# Patent

## Title
Inverter circuit and display

## Abstract

An inverter circuit includes: a first transistor and a second transistor; a first switch and a second switch; and a first capacity element, in which the first and second transistors are connected in series between a first voltage line and a second voltage line, the first and second switches are connected in series between a supply voltage line and a gate of the second transistor, and are alternately turned on and off so as not to be turned on simultaneously, an end of the first capacity element is connected between the first switch and the second switch, and off-state of the first transistor allows a predetermined fixed voltage to be supplied from the supply voltage line to the gate of the second transistor through the first switch, the end of the first capacity element and the second switch.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inverter circuit suitably applicable to, for example, a display using organic EL (Electro Luminescence) elements. Moreover, the invention relates to a display including the above-described inverter circuit.
2. Description of the Related Art
In recent years, in the field of displays displaying an image, displays using, as light-emitting elements of pixels, current drive type optical elements of which light emission luminance changes depending on the value of a current flowing therethrough, for example, organic EL elements have been developed for commercialization. Unlike liquid crystal elements or the like, the organic EL elements are self-luminous elements. Therefore, in displays (organic EL displays) using the organic EL elements, color gradation is obtained by controlling the value of a current flowing through the organic EL elements.
As in the case of liquid crystal displays, the organic EL displays are of a simple (passive) matrix system and an active matrix system as a drive system. In the former system, a configuration thereof is simple; however, there is an issue such as difficulty in achieving a large and high-definition display. Therefore, at present, the active matrix system has been increasingly developed. In this system, a current flowing through a light-emitting element arranged in each pixel is controlled by a driving transistor.
In the above-described driving transistor, in some cases, a threshold voltage Vth or mobility μ temporally changes, or the threshold voltage Vth or mobility μ varies from one pixel to another due to variations in a manufacturing process. In the case where the threshold voltage Vth or mobility μ varies from one pixel to another, the value of a current flowing through the driving transistor varies from one pixel to another, so even if the same voltage is applied to gates of the driving transistors, light emission luminance varies from one organic EL element to another, thereby impairing uniformity of a screen. Therefore, as described in Japanese Unexamined Patent Application Publication No. 2008-083272, a display having a function of correcting a change in the threshold voltage Vth or mobility μ has been developed.
Correction of the threshold voltage Vth or mobility μ is performed by a pixel circuit arranged in each pixel. For example, as illustrated in FIG. 19, the pixel circuit includes a driving transistor Tr100 controlling a current flowing through an organic EL element 111, a writing transistor Tr200 writing a voltage of a signal line DTL to the driving transistor Tr100, and a retention capacitor Cs. In other words, the pixel circuit has a 2Tr1C circuit configuration. The driving transistor Tr100 and the writing transistor Tr200 each are configured of, for example, an n-channel MOS type thin film transistor (TFT).
FIG. 18 illustrates an example of voltage waveforms applied to the pixel circuit and an example of changes in a gate voltage Vg and a source voltage Vs of the driving transistor Tr100. A part (A) in FIG. 18 illustrates a state where a signal voltage Vsig and an offset voltage Vofs are applied to the signal line DTL. A part (B) in FIG. 18 illustrates a state where a voltage Vdd turning the writing transistor Tr200 on and a voltage Vss turning the writing transistor Tr200 off are applied to a writing line WSL. A part (C) in FIG. 18 illustrates a state where a high voltage VccH and a low voltage VccL are applied to a power supply line PSL. Moreover, parts (D) and (E) in FIG. 18 illustrate states where the gate voltage Vg and the source voltage Vs of the driving transistor Tr100 are momentarily changed depending on the application of voltages to the power supply line PSL, the signal line DTL and the writing line WSL.
It is obvious from FIG. 18 that a WS pulse P is applied to the writing line WSL twice in a period of 1 H, and threshold correction is performed by a first WS pulse P and mobility correction and signal writing are performed by a second WS pulse P. In other words, in FIG. 18, WS pulses P are used for not only signal writing but also threshold correction and mobility correction of the driving transistor Tr100.
SUMMARY OF THE INVENTION
In an active matrix system display, a horizontal drive circuit (not illustrated) driving a signal line DTL or a writing scanning circuit (not illustrated) sequentially selecting pixels 113 is basically configured by including a shift register (not illustrated), and includes buffer circuits (not illustrated) corresponding to rows or columns of the pixels 113, respectively. For example, the buffer circuits in the writing scanning circuit each are configured by connecting two inverter circuits to each other in series. In this case, for example, as illustrated in FIG. 20, the inverter circuits each have a single-channel type circuit configuration in which two n-channel MOS type transistors Tr1 and Tr2 are connected to each other in series. An inverter circuit 200 illustrated in FIG. 20 is inserted between a high-voltage wiring line LH to which a high-level voltage is applied and a low-voltage wiring line LL to which a low-level voltage is applied. A gate of the transistor Tr2 on a side close to the high-voltage wiring line LH is connected to the high-voltage wiring line LH, and a gate of the transistor Tr1 on a side close to the low-voltage wiring line LL is connected to an input terminal IN. Moreover, a connection point C between the transistor Tr1 and the transistor Tr2 is connected to an output terminal OUT.
In the inverter circuit 200, for example, as illustrated in FIG. 21, when a voltage Vin of the input terminal IN is at a voltage Vss, a voltage Vout of the output terminal OUT is not at a voltage Vdd but at a voltage Vdd. Vth. In other words, the voltage Vout of the output terminal OUT includes a threshold voltage Vth of the transistor Tr2; therefore the voltage Vout of the output terminal OUT is greatly affected by variations in the threshold voltage Vth of the transistor Tr2.
Therefore, it is considered that, for example, as illustrated in an inverter circuit 300 in FIG. 22, a gate and a drain of the transistor Tr2 are electrically separated from each other, and a high-voltage wiring line LH2 to which a higher voltage Vdd2 (≧Vdd+Vth) than the voltage Vdd of the drain is applied is connected to the gate. Moreover, for example, a bootstrap type circuit configuration as illustrated in an inverter circuit 400 in FIG. 23 is considered. More specifically, a circuit configuration in which a transistor Tr12 is inserted between the gate of the transistor Tr12 and the high-voltage wiring line LH so as to connect a gate of a transistor Tr12 to the high-voltage wiring line LH and a capacity element C10 is inserted between a connection point D between the gate of the transistor Tr2 and a source of the transistor Tr12 and the connection point C is considered.
However, in any of the circuits in FIGS. 20, 22 and 23, even in the case where the voltage Vin of the input terminal IN is high, that is, even in the case where the voltage Vout of the output terminal OUT is low, a current (a through current) flows from the high-voltage wiring line LH to the low-voltage wiring line LL through the transistors Tr1 and Tr2. As a result, power consumption in the inverter circuits is increased. Moreover, in the circuits in FIGS. 20, 22 and 23, for example, as illustrated in a point encircled by a broken line in a part (B) in FIG. 21, when the voltage Vin of the input terminal IN is at the voltage Vdd, the voltage Vout of the output terminal OUT is not at the voltage Vss, and a peak value of the voltage Vout of the output terminal OUT varies. As a result, threshold correction or mobility correction in the driving transistor Tr100 varies from one pixel circuit 112 to another, thereby causing variations in luminance.
The above-described issues may occur not only in a scanning circuit of the display but also any other devices.
It is desirable to provide an inverter circuit allowed to adjust a peak value of an output voltage to a desired value while reducing power consumption, and a display including the inverter circuit.
According to an embodiment of the invention, there is provided a first inverter circuit including: a first transistor, a second transistor, a third transistor, a fourth transistor and a fifth transistor each having channels of same conduction type; a first capacity element; and an input terminal and an output terminal. In this case, the first transistor makes or breaks electrical connection between the output terminal and a first voltage line in response to a potential difference between a voltage of the input terminal (input voltage) and a voltage of the first voltage line or a potential difference corresponding thereto. The second transistor makes or breaks electrical connection between a second voltage line and the output terminal in response to a potential difference between a voltage of a first terminal which is a source or a drain of the fourth transistor and a voltage of the output terminal or a potential difference corresponding thereto. The third transistor makes or breaks electrical connection between the first terminal and a third voltage line in response to a potential difference between the voltage of the input terminal and a voltage of the third voltage line or a potential difference corresponding thereto. The fourth transistor makes or breaks electrical connection between the first capacity element and a gate of the second transistor in response to a first control signal applied to a gate of the fourth transistor. The fifth transistor makes or breaks electrical connection between the first capacity element and a fourth voltage line in response to a second control signal applied to a gate of the fifth transistor. The first capacity element is inserted between a source or a drain not connected to the fourth voltage line of the fifth transistor and a fifth voltage line.
According to an embodiment of the invention, there is provided a first display with a display section and a drive section, the display section including a plurality of scanning lines arranged in rows, a plurality of signal lines arranged in columns, and a plurality of pixels arranged in a matrix form, the drive section including a plurality of inverter circuits each arranged corresponding to the scanning lines to drive each of the pixels, each of the inverter circuits including the same components as those of the first inverter circuit.
