Abstract:
A transmitter includes: a main pull-up driver suitable for pull-up driving an output node; and an auxiliary pull-up driver suitable for pull-up driving the output node based on a voltage of the output node, wherein the auxiliary pull-up driver compensates for non-linear driving current characteristics of the main pull-up driver.

Description:
TECHNICAL FIELD 
     Various embodiments of the present invention relate to a transmitter for transmitting signals to and from an integrated circuit. 
     BACKGROUND 
     Integrated circuits may operate by exchanging signals with peripheral devices. For example, memory devices, such as DRAMs and flash memory devices may exchange signals with a memory controller. Also, central processing units (CPUs) may exchange data with a variety of semiconductor memory devices on a mother board. Furthermore signal transmission may be performed between integrated circuits of different devices as well as between integrated circuits included inside the same semiconductor device. A circuit for transmitting signals is typically referred to as a transmitter or an output driver. 
     DISCUSSION OF THE RELATED ART 
       FIG. 1  is a diagram illustrating a conventional transmitter. 
     Referring to  FIG. 1 , a conventional transmitter includes a P-type metal-oxide-semiconductor (PMOS) transistor  101 , a resistor  102 , an N-type metal-oxide-semiconductor (NMOS) transistor  103  and a resistor  104 . 
     When a pull-up driving signal PUB is activated to a low logic level, the PMOS transistor  101  is turned on, and thus an output node OUTPUT is driven by a pull-up voltage through the PMOS transistor  101  and the resistor  102 . That is, a signal having a high logic level is output through the output node OUTPUT. The pull-up driving signal PUB is activated when the transmitter transmits a signal having a high logic level. 
     When a pull-down driving signal PD is activated to a high logic level, the NMOS transistor  103  is turned on, and thus the output node OUTPUT is driven by a pull-down voltage VSS (i.e., a ground voltage) through the NMOS transistor  103  and the resistor  104 . That is, a signal having a low logic level is output through the output node OUTPUT. The pull-down driving signal PD is activated when the transmitter transmits a signal having a low logic level. 
     Passive resistors  102  and  104  are used for securing the linearity of the driving current flowing through the transmitter. However, the parasitic capacitance of the transmitter may generally be increased due to the use of the resistors  102  and  104 . As a result, it may be difficult for the transmitter to operate at a high speed. 
     SUMMARY 
     Various embodiments of the invention are directed to a transmitter capable of securing the linearity of driving current without the use of passive resistors. 
     In an embodiment of the present invention, a transmitter may include: a main pull-up driver suitable for pull-up driving an output node; and an auxiliary pull-up driver suitable for pull-up driving the output node when the main pull-up driver is enabled based on a level of the output node, wherein the auxiliary pull-up driver compensates for non-linear driving current characteristics of the main pull-up driver. 
     The transmitter may further include a main pull-down driver for pull-down driving the output node; and an auxiliary pull-down driver suitable for pull-down driving the output node when the main pull-down driver is enabled based on the voltage of the output node. The auxiliary pull-down driver may compensate for nonlinear driving characteristics of the main pull-down driver. 
     When the main pull-up driver is disabled, the auxiliary pull-up driver may not drive the output node regardless of the voltage of the output node. 
     When the main pull-down driver is disabled, the auxiliary pull-down driver may not drive the output node regardless of the voltage of the output node. 
     The main pull-up driver may include a first PMOS transistor for pull-up driving the output node in response to a pull-up driving signal. 
     The auxiliary pull-up driver may include a second PMOS transistor for applying a pull-up voltage in response to the pull-up driving signal; a third PMOS transistor for transmitting the voltage of the output node in response to the pull-up driving signal; and a fourth PMOS transistor for pull-up driving the output node using the pull-up voltage applied by the second PMOS transistor in response to the voltage of the output node which is transmitted by the third PMOS transistor. 
     The auxiliary pull-up driver may include the second PMOS transistor for applying the pull-up voltage in response to the pull-up driving signal; and the third PMOS transistor for pull-up driving the output node using the pull-up voltage applied by the second PMOS transistor in response to the voltage of the output node. 
     The main pull-down driver may include a first NMOS transistor for pull-down driving the output node in response to a pull-down driving signal. 
     The auxiliary pull-down driver may include a second NMOS transistor for applying a pull-down voltage in response to the pull-down driving signal; a third NMOS transistor for transmitting the voltage of the output node in response to the pull-down driving signal; and a fourth NMOS transistor for pull-up driving the output node using the pull-down voltage applied by the second NMOS transistor in response to the voltage of the output node which is transmitted by the third NMOS transistor. 
     The auxiliary pull-down driver may include the second NMOS transistor for applying the pull-down voltage in response to the pull-down driving signal; and the third NMOS transistor for pull-down driving the output node using the pull-down voltage applied by the second NMOS transistor in response to the voltage of the output node. 
     In an embodiment of the present invention, a transmitter may include: a main pull-down driver for pull-down driving an output node; and an auxiliary pull-down driver suitable for pull-down driving the output node in response to a voltage of the output node. 
     When the main pulldown driver is disabled, the auxiliary pull-down driver may stop driving the output node regardless of the voltage of the output node. 
