buffer is constructed in a wide bit and has to output a plurality of data at the same time, the output dout is changed from a LOW level to a HIGH level or HIGH level to LOW level. Therefore, generation of noise due to increased peak current is inevitable. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is contrived to substantially obviate one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a data output buffer having a preset structure in which the output of the data output buffer is preset to an intermediate level in advance and is then converted to an effective data level depending on an input data. 
     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 objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a data output buffer having a preset structure according to the present invention is characterized in that it comprises a plurality of groups, each group having two data output buffers, a preset driver for precharging or discharging any one output of two output buffers in each group, a control circuit for generating a control signal to drive the preset driver when outputs of the two output buffers in each group are same, and a set circuit connected between the outputs of the two data output buffers in each group, for making the outputs of the two data output buffer in each group the same level. 
     In another aspect of the present invention, it is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block diagram for generating a control signal for use in semiconductor devices; 
     FIG. 2 is a detailed circuit diagram of a conventional data output buffer; 
     FIG. 3 illustrates a waveform for explaining the operations of the prior art data output buffer 
     FIG. 4 illustrates a simulation result waveform of the prior art data output buffer; 
     FIG. 5 illustrates a waveform showing the output current of the prior art data output buffer. 
     FIG. 6 is a detailed circuit diagram of a data output buffer according to the present invention; 
     FIG. 7 is a detailed circuit diagram of a present unit in FIG. 6; 
     FIG. 8 illustrates an evaluation circuit for driving the present unit of FIG. 7; 
     FIG. 9 illustrates a set circuit for equalizing the outputs of an odd data output buffer and an even data output buffer according to the present invention; 
     FIG. 10 illustrates a waveform for explaining the operations of the data output buffer according to the present invention; 
     FIG. 11 illustrates a simulation result waveform of the data output buffer according to the present invention; and 
     FIG. 12 illustrates a waveform showing the output current of the data output buffer according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 6 is a detailed circuit diagram of a data output buffer having a preset structure according to the present invention. 
     The data output buffer is constructed in plural. In the present invention, the data output buffer is divided into an odd data output buffer and an eves data output buffer. As shown in FIG. 6, a preset driver  100  is connected to the output dout 1  of the odd data output buffer  50 . The even data output buffer  60  has the same construction to the prior art. Furthermore, the output dout 1  of the odd data output buffer  50  and the output dout 2  of the even data output buffer  60  are connected each other through a set circuit  70 . Although only two data output buffers are shown in FIG. 6, those having skill in the art will appreciated that the data output buffer may be constructed in plural numbers such as 4, 16, 32, or the like. Even in this case, the odd data output buffer includes the preset driver  100  and the even data output buffer has the same construction to the prior art. Also, the output dout 1  of the odd data output buffer  50  and the output dout 2  of the even data output buffer  60  are connected each other in pairs by the set circuit  70 . 
     A basic principle of the present invention will be now described by is reference to FIG.  6  and FIG.  10 . 
     The operation of the present invention may be classified into four steps in large part. In other words, there are an evaluation step (a), a preset step (b), a set step (c) and an output step (d), as shown in FIG.  10 . 
     Before the operation of the four steps is explained, the operation of the odd data output buffer  50  will be first described. The construction except for the preset driver  100  is same to that of the prior art. For simplicity, explanation on respective elements will be omitted. 
     The preset driver  100  comprises the PMOS transistor P 2  connected between the power supply Vcc and the output dout 1  and turned on by the control signal dp 12 , and the NMOS transistor N 2  connected between the output dout 2  and the ground Vss and turned on by the control signal dn 12 . 
     The preset driver  100  is driven by the output of the preset circuit  80  shown in FIG.  7 . The preset circuit  80  is driven by the output of the evaluation circuit  90  in FIG.  8 . Accordingly, the evaluation circuit  90 , the preset circuit  80  and the preset driver  100  will be sequentially explained. 
     The evaluation circuit  90  generates a preset signal preset 1  and a preset enable signal preset 1 _enb according to the output signaldout 1  of the odd data output buffer, the output signal dout 2  of the even data output buffer and the equalization signal peq in FIG.  1 . 
     This may be summarized as in the following Table 1 below. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 1 
                 2 
                 3 
                 4 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 dout1 
                 H 
                 L 
                 H 
                 L 
               
