Patent Publication Number: US-11663970-B2

Title: Display device, CMOS operational amplifier, and driving method of display device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/505,884 filed Jul. 9, 2019, which is a continuation of U.S. patent application Ser. No. 15/434,977 filed Feb. 16, 2017, now U.S. Pat. No. 10,395,591 issued Aug. 27, 2019, which is a continuation of U.S. patent application Ser. No. 14/212,391 filed Mar. 14, 2014, now U.S. Pat. No. 9,613,584 issued Apr. 4, 2017, the entireties of which are incorporated herein by reference to the extent permitted by law and the benefits of which are also claimed. This application claims priority to Japanese Priority Patent Application JP 2013-072605 filed Mar. 29, 2013, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to a display device, a CMOS operational amplifier, and a driving method of the display device. 
     In general, in a display device such as a liquid crystal display device and an Electro-Luminescence (EL) display device, which performs a display using a plurality of pixels (liquid crystal or EL elements) which are arranged in a matrix shape, the pixels are driven as a load using an amplifier installed in an output stage of a source driver. A driving capability of such an amplifier is constant if the amplifier is a class A amplifier, and varies within a certain constant range according to the load if the amplifier is a class AB amplifier. 
     Here, there is a case where variation occurs in the load which is driven by the amplifier, due to an influence of a large size or the like of the liquid crystal. In a case where the amplifier is class A, if the load is larger than the driving capability of the amplifier, a problem occurs in which ringing occurs in an output of the amplifier, and if the load is smaller than the driving capability of the amplifier, a problem occurs in which the output of the amplifier is overshot. A technology to solve such problems is disclosed in Japanese Unexamined Patent Application Publication No. 11-85113. 
     In Japanese Unexamined Patent Application Publication No. 11-85113, an amplifier is disclosed which includes a bias variable circuit that varies a bias current flowing in a differential amplifier and an output circuit. The bias variable circuit can adjust the bias current of the differential amplifier or the bias current of an output unit of the output circuit. 
     As a result, regardless of a size of the load of the liquid crystal, by increasing the bias current of the output circuit, it is possible to immediately reach a target voltage. At this time, although the ringing or the overshoot occurs in an output waveform, it is possible to immediately reach the target voltage, and thus, a liquid crystal display can be normally performed. 
     SUMMARY 
     In an organic EL display device or a liquid crystal display device, there is a case where simultaneous driving of a plurality of lines is necessary, and depending on the number of simultaneous driving lines, a size of a load which is driven by each amplifier can be varied greatly such that the variation is hardly included in a variation width of a driving capability of a class AB amplifier. 
     For this reason, when the driving capability is insufficient for the loads of the number of simultaneous driving lines, ringing occurs in an output due to insufficient damping, and when the driving capability exceeds the loads of the number of simultaneous driving lines, a response time for reaching a necessary output increases due to excessive damping. Thus, a normal current in an amplifier designed for driving of N lines is increased. 
     Here, an operational amplifier disclosed in Japanese Unexamined Patent Application Publication No. 11-85113 is a class A amplifier, not a class AB amplifier in which an output current varies according to the load, and vulnerable to an instant pull-in current. For this reason, a peak current of the instant pull-in current is constantly necessary, and a large amount of power is continually consumed. Thus, it is difficult to say that a technology disclosed in Japanese Unexamined Patent Application Publication No. 11-85113 is a technology that sufficiently copes with load variation caused by variation of the number of driving lines. 
     It is desirable to provide a display device, a CMOS operational amplifier, and a driving method of the display device which suppress an increase of ringing or a response time at the time of load variation, and do not increase power consumption. 
     According to an embodiment of the present disclosure, here is provided a display device including: a display unit which includes a plurality of pixels and a plurality of driving lines for driving the plurality of pixels; a driving circuit which drives the plurality of pixels through the plurality of driving lines; and a control unit which adjusts a driving capability of the driving circuit according to the number of simultaneous driving lines of the driving circuit. 
     According to another embodiment of the present disclosure, here is provided a CMOS operational amplifier including: an output stage of a push-pull type output circuit which is configured by a source current output transistor supplying a current to an output terminal, and a sink current output transistor pulling a current from the output terminal; and an adjustment circuit which adjusts size corresponding values of the source current output transistor and the sink current output transistor. 