In the first inverter circuit and the first display according to the embodiment of the invention, the third transistor performing an on/off operation in response to a potential difference between the input voltage and the voltage of the third voltage line is arranged between the gate of the second transistor and the third voltage line. Moreover, the first transistor performing an on/off operation in response to a potential difference between the input voltage and the voltage of the first voltage line is arranged between the source of the second transistor and the first voltage line. Therefore, for example, when the input voltage falls, on-resistances of the third transistor and the first transistor are gradually increased to increase time necessary to charge the gate and the source of the second transistor to the voltages of the third voltage line and the first voltage line. Further, for example, when the input voltage rises, the on-resistances of the third transistor and the first transistor are gradually reduced to reduce time necessary to charge the gate and the source of the second transistor to the voltages of the third voltage line and the first voltage line. Moreover, in the embodiment of the invention, for example, when the input voltage falls, the gate of the second transistor is charged to a voltage equal to or higher than an on-voltage of the second transistor. Therefore, for example, when a falling edge voltage is applied to the input terminal, the third transistor and the first transistor are turned off, and immediately after that, the second transistor is turned on, so an output voltage is changed to a voltage of the second voltage line. Further, for example, in the case where the input voltage rises, the third transistor and the first transistor are turned on, and immediately after that, the second transistor is turned off. Therefore, the output voltage is changed to a voltage of the first voltage line.
According to an embodiment of the invention, there is provided a second inverter circuit including: a first transistor, a second transistor, a third transistor, a fourth transistor and a fifth transistor each having channels of same conduction type; a first capacity element; and an input terminal and an output terminal. In this case, a gate of the first transistor is electrically connected to the input terminal, and one terminal of a drain and a source of the first transistor is electrically connected to a first voltage line, and the other terminal of the first transistor is electrically connected to the output terminal. One terminal of a drain and a source of the second transistor is electrically connected to a second voltage line, and the other terminal of the second transistor is electrically connected to the output terminal. A gate of the third transistor is electrically connected to the input terminal, one terminal of a drain and a source of the third transistor is electrically connected to a third voltage line, and the other terminal of the third transistor is electrically connected to a gate of the second transistor. A gate of the fourth transistor is supplied with first control signal, and one terminal of a drain and a source of the fourth transistor is electrically connected to the gate of the second transistor. A gate of the fifth transistor is supplied with a second control signal, one terminal of a drain and a source of the fifth transistor is electrically connected to a fourth voltage line, and the other terminal of the fifth transistor is electrically connected to the other terminal of the fourth transistor. The first capacity element is inserted between the other terminal of the fifth transistor and a fifth voltage line.
According to an embodiment of the invention, there is provided a second display with a display section and a drive section, the display section including a plurality of scanning lines arranged in rows, a plurality of signal lines arranged in columns, and a plurality of pixels arranged in a matrix form, the drive section including a plurality of inverter circuits each arranged corresponding to the scanning lines to drive each of the pixels, each of the inverter circuits including the same components as those of the second inverter circuit.
In the second inverter circuit and the second display according to the embodiment of the invention, the third transistor of which the gate is connected to the input terminal is arranged between the gate of the second transistor and the third voltage line. Moreover, the first transistor of which the gate is connected to the input terminal is arranged between the source of the second transistor and the first voltage line. Therefore, for example, when an input voltage falls, the on-resistances of the third transistor and the first transistor are gradually increased to increase time necessary to charge the gate and the source of the second transistor to the voltages of the third voltage line and the first voltage line. Moreover, for example, when the input voltage rises, the on-resistances of the third transistor and the first transistor are gradually reduced to reduce time necessary to charge the gate and the source of the second transistor to the voltages of the third voltage line and the first voltage line. Further, in the embodiment of the invention, for example, when the input voltage falls, the gate of the second transistor is charged to a voltage equal to or higher than an on-voltage of the second transistor. Therefore, for example, when a falling edge voltage is applied to the input terminal, the third transistor and the first transistor are turned off, and immediately after that, the second transistor is turned on; therefore, the output voltage is changed to a voltage of the second voltage line. Moreover, for example, when the input voltage rises, the third transistor and the first transistor are turned on, and immediately after that, the second transistor is turned off. Therefore, the output voltage is changed to a voltage of the first voltage line.
In the first and second inverter circuits and the first and second displays according to the embodiment of the invention, a second capacity element may be inserted between a gate and a source of the second transistor. In such a case, the capacity of the second capacity element is preferably smaller than the capacity of the first capacity element.
According to an embodiment of the invention, there is provided an inverter circuit including: a first transistor and a second transistor; a first switch and a second switch; and a first capacity element, in which the first and second transistors are connected in series between a first voltage line and a second voltage line, the first and second switches are connected in series between a supply voltage line and a gate of the second transistor, and are alternately turned on and off so as not to be turned on simultaneously, an end of the first capacity element is connected between the first switch and the second switch, and off-state of the first transistor allows a predetermined fixed voltage to be supplied from the supply voltage line to the gate of the second transistor through the first switch, the end of the first capacity element and the second switch.
In the inverter circuits and the displays according to the embodiment of the invention, a period where the first transistor and the second transistor are turned on simultaneously, or a period where the third transistor, the fourth transistor and the fifth transistor are turned on simultaneously is eliminated. Therefore, a current (a through current) hardly flows between voltage lines through these transistors, so power consumption is allowed to be reduced. Moreover, when the input voltage falls, the output voltage is changed to the voltage of the second voltage line or the voltage of the first voltage line, and when the input voltage rises, the output voltage is changed to a voltage opposite to the above-described voltage. Therefore, a shift of a peak value of the output voltage from a desired value is allowed to be reduced. As a result, for example, variations in threshold correction or mobility correction of a driving transistor from one pixel circuit to another are allowed to be reduced, and variations in luminance from one pixel to another are allowed to be reduced.
Other and further objects, features and advantages of the invention will appear more fully from the following description.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram illustrating an example of an inverter circuit according to an embodiment of the invention.
FIG. 2 is a waveform chart illustrating an example of input/output signal waveforms of the inverter circuit in FIG. 1.
FIG. 3 is a waveform chart illustrating an example of an operation of the inverter circuit in FIG. 1.
FIG. 4 is a circuit diagram for describing an example of an operation of the inverter circuit in FIG. 1.
FIG. 5 is a circuit diagram for describing an example of an operation following FIG. 4.
FIG. 6 is a circuit diagram for describing an example of an operation following FIG. 5.
FIG. 7 is a circuit diagram for describing an example of an operation following FIG. 6.
FIG. 8 is a circuit diagram for describing an example of an operation following FIG. 7.
FIG. 9 is a circuit diagram for describing an example of an operation following FIG. 8.
FIG. 10 is a circuit diagram for describing an example of an operation following FIG. 9.
FIG. 11 is a circuit diagram for describing an example of an operation following FIG. 10.
FIG. 12 is a waveform chart illustrating another example of input/output signal waveforms of the inverter circuit in FIG. 1.
FIG. 13 is a waveform chart illustrating another example of the operation of the inverter circuit in FIG. 1.
FIG. 14 is a circuit diagram illustrating a modification of the inverter circuit in FIG. 1.
FIG. 15 is a waveform chart illustrating an example of an operation of the inverter circuit in FIG. 14.
FIG. 16 is a schematic view of a display as an application example of the inverter circuit according to any of the above-described embodiment and modifications thereof.
FIG. 17 is a circuit diagram illustrating an example of a writing line drive circuit and a pixel circuit in FIG. 16.
FIG. 18 is a waveform chart illustrating an example of an operation of the display in FIG. 16.
FIG. 19 is a circuit diagram illustrating an example of a pixel circuit of a display in related art.
FIG. 20 is a circuit diagram illustrating an example of an inverter circuit in related art.
FIG. 21 is a waveform chart illustrating an example of input/output signal waveforms of the inverter circuit in FIG. 20.
FIG. 22 is a circuit diagram illustrating another example of an inverter circuit in related art.
FIG. 23 is a circuit diagram illustrating still another example of an inverter circuit in related art.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preferred embodiment of the invention will be described in detail below referring to the accompanying drawings. Descriptions will be given in the following order.