               
                 dout2 
                 H 
                 L 
                 L 
                 H 
               
               
                 preset1_enb 
                 L 
                 L 
                 H 
                 H 
               
               
                 preset1 
                 H 
                 L 
                 X 
                 X 
               
               
                   
               
             
          
         
       
     
     As shown in Table 1, if both the output dout 1  of the odd data output buffer and the output dout 2  of the even data output buffer are HIGH, the preset enable signal preset 1 _enb is enabled to be LOW and the preset signal preset 1  becomes HIGH. Furthermore, both the output dout 1  of the odd data output buffer and the output dout 2  of the even data output buffer are LOW, the preset enable signal preset 1 _enb is enable to be LOW and the preset signal preset 1  becomes LOW. 
     If the output dout 1  of the odd data output buffer and the output dout 2  of the even data output buffer are different, the preset enable signal preset 1 _enb is disabled to be HIGH, whereby the preset driver  100  does not operate. 
     The operation of the respective elements will be described taking a case where both the output dout 1  of the odd data output buffer and the output dout 2  of the even data output buffer are HIGH as an example. 
     A transmission gate T 1  is turned on by the equalization signal peq and a signal inverted by the inverter  17  and the output dout 1  is thus latched to a first latch  110  consisting of inverters  18  and  19 . 
     A transmission gate T 2  is turned on by the equalization signal peq and a signal inverted by an inverter I 11  and the output dout 2  is thus latched to a second latch  120  consisting of inverters I 11  and I 12 . 
     As both the outputs dout 1  and dout 2  are HIGH, both the outputs of the first and second latches  110  and  120  become LOW. As both the outputs of a NOR gate NOR 1  and a NAND gate ND 3  are HIGH, the signal through the inverters  13  and  14  becomes HIGH. Therefore, the preset signal preset 1  becomes HIGH. 
     As the output of the inverter I 13  is LOW, the output of the NOR gate NOR 2  becomes LOW. As all of the output of the inverter I 15 , the delayed equalization signal peqdly 1  and the equalization signal inverted by the inverter I 16  are HIGH, the output of the NAND gate ND 4  becomes LOW. Accordingly, the preset enable signal preset 1 _enb becomes LOW. The operation of the preset circuit will be now described by reference to FIG.  4 . 
     The preset circuit  80  drives the preset driver  100  to make the preset signal preset 1  control signals dp 12  and dn 12  in a period when the pulse output enable signal poe is disabled to be LOW and the data output buffer does not output an effective data. 
     In case where the pulse output enable signal poe is enabled to be HIGH or the preset enable signal preset 1 _enb is disabled to be HIGH, the preset driver  100  is disabled. This will be described in more detail by reference to the preset circuit of FIG.  7 . 
     If the pulse output enable signal poe is LOW and the preset enable signal preset 1 _enb of FIG. 8 is LOW, the output of the NOR gate NOR 3  becomes HIGH. Therefore, a PMOS transistor P 3  is turned off and transmission gates T 3  and T 4  are turned on. Furthermore, a NMOS transistor N 3  is turned off by the output of the inverter I 17 . Therefore, the preset signal preset 1  becomes the control signals dp 12  and dn 12 . In other words, if the preset signal preset 1  is LOW, the control signals dp 12  and dn 12  become LOW. The NMOS transistor N 2  of the present driving circuit  100  in FIG. 6 is turned off but the PMOS transistor P 2  is turned on, so that the output dout 1  is precharged with the power supply voltage Vcc. On the contrary, if the preset signal preset 1  is HIGH, the NMOS transistor N 2  is turned on but the PMOS transistor P 2  is turned off, so that the output dout 1  is discharged. 