     The display device or the CMOS operational amplifier includes various forms which are realized in a state where the display device or the CMOS operational amplifier is integrated with other apparatus, realized by other method, or the like. In addition, the present disclosure can also be realized by a display system which includes the display device, a control method of a display device which has a process corresponding to a configuration of the display device, a program which causes a computer to perform a function corresponding to the configuration of the display device, a computer readable recording medium in which the program is recorded, or the like. 
     According to the present disclosure, in a display device or a CMOS operational amplifier, it is possible to suppress an increase of ringing or a response time at the time of load variation, and to prevent power consumption from increasing. In addition, the advantage described in the present specification is not limited to the exemplary illustrations, and there may be an additional advantage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a circuit diagram illustrating a specific example of an operational amplifier according to a first embodiment; 
         FIG.  2    is a diagram illustrating a modification example of an adjustment circuit of an output transistor; 
         FIG.  3    is a diagram illustrating a configuration of a display device according to a second embodiment; 
         FIG.  4    is a diagram illustrating a configuration of an organic EL display device as an example of a display device; and 
         FIG.  5    is a diagram illustrating a corresponding relationship between current consumption of an operational amplifier, an output waveform of the operational amplifier, and a timing chart illustrating selection timing of switches. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, the present disclosure will be described in the following order. 
     (1) First Embodiment 
     (2) Second Embodiment 
     (3) Conclusion 
     (1) FIRST EMBODIMENT 
     An operational amplifier as a CMOS operational amplifier according to the present embodiment includes an output stage of a push-pull type output circuit which is configured by a source current output transistor supplying a current to an output terminal, and a sink current output transistor pulling a current from the output terminal. 
     Hereinafter, there is a case where the source current output transistor and the sink current output transistor are collectively referred to as an “output transistor”. 
     The output transistor according to the present embodiment includes a plurality of transistor elements, and is configured by a combination of one or more transistor elements selected from among the plurality of transistor elements. 
     Here, when all of the output transistors are regarded as one virtual transistor element (hereinafter, referred to as a “virtual transistor element”), a size (channel width W/channel length L) of the virtual transistor element is referred to as a “size corresponding value”, and a channel width of the virtual transistor element is referred to as a “channel width corresponding value”. 
     The size corresponding value or the channel width corresponding value can be adjusted by changing in various ways the number of transistor elements or a connection form of the transistor elements which configure the output transistor, using a switching circuit for switching the number of transistor elements or the connection forms of the transistor elements which configure the output transistor. An adjustment subject of the size corresponding value or the channel width corresponding value may be installed inside the operational amplifier or outside the operational amplifier. 
     If the size corresponding value or the channel width corresponding value is changed, the same result as that obtained by changing the size or the channel width of the virtual transistor element is obtained. That is, if the size corresponding value or the channel width corresponding value of the output transistor is adjusted, an amount of current flowing through the output transistor is adjusted, and furthermore, a load driving capability of the operational amplifier is adjusted. 
     Hereinafter, the operational amplifier as the CMOS operational amplifier according to the present embodiment will be specifically described with reference to  FIG.  1   .  FIG.  1    is a circuit diagram illustrating a specific example of the operational amplifier according to a first embodiment. 
     The operational amplifier  100  illustrated in  FIG.  1    includes a differential amplification circuit  10 , a bias circuit  20 , and an output circuit  30 . 
     The differential amplification circuit  10  includes a PMOS transistor M 1  which configures a current source  11 , PMOS transistors M 2  and M 3  which configure a differential pair  12 , and NMOS transistors M 4  and M 5  which configure a current mirror  13 . 
     When the operational amplifier  100  is used, a bias voltage Vb 1  is input to a gate of the PMOS transistor M 1 . As a result, the PMOS transistor M 1  generates a current according to the bias voltage Vb 1 . 
     A gate of the PMOS transistor M 2  which configures the differential pair  12  is connected to an inverting input terminal INN, and a gate of the PMOS transistor M 3  is connected to a non-inverting input terminal INP. In the present embodiment, an output of the operational amplifier  100  is negatively fed back to the inverting input terminal INN, and an input signal for being amplified by the operational amplifier  100  is input to the non-inverting input terminal INP. 
     Gates of the NMOS transistors M 4  and M 5  which configure the current mirror  13  are connected to each other, and a drain and the gate of the NMOS transistor M 4  are connected to each other, and thereby the NMOS transistor M 4  functions as a diode. As a result, currents according to a size ratio between the NMOS transistors M 4  and M 5  flow through the NMOS transistors M 4  and M 5 . 
