# Patent

## Title
Inverter circuit and display device

## Abstract

An inverter circuit including: first to third transistors; first and second switches; and a first capacitive element. The first and second transistors are connected in series between a first voltage line and a second voltage line. The third transistor is connected between the second voltage line and a gate of the second transistor. The first and second switches are connected in series between a voltage supply line and a gate of the third transistor, and are turned on/off alternately to prevent the first and second switches from simultaneously turning ON. One end of the first capacitive element is connected to a node between the first and second switches. Off-state of the first transistor allows a predetermined fixed voltage to be supplied from the voltage supply line to the gate of the second transistor, via the first switch, the one end of the first capacitive element and the second switch.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inverter circuit that is suitably applicable to, for example, a display device using an organic EL (Electro Luminescence) element. The present invention also relates to a display device provided with the above-mentioned inverter circuit.
2. Description of the Related Art
In recent years, in the field of display devices that display images, a display device that uses, as a light emitting element for a pixel, an optical element of current-driven type whose light emission luminance changes according to the value of a flowing current, e.g. an organic EL element, has been developed, and its commercialization is proceeding. In contrast to a liquid crystal device and the like, the organic EL element is a self-luminous element. Therefore, in the display device using the organic EL element (organic EL display device), gradation of coloring is achieved by controlling the value of a current flowing in the organic EL element.
As a drive system in the organic EL display device, like a liquid crystal display, there are a simple (passive) matrix system and an active matrix system. The former is simple in structure, but has, for example, such a disadvantage that it is difficult to realize a large and high-resolution display device. Therefore, currently, development of the active matrix system is brisk. In this system, the current flowing in a light emitting element arranged for each pixel is controlled by a drive transistor.
In the above-mentioned drive transistor, there is a case in which a threshold voltage Vth or a mobility μ changes over time, or varies from pixel to pixel due to variations in production process. When the threshold voltage Vth or the mobility μ varies from pixel to pixel, the value of the current flowing in the drive transistor varies from pixel to pixel and therefore, even when the same voltage is applied to the gate of the drive transistor, the light emission luminance of the organic EL element varies and uniformity of a screen is impaired. Thus, there has been developed a display device in which a correction function to address a change in the threshold voltage Vth or the mobility μ is incorporated (see, for example, Japanese Unexamined Patent Application Publication No. 2008-083272).
A correction to address the change in the threshold voltage Vth or the mobility μ is performed by a pixel circuit provided for each pixel. As illustrated in, for example, FIG. 16, this pixel circuit includes: a drive transistor Tr100 that controls a current flowing in an organic EL element 111, a write transistor Tr200 that writes a voltage of a signal line DTL into the drive transistor Tr100, and a retention capacitor Cs, and therefore, the pixel circuit has a 2Tr1C circuit configuration. The drive transistor Tr100 and the write transistor Tr200 are each formed by, for example, an n-channel MOS Thin Film Transistor (TFT).
FIG. 15 illustrates an example of the waveform of a voltage applied to the pixel circuit and an example of a change in each of the gate voltage Vg and the source voltage Vs of the drive transistor Tr100. In Part (A) of FIG. 15, there is illustrated a state in which a signal voltage Vsig and an offset voltage Vofs are applied to the signal line DTL. In Part (B) of FIG. 15, there is illustrated a state in which a voltage Vdd for turning on the write transistor Tr200 and a voltage Vss for turning off the write transistor Tr200 are applied to a write line WSL. In Part (C) of FIG. 15, there is illustrated a state in which a high voltage VccH and a low voltage VccL are applied to a power-source line PSL. Further, in Part (D) and (E) of FIG. 15, there is illustrated a state in which the gate voltage Vg and the source voltage Vs of the drive transistor Tr100 change over time in response to the application of the voltages to the power-source line PSL, the signal line DTL and the write line WSL.
From FIG. 15, it is found that a WS pulse P is applied to the write line WSL twice within 1 H, a threshold correction is performed by the first WS pulse P, and a mobility correction and signal writing are performed by the second WS pulse P. In other words, in FIG. 15, the WS pulse P is used for not only the signal writing but also the threshold correction and the mobility correction of the drive transistor Tr100.