    1. Embodiment (refer to FIGS. 1 to 11)
    2. Modifications (refer to FIGS. 12 to 15)
    3. Application Example (refer to FIGS. 16 to 18)
    4. Description of related art (refer to FIGS. 19 to 23)


Embodiment
Configuration
FIG. 1 illustrates an example of a whole configuration of an inverter circuit 1 according to an embodiment of the invention. The inverter circuit 1 outputs, from an output terminal OUT, a pulse signal (for example, refer to a part (B) in FIG. 2) with a substantially inverted signal waveform of a signal waveform (for example, refer to a part (A) in FIG. 2) of a pulse signal applied to an input terminal IN. The inverter circuit 1 is preferably formed on amorphous silicon or amorphous oxide semiconductor, and includes five transistors Tr1 to Tr5 each having channels of same conduction type. In addition to the above-described five transistors Tr1 to Tr5, the inverter circuit 1 includes two capacity elements C1 and C2, the input terminal IN and the output terminal OUT. In other words, the inverter circuit 1 has a 5Tr2C circuit configuration.
The transistors Tr1, Tr2 and Tr3 correspond to specific examples of “a first transistor”, “a second transistor” and “a third transistor” in the invention, respectively. Moreover, the transistors Tr4 and Tr5 correspond to specific examples of “a fourth transistor” and “a fifth transistor” in the invention, respectively. Further, the capacity elements C1 and C2 correspond to specific examples of “a first capacity element” and “a second capacity element” in the invention, respectively.
The transistors Tr1 to Tr5 are configured of thin-film transistors (TFTs) each having channels of same conduction type, for example, n-channel MOS (Metal Oxide Semiconductor) type thin-film transistors (TFTs). The transistor Tr1 makes or breaks electrical connection between the output terminal OUT and a low-voltage line LL in response to, for example, a potential difference Vgs1 between a voltage (an input voltage Vin) of the input terminal IN and a voltage VL of the low-voltage line LL (or a potential difference corresponding thereto). A gate of the transistor Tr1 is electrically connected to the input terminal IN, and one terminal of a source and a drain of the transistor Tr1 is electrically connected to the low-voltage line LL, and the other terminal not connected to the low-voltage line LL of the transistor Tr1 is electrically connected to the output terminal OUT. The transistor Tr2 makes or breaks electrical connection between a high-voltage line LH1 and the output terminal OUT in response to a potential difference Vgs2 between a voltage Vs3 of one terminal (a terminal A) which is not connected to the low-voltage line LL of a source and a drain of the transistor Tr3 and a voltage (an output voltage Vout) of the output terminal OUT (or a potential difference corresponding thereto). A gate of the transistor Tr2 is electrically connected to the terminal A of the transistor Tr3. One terminal of a source and a drain of the transistor Tr2 is electrically connected to the output terminal OUT, and the other terminal not connected to the output terminal OUT of the transistor Tr2 is electrically connected to a high-voltage line LH1.
The transistor Tr3 makes or breaks electrical connection between the gate of the transistor Tr2 and the low-voltage line LL in response to a potential difference Vgs3 between the input voltage Vin and the voltage VL of the low-voltage line LL (or a potential difference corresponding thereto). A gate of the transistor Tr3 is electrically connected to the input terminal IN. The other terminal of the source and the drain of the transistor Tr3 is electrically connected to the low-voltage line LL, and the terminal A of the transistor Tr3 is electrically connected to the gate of the transistor Tr2. In other words, the transistors Tr1 and Tr3 are connected to the same voltage line (the low-voltage line LL). Therefore, a terminal on a side close to the low-voltage line LL of the transistor Tr1 and a terminal on a side close to the low-voltage line LL of the transistor Tr3 have the same potential. The transistor Tr4 makes or breaks electrical connection between the capacity element C1 and the gate of the transistor Tr2 in response to a control signal applied to a control terminal AZ1. A gate of the transistor Tr4 is electrically connected to the control terminal AZ1. One terminal of a source and a drain of the transistor Tr4 is electrically connected to the capacity element C1, and the other terminal not connected to the capacity element C1 of the transistor Tr4 is electrically connected to the gate of the transistor Tr2. The transistor Tr5 makes and breaks electrical connection between a high-voltage line LH2 and the capacity element C1 in response to a control signal applied to a control terminal AZ2. A gate of the transistor Tr5 is electrically connected to the control terminal AZ2. One terminal of a source and a drain of the transistor Tr5 is electrically connected to the high-voltage line LH2. The other terminal not connected to the high-voltage line LH2 of the transistor Tr5 is electrically connected to the capacity element C1.
The low-voltage line LL corresponds to a specific example of “a first voltage line” and “a third voltage line” in the invention. The high-voltage line LH1 and the high-voltage line LH2 correspond to specific examples of “a second voltage line” and “a fourth voltage line” in the invention, respectively.
The high-voltage lines LH1 and LH2 are connected to a power supply (not illustrated) outputting a higher voltage (a constant voltage) than the voltage VL of the low-voltage line LL. A voltage VH1 of the high-voltage line LH1 is at a voltage Vdd1 during the drive of the inverter circuit 1, and a voltage VH2 of the high-voltage line LH2 is at a voltage Vdd2 (≧Vdd1+Vth2) during the drive of the inverter circuit 1. Note that a voltage Vth2 is a threshold voltage of the transistor Tr2. On the other hand, the low-voltage line LL is connected to a power supply (not illustrated) outputting a lower voltage (a constant voltage) than the voltage VH1 of the high-voltage line LH1, and the voltage VL of the low-voltage line LL is at a voltage Vss (<Vdd1) during the drive of the inverter circuit 1.
The control terminal AZ1 is connected to a power supply S1 (not illustrated) outputting a predetermined pulse signal. The control terminal AZ2 is connected to a power supply S2 (not illustrated) outputting a predetermined pulse signal. For example, as illustrated in a part (C) in FIG. 2, the power supply S1 outputs a high while a low is applied to the control terminal AZ2. On the other hand, as illustrated in a part (B) in FIG. 2, the power supply S2 outputs a high while a low is applied to the control terminal AZ1. In other words, the power supply S1 and the power supply S2 alternately outputs a high so as to prevent the transistors Tr4 and Tr5 from being turned on simultaneously (that is, to alternately turn the transistors Tr4 and Tr5 on and off). The power supply S1 switches the output voltage thereof from low to high (that is, the power supply S1 turns the transistor Tr4 on) at a different timing from a falling edge of the input voltage Vin. The power supply S1 switches the output voltage thereof from low to high, for example, immediately before the falling edge of the input voltage Vin.
The capacity element C1 is inserted between the source or the drain which is not connected to the high-voltage line LH2 of the transistor Tr5 and the low-voltage line LL. The capacity element C2 is inserted between the gate of the transistor Tr2 and the source of the transistor Tr2. The capacities of the capacity elements C1 and C2 are sufficiently larger than parasitic capacitances of the transistors Tr1 to Tr5. The capacity of the capacity element C2 is smaller than the capacity of the capacity element C1. The capacity of the capacity element C1 has a value allowed to charge the gate of the transistor Tr2 to a voltage Vss+Vth2 or over when a falling edge voltage is applied to the input terminal IN and the transistor Tr3 is turned off. Note that a voltage Vth2 is a threshold voltage of the transistor Tr2. The capacities of the capacity elements C1 and C2 each preferably satisfy the following Mathematical Expression 1. In the case where the capacity elements C1 and C2 have a sufficiently smaller value than a parasitic capacitance Cout (not illustrated) generated between the output terminal OUT and the low-voltage line LL, if the capacities of the capacity elements C1 and C2 satisfy Mathematical Expression 1, at a falling edge of the input voltage Vin which will be described later, the transistor Tr4 is on, and allows a gate-source voltage of the transistor Tr2 to reach the threshold voltage Vth2 or over of the transistor Tr2, and allows the output voltage Vout to be switched from low to high.