     In the differential amplification circuit  10  configured as described above, a voltage Va 1  which is proportional to a difference between the voltage of the inverting input terminal INN and the voltage input to the non-inverting input terminal INP is generated at a point P 1 . A voltage of the point P 1  is output to the output circuit  30  as an output voltage of the differential amplification circuit  10 . 
     The configuration of the differential amplification circuit  10  is not limited to the configuration illustrated in  FIG.  1   . For example, in  FIG.  1   , the differential pair  12  using the PMOS transistors, the current mirror  13  using the NMOS transistors, and the current source  11  using the PMOS transistor are respectively illustrated, but the differential pair  12  may be configured using NMOS transistors, the current mirror  13  may be configured using PMOS transistors, and the current source  11  may be configured using an NMOS transistor. 
     The bias circuit  20  includes a PMOS transistor M 6  which configures a current source  21 , a PMOS transistor M 7  and an NMOS transistor M 8  which configure a switch circuit  22 , and an NMOS transistor M 9  which configures a current source  23 . In the present embodiment, the switch circuit  22  is configured by a complementary switch circuit in which the PMOS transistor M 7  and the NMOS transistor M 8  are arranged so as to face each other. 
     When the operational amplifier  100  is used, a bias voltage Vb 2  is input to a gate of the PMOS transistor M 6 , a bias voltage Vb 3  is input to a gate of the PMOS transistor M 7 , a bias voltage Vb 4  is input to a gate of the NMOS transistor M 8 , and a bias voltage Vb 5  is input to a gate of the NMOS transistor M 9 . 
     The bias voltages Vb 2  and Vb 5  are determined such that a bias current Ibias flows through the PMOS transistor M 6  and the NMOS transistor M 9 , the bias voltages Vb 3  and Vb 4  are determined such that a sum of a current I 7  flowing through the PMOS transistor M 7  and a current I 8  flowing through the NMOS transistor M 8  may be the same as the bias current Ibias. 
     A point P 2  between the switch circuit  22  and the current source  23  is connected to the point P 1  of the differential amplification circuit  10 , and the voltage Va 1  of the differential amplification circuit  10  is input to the point P 2 . 
     If the voltage Va 1  decreases, a gate-source voltage Vgs 8  of the NMOS transistor M 8  increases, and a current I 8  flowing through NMOS transistor M 8  increases. At this time, I 7 =Ibias−I 8 , and thereby the current I 7  flowing through the PMOS transistor M 7  decreases. As a result, a source-gate voltage Vsg 7  of the PMOS transistor M 7  decreases, and a voltage Va 2  of a point P 3  between the current source  21  and the switch circuit  22  decreases. 
     On the other hand, if the voltage Va 1  increases, the gate-source voltage Vgs 8  of the NMOS transistor M 8  decreases, and a current I 8  flowing through the NMOS transistor M 8  decreases. At this time, I 7 =Ibias−I 8 , and thereby the current I 7  flowing through the PMOS transistor M 7  increases. As a result, the source-gate voltage Vsg 7  of the PMOS transistor M 7  increases, and the voltage Va 2  of the point P 3  increases. 
     The output circuit  30  includes PMOS transistors M 10  and M 11  which configure the source current output transistor  31 , NMOS transistors M 12  and M 13  which configure the sink current output transistor  32 , adjustment circuits  33  and  34  and phase compensation capacitors  35  and  36 . 
     The source current output transistor  31  and the sink current output transistor  32  configure a push-pull type output circuit which connects in series a power supply voltage Vdd and a ground voltage Vss. A point P 4  which is a connection point of such output transistors is connected to the output terminal OUT. The source current output transistor  31  supplies the current to the output terminal OUT, and the sink current output transistor  32  pulls the current from the output terminal OUT. 
     Gates as control terminals of the PMOS transistors M 10  and M 11  which configure the source current output transistor  31  are connected to the point P 3  of the bias circuit  20 . Gates as control terminals of the NMOS transistors M 12  and M 13  which configure the sink current output transistor  32  are connected to the point P 1  of the differential amplification circuit  10  and the point P 2  of the bias circuit  20 . As a result, the output circuit  30  outputs a voltage in which the voltage Va 1  input from the differential amplification circuit  10  is amplified in a class AB, to the output terminal OUT. 
