Patent Publication Number: US-2023146284-A1

Title: Slew boost amplifier and display driver having the same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2021-0151942, filed Nov. 8, 2021, the entire contents of which are incorporated herein for all purposes by this reference. 
     FIELD 
     The present disclosure relates to a slew boost amplifier and a display driver having the same. More particularly, the present disclosure relates to a slew boost amplifier and a display driver having the same, which include a first current generation circuit configured to apply a first current to an upper current mirror circuit (or an output terminal thereof); a second current generation circuit configured to apply a second current to a lower current mirror circuit (or an output terminal thereof); and comparison circuit configured to detect a difference between an input voltage and an output voltage and to cause the first current generation circuit to apply the first current when the difference is greater than or equal to a first predetermined threshold and the second current generation circuit to apply the second current when the difference is less than a second predetermined threshold. 
     BACKGROUND 
     Recently, as a display is configured with a high resolution and an enlarged size, driving time of display elements in the display decreases. When a source driving circuit fails to drive a data line of a display panel to a target voltage within the driving time, a problem occurs in image quality. Therefore, the need for a source driving circuit having a high slew rate is continuously increasing. 
     In addition, as the demand for low-power and high-resolution portable terminals and electronic displays is rapidly increasing, demand for a Display Driver IC (DDI) with a high slew rate performance to charge a display panel in a short time increases. At this time, there is a technique for improving an overall performance by increasing the current consumption of an amplifier (AMP) that serves as a source driver in the DDI to implement the high slew rate. 
     However, the DDI with increased current consumption by the amplifier has difficulties in portable electronic device applications using a battery (e.g., due to the current consumption). 
     Accordingly, research on a display driver having a high slew rate, but without an increase in current consumption, is continuously being conducted. 
     The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art, or that is already known to those skilled in the art. 
     Document of Related Art 
     Korean Patent No. 10-1579839, entitled “Output buffer having high slew rate, method for controlling output buffer, and display drive IC having same.” 
     BRIEF DESCRIPTION 
     Accordingly, the present inventor has conceived a novel slew boost amplifier and a display driver having the same, the details of which will be described later. 
     The present disclosure has been made keeping in mind the above problems occurring in the related art, and an objective of the present disclosure is to provide a slew boost amplifier and a display driver having the same, wherein the slew boost amplifier and the display driver provide a current path by comparing an input voltage and an output voltage, thereby amplifying a signal at a high slew rate (or increasing the slew rate) without increasing power consumption (current consumption). 
     In addition, another objective of the present disclosure is to provide the slew boost amplifier and the display driver having the same, wherein the slew boost amplifier and the display driver provide a high slew rate without an increase in power consumption, thereby allowing the high slew rate to be embodied even in a portable electronic device. 
     In addition, still another objective of the present disclosure is to provide the slew boost amplifier and the display driver having the same, wherein the slew boost amplifier and the display driver amplify the slew rate by comparing the input voltage and the output voltage, thereby allowing the slew rate to be increased and/or a driver signal to be quickly amplified even without an additional control circuit, and the slew rate increase and/or signal amplification to be embodied with a circuit having a small area. 
     In order to achieve the above-described objectives, the present disclosure may be implemented by one or more embodiments having one or more of the following configurations. 
     According to one or more embodiments of the present disclosure, there may be provided a slew boost amplifier, including a first current generation circuit configured to apply a first current to an upper current mirror circuit (or an output terminal thereof); a second current generation circuit configured to apply a second current to a lower current mirror circuit (or an output terminal thereof); and a comparison circuit configured to detect a difference between an input voltage and an output voltage and to cause the first current generation circuit to apply the first current when the difference is greater than or equal to a first predetermined threshold and the second current generation circuit to apply the second current when the difference is less than a second predetermined threshold. 
     According to another embodiment of the present disclosure, in the slew boost amplifier according to the present disclosure, is at least a first set value greater than the output voltage, the first current generation circuit may apply the first current to a first output terminal of the upper current mirror circuit. 