C1(Vdd2−Vss)/(C1+C2)>Vth2  Mathematical Expression 1

The inverter circuit 1 corresponds to an inverter circuit (an inverter circuit 200 in FIG. 20) in related art further including a control element 10 and the capacity element C2 which are inserted between the transistors Tr1 and Tr2 in an output stage and the input terminal IN. In this case, for example, as illustrated in FIG. 1, the control element 10 includes a terminal P1 electrically connected to the input terminal IN, a terminal P2 electrically connected to the low-voltage line LL, a terminal P3 electrically connected to the gate of the transistor Tr2, and a terminal P4 electrically connected to the high-voltage line LH2. Moreover, for example, as illustrated in FIG. 1, the control element 10 includes the transistors Tr3 to Tr5 and the capacity element C1.
For example, when a falling edge voltage is applied to the terminal P1, the control element 10 charges the gate of the transistor Tr2 electrically connected to the terminal P3 to the voltage Vss+Vth2 or over. Moreover, for example, when a rising edge voltage is applied to the terminal P1, the control element 10 reduces the gate voltage Vg2 of the transistor Tr2 electrically connected to the terminal P3 to a voltage smaller than the voltage Vss+Vth2. Note that the operation of the control element 10 will be described with the following description of the operation of the inverter circuit 1.
Operation
Next, an example of the operation of the inverter circuit 1 will be described below referring to FIGS. 3 to 11. FIG. 3 is a waveform chart illustrating an example of the operation of the inverter circuit 1. FIGS. 4 to 11 are circuit diagrams sequentially illustrating an example of the operation of the inverter circuit 1.
First, as illustrated in FIG. 4, the input voltage Vin is low (Vss), and the transistor Tr5 is turned on, and the transistor Tr4 is turned off. At this time, the transistors Tr1 and Tr3 are off, and the capacity element C1 is charged to the voltage Vdd2, and a source voltage Vs5 of the transistor Tr5 is at the voltage Vdd2. Moreover, the gate voltage Vg2 of the transistor Tr2 is also at the voltage Vdd2, and the transistor Tr2 is on. Therefore, at this time, the voltage Vdd1 as the output voltage Vout is transmitted to the output terminal OUT.
Next, as illustrated in FIG. 5, in a state where the input voltage Vin is low (Vss), the transistor Tr5 is turned off, and then the transistor Tr4 is turned on. In other words, before the input voltage Vin is switched from low (Vss) to high (Vdd1), the transistor Tr4 is turned on. The gate voltage Vg2 of the transistor Tr2 is at the voltage Vdd2 before the transistor Tr4 is turned on. Therefore, even if the transistor Tr4 is switched from off to on, the transistor Tr2 is kept on, and the output voltage Vout is kept at the voltage Vdd1.
Next, in a state where the input voltage Vin is low (Vss), the transistor Tr4 is turned off, and then the transistor Tr5 is turned on. Likewise, the transistor Tr4 and Tr5 are repeatedly turned on and off, and then when the transistor Tr4 is on (the transistor Tr5 is off), the input voltage Vin is switched from low (Vss) to high (Vdd1) (refer to FIG. 6). Then, the transistors Tr1 and Tr3 are turned on, and the gate and the source of the transistor Tr2 are charged to the voltage VL (=Vss) of the low-voltage line LL. Therefore, the transistor Tr2 is turned off, and the voltage Vss as the output voltage Vout is transmitted to the output terminal OUT. Moreover, when the transistor Tr4 is turned on, the capacity element C1 charged to the voltage Vdd2 is connected to the low-voltage line LL through the transistor Tr4. Thus, the voltage of a terminal (a terminal B) on a side close to the transistor Tr5 of the capacity element C1 is gradually reduced from the voltage Vdd2, eventually to the voltage Vss.
After that, in a state where the input voltage Vin is high (Vdd1), the transistor Tr4 is turned off, and then the transistor Tr5 is turned on. Likewise, the transistors Tr4 and Tr5 are repeatedly turned on and off, and then when transistor Tr4 is on (the transistor Tr5 is off), the input voltage Vin is switched from high (Vdd1) to low (Vss). Then, the transistors Tr1 and Tr3 are turned off.
In this case, when the transistor Tr4 is turned on, as described above, the voltage of the capacity element C1 (a voltage of the terminal B) is gradually reduced from the voltage Vdd2 (refer to FIG. 7). Note that a voltage Vx in FIG. 7 is the voltage of the capacity element C1 (the voltage of the terminal B) immediately before the input voltage Vin is switched from high (Vdd1) to low (Vss). After that, after the transistor Tr4 is turned on, the input voltage Vin is switched from high (Vdd1) to low (Vss) to turn the transistor Tr3 off (refer to FIG. 8). At this time, the capacity element C1 is connected to the gate of the transistor Tr2 through the transistor Tr4; therefore, the capacity element C1 charges the gate of the transistor Tr2. As a result, the voltage of the capacity element C1 and the gate voltage Vg2 of the transistor Tr2 are switched to a voltage Vy.
At this time, in the case where the voltage Vy is equal to or higher than the sum of the voltage (=Vss) of the low-voltage line LL and the threshold voltage Vth2 of the transistor Tr2, the transistor Tr2 is turned on, and a current flows through the transistor Tr2 to gradually increase the output voltage Vout (refer to FIG. 8). After the lapse of a certain period, the output voltage Vout is changed to a voltage Vz. The capacity element C2 is connected between the gate and the source of the transistor Tr2. Therefore, by a bootstrap operation by the capacity element C2, the gate voltage Vg2 of the transistor Tr2 is intended to change with a change in the source voltage Vs2 of the transistor Tr2. However, as the transistor Tr4 is on and the capacity element C1 is connected to the transistor Tr2, the gate voltage Vg2 of the transistor Tr2 is substantially at the voltage Vy.
The voltage Vy will be considered below. In the case where the parasitic capacitances of the transistors Tr1 to Tr5 are as small as a negligible amount, compared to the capacity elements C1 and C2, and the parasitic capacitance Cout of the output terminal OUT (refer to FIG. 9) is extremely larger than the capacity element C2, the voltage Vy is represented by an expression (1) with use of the voltage Vx.