SUMMARY OF THE INVENTION
Incidentally, in the display device employing the active matrix system, each of a horizontal drive circuit (not illustrated) that drives the signal line DTL and a write scan circuit (not illustrated) that selects each pixel 113 sequentially is configured to basically include a shift resister (not illustrated), and has a buffer circuit (not illustrated) for each stage, corresponding to each column or each row of pixels 113. For example, the buffer circuit within the write scan circuit is typically configured such that two inverter circuits are connected in series. Here the inverter circuit has, as illustrated in FIG. 17, for example, a single channel type of circuit configuration in which two n-channel MOS transistors Tr1 and Tr2 are connected in series. An inverter circuit 200 illustrated in FIG. 17 is inserted between high voltage wiring LH to which a high-level voltage is applied and low voltage wiring LL to which a low-level voltage is applied. The gate of the transistor Tr2 on the high voltage wiring LH side is connected to the high voltage wiring LH, and the gate of the transistor Tr1 on the low voltage wiring LL side is connected to an input terminal IN. Further, a connection point C between the transistor Tr1 and the transistor Tr2 is connected to an output terminal OUT.
In the inverter circuit 200, as illustrated in FIG. 18, for example, when a voltage Vin of the input terminal IN is Vss, a voltage Vout of the output terminal OUT is not Vdd, and instead is Vdd-Vth. In other words, the threshold voltage Vth of the transistor Tr2 is included in the voltage Vout of the output terminal OUT, and the voltage Vout of the output terminal OUT is largely affected by variations in the threshold voltage Vth of the transistor Tr2.
Thus, for example, as illustrated by an inverter circuit 300 in FIG. 19, it is conceivable that the gate and the drain of the transistor Tr2 may be electrically separated from each other, and the gate may be connected to high voltage wiring LH2 to which a voltage Vdd2 (≧Vdd Vth) that is higher than the voltage Vdd of the drain is applied. In addition, for example, a bootstrap type of circuit configuration as illustrated by an inverter circuit 400 in FIG. 20 is conceivable. Specifically, it is conceivable to provide a circuit configuration in which a transistor Tr12 is inserted between the gate of the transistor Tr2 and the high voltage wiring LH, the gate of the transistor Tr12 is connected to the high voltage wiring LH, and a capacitive element C10 is inserted between: a connection point D between the gate of the transistor Tr2 and the source of the transistor Tr12; and the connection point C.
However, in the circuit in any of FIG. 17, FIG. 19 and FIG. 20, until the time when the input voltage Vin becomes high, namely when the output voltage Vout becomes low, a current (through current) flows from the high voltage wiring LH side to the low voltage wiring LL side via the transistors Tr1 and Tr2. As a result, power consumption in the inverter circuit also becomes large. In addition, in the circuits of FIG. 17, FIG. 19 and FIG. 20, when, for example, the input voltage Vin is Vdd as indicated with a point surrounded by a broken line in Part (B) of FIG. 18, the output voltage Vout is not Vss, and the peak value of the output voltage Vout varies. As a result, there has been such a shortcoming that the threshold corrections and the mobility corrections of the drive transistors Tr100 in pixel circuits 112 vary among the pixel circuits 112, and such variations result in variations in luminance.
Incidentally, the above-described shortcoming not only occurs in the scan circuit of the display device, but may take place similarly in any other devices.
In view of the foregoing, it is desirable to provide an inverter circuit capable of setting the peak value of an output voltage at a desired value while suppressing power consumption, and a display device having this inverter circuit.
According to an embodiment of the present invention, there is provided a first inverter circuit including: a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor and a seventh transistor each having channels of same conduction type; a first capacitive element; and an input terminal and an output terminal. The first transistor makes or breaks electric 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 electric connection between a second voltage line and the output terminal, in response to a potential difference between a voltage of a first terminal that is a source or a drain of the seventh transistor and a voltage of the output terminal or a potential difference corresponding thereto. The third transistor makes or breaks electric connection between a gate of the seventh transistor and the third voltage line, in response to a potential difference between the voltage of the input terminal and a voltage of a third voltage line or a potential difference corresponding thereto. The fourth transistor makes or breaks electric connection between the first capacitive element and the gate of the seventh transistor, in response to a first control signal inputted into a gate of the fourth transistor. The fifth transistor makes or breaks electric connection between the first capacitive element and a fourth voltage line, in response to a second control signal inputted into a gate of the fifth transistor. The sixth transistor makes or breaks electric connection between the first terminal and the fifth voltage line, in response to a potential difference between the voltage of the input terminal and a voltage of a fifth voltage line or a potential difference corresponding thereto. The seventh transistor makes or breaks electric connection between the first terminal and a sixth voltage line, in response to a potential difference between a gate voltage of the seventh transistor and a gate voltage of the second transistor or a potential difference corresponding thereto. The first capacitive element is inserted between a drain or a source of the fifth transistor and a seventh voltage line.