     According to still another embodiment of the present disclosure, in the slew boost amplifier according to the present disclosure, when the input voltage is less than the output voltage by at least a second set value, the second current generation circuit may apply the second current to a first output terminal of the lower current mirror circuit. 
     According to still another embodiment of the present disclosure, a slew boost amplifier, connected to an output buffer circuit having an upper current mirror circuit and a lower current mirror circuit, according to the present disclosure may include a first current generation circuit configured to apply a first current to a first output terminal of the upper current mirror circuit; a second current generation circuit configured to apply a second current to a first output terminal of the lower current mirror circuit; and a comparison circuit configured to detect a difference between an input voltage and an output voltage and to cause one of the first current generation circuit and the second current generation circuit to apply the first current or the second current when the difference occurs, wherein the comparison circuit may include a first transistor providing a first current path, having a gate node connected to a power input line and/or configured to receive the input voltage, a source node connected to a line providing the output voltage, and a drain node connected to the first current generating circuit, and a second transistor providing a second current path, having a gate node connected to the power input line and/or configured to receive the input voltage, a source node connected to the line providing the output voltage, and a drain node connected to the second current generating circuit. 
     According to still another embodiment of the present disclosure, the first current generation circuit in the slew boost amplifier according to the present disclosure may include a third transistor having a gate node and a source node connected to the drain node of the first transistor; a fourth transistor having a gate node configured to receive a first bias signal, and a source node connected to a drain node of the third transistor; and a fifth transistor having a gate node connected to the drain node of the first transistor, a source node connected to a power supply, and a drain node connected to the first output terminal of the upper current mirror circuit. 
     According to still another embodiment of the present disclosure, when the input voltage is greater than or equal to (i) the output voltage, (ii) a first set value greater than the output voltage, or (iii) greater that a threshold voltage of the first transistor in the slew boost amplifier according to the present disclosure, the first transistor provides the first current path, the first current path being connected to the third transistor and the fourth transistor, and the fifth transistor may apply a third current mirroring the first current to the first output terminal of the upper current mirror circuit. 
     According to still another embodiment of the present disclosure, the second current generation circuit in the slew boost amplifier according to the present disclosure may include a sixth transistor having a gate node and a source node connected to the drain node of the second transistor; a seventh transistor having a gate node configured to receive a second bias signal, and a source node connected to a drain node of the sixth transistor; and an eighth transistor having a gate node connected to the drain node of the second transistor, a source node connected to a ground potential, and a drain node connected to the first output terminal of the lower current mirror circuit. 
     According to still another embodiment of the present disclosure, when the input voltage is less than (i) the output voltage, (ii) a second set value less than the output voltage, or (iii) less than a power supply minus a threshold voltage of the second transistor in the slew boost amplifier according to the present disclosure, the second transistor provides the second current path, the second current path being connected to the sixth transistor and the seventh transistor, and the eighth transistor may apply a fourth current mirroring the second current to the first output terminal of the lower current mirror circuit. 
     According to one or more embodiments of the present disclosure, there may be provided a display driver, the display driver including an output buffer circuit comprising an upper current mirror circuit and a lower current mirror circuit and outputting a first signal and a second signal in response to an input signal; and a slew boost amplifier configured to apply a current to one of the upper current mirror circuit and the lower current mirror circuit on the basis of a difference between the input signal and an output signal. 
     According to another embodiment of the present disclosure, the amplifier in the display driver according to the present disclosure may include a first current generation circuit configured to apply a first current to an output terminal of the upper current mirror circuit; a second current generation circuit configured to apply a second current to an output terminal of the lower current mirror circuit; and a comparison circuit configured to detect the difference between the input voltage and the output voltage and to output the output voltage by opening a current path in one of the first current generation circuit and the second current generation circuit when the difference occurs. 