Vy=C1(Vx−Vss)/(C1+C2)+Vss  (1)

It is obvious from the expression (1) that the voltage Vy is determined by the capacities of the capacity elements C1 and C2, and when the capacity of the capacity element C1 is large, the voltage Vy is substantially equal to the voltage Vx.
After the input voltage Vin is switched from high (Vdd1) to low (Vss), the transistor Tr4 is turned off. At this time, when the gate-source voltage Vgs2 of the transistor Tr2 is equal to or higher than the threshold voltage Vth2 of the transistor Tr2 (Vy−VZ>Vth2), the transistor Tr2 is turned on, and the source voltage Vs2 of the transistor Tr2 keeps increasing (refer to FIG. 10). When the source voltage Vs2 of the transistor Tr2 increases, the transistor Tr4 is turned off, so the gate of the transistor Tr2 and the capacity element C1 are separated from each other. Therefore, the gate voltage Vg2 of the transistor Tr2 changes with a change in the source voltage Vs2 of the transistor Tr2 by a bootstrap operation by the capacity element C2. After the lapse of a certain period, the voltage Vdd1 as the output voltage Vout is transmitted to the output terminal OUT. After the transistor Tr4 is turned off, the transistor Tr5 is turned on again. Therefore, the capacity element C1 is charged to the voltage Vdd2.
After the transistor Tr5 is turned off, the transistor Tr4 is turned on again (refer to FIG. 11). Therefore, capacity coupling occurs again, and the capacity element C1 charges the gate of the transistor Tr2. As a result, the voltages of the capacity element C1 and the gate of the transistor Tr2 are equal to each other. In the case where the gate voltage Vg2 of the transistor Tr2 at this time is at a voltage Va, the gate-source voltage Vgs2 of the transistor Tr2 is changed to a voltage Va−Vdd1, and the transistor Tr4 is turned off. When such an operation is repeated, the gate voltage Vg2 of the transistor Tr2 is changed to the voltage Vdd2. Therefore, the voltage Vdd1 as the output voltage Vout is transmitted to the output terminal OUT.
Thus, in the inverter circuit 1 according to the embodiment, the output terminal OUT outputs a pulse signal (for example, refer to the part (B) in FIG. 2) with a substantially inverted waveform of the waveform (for example, refer to the part (A) in FIG. 2) of a pulse signal applied to the input terminal IN.
Effects
The inverter circuit 200 in related art illustrated in FIG. 20 has, for example, a single channel type circuit configuration in which two n-channel MOS type transistors Tr1 and Tr2 are connected to each other in series. In the inverter circuit 200, for example, as illustrated in FIG. 21, when the input voltage Vin is at the voltage Vss, the output voltage Vout is not at the voltage Vdd but at a voltage Vdd−Vth2. In other words, the output voltage Vout includes the threshold voltage Vth2 of the transistor Tr2, and the output voltage Vout is greatly affected by variations in the threshold voltage Vth2 of the transistor Tr2.
Therefore, it is considered that, for example, as illustrated in an inverter circuit 300 in FIG. 22, the gate and the drain of the transistor Tr2 are electrically separated from each other, and the gate is connected to the high-voltage wiring line LH2 to which a higher voltage Vdd2 (=Vdd+Vth2) than the voltage Vdd of the drain is applied. Moreover, for example, a bootstrap type circuit configuration represented by an inverter circuit 400 in FIG. 23 is considered.
However, in any of the circuits in FIGS. 20, 22 and 23, even in the case where the input voltage Vin is high, that is, even in the case where the output voltage Vout is low, a current (a through current) flows from the high-voltage wiring line LH to the low-voltage wiring line LL through the transistors Tr1 and Tr2. As a result, power consumption in the inverter circuits is increased. Moreover, in the circuits in FIGS. 20, 22 and 23, for example, as illustrated in a point encircled by a broken line in a part (B) in FIG. 21, when the input voltage Vin is at the voltage Vdd, the output voltage Vout is not at the voltage Vss, and a peak value of the output voltage Vout varies. Therefore, for example, in the case where the inverter circuits are used in a scanner in an active matrix organic EL display, threshold correction or mobility correction in the driving transistor varies from one pixel circuit to another, thereby causing variations in luminance.
On the other hand, in the inverter circuit 1 according to the embodiment, the transistors Tr1 and Tr3 performing an ON/OFF operation in response to a potential difference between the input voltage Vin and the voltage VL of the low-voltage line LL are arranged between the gate of the transistor Tr2 and the low-voltage line LL and between the source of the transistor Tr2 and the low-voltage line LL. Therefore, when the gate voltages of the transistors Tr1 and Tr3 are switched (reduced) from high (Vdd1) to low (Vss), on-resistances of the transistors Tr1 and Tr3 are gradually increased to increase time necessary to charge the gate and the source of the transistor Tr2 to the voltage VL of the low-voltage line LL. Moreover, when the gate voltages of the transistors Tr1 and Tr3 are switched (increased) from low (Vss) to high (Vdd1), the on-resistances of the transistors Tr1 and Tr3 are gradually reduced to reduce time necessary to charge the gate and the source of the transistor Tr2 to the voltage VL of the low-voltage line LL. Further, in the inverter circuit 1 according to the embodiment, the capacity element C1 is connected to the source of the transistor Tr5, and is connected to the gate of the transistor Tr2 through the transistor Tr4. Therefore, when a rising edge voltage is applied to the input terminal IN to turn the transistors Tr1 and Tr3 off, the gate of the transistor Tr2 is charged to a voltage equal to or higher than the voltage Vss+Vth2 by the capacity element C1 to which the voltage Vdd2 is charged. As a result, the transistor Tr2 is turned on, and the output voltage Vout is changed to the voltage (Vdd1) of the high-voltage line LH1.
Thus, in the inverter circuit 1 according to the embodiment, a period where the transistor Tr1 and the transistor Tr2 are simultaneously turned on or a period where the transistors Tr1 to Tr5 are simultaneously turned on is eliminated. Therefore, a current (a through current) hardly flows between the high-voltage line VH1 and the low-voltage line LL and between the high-voltage line VH2 and the low-voltage line LL through the transistors Tr1 and Tr2 or through the transistors Tr3 to Tr5. As a result, power consumption is allowed to be reduced. Moreover, when the input voltage Vin is switched (reduced) from high (Vdd1) to low (Vss), the output voltage Vout is changed to a voltage of the high-voltage line VH1, and when the input voltage Vin is switched (increased) from low (Vss) to high (Vdd1), the output voltage Vout is changed to a voltage of the low-voltage line LL. Therefore, variations in the output voltage Vout are allowed to be eliminated. As a result, for example, variations in threshold correction or mobility correction in the driving transistor from one pixel circuit to another are allowed to be reduced, and variations in luminance from one pixel to another are allowed to be reduced.
Modifications
In the above-described embodiment, for example, as illustrated in FIGS. 12 and 13, when a falling edge voltage is applied to the input terminal IN, the transistor Tr4 may be turned off, and after the falling edge voltage is applied to the input terminal IN, the transistor Tr4 may be turned on. In such a case, the voltage of the capacity element C1 (the source voltage of the transistor Tr5) is prevented from being reduced from the voltage Vdd2 by the transistor Tr3. As a result, the inverter circuit 1 is allowed to be operated at high speed.
Moreover, in the above-described embodiment and the modification thereof, for example, as illustrated in FIG. 14, the capacity element C2 may be removed from the inverter circuit 1. In such a case, the gate voltage Vy represented by the above-described expression (1) is allowed to be substantially equal to the voltage Vx (refer to a part (E) in FIG. 15). Therefore, the inverter circuit 1 is allowed to be operated at higher speed.
Further, in the above-described embodiment and the modifications thereof, the transistors Tr1 to Tr5 are configured of n-channel MOS type TFTs; however, they may be configured of p-channel MOS type TFTs. In this case, a transient response when the transistors Tr1 to Tr5 are switched (increased) from low to high and a transient response when the transistors Tr1 to Tr5 are switched (reduced) from high to low are opposite to each other. Moreover, the high-voltage line VH1 is replaced with a low-voltage line LL1, and the high-voltage line VH2 is replaced with a low-voltage line LL2, and the low-voltage line LL is replaced with the high-voltage line VH.
In this case, the low-voltage lines LL1 and LL2 are connected to a power supply (not illustrated) outputting a lower voltage (a constant voltage) than the voltage of the high-voltage line VH. The voltage of the low-voltage line LL1 is at a voltage Vss1 during the drive of the inverter circuit, and the voltage of the low-voltage line LL2 is at a voltage Vss2 (≦Vss1−Vth2) during the drive of the inverter circuit. On the other hand, the high-voltage line VH is connected to a power supply (not illustrated) outputting a higher voltage (a constant voltage) than the voltages of the low-voltage lines LL1 and LL2, and the voltage of the high-voltage line VH is at the voltage Vdd (>Vss1) during the drive of the inverter circuit.
