Abstract:
There are provided an output driver for a semiconductor device for securing the constant pull-up and pull-down drivability regardless of temperature condition and process characteristic. The output driver for a semiconductor device includes a first driving unit for transmitting an output data; a detecting unit for detecting at least one of a temperature condition and a process characteristic; an auxiliary pull-up driving unit for pulling up a level of the output data in response to the detection result of the detecting unit; and an auxiliary pull-down driving unit for pulling down the level of the output data in response to the detection result of the detecting unit.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a semiconductor design technology; and, more particularly, to an output driver for a semiconductor device.  
       DESCRIPTION OF RELATED ART  
       [0002]     Semiconductor devices are fabricated using overall semiconductor technologies, including a silicon wafer processing technology and a logic design technology. Final products of the semiconductor fabrication process are plastic package type chips. They have different logics and functions depending on objects of use. Most of semiconductor chips are mounted on printed circuit board (PCB), which is an important element in a system configuration, and appropriate driving voltages are supplied to them.  
         [0003]     All semiconductor devices including semiconductor memory devices are operated according to input/output of specific signals. That is, the operations and operating methods of the semiconductor devices are determined by a combination of these input signals. Also, their results are outputted according to the flow of the output signals. Meanwhile, an output signal of a certain semiconductor device may be used as an input signal of another semiconductor device within the same system.  
         [0004]      FIG. 1  is a circuit diagram of an input/output interface unit in a conventional semiconductor device.  
         [0005]     Referring to  FIG. 1 , the input/output interface unit  10  of the semiconductor device includes an input buffer  12  and an output driver  14 .  
         [0006]     The input buffer  12  buffers an external signal inputted through an input terminal DQ and inputs the buffered signal to the inside of the semiconductor device. A static input buffer and a differential input buffer are generally used as the input buffer  12 .  
         [0007]     Meanwhile, the output driver  14  drives an output terminal DQ and a load connected thereto by using an output data of the semiconductor device. A CMOS inverter type main driver is used as the output driver  14 . The CMOS inverter type main driver is configured with a pull-up PMOS transistor and a pull-down NMOS transistor, which are connected in series between a source voltage and a ground voltage. Also, a pre-driver may be provided in a previous stage of the main driver.  
         [0008]     As an operating voltage of the semiconductor device is lower and an operating speed is faster, performance of the output driver is important in association with signal integrity. It is because voltage level and slew rate of the output data are determined by the output driver.  
         [0009]     In such a conventional output driver, a current drivability of the pull-up transistor and the pull-down transistor is different depending on temperature condition and process characteristic. In general, the operation characteristic is divided into a best case, a typical case, a worst case. In the worst case, the drivability in the output terminal DQ of the output driver is low. In addition, when temperature is high, the drivability is also degraded. The low drivability of the output driver is a factor that degrades the output characteristic of the semiconductor device.  
       SUMMARY OF THE INVENTION  
       [0010]     It is, therefore, an object of the present invention to provide an output driver for a semiconductor device for securing a constant pull-up and pull-down drivability regardless of process characteristic or temperature condition.  
         [0011]     In accordance with an aspect of the present invention, there is provided an output driver of a semiconductor device including: a first driving unit for transmitting an output data; and a second driving unit for controlling the output data based on at least one of a temperature condition and a process characteristic in order to stabilize the output data.  
         [0012]     In accordance with another aspect of the present invention, there is provided a semiconductor memory device for stably driving an output data including: a first driving unit for transmitting an output data; a detecting unit for detecting at least one of a temperature condition and a process characteristic; and a second driving unit for controlling the output data based on detection result of the detecting unit in order to stabilize the output data.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:  
         [0014]      FIG. 1  is a circuit diagram of a data input/output interface unit in a conventional semiconductor device;  
         [0015]      FIG. 2  is a circuit diagram of an output driver in accordance with an embodiment of the present invention;  
         [0016]      FIG. 3  is a pull-up current curve with respect to an operation characteristic-temperature condition; and  
         [0017]      FIG. 4  is a pull-down current curve with respect to an operation characteristic-temperature condition. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter.  
         [0019]      FIG. 2  is a circuit diagram of an output driver in accordance with an embodiment of the present invention.  