     According to still another embodiment of the present disclosure, in the display driver according to the present disclosure, when the input voltage is greater than or equal to (i) the output voltage, (ii) a first set value greater than the output voltage, or (iii) greater than a threshold voltage of a first transistor in the comparison circuit, to the first current generation circuit carries the first current on a first current path, and the first current generation circuit may apply the first current on the first current path to the output terminal of the upper current mirror circuit. 
     According to still another embodiment of the present disclosure, in the display driver according to the present disclosure, when the input voltage is less than (i) the output voltage, (ii) a second set value less than the output voltage, or (iii) less than a power supply minus a threshold voltage of a second transistor in the comparison circuit, the second current generation circuit carries the second current on a second current path, and the second current generation circuit may apply the second current on the second current path to the output terminal of the lower current mirror circuit. 
     According to still another embodiment of the present disclosure, the display driver according to the present disclosure may include an output buffer circuit comprising an upper current mirror circuit and a lower current mirror circuit and outputting a first signal and a second signal in response to an input signal; and a slew boost amplifier configured to apply a current to one of a first output terminal of the upper current mirror circuit and a first output terminal of the lower current mirror circuit on a basis of a difference between the input signal and an output signal, wherein the slew boost amplifier may include a first current generation circuit configured to apply a first current to the first output terminal of the upper current mirror circuit; a second current generation circuit configured to apply a second current to the first output terminal of the lower current mirror circuit; and a comparison circuit configured to detect the difference between the input voltage and the output voltage and to apply the first current to the first output terminal of the upper current mirror circuit or the second current to the first output terminal of the lower current mirror circuit from a first current path in the first current generation circuit or a second current path in the second current generation circuit when the difference occurs. 
     According to still another embodiment of the present disclosure, the comparison circuit in the display driver according to the present disclosure may include a first transistor providing the first current path, having a gate node connected to a power input line and/or configured to receive the input voltage, a source node connected to a line providing the output voltage, and a drain node connected to the first current generating circuit, and a second transistor providing a second current path, having a gate node connected to the power input line and/or configured to receive the input voltage, a source node connected to the line providing the output voltage, and a drain node connected to the second current generating circuit. 
     According to still another embodiment of the present disclosure, the first current generation circuit in the display driver according to the present disclosure may include a third transistor having a gate node and a source node connected to the drain node of the first transistor; a fourth transistor having a gate node configured to receive a first bias signal, and a source node connected to a drain node of the third transistor; and fifth a transistor having a gate node connected to the drain node of the first transistor, a source node connected to a power supply, and a drain node connected to the first output terminal of the upper current mirror circuit. 
     According to still another embodiment of the present disclosure, when the input voltage is greater than or equal to (i) the output voltage, (ii) a first set value greater than the output voltage, or (iii) greater than a threshold voltage of the first transistor, the first transistor in the display driver according to the present disclosure may provide the first current path, and the first current path may be connected to the third transistor and the fourth transistor, and the fifth transistor may apply a third current mirroring the first current to the first output terminal of the upper current mirror circuit. 
     According to still another embodiment of the present disclosure, the second current generation circuit in the display driver according to the present disclosure may include a sixth transistor having a gate node and a source node connected to the drain node of the second transistor; a seventh transistor having a gate node configured to receive a second bias signal, and a source node connected to a drain node of the sixth transistor; and an eighth transistor having a gate node connected to the drain node of the second transistor, a source node connected to a ground potential, and a drain node connected to the first output terminal of the lower current mirror circuit. 
     According to still another embodiment of the present disclosure, when the input voltage is less than (i) the output voltage, (ii) a second set value less than the output voltage, or (iii) less than a power supply minus a threshold voltage of the second transistor, the second transistor in the display driver according to the present disclosure may provide the second current path, the second current path being connected to the sixth transistor and the seventh transistor, and the eighth transistor applies a fourth current mirroring the second current to the first output terminal of the lower current mirror circuit. 