According to an embodiment of the present invention, there is provided a first display device having 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 rows and columns, and the drive section including a plurality of inverter circuits each provided for each of the scanning lines to drive each of the pixels. Each of the inverter circuits in the drive section includes the same elements as those of the above-described first inverter circuit.
In the first inverter circuit and the first display device according to the above embodiments of the present invention, between the gate of the seventh transistor and the first voltage line, between the gate of the second transistor and the first voltage line, between the source of the second transistor and the first voltage line, there are provided the first transistor, the third transistor and the sixth transistor, respectively, which perform on-off operation according to a potential difference between the input voltage and the voltage of the first voltage line. As a result, for example, when the input voltage falls, on-resistance of each of the first transistor, the third transistor and the sixth transistor gradually becomes large, and the time necessary to charge the gates and the sources of the second transistor and the seventh transistor to the voltage of the first voltage line becomes longer. Further, for example, when the input voltage rises, the on-resistance of each of the first transistor, the third transistor and the sixth transistor gradually becomes small, and the time necessary to charge the gate and the source of the second transistor to the voltage of the first voltage line becomes short. In addition, in the above embodiments of the present invention, when the input voltage falls, the gate of the seventh transistor is charged to a voltage equal to or higher than an on-voltage of the seventh transistor. As a result, for example, when a falling voltage is input into the input terminal, the first transistor, the third transistor and the sixth transistor are turned off, and immediately after that, the seventh transistor is turned on and further, the second transistor is turned on and therefore, the output voltage becomes the voltage on the second voltage line side. Moreover, for example, when the input voltage rises, the first transistor, the third transistor and the sixth transistor are turned on and immediately after that, the second transistor is turned off. As a result, the output voltage becomes the voltage on the first voltage line side.
According to an embodiment of the present invention, there is provided a second inverter circuit including: a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor and a seventh transistor each having channels of same conduction type; a first capacitive element; and an input terminal and an output terminal. A gate of the first transistor is electrically connected to the input terminal, 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 a gate of the seventh 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. A gate of the sixth transistor is electrically connected to the input terminal, one terminal of a drain and a source of the sixth transistor is electrically connected to a fifth voltage line, and the other terminal of the sixth transistor is electrically connected to the gate of the second transistor. One terminal of a drain and a source of the seventh transistor is electrically connected to a sixth voltage line, and the other terminal of the seventh transistor is electrically connected to the gate of the second transistor. The first capacitive element is inserted between the other terminal of the fifth transistor and a seventh voltage line.
According to an embodiment of the present invention, there is provided a second display device having 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 rows and columns, and the drive section including a plurality of inverter circuits each provided for each of the scanning lines to drive each of the pixels. Each of the inverter circuits in the drive section includes the same elements as those of the above-described second inverter circuit.
In the second inverter circuit and the second display device according to the above embodiments of the present invention, between the gate of the seventh transistor and the first voltage line, between the gate of the second transistor and the first voltage line, between the source of the second transistor and the first voltage line, there are provided the first transistor, the third transistor and the sixth transistor, respectively, whose gates are connected to the input terminal. As a result, for example, when the input voltage falls, on-resistance of each of the first transistor, the third transistor and the sixth transistor gradually becomes large, and the time necessary to charge the gates and the sources of the second transistor and the seventh transistor to the voltage of the first voltage line becomes longer. Further, for example, when the input voltage rises, the on-resistance of each of the first transistor, the third transistor and the sixth transistor gradually becomes small, and the time necessary to charge the gate and the source of the second transistor to the voltage of the first voltage line becomes short. In addition, in the above embodiments of the present invention, when the input voltage falls, the gate of the seventh transistor is charged to a voltage equal to or higher than an on-voltage of the seventh transistor. As a result, for example, when a falling voltage is input into the input terminal, the first transistor, the third transistor and the sixth transistor are turned off, and immediately after that, the seventh transistor is turned on and further, the second transistor is turned on and therefore, the output voltage becomes the voltage on the second voltage line side. Moreover, for example, when the input voltage rises, the first transistor, the third transistor and the sixth transistor are turned on and immediately after that, the second transistor is turned off. As a result, the output voltage becomes the voltage on the first voltage line side.