     The adjustment circuit  33  is a circuit for adjusting the size corresponding value or the channel width corresponding value of the source current output transistor  31 , and the adjustment circuit  34  is a circuit for adjusting the size corresponding value or the channel width corresponding value of the sink current output transistor  32 . 
     In the circuit illustrated in  FIG.  1   , the adjustment circuit  33  is realized as a switch SW 1  which is installed between the PMOS transistor M 10  and the power supply voltage Vdd, the adjustment circuit  34  is realized as a switch SW 2  which is installed between the NMOS transistor M 12  and the ground voltage Vss. ON and OFF of the switches SW 1  and SW 2  are controlled by a control unit  50 . The control unit  50  may be installed inside the operational amplifier  100  or outside the operational amplifier  100 . 
     If the switch SW 1  is controlled to be in an OFF state, only the PMOS transistor M 11  in the source current output transistor  31  connects the power supply voltage Vdd to the point P 4 , and if the switch SW 1  is controlled to be in an ON state, the PMOS transistors M 10  and M 11  in the source current output transistor  31  are connected in parallel to each other and connect the power supply voltage Vdd to the point P 4 . 
     Here, if the size of the PMOS transistor M 10  is set as W 10 /L 10  and the size of the PMOS transistor M 11  is set as W 11 /L 11 , the size corresponding value of the source current output transistor  31  occurring when the switch SW 1  is controlled to be in the OFF state is denoted by W 11 /L 11 , and the size corresponding value of the source current output transistor  31  occurring when the switch SW 1  is controlled to be in the ON state is denoted by ((W 10 /L 10 )+(W 11 /L 11 )). 
     In addition, the channel width corresponding value of the source current output transistor  31  occurring when the switch SW 1  is controlled to be in the OFF state is denoted by W 11 , and the channel width corresponding value of the source current output transistor  31  occurring when the switch SW 1  is controlled to be in the ON state is denoted by (W 10 +W 11 ). 
     That is, according to an ON and OFF control of the switch SW 1 , the size corresponding value or the channel width corresponding value of the source current output transistor  31  is adjusted, and as a result, a current supply capability of the source current output transistor  31  to the output terminal OUT, that is, the load driving capability of the operational amplifier  100  is adjusted. 
     Similarly, if the switch SW 2  is controlled to be in the OFF state, only the NMOS transistor M 13  in the sink current output transistor  32  connects the point P 4  to the ground voltage Vss, and if the switch SW 2  is controlled to be in the ON state, the NMOS transistors M 12  and M 13  in the sink current output transistor  32  are connected in parallel to each other and connect the point P 4  to the ground voltage Vss. 
     Here, if the size of the NMOS transistor M 12  is set as W 12 /L 12  and the size of the NMOS transistor M 13  is set as W 13 /L 13 , the size corresponding value of the sink current output transistor  32  occurring when the switch SW 2  is controlled to be in the OFF state is denoted by W 13 /L 13 , and the size corresponding value of the sink current output transistor  32  occurring when the switch SW 2  is controlled to be in the ON state is denoted by ((W 12 /L 12 )+(W 13 /L 13 )). 
     In addition, the channel width corresponding value of the sink current output transistor  32  occurring when the switch SW 2  is controlled to be in the OFF state is denoted by W 13 , and the channel width corresponding value of the sink current output transistor  32  occurring when the switch SW 2  is controlled to be in the ON state is denoted by (W 12 +W 13 ). 
     That is, according to an ON and OFF control of the switch SW 2 , the size corresponding value or the channel width corresponding value of the sink current output transistor  32  is adjusted, and as a result, a current pulling capability of the sink current output transistor  32  from the output terminal OUT, that is, the load driving capability of the operational amplifier  100  is adjusted. 
     Even in the operational amplifier described in the above-described Japanese Unexamined Patent Application Publication No. 11-85113, a current flowing through a sink current output transistor is configured so as to be adjustable, but the current is adjusted in conjunction with a current flowing through a current source which configures a differential amplification circuit. In contrast, in the operational amplifier  100  according to the present embodiment, the current flowing through the current source  11  of the differential amplification circuit  10  is constant, and the adjustment of the size corresponding value of the output transistor and the change of the amount of current flowing in the differential amplification circuit  10  are not consistent with each other. 