     According to still another embodiment of the present disclosure, the output buffer circuit in the display driver according to the present disclosure may include a load circuit and an output circuit, where the load circuit may include an upper current mirror circuit comprising ninth and tenth transistors, each having a gate connected to the drain node of the fifth transistor; and a lower current mirror circuit comprising eleventh and twelfth transistors, each having a gate connected to the drain node of the eighth transistor, and the output circuit may include a thirteenth transistor having a gate connected to a second output terminal of the upper current mirror circuit and connected between the power supply and an output terminal of the output circuit; and a fourteenth transistor having a gate connected to a second output terminal of the lower current mirror circuit and connected between the output terminal of the output circuit and the ground potential. 
     According to still another embodiment of the present disclosure, the load circuit in the display driver according to the present disclosure may further include a first connection circuit including a fifteenth transistor configured to receive a first bias voltage and a sixteenth transistor configured to receive a second bias voltage; and a second connection circuit including a seventeenth transistor configured to receive the first bias voltage and an eighteenth transistor MN 6  configured to receive the second bias voltage, wherein the first connection circuit electrically connects the second output terminal of the upper current mirror circuit and the second output terminal of the lower current mirror circuit, and the second connection circuit electrically connects the first output terminal of the upper current mirror circuit and the first output terminal of the lower current mirror circuit. 
     The present disclosure has the following effects by the above configuration. 
     The present slew boost amplifier and display driver having the same may provide a current path by comparing an input voltage and an output voltage, thereby increasing or amplifying a high slew rate without increasing power consumption (current consumption). 
     In addition, the present slew boost amplifier and display driver having the same can provide a high slew rate without an increase in power consumption, and may allow a high slew rate to be embodied in a portable electronic device. 
     In addition, the present slew boost amplifier and display driver having the same can increase or amplify the slew rate by comparing the input voltage and the output voltage, thereby allowing the slew rate to be increased or amplified without an additional control circuit and/or the slew rate increase or amplification to be embodied in a circuit having a small area. 
     On the other hand, even if certain effects are not explicitly mentioned herein, the effects described in the following specification expected by the technical features of the present disclosure and potential effects thereof are treated as if they were described in the present specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram illustrating a display driving apparatus including a slew boost amplifier and an output buffer circuit according to one or more embodiments of the present disclosure; 
         FIG.  2    is a circuit diagram illustrating an output buffer circuit according to one or more embodiments of the present disclosure; 
         FIG.  3    is a circuit diagram illustrating a slew boost amplifier according to an embodiment of the present disclosure; 
         FIGS.  4  and  5    are circuit diagrams illustrating a link operation between a slew boost amplifier and an output buffer circuit according to an embodiment of the present disclosure; and 
         FIG.  6    shows graphs comparing and illustrating output waveforms of a slew boost amplifier circuit according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Embodiments of the present disclosure may be modified in various forms, and the scope of the present disclosure should not be construed as being limited to the following embodiments but should be interpreted on the basis of matters described in the claims. In addition, the present embodiment is provided for reference in order to more completely explain the present disclosure to those skilled in the art. 
     As used herein, a singular form may include a plural form unless the context clearly dictates otherwise. In addition, as used herein, the terms “comprise” and/or “comprising” refer to the presence of the recited shapes, numbers, steps, actions, members, elements, and/or groups thereof and does not exclude the presence or addition of one or more other shapes, numbers, movements, members, elements and/or groups thereof. 
     In addition, it should be noted that, although numbers may be used in describing configurations such as “first” and “second” below, the second configuration does not presuppose the first configuration, and each configuration may be mutually independent. 
     The slew boost amplifier and the display driver having the same according to embodiment(s) of the present disclosure are configured to amplify a signal and/or increase the slew rate without increasing current consumption, and thus may also be applied to displays that need to charge the display panel in a short time and to have a high slew rate performance together. 
     Hereinafter, a display driver to which the slew boost amplifier and an output buffer circuit according to embodiment(s) of the present disclosure are applied will be described with reference to the accompanying drawings. 
       FIG.  1    is a block diagram illustrating a display driving apparatus including a slew amplification circuit and an output buffer circuit according to one or more embodiments of the present disclosure. 