         [0020]     Referring to  FIG. 2 , the output driver  100  includes a main driving unit  120 , an auxiliary driving unit  140  and  160 . The main driving unit  120  drives an output terminal by using an output data of an output driver controlling unit  180 . The auxiliary driving unit  140  and  160  auxiliarily drives the output terminal DQ by using an amount of a current depending on temperature condition and process characteristic.  
         [0021]     Also, the main driving unit  120  includes a pull-up pre-driver  122 , a pull-down pre-driver  124 , a main pull-up driver PMOS transistor Q 11 , and a main pull-down driver NMOS transistor Q 12 . The pull-up pre-driver  122  pre-drives the output data to generate a pull-up control signal PUE, and the pull-down pre-driver  124  pre-drives the output data to generate a pull-down control signal PDE. The main pull-up driver PMOS transistor Q 11  pulls up the output terminal DQ in response to the pull-up control signal PUE, and the main pull-down driver NMOS transistor Q 12  pulls down the output terminal DQ in response to the pull-down control signal PDE.  
         [0022]     The auxiliary driving unit  140  and  160  is used for controlling the drivability and includes an auxiliary pull-up driving unit  140  and an auxiliary pull-down driving unit  160 . The auxiliary pull-up driving unit  140  auxiliarily pulls up the output terminal DQ by using the amount of the current depending on the temperature condition and the process characteristic. The auxiliary pull-down driving unit  160  auxiliarily pulls down the output terminal DQ by using the amount of the current depending on the temperature condition and the process characteristic.  
         [0023]     The auxiliary pull-up driving unit  140  is provided for controlling the pull-up drivability of the output terminal DQ in each step, depending on the temperature condition and the process characteristic. The auxiliary pull-up driving unit  140  includes a pull-up (PU) detector  142 , a first decoder  144 , a plurality of driver PMOS transistors Q 4 , Q 3 , Q 2  and Q 1 , and an auxiliary pull-up driver PMOS transistor Q 5 . The pull-up (PU) detector  142  detects the temperature condition and the process characteristic. The first decoder  144  decodes an m-bit output value (m is a positive integer, m=2 in this embodiment) of the pull-up detector  142 . The driver PMOS transistors Q 4 , Q 3 , Q 2  and Q 1  are connected in parallel to a source voltage VDDQ supply. Each gate of the driver PMOS transistors Q 4 , Q 3 , Q 2  and Q 1  receives the output signals ISU_ 0 , ISU_ 1 , ISU_ 2  and ISU_ 3  of the first decoder  144 , respectively. The auxiliary pull-up driver PMOS transistor Q 5  is connected between the output terminal DQ and the driver PMOS transistors Q 4 , Q 3 , Q 2  and Q 1 , and has a gate receiving the pull-up control signal PUE. Preferably, all the driver PMOS transistors Q 4 , Q 3 , Q 2  and Q 1  of the auxiliary pull-up driving unit  140  are designed with the equal size.  
         [0024]     The auxiliary pull-down driving unit  160  is provided for controlling the pull-down drivability of the output terminal DQ in each step, depending on the temperature condition and the process characteristic. The auxiliary pull-down driving unit  160  includes a pull-down (PD) detector  162 , a second decoder  164 , a plurality of driver NMOS transistors Q 6 , Q 7 , Q 8  and Q 9 , and an auxiliary pull-down driver NMOS transistor Q 10 . The pull-down (PD) detector  162  detects the temperature condition and the process characteristic. The second decoder  164  decodes an m-bit output value of the pull-down detector  162 . The driver NMOS transistors Q 6 , Q 7 , Q 8  and Q 9  are connected in parallel to a ground voltage supply VSSQ. Gates of the driver NMOS transistors Q 6 , Q 7 , Q 8  and Q 9  receive the output signals ISD_ 0 , ISD_ 1 , ISD_ 2  and ISD_ 3  of the second decoder  164 , respectively. The auxiliary pull-down driver NMOS transistor Q 10  is connected between the output terminal DQ and the driver NMOS transistors Q 6 , Q 7 , Q 8  and Q 9 , and has a gate receiving the pull-down control signal PDE. Preferably, all the driver NMOS transistors Q 6 , Q 7 , Q 8  and Q 9  of the auxiliary pull-down driving unit  160  are designed with the equal size.  
         [0025]     Each of the pull-up detector  142  and the pull-down detector  162  can be configured with a temperature sensor, a process characteristic sensor, and a binary adder for adding outputs of the two sensors.  
         [0026]     Meanwhile, the first decoder  144  is a 2×4 decoder. PUSW_ 0 , PUSW_ 1 , PUSW_ 2  and PUSW_ 3  represent four switching elements each of which receives a different combination of 2-bit values outputted from the pull-up detector  142 . These switching elements can be configured with a NAND gate and so on. The second decoder  164  is a 2×4 decoder. PDSW_ 0 , PDSW_ 1 , PDSW_ 2  and PDSW_ 3  represent four switching elements each of which receives a different combination of 2-bit values outputted from the pull-down detector  162 . These switching elements can be configured with a NAND gate and so on.  
         [0027]     Tables 1 to 3 below show exemplary controls of the pull-up drivability in the output driver  100  of  FIG. 2  according to the process characteristic and the temperature condition. An operation of the output driver  100  in accordance with the present invention will be described below with reference to Tables 1 to 3.  
                                   TABLE 1                           Temperature                       Process   Condition       Characteristic   (° C.)   ISU_0   ISU_1   ISU_2   ISU_3                   Best Case   &lt;−10   H   H   H   H           −10-25     L   H   H   H           25-55   L   L   H   H             &gt;55   L   L   L   H                  
 