     The phase compensation capacitor  35  connects the point P 1  of the differential amplification circuit  10  to the output terminal OUT, and the phase compensation capacitor  36  connects the point P 3  of the bias circuit  20  to the output terminal OUT. Such phase compensation capacitors  35  and  36  move a plurality of poles (first pole and second pole) of frequency characteristics of voltage gain of the operational amplifier  100  to a low frequency side. 
     Since the operational amplifier  100  has an open-loop to which a negative feedback is applied, if input and output phases are reversed, an oscillation is generated even by a small amount of feedback. Then, the phase compensation capacitors  35  and  36  with appropriate values are installed so as to avoid the reverse of the input and output phases. As a result, it is possible to suppress an occurrence of transient ringing caused by a plurality of poles being too close, and transient overdamping caused by the plurality of poles being too far, and to maintain a state of critical damping. 
     When a sum of a transconductance gm 31  (not illustrated) of the source current output transistor  31  and a transconductance gm 32  (not illustrated) of the sink current output transistor  32  is set as gm, and total capacitances of the load connected to the output terminal OUT are set as C, the size corresponding values or the channel width corresponding values of the source current output transistor  31  and the sink current output transistor  32  are selected in such a manner that gm/C may be not changed before and after the adjustment. 
     In addition, in the source current output transistor  31  and the sink current output transistor  32  of the above-described operational amplifier  100 , the PMOS transistor M 11  and the NMOS transistor M 13  are typically connected to each other, and the connection of the PMOS transistor M 10  or the connection of the NMOS transistor M 12  is configured so as to be switchable by adjustment circuit  33  or  34 , but the configuration of the source current output transistor  31  or the configuration of the sink current output transistor  32  is not limited thereto. 
       FIG.  2    is a diagram illustrating another example of the output circuit. In  FIG.  2   , a switch is installed for each MOS transistor which configures each output transistor. At this time, the source current output transistor  31  can be realized by switching three states: a state in which the power supply voltage Vdd is connected to the point P 4  by the PMOS transistor M 10  only, a state in which the power supply voltage Vdd is connected to the point P 4  by the PMOS transistor M 11  only, and a state in which the power supply voltage Vdd is connected to the point P 4  by the PMOS transistors M 10  and M 11  which are connected in parallel to each other. 
     In addition, the sink current output transistor  32  can be realized by switching three states: a state in which the point P 4  is connected to the ground voltage Vss by the NMOS transistor M 12  only, a state in which the point P 4  is connected to the ground voltage Vss by the NMOS transistor M 13  only, and a state in which the point P 4  is connected to the ground voltage Vss by the NMOS transistors M 12  and M 13  which are connected in parallel to each other. 
     In addition, the number of MOS transistors which configure each output transistor is not limited to two pieces, and can be set as an arbitrary number equal to or greater than 2. In this case, the switches may be all configured by the MOS transistors, and may be partially configured by the MOS transistors. 
     (2) SECOND EMBODIMENT 
       FIG.  3    is a diagram illustrating a configuration of a display device according to a second embodiment, and  FIG.  4    is a diagram illustrating a configuration of an organic EL display device as an example of a display device. 
     The display device  200  illustrated in  FIGS.  3  and  4    includes a display unit  280  which has a plurality of pixels Pxl arranged in a matrix shape and driving lines L 1 , L 2 , . . . , and Ln (only three driving lines L 1 ,  12 , and L 3  are illustrated in  FIG.  4   ) installed for each row of the plurality of pixels Pxl, a plurality of switches SW 1 , SW 2 , . . . , and SWn (only three switches SW 1 , SW 2 , and SW 3  are illustrated in  FIG.  4   ) installed in an input side of each driving line, an operational amplifier Op, a digital analog converter (DAC)  240 , and a control unit  250 . 
     Various signals such as digital image data or a clock signal are input to the control unit  250 . The control unit  250  performs a control which inputs digital image data D to a latch circuit  265  (not illustrated in  FIG.  3   ) included in a horizontal driving circuit  260  (not illustrated in  FIG.  3   ) and stores the digital image data D therein at an appropriate timing, based on the clock signal, and inputs the digital image data D to the DAC  240  by controlling the latch circuit  265  at an appropriate timing. 
     The DAC  240  converts the digital image data D into an analog voltage signal. Specifically, the DAC  240  receives a plurality of gradation voltages corresponding to a plurality of gradation values and the digital image data D, and inputs the gradation voltage corresponding to the gradation value of the image data D selected from the plurality of gradation voltages to the operational amplifier Op. 