     With reference to  FIG.  1   , the display driver includes a digital-to-analog converter circuit  10 , an output buffer circuit  100 , and a slew boost amplifier  200 . Though not shown in  FIG.  1   , the display driver may include a restoration circuit configured to restore a data signal (e.g., in response to an input signal from a timing controller), a latch circuit configured to latch the restored data signal, and the like. 
     The digital-to-analog converter circuit  10  selects the grayscale voltages VGR&lt;1:j&gt; corresponding to the data signals D 1  to Dn, converts the selected grayscale voltages VGR&lt;1:j&gt; to the data voltages VIN 1  to VINn, and then provides the data voltages VIN 1  to VINn to the output buffer circuit  100 . 
     The output buffer circuit  100  buffers, outputs and/or drives the data voltages VIN 1  to VINn from the digital-to-analog converter circuit  10  and provides the source driving signals VOUT 1  to VOUTn to data lines of a display panel (not shown). Such an output buffer circuit  100  includes a plurality of output buffers configured to buffer, output and/or drive signals to prevent distortion of the source driving signals VIN 1  to VINn supplied to the data line. In this case, an operational amplifier (op-amp) may be used as the output buffer. 
     The slew boost amplifier  200  compares the input voltage and the output voltage and, when the difference between the input voltage and the output voltage occurs (e.g., exceeds a predetermined threshold), outputs a current to the output buffer circuit  100  to increase or amplify the slew rate of the output buffer circuit  100 . In this case, it is assumed that the input voltage is the data voltage VIN and the output voltage is the source driving signal VOUT. 
     The output buffer circuit  100  increases the slew rate by the current applied from the slew amplification circuit  200  and, through this, is capable of increasing the slew rate without additional current consumption. 
     Hereinafter, the output buffer circuit  100  according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. 
       FIG.  2    is a circuit diagram illustrating an output buffer circuit  100  according to an embodiment of the present disclosure. 
     With reference to  FIG.  2   , the output buffer circuit  100  includes a load circuit  130  and an output circuit  150 . Hereinafter, only the configuration and operation of the output buffer circuit  100  will be described, and the connection and an operation of the slew boost amplifier  200  will be described in detail in the description of the slew boost amplifier  200 . 
     The load circuit  130  may include an upper current mirror circuit comprising PMOS transistors MP 4 _ 1  and MP 5 _ 1  that operate in response to a bias voltage VB 5 , and composed of PMOS transistors MP 4  and MP 5 . The load circuit  130  may further include, or one or more pairs of the transistors MP 4 _ 1 , MP 5 _ 1 , MP 4  and MP 5  may form, an upper cascode circuit connected between first and second connection circuits. In addition, the load circuit  130  may include a lower current mirror circuit comprising NMOS transistors MN 4 _ 1  and MN 5 _ 1  that operate in response to a bias voltage VB 6 , and NMOS transistors MN 4  and MN 5 . The load circuit  130  may further include, or one or more pairs of the transistors MN 4 _ 1 , MN 5 _ 1 , MN 4  and MN 5  may form, a lower cascode circuit connected between the first and second connection circuits. The load circuit  130  having the cascode circuits has a large output impedance, so the output buffer circuit  100  including the load circuit  130  may obtain a high voltage gain. 
     The upper current mirror circuit may include PMOS transistors MP 4  and MP 5  connected in the form of a current mirror, and the lower current mirror circuit may include NMOS transistors MN 4  and MN 5  connected in the form of a current mirror. The first connection circuit may include a PMOS transistor MP 7  that operates in response to a third bias voltage VB 3  and an NMOS transistor MN 7  that operates in response to a fourth bias voltage VB 4 . The second connection circuit may include a PMOS transistor MP 6  that operates in response to the third bias voltage VB 3  and an NMOS transistor MN 6  that operates in response to the fourth bias voltage VB 4 . 
     The upper current mirror circuit is electrically connected to a first input stage comprising PMOS transistors MP 1  and MP 2 , which may be in an input terminal (not shown) and which may supply a current to the load circuit  130 . 