     Meanwhile, if the pulse output enable signal poe is enabled to be HIGH and is being outputted, or though the pulse output enable signal poe is LOW, the pulse output enable signal poe corresponds to  3  and  4  columns in Table 1 as the result of evaluation, the preset operation is not necessary and the set operation only is necessary, the transmission gates T 3  and T 4  are turned off, and the PMOS transistor P 3  and the NMOS transistor N 3  are turned on. As the control signal dp 12  becomes HIGH and control signal dn 12  becomes LOW, both the transistors N 2  and P 2  are turned off. For reference, when the pulse output enable signal poe is enabled, the transistors P 2  and N 2  must have been disabled. 
     The operation of the set circuit will be now described by reference to FIG.  6 . 
     The output dout 1  of the odd data output buffer  50  and the output dout 2  of the even data output buffer  60  are connected each other according to the operation of the transmission gate T 5 . 
     In other words, if the equalization signal peqdly 1  delayed in a period where the pulse output enable signal poe is disabled to be LOW and the data output buffers  50  and  60  do not output effective data, is LOW, the output of the NOR gate NOR 4  becomes HIGH. Therefore, the signal through the inverters I 18  and I 19  becomes HIGH and the output of the inverter I 9  becomes LOW. The transmission gate T 5  is thus turned on. Accordingly, the outputs dout 1  and dout 2  of the odd and even data output buffers  50  and  60  are shorted. As described above, if the control signal dp 12  of the preset circuit  80  is LOW, the PMOS transistor P 2  of the preset driver  100  is turned on. If the output dout 1  of the odd data output buffer  50  was thus charged with the power supply voltage Vcc, the outputs dout 1  and dout 2  of the odd and even data output buffers  50  and  60  become ½ Vcc by the operation of the set circuit  70 . If the pulse output enable signal poe is enabled to be HIGH in a state that the outputs dout 1  and dout 2  are precharged with ½ Vcc, an effective data is outputted according to the data from the sense amplifier. 
     The evaluation step (a), the preset step (b), the set step (c) and the output step (d), being the basic four steps of the present invention, will be described based on the above explanation. 
     1. Evaluation Step (â period in FIG. 10) 
     In a period where the equalization signal peq is HIGH, the output dout 1  of the odd data output buffer  50  and the output dout 2  of the even data output buffer  60  are evaluated using the evaluation circuit  90  in FIG. 8, thus generating the preset enable signal preset 1 _enb and the preset signal preset 1 , as in Table 1. 
     2. Preset Step ({circle around (b)} period in FIG. 10) 
     In a period where the equalization signal peq is LOW and the delayed equalization signal peqdly 1  is HIGH, the preset driver  100  of FIG. 6 is driven by the output of the preset circuit  80  in FIG.  7 . (the present driver  100  is driven when both the outputs dout 1  and dout 2  are HIGH or LOW). For this reason, the output dout 1  of the odd data output buffer  50  is precharged with the power supply voltage Vcc. 
     3. Set Step (ĉ period in FIG. 10) 
     In a period where both the equalization signal peq and the pulse output enable signal poe are LOW, the outputs dout 1  and dout 2  are connected through the set circuit  70  in FIG. 9, whereby the outputs dout 1  and dout 2  make ½ Vcc. 
     4. Output Step ({circle around (d)} period in FIG. 10) 
     As the pulse output enable signal poe is enabled to be HIGH, an actual data of the output sodin of the sense amplifier is outputted. 
     FIG. 11 illustrates a simulation result waveform of the data output buffer according to the present invention and a simulating result waveform of the prior art data output buffer. From FIG. 11, it can be seen that the output of the data output buffer in the present invention is rapidly changed than those in the prior art. 
     FIG. 12 illustrates a waveform showing the output current of the data output buffer according to the present invention. FIG. 5 illustrates a waveform showing the output current of the prior art data output buffer. 
     From FIG.  12  and FIG. 5, it can be seen that the peak current of the data output buffer according to the present invention flows by about below 60% than those in the prior art. 
     As described above, the present invention has new effects that it can improve a data output speed of the data output buffer and reduce the peak current. 
     The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings 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.