     The operational amplifier Op functions as an output buffer which amplifies and outputs the gradation voltage input from the DAC  240 . The operational amplifier Op is configured so as to vary the size corresponding value or the channel width corresponding value of the output stage in the same manner as the operational amplifier  100  according to the first embodiment described above. For example, the size corresponding value or the channel width corresponding value is adjusted by a control signal Ctl output from the control unit  250 . 
     The switches SW 1 , SW 2 , . . . , and SWn function as a selection circuit for selecting a driving line to which the output signal of the operational amplifier Op is to be input. Specifically, the switches SW 1 , SW 2 , . . . , and SWn are installed in each of driving lines L 1 , L 2 , . . . , and Ln, and performs an ON and OFF switching of a connection of a corresponding driving line to the operational amplifier Op. For example, the switching is performed according to a selection signal Sel output from the control unit  250 . 
     In  FIG.  4   , a case where a timing controller TCON configures the control unit  250  is exemplarily illustrated, but there is also a case where the timing controller ICON generates the control signal Ctl according to a control of a control subject such as an external microcomputer connected to a PAD, and inputs the generated control signal to the operational amplifier Op. In this case, the control unit  250  configures the direct control subject of the operational amplifier Op, and the external control subject configures an indirect control subject of the operational amplifier Op. 
     The driving lines L 1 , L 2 , . . . , and Ln are connected to each pixel of a corresponding column, and input a signal input from the operational amplifier Op to the pixels of a row selected by a vertical driving circuit  270  (not illustrated in  FIG.  3   ). As a result, the pixel to which the signal is input emits light using the gradation value according to the image data. 
     Here, with reference to  FIG.  5   , a relationship between the number of simultaneous driving lines of the operational amplifier Op and the adjustment of the operational amplifier Op, will be described.  FIG.  4    illustrates a corresponding relationship between current consumption of the operational amplifier Op, an output waveform of the operational amplifier Op, and a timing chart illustrating selection timing of the switches SW 1 , SW 2 , . . . , and SWn. 
     In the timing chart illustrated in  FIG.  5   , all pixel selection in which the selection signal Sel is input to all switches SW 1  to SWn is first performed, and thereafter, each pixel selection in which the selection signal Sel is sequentially input to the switches SW 1  to SWn is performed. At the time of the all pixel selection, a writing control of a reference voltage with respect to all pixels of a row is performed, and at the time of the each pixel selection, a control which writes a voltage according to the image data to each pixel of the row is sequentially performed. 
     As illustrated in the current consumption of the operational amplifier, in the related art, the same steady-state current flows even at the time of the all pixel selection and even at the time of the each pixel selection. It is because the operational amplifier in the related art has no function of adjusting the size corresponding value or the channel width corresponding value of the output transistor, and in conjunction with the time of the all pixel selection which asks for larger steady-state current, the size corresponding value or the channel width corresponding value of the output transistor is optimized. 
     On the other hand, the operational amplifier Op according to the present embodiment, flows the same steady-state current as that in the related art at the time of the all pixel selection, but adjusts the size corresponding value or the channel width corresponding value of the output transistor using the control signal Ctl, and lowers the steady-state current at the time of the each pixel selection compared to that at the time of the all pixel selection. As a result, it is possible to decrease the current consumption compared to the related art. 
     In addition, the size corresponding value or the channel width corresponding value of the output transistor is adjusted according to an amount of load. In the display device according to the present embodiment, the amount of load is approximately proportional to the number of simultaneous driving lines. 
     That is, the size corresponding value or the channel width corresponding value of the output transistor at the time of the all pixel selection is adjusted to a value in which an optimal current can be output by simultaneous driving of n driving lines, and the size corresponding value or the channel width corresponding value of the output transistor at the time of the each pixel selection is adjusted to a value in which an optimal current can be output by driving of one driving line. In this way, there is enough load driving capability both at the time of the all pixel selection and at the time of the each pixel selection, and thus, ringing characteristics and response time characteristics are also not deteriorated compared to the related art. 