APPLICATION EXAMPLE
FIG. 16 illustrates an example of a whole configuration of a display 100 as an application example of the inverter circuit 1 according to any of the above-described embodiment and the modifications thereof. The display 100 includes, for example, a display panel 110 (a display section) and a drive circuit 120 (a drive section).
Display Panel 110
The display panel 110 includes a display region 110A in which three kinds of organic EL elements 111R, 111G and 111B emitting light of different colors are two-dimensionally arranged. The display region 110A is a region where a picture is displayed with use of light emitted from the organic EL elements 111R, 111G and 111B. The organic EL element 111R is an organic EL element emitting red light, the organic EL element 111G is an organic EL element emitting green light, and the organic EL element 111B is an organic EL element emitting blue light. In addition, the organic EL elements 111R, 111G and 111B are collectively called organic EL elements 111 as necessary.
Display Region 110A
FIG. 17 illustrates an example of a circuit configuration in the display region 10A with an example of a writing line drive circuit 124 which will be described later. In the display region 110A, a plurality of pixel circuits 112 are two-dimensionally arranged so as to be paired with the organic EL elements 111, respectively. In the application example, a pair of the organic EL element 111 and the pixel circuit 112 configures one pixel 113. More specifically, as illustrated in FIG. 12, a pair of the organic EL element 111R and the pixel circuit 112 configures one red pixel 113R, and a pair of the organic EL element 111G and the pixel circuit 112 configures one green pixel 113G, and a pair of the organic EL element 111B and the pixel circuit 112 configures one blue pixel 113B. Moreover, three adjacent pixels 113R, 113G and 113B configure one display pixel 114.
Each pixel circuit 112 includes, for example, a driving transistor Tr100 controlling a current flowing through the organic EL element 111, a writing transistor Tr200 writing a voltage of a signal line DTL to the driving transistor Tr100, and a retention capacitor Cs. In other words, each pixel circuit 112 has a 2Tr1C circuit configuration. The driving transistor Tr100 and the writing transistor Tr200 each are configured of, for example, an n-channel MOS type thin film transistor (TFT). The driving transistor Tr100 or the writing transistor Tr200 may be configured of, for example, a p-channel MOS type TFT.
In the display region 110A, a plurality of writing lines WSL (scanning lines) are arranged in rows, and a plurality of signal lines DTL are arranged in columns. In the display region 110A, a plurality of power supply lines PSL (members to which a power supply voltage is supplied) are arranged in rows along the writing lines WSL. One organic EL element 111 is arranged around an intersection of each of the signal lines DTL and each of the writing lines WSL. Each of the signal lines DTL is connected to an output end (not illustrated) of a signal line drive circuit 123 which will be described later and one of a drain electrode and a source electrode (both not illustrated) of the writing transistor Tr200. Each of the writing lines WSL is connected to an output end (not illustrated) of a writing line drive circuit 124 which will be described later and a gate electrode (not illustrated) of the writing transistor Tr200. Each of the power supply lines PSL is connected to an output end (not illustrated) of a power supply line drive circuit 125 which will be described later and one of a drain electrode and a source electrode (both not illustrated) of the driving transistor Tr100. The other which is not connected to the signal line DTL of the drain electrode and the source electrode (both not illustrated) of the writing transistor Tr200 is connected to a gate electrode (not illustrated) of the driving transistor Tr100 and an end of the retention capacitor Cs. The other which is not connected to the power supply line PSL of the drain electrode and the source electrode (both not illustrated) of the driving transistor Tr100 and the other end of retention capacitor Cs are connected to an anode electrode (not illustrated) of the organic EL element 111. A cathode electrode (not illustrated) of the organic EL element 111 is connected to, for example, a ground line GND.
Drive Circuit 120
Next, each circuit in the drive circuit 120 will be described referring to FIGS. 16 and 17. The drive circuit 120 includes a timing generation circuit 121, a picture signal processing circuit 122, the signal line drive circuit 123, the writing line drive circuit 124 and the power supply line drive circuit 125.
The timing generation circuit 121 controls the picture signal processing circuit 122, the signal line drive circuit 123, the writing line drive circuit 124 and the power supply line drive circuit 125 to operate in conjunction with one another. The timing generation circuit 21 outputs a control signal 121A to each of the above-described circuits in response to (in synchronization with), for example, a synchronization signal 120B entered from outside.
The picture signal processing circuit 122 performs predetermined correction on the picture signal 120A entered from outside, and outputs a corrected picture signal 122A to the signal line drive circuit 123. Examples of the predetermined correction include gamma correction and overdrive correction.
The signal line drive circuit 123 applies the picture signal 122A (a signal voltage Vsig) entered from the picture signal processing circuit 122 to each of the signal lines DTL in response to (in synchronization with) the input of the control signal 121A so as to write the picture signal 122A to selected pixels 113. Note that writing means applying a predetermined voltage to a gate of the driving transistor Tr100.
The signal line drive circuit 123 is configured by including, for example, a shift register (not illustrated), and includes buffer circuits (not illustrated) corresponding to columns of pixels 113, respectively. The signal line drive circuit 123 is allowed to output two kinds of voltages (Vofs and Vsig) to each of the signal lines DTL in response to (in synchronization with) the input of the control signal 121A. More specifically, the signal line drive circuit 123 sequentially supplies two kinds of voltages (Vofs and Vsig) to pixels 113 selected by the wiring line drive circuit 124 through the signal lines DTL connected to the pixels 113.
In this case, an offset voltage Vofs has a constant voltage value irrespective of the value of a signal voltage Vsig. Moreover, the signal voltage Vsig has a voltage value corresponding to the picture signal 122A. The minimum voltage of the signal voltage Vsig is lower than the offset voltage Vofs, and the maximum voltage of the signal voltage Vsig is higher than offset voltage Vofs.
The writing line drive circuit 124 is configured by including, for example, a shift register (not illustrated), and includes buffer circuits 5 corresponding to rows of pixels 113, respectively. The buffer circuits 5 each are configured of a plurality of the above-described inverter circuits 1, and outputs a pulse signal with substantially the same phase as that of a pulse signal applied to an input end thereof to an output end thereof The writing line drive circuit 124 is allowed to output two kinds of voltages (Vdd1 and Vss) to each of the wiring lines WSL in response to (in synchronization with) the input of the control signal 121A. More specifically, the writing line drive circuit 124 supplies two kinds of voltages (Vdd1 and Vss) to pixels 113 to be driven through the writing lines WSL connected to the pixels 113 so as to control the writing transistor Tr200.
In this case, the voltage Vdd1 has a value equal to or higher than an on-voltage of the writing transistor Tr200. The voltage Vdd1 is a voltage value generated from the writing line drive circuit 124 during light extinction which will be described later or during threshold correction. The voltage Vss has a lower value than the on-voltage of the writing transistor Tr200 and the voltage Vdd1.
The power supply line drive circuit 125 is configured by including, for example, a shift register (not illustrated), and includes buffer circuits (not illustrated) corresponding to the rows of the pixels 113, respectively. The power supply line drive circuit 125 is allowed to output two kinds of voltages (VccH and VccL) in response to (in synchronization with) the input of the control signal 121A. More specifically, the power supply line drive circuit 125 supplies two kinds of voltages (VccH and VccL) to pixels 113 to be driven through the power supply lines PSL connected to the pixels 113 to control light emission and extinction of the organic EL elements 11.
In this case, the voltage VccL has a lower voltage value than a voltage (Vel+Vca) which is the sum of a threshold voltage Vel of the organic EL element 111 and a voltage Vca of a cathode of the organic EL element 111. Moreover, the voltage VccH has a voltage value equal to or higher than the voltage (Vel+Vca).