         [0028]    
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
               
               
                   
                 Temperature 
                   
                   
                   
                   
               
               
                 Process 
                 Condition 
               
               
                 Characteristic 
                 (° C.) 
                 ISU_0 
                 ISU_1 
                 ISU_2 
                 ISU_3 
               
               
                   
               
             
             
               
                 Typical Case 
                 &lt;−10 
                 L 
                 H 
                 H 
                 H 
               
               
                   
                 −10-25   
                 L 
                 L 
                 H 
                 H 
               
               
                   
                 25-55 
                 L 
                 L 
                 L 
                 H 
               
               
                   
                   &gt;55 
                 L 
                 L 
                 L 
                 L 
               
               
                   
               
             
          
         
       
     
         [0029]    
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
               
               
                   
                 Temperature 
                   
                   
                   
                   
               
               
                 Process 
                 Condition 
               
               
                 Characteristic 
                 (° C.) 
                 ISU_0 
                 ISU_1 
                 ISU_2 
                 ISU_3 
               
               
                   
               
             
             
               
                 Worst Case 
                 &lt;−10 
                 L 
                 L 
                 H 
                 H 
               
               
                   
                 −10-25   
                 L 
                 L 
                 L 
                 H 
               
               
                   
                 25-55 
                 L 
                 L 
                 L 
                 L 
               
               
                   
                   &gt;55 
                 L 
                 L 
                 L 
                 L 
               
               
                   
               
             
          
         
       
     