     The main pull-down driver may include a first NMOS transistor for pull-down driving the output node in response to a pull-down driving signal. 
     The auxiliary pull-down driver may include a second NMOS transistor for applying a pull-down voltage in response to the pull-down driving signal; a third NMOS transistor for transmitting the voltage of the output node in response to the pull-down driving signal; and a fourth NMOS transistor for pull-down driving the output node using the pull-down voltage applied by the second NMOS transistor in response to the voltage of the output node which is transmitted by the third NMOS transistor. 
     The auxiliary pull-down driver may include the second NMOS transistor for applying the pull-down voltage in response to the pull-down driving signal; and the fourth NMOS transistor for pull-down driving the output node using the pull-down voltage applied by the second NMOS transistor in response to the voltage of the output node. 
     In an embodiment of the present invention, a transmitter may include: a first PMOS transistor suitable for pull-up driving an output node based on a pull-up driving signal; a second PMOS transistor suitable for supplying a pull-up voltage based on the pull-up driving signal; a third PMOS transistor suitable for pull-up driving the output node using the pull-up voltage supplied through the second PMOS transistor based on a voltage of the output node; a first NMOS transistor suitable for pull-down driving the output node based on a pull-down driving signal; a second NMOS transistor suitable for supplying a pull-down voltage based on the pull-down driving signal; and a third NMOS transistor suitable for pull-down driving the output node using the pull-down voltage supplied through the second NMOS transistor based on the voltage of the output node. 
     The transmitter may further include a fourth PMOS transistor suitable for transmitting the voltage of the output node based on the pull-up driving signal. 
     The transmitter may further include a fourth NMOS transistor suitable for transmitting the voltage of the output node based on the pull-down driving signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a conventional transmitter. 
         FIG. 2  is a diagram illustrating a transmitter in accordance with an embodiment of the present invention. 
         FIG. 3  is a diagram illustrating a transmitter in accordance with another embodiment of the present invention. 
         FIGS. 4 to 6  are diagrams illustrating the driving current of the transmitters shown in  FIGS. 2 and 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will be described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Throughout the disclosure, like reference numerals refer to like parts throughout the various figures and embodiments of the present invention. 
     The drawings are not necessarily to scale and, in some instances, proportions may have been exaggerated to clearly illustrate features of the embodiments. It is also noted that in this specification, “connected/coupled” refers to one component not only directly coupling another component, but also indirectly coupling another component through an intermediate component. In addition, a singular form may include a plural form as long as it is not specifically mentioned. 
       FIG. 2  illustrates an example of a transmitter in accordance with the present invention. 
     Referring to  FIG. 2 , a transmitter may include a main pull-up driver  210 , an auxiliary pull-up driver  220 , a main pull-down driver  230  and an auxiliary pull-down driver  240 . 
     The main pull-up driver  210  may pull-up drive an output node in a high logic signal driving period. The main pull-up driver  210  may include a PMOS transistor  211  for pull-up driving the output node OUTPUT in response to a pull-up driving signal PUB. Unlike the conventional transmitter of  FIG. 1 , the main pull-up driver  210  does not include a passive resistor. The pull-up driving signal PUB may be activated to a low logic level when the transmitter transmits a signal having a high logic level. 
     The auxiliary pull-up driver  220  may be activated in the high logic signal driving period, and may pull-up drive the output node OUTPUT in response to a voltage of the output node. The auxiliary pull-up driver  220  may not drive the output node OUTPUT regardless of the voltage of the output node OUTPUT in a period other than the high logic signal driving period. The auxiliary pull-up driver  220  may compensate for non-linear driving current characteristics of the main pull-up driver  210 . 
     The auxiliary pull-up driver  220  may include a PMOS transistor  221  for applying a pull-up voltage VDD in response to the pull-up driving signal PUB, a PMOS transistor  223  for transmitting the voltage of the output node OUTPUT in response to the pull-up driving signal PUB and a PMOS transistor  222  for pull-up driving the output node OUTPUT using the pull-up voltage VDD applied through the PMOS transistor  221  in response to the voltage of the output node OUTPUT which is transmitted through the PMOS transistor  223 . 
     In operation, the PMOS transistors  221  and  223  may be turned on when the pull-up driving signal PUB is activated to a low logic level. A pull-up voltage VDD may be applied to the PMOS transistor  222 , the voltage of the output node OUTPUT may be transmitted to a gate of the PMOS transistor  222  and the output node OUTPUT may be driven according to the voltage of the output node OUTPUT. When the pull-up driving signal PUB is deactivated to a high logic level, the auxiliary pull-up driver  220  may not drive the output node OUTPUT because the PMOS transistors  221  and  223  are turned off. The PMOS transistor  221  may activate/deactivate the auxiliary pull-up driver  220  and the PMOS transistor  222  may drive the output node OUTPUT. The PMOS transistor  223  may prevent the gate of the PMOS transistor  222  from being damaged or destroyed by static electricity which may flow into the output node OUTPUT. 