Next, an example of the operation (operation from light extinction to light emission) of the display 100 will be described below. In the application example, to maintain light emission luminance of the organic EL elements 111 constant even if the threshold voltage Vth or the mobility μ of the driving transistor Tr100 temporally changes, a correction operation on a change in the threshold voltage Vth or the mobility μ is incorporated.
FIG. 18 illustrates an example of voltage waveforms applied to the pixel circuit 112 and an example of changes in the gate voltage Vg and the source voltage Vs of the driving transistor Tr100. A part (A) in FIG. 18 illustrates a state where the signal voltage Vsig and the offset voltage Vofs are applied to the signal line DTL. A part (B) in FIG. 18 illustrates a state where the voltage Vdd turning the writing transistor Tr200 on and the voltage Vss turning the writing transistor Tr200 off are applied to the writing line WSL. A part (C) in FIG. 18 illustrates a state where the voltage VccH and the voltage VccL are applied to the power supply line PSL. Moreover, parts (D) and (E) in FIG. 18 illustrate states where the gate voltage Vg and the source voltage Vs of the driving transistor Tr100 are momentarily changed with the application of voltages to the power supply line PSL, the signal line DTL and the writing line WSL.
Vth Correction Preparation Period
First, preparation for Vth correction is made. More specifically, when the voltage of the writing line WSL is at the voltage Voff and the voltage of the power supply line DSL is at the voltage VccH (that is, when the organic EL element 111 emits light), the power source line drive circuit 125 reduces the voltage of the power source line DSL from the voltage VccH to the voltage VccL (T1). Then, the source voltage Vs is changed to the voltage VccL to turn the organic EL element 111 off. After that, when the voltage of the signal line DTL is at the voltage Vofs, the writing line drive circuit 124 increases the voltage of the writing line WSL from the voltage Voff to the voltage Von to change the voltage of the gate of the driving transistor Tr100 to the voltage Vofs.
First Vth Correction Period
Next, the Vth correction is performed. More specifically, while the writing transistor Tr200 is on and the voltage of the signal line DTL is at the voltage Vofs, the power source line drive circuit 125 increases the voltage of the power source line DSL from the voltage VccL to the voltage VccH (T2). Then, a current Ids flows between the drain and the source of the driving transistor Tr100, and the source voltage Vs is increased. After that, before the signal line drive circuit 123 switches the voltage of the signal line DTL from the voltage Vofs to the voltage Vsig, the writing line drive circuit 124 reduces the voltage of the writing line WSL from the voltage Von to the voltage Voff (T3). As a result, the gate of the driving transistor Tr100 is turned to a floating state, and the Vth correction stops.
First Vth Correction Stop Period
During a period where the Vth correction stops, sampling of the voltage of the signal line DTL is performed in a row (a pixel) different from a row (a pixel) on which the Vth correction has already been performed. In addition, at this time, the source voltage Vs is lower than a voltage Vofs−Vth in the row (the pixel) on which the Vth correction has already been performed; therefore, during a Vth correction stop period, the current Ids flows between the drain and the source of the driving transistor Tr100 in the row (the pixel) on which the Vth correction has already been performed, and the source voltage Vs is increased, and the gate voltage Vg is also increased by coupling through the retention capacitor Cs.
Second Vth Correction Period
Next, the Vth correction is performed again. More specifically, when the voltage of the signal line DTL is at the voltage Vofs, thereby allowing the Vth correction, the writing line drive circuit 124 increases the voltage of the writing line WSL from the voltage Voff to the voltage Von, and the gate of the driving transistor Tr100 is changed to the voltage Vofs (T4). At this time, in the case where the source voltage Vs is lower than a voltage Vofs−Vth (in the case where the Vth correction is not yet completed), the current Ids flows between the drain and the source of the driving transistor Tr100 until cutting the driving transistor Tr100 off (until the gate-source voltage Vgs is changed to the voltage Vth). After that, before the signal line drive circuit 123 switches the voltage of the signal line DTL from the voltage Vofs to the voltage Vsig, the writing line drive circuit 24 reduces the voltage of the writing line WSL from the voltage Von to the voltage Voff (T5). Therefore, the gate of the driving transistor Tr100 turns into a floating state, so the gate-source voltage Vgs is allowed to be maintained constant irrespective of the magnitude of the voltage of the signal line DTL.
Note that in the Vth correction period, in the case where the retention capacitor Cs is charged to the voltage Vth and the gate-source voltage Vgs is changed to the voltage Vth, the drive circuit 120 completes the Vth correction. However, in the case where the gate-source voltage Vgs does not reach the voltage Vth, the drive circuit 120 repeatedly executes and stops the Vth correction until the gate-source voltage Vgs reaches the voltage Vth.
Writing μ Correction Period
After the Vth correction stop period is completed, writing and μ correction are performed. More specifically, while the voltage of the signal line DTL is at the voltage Vsig, the writing line drive circuit 124 increases the voltage of the writing line WSL from the voltage Voff to the voltage Von (T6), and the gate of the driving transistor Tr100 is connected to the signal line DTL. Therefore, the gate voltage Vg of the driving transistor Tr100 is changed to the voltage Vsig of the signal line DTL. At this time, an anode voltage of the organic EL element 11 at this stage is still smaller than the threshold voltage Vel of the organic EL element 111, so the organic EL element 111 is cut off Therefore, the current Ids flows into an element capacitance (not illustrated) of the organic EL element 111, and the element capacitance is charged, so the source voltage Vs is increased only by a voltage ΔVy, and then the gate-source voltage Vgs reaches a voltage Vsig+Vth−ΔVy. Thus, μ correction is performed simultaneously with writing. In this case, the larger mobility μ of the driving transistor Tr100 is, the more the voltage ΔVy is increased, so when the gate-source voltage Vgs is reduced only by the voltage ΔVy before light emission, variations in mobility μ from one pixel circuit 113 to another are preventable.
Light Emission Period
Finally, the writing line drive circuit 124 reduces the voltage of the writing line WSL from the voltage Von to the voltage Voff (T7). Then, the gate of the driving transistor Tr100 is turned into a floating state, and the current Ids flows between the drain and the source of the driving transistor Tr100 to increase the source voltage Vs. As a result, a voltage equal to or higher than the threshold voltage Vel is applied to the organic EL element 111, and the organic EL element 111 emits light with desired luminance.
In the display 100 in the application example, as described above, in each pixel 113, on/off control of the pixel circuit 112 is performed, and a drive current is thereby injected into the organic EL element 111 of each pixel 113 to cause emission of light by the recombination of holes and electrons, and then the light is extracted to outside. As a result, an image is displayed on the display region 110A of the display panel 110.
In the application example, for example, the buffer circuits 5 in the writing line drive circuit 124 each are configured of a plurality of the above-described inverter circuits 1. Therefore, a through current hardly flows through the buffer circuits 5; therefore, the power consumption of the buffer circuits 5 is allowed to be reduced. Moreover, variations in the output voltages of the buffer circuits 5 is small; therefore, variations in threshold correction or mobility correction of the driving transistor Tr100 from one pixel circuit 112 to another are allowed to be reduced, and variations in luminance from one pixel 113 to another are allowed to be reduced.
Although the present invention is described referring to the embodiment, the modifications and the application example, the invention is not limited thereto, and may be variously modified.
For example, in the above-described application example, the inverter circuit 1 according to the above-described embodiment is used in an output stage of the writing line drive circuit 124; however, instead of the output stage of the writing line drive circuit 124, the inverter circuit 1 may be used in an output stage of the power supply line drive circuit 125, or may be used in both of the output stage of the writing line drive circuit 124 and the output stage of the power supply line drive circuit 125.
The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2010-084224 filed in the Japan Patent Office on Mar. 31, 2010, the entire content of which is hereby incorporated by reference.
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.