     The lower current mirror circuit is electrically connected to a second input stage including NMOS transistors MN 1  and MN 2 , which may be in the input terminal (not shown) and which may supply a current to the load circuit  130 . The first connection circuit may be electrically and/or indirectly connected to a first output terminal NCU of the upper current mirror circuit and a first output terminal NCD of the lower current mirror circuit. The second connection circuit may electrically connect a second output terminal NCSP of the upper current mirror circuit and a second output terminal NCSN of the lower current mirror circuit. A first capacitor C 1  may be connected between the first output terminal NCU of the upper current mirror circuit and an output terminal NOUT of the output circuit  150 , and a second capacitor C 2  may be connected between the first output terminal NCD of the lower current mirror circuit and the output terminal NOUT of the output circuit  150 . 
     The output circuit  150  may include a PMOS transistor MP 8  having a gate connected to the first output terminal NCU of the upper current mirror circuit. The PMOS transistor MP 8  may be a pull-up driver connected between a power supply voltage VDD and the output terminal NOUT. The output circuit  150  may further include an NMOS transistor MN 8  having a gate connected to the first output terminal NCD of the lower current mirror circuit. The NMOS transistor MN 8  may be a pull-down driver connected between the output terminal NOUT and the ground. 
     A push compensation current ICOMP_PUSH may be provided to the first output terminal NCU of the upper current mirror circuit, and a pull compensation current ICOMP_PULL may be provided to the first output terminal NCD of the lower current mirror circuit. 
     A pushing load current ILU may flow from the first output terminal NCU of the upper current mirror circuit (e.g., to a second input terminal, from a circuit comprising NMOS transistors, or another input terminal; not shown), and another (e.g., complementary) pushing load current ILUB may flow from the second output terminal NCSP of the upper current mirror circuit (e.g., to another second input terminal or the other input terminal; not shown). 
     A pulling load current ILD may flow from a first input terminal, from a circuit comprising PMOS transistors, and/or from another input terminal (not shown) to the first output terminal NCD of the lower current mirror circuit, and another (e.g., complementary) pulling load current ILDB may flow from a different first input terminal or a different other input terminal (not shown) to the second output terminal NCSN of the lower current mirror circuit. 
     Hereinafter, the slew boost amplifier  200  according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. 
       FIG.  3    is a circuit diagram illustrating a slew amplification circuit according to an embodiment of the present disclosure. 
     With reference to  FIG.  3   , the slew amplification circuit  200  generates a current path for slew increase or amplification when a difference between an input voltage and an output voltage occurs (e.g., crosses a predetermined threshold). In this case, the slew amplification circuit  200  includes a comparison circuit  210  that compares a difference between the input voltage and the output voltage or determines whether the difference between the input voltage and the output voltage crosses a threshold, a first current generation circuit  230 , and a second current generation circuit  250 . 
     The comparison circuit  210  generates a current path to the first current generation circuit  230  when the input voltage VIN is at least a set or predetermined value greater than the output voltage VOUT (e.g., is greater than the threshold voltage of the NMOS transistor MN 3 ). The comparison circuit  210  generates a current path to the second current generation circuit  250  when difference between the input voltage VIN and the output voltage VOUT is less than the set or predetermined value (e.g., the input voltage VIN is less than the supply voltage VDD minus the threshold voltage of the PMOS transistor MP 3 ). 
     To this end, the comparison circuit  210  includes a transistor MP 3  and a transistor MN 3 . Here, a gate node of the transistor MP 3  and a gate node of the transistor MN 3  are connected to a power input line to receive an input voltage VIN. In addition, a source node of the transistor MP 3  and a source node of the transistor MN 3  are connected to a power output line to receive an output voltage VOUT. In addition, a drain node of the transistor MP 3  is connected to the first current generation circuit  230 , and a drain node of the transistor MN 3  is connected to a second current generation circuit  250 . 