         [0030]     It will be assumed that the pull-up control signal PUE is activated to a logic low level.  
         [0031]     Table 1 shows logic levels of the output signals ISU_ 0 , ISU_ 1 , ISU_ 2  and ISU_ 3  of the first decoder  144  in the auxiliary pull-up driving unit  140  when the process characteristic is the best case, depending on the respective temperature conditions.  
         [0032]     Referring to Table 1, all the driver PMOS transistors Q 1 , Q 2 , Q 3  and Q 4  are turned off under the temperature condition of below −10° C., and only one transistor Q 4  is turned on under the temperature condition of −10° C. to 25° C. Two transistors Q 4  and Q 3  are turned on under the temperature condition of 25° C. to 55° C., and three transistors Q 4 , Q 3  and Q 2  are turned on under the temperature condition of above 55° C. Therefore, the turned-on transistor(s) forms a current path together with the auxiliary pull-up driver PMOS transistor Q 5 . That is, in the best case of the process characteristic, a current drivability of the main pull-up driver PMOS transistor Q 11  is secured somewhat. Therefore, the auxiliary pull-up driver PMOS transistor Q 5  does not have to operate at a low temperature. As the temperature increases higher, more transistors are turned on stepwise. Therefore, the constant pull-up drivability can be secured regardless of the process characteristic and the temperature condition.  
         [0033]     Table 2 shows logic levels of the output signals ISU_ 0 , ISU_ 1 , ISU_ 2  and ISU_ 3  of the first decoder  144  in the auxiliary pull-up driving unit  140  when the process characteristic is the typical case, depending on the respective temperature conditions.  
         [0034]     Referring to Table 2, only one transistor Q 4  is turned on under the temperature condition of below −10° C., and two transistors Q 4  and Q 3  are turned on under the temperature condition of −10° C. to 25° C. Three transistors Q 4 , Q 3  and Q 2  are turned on under the temperature condition of 25° C. to 55° C., and all the driver PMOS transistors Q 1 , Q 2 , Q 3  and Q 4  are turned on under the temperature condition of above 55° C. Therefore, the turned-on transistor(s) forms a current path together with the auxiliary pull-up driver PMOS transistor Q 5 . That is, in the typical case of the process characteristic, a current drivability of the main pull-up driver PMOS transistor Q 11  is typical. Therefore, by turning on more transistors compared with the best case, the constant pull-up drivability can be secured regardless of the process characteristic and the temperature condition.  
         [0035]     Table 3 shows logic levels of the output signals ISU_ 0 , ISU_ 1 , ISU_ 2  and ISU_ 3  of the first decoder  144  in the auxiliary pull-up driving unit  140  when the process characteristic is the worst case, depending on the respective temperature conditions.  
         [0036]     Referring to Table 3, two transistors Q 4  and Q 3  are turned on under the temperature condition of below −10° C., and three transistors Q 4 , Q 3  and Q 2  are turned on under the temperature condition of −10° C. to 25° C. All the driver PMOS transistors Q 1 , Q 2 , Q 3  and Q 4  are turned on under the temperature condition of 25° C. to 55° C. and above 55° C. Therefore, the turned-on transistors form a current path together with the auxiliary pull-up driver PMOS transistor Q 5 . That is, in the worst case of the process characteristic, a current drivability of the main pull-up driver PMOS transistor Q 11  is lowered. Therefore, by turning on more transistors compared with the typical case, the constant pull-up drivability can be secured regardless of the process characteristic and the temperature condition. Meanwhile, the equal current drivability is exhibited under the temperature condition of 25° C. to 55° C. and above 55° C. In this embodiment, it can be understood that the maximum value is selected according as four driver PMOS transistors Q 1 , Q 2 , Q 3  and Q 4  are provided.  
         [0037]     As described above, an amount of a current flowing through the auxiliary pull-up driver PMOS transistor Q 5  is controlled depending on the process characteristic and the temperature condition. That is, the drivability due to the auxiliary pull-up driver PMOS transistor Q 5  is made to relatively decrease when the process characteristic and the temperature condition are good, and it is made to relatively increase when they are bad. In this manner, the degradation in the drivability of the main pull-up driver PMOS transistor Q 11  can be compensated.  
         [0038]      FIG. 3  is a pull-up current curve with respect to an operation characteristic-temperature condition.  
         [0039]     As illustrated in  FIG. 3 , the pull-up drivability for the output terminal DQ can be maintained constantly depending on the process characteristic and the temperature condition.  
         [0040]     In  FIG. 3 , A, B, C and D represent pull-up current curves when the process characteristic and the temperature condition are worst, bad, good, and best, respectively. These curves are results according to the prior art. However, when the present invention is applied, the pull-up current curve can exhibit the desired target value.  
         [0041]     Meanwhile, since the operations according to the temperature and the process characteristic are dependent on the 2-bit output value of the pull-up detector  142 , the 2-bit output value must be able to be generated through a combination of the detection results of the temperature sensor and the process characteristic sensor within the pull-up detector  142 . An example of the pull-up detector  142  satisfying Tables 1 to 3 will be described below.  
         [0042]     For the best/typical/worst cases, the process characteristic sensor of the pull-up detector  142  outputs ‘01/11/01’ as its detection result. Also, the temperature sensor outputs ‘00/01/10/11’ as its detection results with respect to four steps of Tables 1 to 3. The binary adder of the pull-up detector  142  adds the two output values.  
         [0043]     For example, when the typical process characteristic is typical and the temperature condition is 25° C. to 55° C., the output value of the process characteristic sensor is ‘00’ and the output value of the temperature sensor is ‘10’. Therefore, the 2-bit output value of the first pull-up detector  142  is ‘10’. The output signal of the first decoder  144  is ‘0011’ when the 2-bit output value of the pull-up detector  142  is ‘00’, and the output signal of the first decoder  144  is ‘0011’ when the 2-bit output value of the pull-up detector  142  is ‘01’. The output signal of the first decoder  144  is ‘0001’ when the 2-bit output value of the pull-up detector  142  is ‘10’, and the output signal of the first decoder  144  is ‘0000’ when the 2-bit output value of the pull-up detector  142  is ‘11’. Consequently, the output signal of the first decoder  144  is ‘0001’, so that three transistors Q 4 , Q 3  and Q 2  of the driver PMOS transistors Q 1 , Q 2 , Q 3  and Q 4  are turned on (refer to Table 2). Meanwhile, assuming that the first decoder  144  is disabled when the 2-bit output value of the pull-up detector  142  is negative like when the process characteristic is best and the temperature condition is below −10° C., all the PMOS transistors Q 1 , Q 2 , Q 3  and Q 4  can be turned off.  
         [0044]     Tables 4 to 6 below show exemplary controls of the pull-up drivability in the output driver  100  of  FIG. 2  according to the process characteristic and the temperature condition.  
                                   TABLE 4                           Temperature                       Process   Condition       Characteristic   (° C.)   ISD_0   ISD_1   ISD_2   ISD_3                   Best Case   &lt;−10   L   L   L   L           −10-25     H   L   L   L           25-55   H   H   L   L             &gt;55   H   H   H   L                  
 