In the first and second inverter circuits and the first and second display devices according to the above-described embodiments of the present invention, a second capacitive element may be inserted between the gate and the source of the second transistor. In this case, a capacity of the second capacitive element is desired to be smaller than a capacity of the first capacitive element.
According to the first and second inverter circuits and the first and second display devices in the above-described embodiments of the present invention, there is no time period over which the first transistor and the second transistor are turned on at the same time, and the fourth transistor and the seventh transistor are turned on at the same time, and the third transistor, the fourth transistor and the fifth transistor are turned on at the same time. This makes it possible to suppress power consumption, because almost no current (through current) flows between the voltage lines, via these transistors. In addition, when the gate of the first transistor changes from high to low, the output voltage becomes a voltage on the second voltage line side or a voltage on the first voltage line side, and when the gate of the first transistor changes from low to high, the output voltage becomes a voltage on the reverse side of the above-mentioned side. This makes it possible to reduce a shift of the peak value of the output voltage from a desired value. As a result, for example, it is possible to reduce variations in the threshold correction and the mobility correction of the drive transistor in the pixel circuit, among the pixel circuits, and further, variations in the luminance among the pixels may be reduced.
Moreover, in the above-described embodiments of the present invention, on either of the low voltage side and the high voltage side, voltage lines may be provided as a single common voltage line. Therefore, in this case, there is no need to increase the withstand voltage of the inverter circuit.
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 present invention;
FIG. 2 is a waveform diagram illustrating an example of input-output signal waveforms of the inverter circuit in FIG. 1;
FIG. 3 is a waveform diagram illustrating an example of the operation of the inverter circuit in FIG. 1;
FIG. 4 is a circuit diagram for explaining an example of the operation of the inverter circuit in FIG. 1;
FIG. 5 is a circuit diagram for explaining an example of the operation following FIG. 4;
FIG. 6 is a circuit diagram for explaining an example of the operation following FIG. 5;
FIG. 7 is a circuit diagram for explaining an example of the operation following FIG. 6;
FIG. 8 is a circuit diagram for explaining an example of the operation following FIG. 7;
FIG. 9 is a circuit diagram for explaining an example of the operation following FIG. 8;
FIG. 10 is a circuit diagram for explaining an example of the operation following FIG. 9;
FIG. 11 is a waveform diagram illustrating another example of the input-output signal waveforms of the inverter circuit in FIG. 1;
FIG. 12 is a waveform diagram illustrating another example of the operation of the inverter circuit in FIG. 1;
FIG. 13 is a schematic configuration diagram of a display device that is one of application examples of the inverter circuit in the present embodiment and its modification;
FIG. 14 is a circuit diagram illustrating an example of a write-line driving circuit and an example of a pixel circuit in FIG. 13;
FIG. 15 is a waveform diagram illustrating an example of the operation of the display device in FIG. 13;
FIG. 16 is a circuit diagram illustrating an example of a pixel circuit in a display device in related art;
FIG. 17 is a circuit diagram illustrating an example of an inverter circuit in related art;
FIG. 18 is a waveform diagram illustrating an example of input-output signal waveforms of the inverter circuit in FIG. 17;
FIG. 19 is a circuit diagram illustrating another example of the inverter circuit in related art;
FIG. 20 is a circuit diagram illustrating another example of the inverter circuit in related art;
FIG. 21 is a circuit diagram illustrating an example of an inverter circuit according to a reference example; and
FIG. 22 is a waveform diagram illustrating an example of input-output signal waveforms of the inverter circuit in FIG. 21.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention will be described below in detail with reference to the drawings. The description will be provided in the following order.