     The first current generation circuit  230  generates a current on a first current path along with the comparison circuit  210  (e.g., when the transistor MN 3  is conducting a current). The first current generation circuit  230  applies the current from the first current path to the second output terminal NCSP of the output buffer circuit  100 . 
     To this end, the first current generation circuit  230  includes a transistor MP 2 , a transistor MP 1 , and a transistor MP 21 , all of which may be PMOS transistors. 
     A gate node and a source node of the transistor MP 2  are connected to the comparison circuit  210 . That is, the gate node and the source node of the transistor MP 2  are connected to the drain node of the transistor MN 3 . In addition, a drain node of the transistor MP 2  is connected to a source node of the transistor MP 1 . 
     A gate node of the transistor MP 1  is connected to a signal line that receives a bias signal BIASP. In addition, a source node of the transistor MP 1  is connected to the drain node of the transistor MP 2 . In addition, a drain node of the transistor MP 1  is connected to a power supply VDD. 
     A gate node of the transistor MP 21  is also connected to the comparison circuit  210 . That is, the gate node of the transistor MP 21  is connected to the drain node of the transistor MN 3 . The gate node of the transistor MP 21  is also connected to the gate node of the transistor MP 2 . In addition, a source node of the transistor MP 21  is connected to the power supply VDD, and a drain node of the transistor MP 21  is connected to the output terminal NCSP of the output buffer circuit  100 . 
     The second current generation circuit  250  generates a current on a second current path along with the comparison circuit  210  (e.g., when the transistor MP 3  is conducting a current). The second current generation circuit  250  applies the current from the second current path to the second output terminal NCSN of the output buffer circuit  100 . 
     To this end, the second current generation circuit  250  includes a transistor MN 2 , a transistor MN 1 , and a transistor MN 21 , all of which may be NMOS transistors. 
     A gate node and a source node of the transistor MN 2  are connected to the comparison circuit  210 . That is, the gate node and the source node of the transistor MN 2  are connected to the drain node of the transistor MP 3 . In addition, a drain node of the transistor MN 2  is connected to a source node of the transistor MN 1 . 
     A gate node of the transistor MN 1  is connected to a signal line that receives a bias signal BIASN. In addition, the source node of the transistor MN 1  is connected to the drain node of the transistor MN 2 . In addition, the drain node of the transistor MN 1  is connected to a ground potential VSS. 
     A gate node of the transistor MN 21  is also connected to the comparison circuit  210 . That is, a gate node of the transistor MN 21  is connected to the drain node of the transistor MP 3 . The gate node of the transistor MN 21  is also connected to the gate node of the transistor MN 2 . In addition, a source node of the transistor MN 21  is connected to the ground potential VSS, and a drain node of the transistor MN 21  is connected to the output terminal NCSN of the output buffer circuit  100 . 
       FIGS.  4  and  5    are circuit diagrams illustrating a link operation between a slew amplification circuit and an output buffer circuit according to an embodiment of the present disclosure. 
     With reference to  FIG.  4   , when the input voltage VIN (which may be an input signal to an amplifier elsewhere in the DDI) has a voltage equal to or greater than the output voltage VOUT (which is an output signal from the amplifier elsewhere in the DDI), optionally plus |Vth|, the threshold voltage of the transistor MN 3 , whereby a first current path from the transistor MP 1  through the transistor MN 3  carries a current. Alternatively, when the input voltage VIN is equal to or greater than the threshold voltage of the transistor MN 3 , the transistor MN 3  may conduct a current and may output the current on the output node VOUT. The current flowing on the first current path is reproduced or “mirrored” by the transistor MP 21 . 
     A drain node of the transistor MP 21  is connected to the gate nodes of the transistors MP 4  and MP 5  of the output buffer circuit  100 , thereby increasing the voltage on the gates of the transistors MP 4  and MP 5 . Accordingly, the currents conducted by the transistors MP 4  and MP 5  decrease, the voltage on the gate of the transistor MP 8  (e.g., the pull-up driver) rapidly decreases, and thus the output voltage VOUT (e.g., on the node NOUT), which is the output of the output circuit  150  in the output buffer  100 , rises. 