     The main pull-down driver  230  may pull-down drive the output node OUTPUT in a ‘low’ signal (data) driving period. The main pull-down driver  230  may include a NMOS transistor  231  for pull-down driving the output node in response to a pull-down driving signal PD. Unlike the conventional transmitter of  FIG. 1 , the main pull-down driver  230  does not include a passive resistor. The pull-down driving signal PD may be activated to the high logic level when the transmitter transmits a signal having a low logic level. 
     The auxiliary pull-down driver  240  may include a NMOS transistor  241  for applying a pull-down voltage VSS (i.e., a ground voltage) in response to the pull-down driving signal PD, a NMOS transistor  243  for transmitting the voltage of the output node OUTPUT in response to the pull-down driving signal PD and a NMOS transistor  242  for pull-down driving the output node OUTPUT using the pull-down voltage VSS applied through the NMOS transistor  241  in response to the voltage of the output node OUTPUT which is transmitted through the NMOS transistor  243 . 
     In operation, if the pull-down driving signal PD is activated to the high logic level, the NMOS transistors  241  and  243  may be turned on. Therefore, the pull-down voltage VSS may be applied to the NMOS transistor  242 , the voltage of the output node OUTPUT may be transmitted to a gate of the NMOS transistor  242  and the output node OUTPUT may be driven according to the voltage of the output node OUTPUT. When the pull-down driving signal PD is deactivated to the low logic level, the auxiliary pull-down driver  240  does not drive the output node OUTPUT because the NMOS transistors  241  and  243  are turned off. In the auxiliary pull-down driver  240 , the NMOS transistor  241  may activate or deactivate the auxiliary pull-down driver  240  and the NMOS transistor  242  may drive the output node OUTPUT. The NMOS transistor  243  may prevent the gate of the NMOS transistor  242  from being damaged or destroyed by the static electricity which may flow into the output node OUTPUT. 
     In  FIG. 2 , the transmitter may be used in signal (e.g., data) transmission between two or more semiconductor devices as well as between internal circuits in a single semiconductor device. 
     The main pull-up driver  210 , the auxiliary pull-up driver  220 , the main pull-down driver  230  and the auxiliary pull-down driver  240  of  FIG. 2  may be used separately. For example, the main pull-up driver  210  and the auxiliary pull-up driver  220  may be used with a pull-down driver having a conventional configuration such as, for example, the NMOS transistor  103  and the resistor  104  in  FIG. 1 . Also, the main pull-down driver  230  and the auxiliary pull-down driver  240  may be used with a pull-up driver having a conventional configuration such as, for example, the PMOS transistor  101  and the resistor  102  in  FIG. 1 ). The transmitter shown in  FIG. 3  has a similar configuration to the transmitter shown in  FIG. 2 , except that the transmitter of  FIG. 3  does not have the PMOS transistor  223  and the NMOS transistor  243  shown in  FIG. 2 . 
     Referring now to  FIG. 3 , it should be noted that the PMOS transistor  223  is omitted from the auxiliary pull-up driver  220  in  FIG. 3  and the gate of the PMOS transistor  222  is directly coupled to the output node OUTPUT. Also, the NMOS transistor  243  is omitted from the auxiliary pull-down driver  240  in  FIG. 2  and the gate of the NMOS transistor  242  is directly coupled to the output node OUTPUT. 
     The design of  FIG. 2  is advantageous when it is desired to protect the transmitter from static electricity. However, when there is no need to protect the gates of the PMOS transistor  223  and NMOS transistor  243  because static electricity is less likely to occur in the output node OUTPUT, it may then be possible to design the transmitter as shown in  FIG. 3 . The transmitter of  FIG. 3  may be advantageous because of its simpler structure in applications not concerned with damage that may be caused by static electricity. 
       FIG. 4  to  FIG. 6  are diagrams illustrating the linearity of the driving current of the transmitters of  FIGS. 2 and 3 . 
       FIG. 4  shows the driving current IOUT_MAIN that the main pull-up driver  210  drives the output node OUTPUT when the pull-up driving signal PUB is activated, according to the voltage of the output node OUTPUT. Referring to  FIG. 4 , the driving current IOUT_MAIN of the main pull-up driver  210  is non-linear in a section that the voltage of the output node OUTPUT is low. 
       FIG. 5  shows the driving current IOUT_SUB that the auxiliary pull-up driver  220  drives the output node OUTPUT when the pull-up driving signal PUB is activated, according to the voltage of the output node OUTPUT. Referring to  FIG. 5 , the driving current IOUT_SUB of the auxiliary pull-up driver  220  has a linear characteristic in a section that the voltage of the output node OUTPUT is low. However, the driving current IOUT_SUB of the auxiliary pull-up driver  220  is zero in the section that the voltage of the output node OUTPUT is high. 
       FIG. 6  shows the driving current IOUT_SUM of the transmitter which is the sum of the driving current IOUT_MAIN of the main pull-up driver  210  and the driving current IOUT_SUB of the auxiliary pull-up driver  220 . Referring to  FIG. 6 , the driving current IOUT_SUM of the transmitter has a substantially linear characteristic in the voltage fluctuation range of the output node OUTPUT. 
     Although various embodiments of the invention have been described for illustrative purposes, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.