         [0045]    
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
               
               
                   
                 Temperature 
                   
                   
                   
                   
               
               
                 Process 
                 Condition 
               
               
                 Characteristic 
                 (° C.) 
                 ISD_0 
                 ISD_1 
                 ISD_2 
                 ISD_3 
               
               
                   
               
             
             
               
                 Typical Case 
                 &lt;−10 
                 H 
                 L 
                 L 
                 L 
               
               
                   
                 −10-25   
                 H 
                 H 
                 L 
                 L 
               
               
                   
                 25-55 
                 H 
                 H 
                 H 
                 L 
               
               
                   
                   &gt;55 
                 H 
                 H 
                 H 
                 H 
               
               
                   
               
             
          
         
       
     
         [0046]    
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                   
               
               
                   
                 Temperature 
                   
                   
                   
                   
               
               
                 Process 
                 Condition 
               
               
                 Characteristic 
                 (° C.) 
                 ISD_0 
                 ISU_1 
                 ISU_2 
                 ISU_3 
               
               
                   
               
             
             
               
                 Worst Case 
                 &lt;−10 
                 H 
                 H 
                 L 
                 L 
               
               
                   
                 −10-25   
                 H 
                 H 
                 H 
                 L 
               
               
                   
                 25-55 
                 H 
                 H 
                 H 
                 H 
               
               
                   