     In addition, the current flowing through the transistor MP 21  may increase the current of the transistor MN 4  of the output buffer circuit  100  so that the current of the transistor MN 5  of the output buffer circuit  100  may also increase. 
     Accordingly, the voltage on the gate of the transistor MP 8  decreases, and the gate-source potential across the transistor MP 8  may also rapidly decrease, thereby increasing the slew rate of the output voltage VOUT. When the output voltage VOUT decreases, and the difference between the input voltage and the output voltage is no greater than |Vth|, the slew boost amplifier  200  may turn off the first current path, so additional current consumption of the slew boost amplifier  200  may not occur. 
     As for the opposite operation, with reference to  FIG.  5   , when the input voltage VIN (which may be an input signal to an amplifier elsewhere in the DDI) has a voltage less than the output voltage VOUT (which may be an output signal from the amplifier elsewhere in the DDI), either absolutely or by at least |Vth| (which may be the threshold voltage of the transistor MP 3 ), a second current path from the transistor MP 3  through the transistor MN 1  carries a current. Alternatively, when the input voltage VIN is less than the power supply VDD, alone or minus the threshold voltage of the transistor MP 3 , the transistor MP 3  may conduct a current and may draw or sink the current from the output node VOUT. The current flowing on the second current path is reproduced by the transistor MN 21 . 
     A drain node of the transistor MN 21  is connected to the gate nodes of the transistors MN 4  and MN 5  of the output buffer circuit  100 , thereby decreasing the voltage on the gates of the transistors MN 4  and MN 5 . As a result, the currents conducted by the transistors MN 4  and MN 5  decrease, and the voltage on the gate of the transistor MN 8  (e.g., the pull-down driver) rapidly increases. 
     In addition, the current flowing through the transistor MN 21  may increase the current of the transistor MP 4  of the output buffer circuit  100  so that the current of the transistor MP 5  of the output buffer circuit  100  may also increase. 
     Accordingly, since the voltage on the gate of the transistor MN 8  rapidly increases, the gate-source potential across the transistor MN 8  also rapidly increases, thereby increasing the slew rate of the output voltage VOUT. When the output voltage VOUT decreases, and the difference between the input voltage and the output voltage is no greater than |Vth|, the second current path may not conduct a current, so additional current consumption of the slew boost amplifier  200  may not occur. 
       FIG.  6    shows graphs for comparing and illustrating output waveforms of a slew boost amplifier circuit according to an embodiment of the present disclosure. 
     With reference to  FIG.  6   , it may be seen that a high slew rate is realized when the slew boost amplifier  200  according to an embodiment of the present disclosure is used, when compared to the slew boost amplifier not being used (OFFOutput). 
     As described above, the slew boost amplifier  200  and the display driver having the same may provide a current path by comparing an input voltage and an output voltage, thereby amplifying a high slew rate without increasing power consumption (current consumption). 
     In addition, the slew boost amplifier  200  and the display driver having the same may provide a high slew rate without an increase in power consumption, thereby realizing a high slew rate even in a portable electronic device. 
     In addition, the slew boost amplifier  200  and the display driver having the same may increase or amplify the slew rate by comparing the input voltage and the output voltage, thereby allowing the slew rate to be increases or amplified even without an additional control circuit, and may embody slew amplification or slew rate improvement using a circuit having a small area. 
     The above-detailed description is illustrative of the present disclosure. In addition, the above description shows and describes exemplary embodiments of the present disclosure, and the present disclosure may be used in various other combinations, modifications, and environments. That is, changes or modifications are possible within the scope of the concept of the invention disclosed herein, the scope equivalent to the written disclosure, and/or within the scope of skill or knowledge in the art. The above-described embodiments may describe the best state for implementing the technical idea of the present disclosure, and various modifications for specific fields and/or applications and uses of the present disclosure are possible. Accordingly, the detailed description of the present disclosure is not intended to limit the present disclosure to the disclosed embodiments.