## Claims

1. An inverter circuit comprising:
a first transistor, a second transistor, a third transistor, a fourth transistor and a fifth transistor each having channels of same conduction type;
a first capacity element; and
an input terminal and an output terminal,
wherein the first transistor makes or breaks electrical connection between the output terminal and a first voltage line in response to a potential difference between a voltage of the input terminal and a voltage of the first voltage line or a potential difference corresponding thereto,
the second transistor makes or breaks electrical connection between a second voltage line and the output terminal in response to a potential difference between a voltage of a first terminal which is a source or a drain of the fourth transistor and a voltage of the output terminal or a potential difference corresponding thereto,
the third transistor makes or breaks electrical connection between the first terminal and a third voltage line in response to a potential difference between the voltage of the input terminal and a voltage of the third voltage line or a potential difference corresponding thereto,
the fourth transistor makes or breaks electrical connection between the first capacity element and a gate of the second transistor in response to a first control signal applied to a gate of the fourth transistor,
the fifth transistor makes or breaks electrical connection between the first capacity element and a fourth voltage line in response to a second control signal applied to a gate of the fifth transistor, and
the first capacity element is inserted between a source or a drain not connected to the fourth voltage line of the fifth transistor and a fifth voltage line.

2. An inverter circuit comprising:
a first transistor, a second transistor, a third transistor, a fourth transistor and a fifth transistor each having channels of same conduction type;
a first capacity element; and
an input terminal and an output terminal,
wherein a gate of the first transistor is electrically connected to the input terminal, and one terminal of a drain and a source of the first transistor is electrically connected to a first voltage line, and the other terminal of the first transistor is electrically connected to the output terminal,
one terminal of a drain and a source of the second transistor is electrically connected to a second voltage line, and the other terminal of the second transistor is electrically connected to the output terminal,
a gate of the third transistor is electrically connected to the input terminal, one terminal of a drain and a source of the third transistor is electrically connected to a third voltage line, and the other terminal of the third transistor is electrically connected to a gate of the second transistor,
a gate of the fourth transistor is supplied with a first control signal, and one terminal of a drain and a source of the fourth transistor is electrically connected to the gate of the second transistor,
a gate of the fifth transistor is supplied with a second control signal, one terminal of a drain and a source of the fifth transistor is electrically connected to a fourth voltage line, and the other terminal of the fifth transistor is electrically connected to the other terminal of the fourth transistor, and
the first capacity element is inserted between the other terminal of the fifth transistor and a fifth voltage line.

3. The inverter circuit according to claim 2, further comprising:
a second capacity element inserted between the gate and the source of the second transistor.

4. The inverter circuit according to claim 3, wherein
the capacity of the second capacity element is smaller than that of the first capacity element.

5. The inverter circuit according to claim 4, wherein
the capacities of the first capacity element and the second capacity element satisfy the following expression:


C1(Vdd2−Vss)/(C1+C2)>Vth2 


where C1 is the capacity of the first capacity element, C2 is the capacity of the second capacity element, Vdd2 is a voltage of the fourth voltage line, Vss is a voltage of the first voltage line, and Vth2 is a threshold voltage of the second transistor.

6. The inverter circuit according to claim 2, wherein
the first voltage line, the third voltage line and the fifth voltage line have the same potential.

7. The inverter circuit according to claim 6, wherein
the second voltage line and the fourth voltage line are connected to a power supply outputting a voltage higher than a common voltage of the first voltage line, the third voltage line and the fifth voltage line.

8. The inverter circuit according to claim 7, wherein
the fourth voltage line is connected to a power supply outputting a voltage higher than the voltage of the second voltage line by a threshold voltage of the second transistor or over.

9. The inverter circuit according to claim 2, wherein
the fourth transistor and the fifth transistor are alternately turned on and off so as not to be turned on simultaneously.

10. The inverter circuit according to claim 9, wherein
the fourth transistor is turned on before a voltage of the input terminal falls.

11. The inverter circuit according to claim 9, wherein
the fourth transistor is turned on after a voltage of the input terminal falls.

12. A display with a display section and a drive section, the display section including a plurality of scanning lines arranged in rows, a plurality of signal lines arranged in columns, and a plurality of pixels arranged in a matrix form, the drive section including a plurality of inverter circuits each arranged corresponding to the scanning lines to drive each of the pixels, each of the inverter circuits comprising:
a first transistor, a second transistor, a third transistor, a fourth transistor and a fifth transistor each having channels of same conduction type;
a first capacity element; and
an input terminal and an output terminal,
wherein the first transistor makes or breaks electrical connection between the output terminal and a first voltage line in response to a potential difference between a voltage of the input terminal and a voltage of the first voltage line or a potential difference corresponding thereto,
the second transistor makes or breaks electrical connection between a second voltage line and the output terminal in response to a potential difference between a voltage of a first terminal which is a source or a drain of the fourth transistor and a voltage of the output terminal or a potential difference corresponding thereto,
the third transistor makes or breaks electrical connection between the first terminal and a third voltage line in response to a potential difference between the voltage of the input terminal and a voltage of the third voltage line or a potential difference corresponding thereto,
the fourth transistor makes or breaks electrical connection between the first capacity element and a gate of the second transistor in response to a first control signal applied to a gate of the fourth transistor,
the fifth transistor makes or breaks electrical connection between the first capacity element and a fourth voltage line in response to a second control signal applied to a gate of the fifth transistor, and
the first capacity element is inserted between a source or a drain not connected to the fourth voltage line of the fifth transistor and a fifth voltage line.

13. A display with a display section and a drive section, the display section including a plurality of scanning lines arranged in rows, a plurality of signal lines arranged in columns, and a plurality of pixels arranged in a matrix form, the drive section including a plurality of inverter circuits each arranged corresponding to the scanning lines to drive each of the pixels, each of the inverter circuits comprising:
a first transistor, a second transistor, a third transistor, a fourth transistor and a fifth transistor each having channels of same conduction type;
a first capacity element; and
an input terminal and an output terminal,
wherein a gate of the first transistor is electrically connected to the input terminal, and one terminal of a drain and a source of the first transistor is electrically connected to a first voltage line, and the other terminal of the first transistor is electrically connected to the output terminal,
one terminal of a drain and a source of the second transistor is electrically connected to a second voltage line, and the other terminal of the second transistor is electrically connected to the output terminal,
a gate of the third transistor is electrically connected to the input terminal, one terminal of a drain and a source of the third transistor is electrically connected to a third voltage line, and the other terminal of the third transistor is electrically connected to a gate of the second transistor,
a gate of the fourth transistor is supplied with a first control signal, and one terminal of a drain and a source of the fourth transistor is electrically connected to the gate of the second transistor,
a gate of the fifth transistor is supplied with a second control signal, one terminal of a drain and a source of the fifth transistor is electrically connected to a fourth voltage line, and the other terminal of the fifth transistor is electrically connected to the other terminal of the fourth transistor, and
the first capacity element is inserted between the other terminal of the fifth transistor and a fifth voltage line.