                   &gt;55 
                 H 
                 H 
                 H 
                 H 
               
               
                   
               
             
          
         
       
     
         [0047]     Table 4 shows logic levels of the output signals ISD_ 0 , ISD_ 1 , ISD_ 2  and ISD_ 3  of the second decoder  164  in the auxiliary pull-down driving unit  160  when the process characteristic is the best case, depending on the respective temperature conditions. Table 5 shows logic levels of the output signals ISD_ 0 , ISD_ 1 , ISD_ 2  and ISD_ 3  of the second decoder  164  in the auxiliary pull-down driving unit  160  when the process characteristic is the typical case, depending on the respective temperature conditions. Table 6 shows logic levels of the output signals ISD_ 0 , ISD_ 1 , ISD_ 2  and ISD_ 3  of the second decoder  164  in the auxiliary pull-down driving unit  160  when the process characteristic is the worst case, depending on the respective temperature conditions.  
         [0048]     Since data of Tables 4 to 6 has opposite polarities to data of Tables 1 to 3, the number of the driver NMOS transistors Q 6 , Q 7 , Q 8  and Q 9  selected according to the respective conditions is equal. Accordingly, the pull-down detector  162  satisfying Tables 4 to 6 can be implemented with the same structure as that of the pull-up detector  142 . At this point, the second decoder  164  is configured to have the polarity opposite to that of the first decoder  144 .  
         [0049]     The pull-down operation of the output driver according to Tables 4 to 6 is equal to the above-described pull-up operation. That is, in this embodiment, the output driver controls an amount of a current flowing through the auxiliary pull-down driver NMOS transistor Q 10  depending on the operation characteristic and the temperature condition during the pull-down operation. The drivability due to the auxiliary pull-down driver NMOS transistor Q 10  is made to relatively decrease when the process characteristic and the temperature condition are good, and it is made to relatively increase when they are bad. In this manner, the degradation in the drivability of the pull-down NMOS transistor Q 12  can be compensated.  
         [0050]      FIG. 4  is a pull-down current curve with respect to an operation characteristic-temperature condition.  
         [0051]     As illustrated in  FIG. 4 , the pull-down drivability for the output terminal DQ can be maintained constantly depending on the process characteristic and the temperature condition.  
         [0052]     In  FIG. 4 , A′, B′, C′ and D′ represent pull-down current curves when the process characteristic and the temperature condition are worst, bad, good, and best, respectively. These curves are results according to the prior art. However, when the present invention is applied, the pull-down current curve can exhibit the desired target value.  
         [0053]     Meanwhile, as described above, if the pull-up detector  142  and the pull-down detector  162  are implemented with the equal structures, the auxiliary pull-up driving unit  140  and the auxiliary pull-down driving unit  160  need not have the detector. Therefore, the auxiliary pull-up driving unit  140  and the auxiliary pull-down driving unit  160  can share one detector.  
         [0054]     If necessary, it is necessary to differently control the pull-up drivability and the pull-down drivability. In this case, the drivability of the pull-up side and the pull-down side can be differently controlled by making the pull-up driver  142  and the pull-down driver  162  have the different outputs.  
         [0055]     In the above-described embodiment, although the auxiliary pull-up and pull-down driving units  140  and  160  use four driver PMOS transistors and four driver NMOS transistors, respectively, the driver transistors can use transistors of opposite polarity and the number of the driver transistors can be changed.  
         [0056]     In addition, although both the temperature sensor and the process characteristic sensor are applied for considering the temperature condition and the process characteristic, only one of them can be applied.  
         [0057]     As described above, the pull-up and pull-down drivability can be secured regardless of the process characteristic and the temperature condition. Thus, the signal integrity of the output driver can be secured and the reliability of the semiconductor device can be improved.  
         [0058]     The present application contains subject matter related to Korean patent application No. 2005-27339, filed in the Korean Intellectual Property Office on Mar. 31, 2005, the entire contents of which is incorporated herein by reference.  
         [0059]     While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.