     (3) CONCLUSION 
     The operational amplifier  100  (operational amplifier Op) as the CMOS operational amplifier described above includes, the output stage of the push-pull type output circuit  30  which is configured by the source current output transistor  31  supplying the current to the output terminal OUT and the sink current output transistor  32  pulling the current from the output terminal OUT, and the adjustment circuits  33  and  34  which adjust the size corresponding values of the source current output transistor  31  and the sink current output transistor  32 . That is, the size corresponding value or the channel width corresponding value is adjustably designed according to the load of each state, and the size corresponding value or the channel width corresponding value is adjusted, thereby suppressing an increase of the ringing or the response time at the time of load variation and preventing the current consumption from increasing. 
     In addition, the above-described display device  200  includes, the display unit  280  which has the plurality of pixels Pxl and the plurality of driving lines L 1 , L 2 , . . . , and Ln for driving the plurality of pixels Pxl, the horizontal driving circuit  260  which drives the plurality of pixels Pxl through the plurality of driving lines L 1 , L 2 , . . . , and Ln, the control unit  250  which adjusts the driving capability of the driving circuit according to the number of simultaneous driving lines of the driving circuit. That is, the driving capability of the driving circuit is adjustably designed according to the load of each state, and the driving capability of the driving circuit is adjusted according to the number of simultaneous driving lines of the driving circuit, and thereby it is possible to suppress an increase of the ringing or the response time at the time of the load variation, and to prevent the current consumption from increasing. 
     The present disclosure is not limited to the embodiments described above, and includes a configuration in which respective configuration elements disclosed in the above-described embodiments are replaced with each other or a combination thereof is changed, a configuration in which respective configuration elements disclosed in an existing technology and the above-described embodiments are replaced with each other or a combination thereof is changed, and the like. In addition, a technical scope of the present disclosure is not limited to the above-described embodiments, and includes description of the claims and equivalents thereof. 
     Then, the present disclosure can include the following configurations. 
     (A) A display device includes, a display unit which includes a plurality of pixels and a plurality of driving lines for driving the plurality of pixels; a driving circuit which drives the plurality of pixels through the plurality of driving lines; and a control unit which adjusts a driving capability of the driving circuit according to the number of simultaneous driving lines of the driving circuit. 
     (B) The display device according to (A) in which the control circuit adjusts the driving circuit in such a manner that the driving capability is approximately proportional to the number of simultaneous driving lines. 
     (C) The display device according to (A) or (B) in which the driving circuit includes a CMOS operational amplification circuit, in which the CMOS operational amplification circuit includes an output stage of a push-pull type output circuit which is configured by a source current output transistor supplying a current to an output terminal, and a sink current output transistor pulling a current from the output terminal, and in which the control unit adjusts the driving capability of the driving circuit by adjusting size corresponding values of the source current output transistor and the sink current output transistor. 
     (D) The display device according to (C) in which a ratio between a sum of a transconductance of the source current output transistor and a transconductance of the sink current output transistor, and a capacitance of a load which is driven by the output circuit, is constant before and after the adjustment of the size corresponding value. 
     (E) The display device according to (C) or (D) further includes a differential amplification circuit which amplifies and outputs a difference between two inputs, in which the output circuit amplifies the output of the differential amplification circuit and outputs the amplified output to the output terminal, and in which the adjustment of the size corresponding value and a change of an amount of current flowing in the differential amplification circuit are not in conjunction with each other. 
     (F) The display device according to any one of (C) to (E) in which the output circuit includes a configuration in which the source current output transistor and the sink current output transistor are connected in series to each other between a power supply and a ground, and outputs a voltage of a connection point of the source current output transistor and the sink current output transistor, in which the source current output transistor includes a plurality of transistor elements, and one or more transistor elements selected by an adjustment circuit from among the plurality of transistor elements are connected in parallel between the power supply and the sink current output transistor, and in which the sink current output transistor includes a plurality of transistor elements, and one or more transistor elements selected by the adjustment circuit from among the plurality of transistor elements are connected in parallel between the source current output transistor and the ground. 
     (G) A CMOS operational amplifier includes, an output stage of a push-pull type output circuit which is configured by a source current output transistor supplying a current to an output terminal, and a sink current output transistor pulling a current from the output terminal; and an adjustment circuit which adjusts size corresponding values of the source current output transistor and the sink current output transistor. 
     (H) A control method of a display device that includes a display unit which has a plurality of pixels and a plurality of driving lines for driving the plurality of pixels, and a driving circuit which drives the plurality of pixels through the plurality of driving lines, the method includes adjusting a driving capability of the driving circuit according to the number of simultaneous driving lines of the driving circuit. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.