1. Embodiment (FIG. 1 through FIG. 10)
2. Modification (FIG. 11 and FIG. 12)
3. Application example (FIG. 13 through FIG. 15)
4. Description of related art (FIG. 16 through FIG. 20)
5. Description of reference technique (FIG. 21 and FIG. 22)
Embodiment
Configuration
FIG. 1 illustrates an example of the entire configuration of an inverter circuit 1 according to an embodiment of the present invention. The inverter circuit 1 outputs, from an output terminal OUT, a pulse signal (e.g., Part (B) of FIG. 2) whose waveform is approximately the inverse of the signal waveform of a pulse signal (e.g., Part (A) of FIG. 2) input into an input terminal IN. The inverter circuit 1 is suitably formed on an amorphous silicon or amorphous oxide semiconductor and has, for example, seven transistors Tr1 to Tr7 of the same channel type. In addition to the seven transistors Tr1 to Tr7, the inverter circuit 1 includes two capacitive elements C1 and C2, the input terminal IN and the output terminal OUT, and has a 7Tr2C circuit configuration.
The transistor Tr1 is equivalent to a specific example of “the first transistor” according to the embodiment of the present invention, and the transistor Tr2 is equivalent to a specific example of “the second transistor” according to the embodiment of the present invention, and the transistor Tr1 is equivalent to a specific example of “the third transistor” according to the embodiment of the present invention. Further, the transistor Tr4 is equivalent to a specific example of “the fourth transistor” according to the embodiment of the present invention, and the transistor Tr5 is equivalent to a specific example of “the fifth transistor” according to the embodiment of the present invention. Furthermore, the transistor Tr6 is equivalent to a specific example of “the sixth transistor” according to the embodiment of the present invention, and the transistor Tr7 is equivalent to a specific example of “the seventh transistor” according to the embodiment of the present invention. Moreover, the capacitive element C1 is equivalent to a specific example of “the first capacitive element” according to the embodiment of the present invention, and the capacitive element C2 is equivalent to a specific example of “the second capacitive element” according to the embodiment of the present invention.
The transistors Tr1 to Tr7 are thin-film transistors (TFTs) of the same channel type and are, for example, n-channel MOS (Metal Oxide Film Semiconductor) type of thin-film transistors (TFTs). The transistor Tr1 is, for example, configured to establish and cut off electric connection between the output terminal OUT and the low voltage line LL, according to a potential difference Vgs1 (or a potential difference corresponding thereto) between a voltage (input voltage Vin) of the input terminal IN and a voltage VL of a low voltage line LL. The gate of the transistor Tr1 is electrically connected to the input terminal IN, and the source or the drain of the transistor Tr1 is electrically connected to the low voltage line LL. Of the source and the drain of the transistor Tr1, one that is a terminal unconnected with the low voltage line LL is electrically connected to the output terminal OUT. The transistor Tr2 is configured to establish and cut off electric connection between a high voltage line LH and the output terminal OUT, according to a potential difference Vgs2 (or a potential difference corresponding to thereto) between a voltage Vs7 of a terminal (terminal A) unconnected with the high voltage line LH and the voltage (output voltage Vout) of the output terminal OUT. The terminal A is one of the source and the drain of the transistor Tr7. The gate of the transistor Tr2 is electrically connected to the terminal A of the transistor Tr7. The source or the drain of the transistor Tr2 is electrically connected to the output terminal OUT, and of the source and the drain of the transistor Tr2, one that is a terminal unconnected with the output terminal OUT is electrically connected to the high voltage line LH.
The transistor Tr3 is configured to establish and cut off electric connection between the gate of the transistor Tr7 and the low voltage line LL, according to a potential difference Vgs3 (or a potential difference corresponding thereto) between the input voltage Vin and the voltage VL of the low voltage line LL. The gate of the transistor Tr3 is electrically connected to the input terminal IN. The source or the drain of the transistor Tr3 is electrically connected to the low voltage line LL, and of the source and the drain of the transistor Tr3, one that is a terminal unconnected with the low voltage line LL is electrically connected to the gate of the transistor Tr7. The transistor Tr4 is configured to establish and cut off electric connection between the capacitive element C1 and the gate of the transistor Tr7, according to a control signal input into a control terminal AZ1. The gate of the transistor Tr4 is electrically connected to the control terminal AZ1. The source or the drain of the transistor Tr4 is electrically connected to the capacitive element C1, and of the source and the drain of the transistor Tr4, one that is a terminal unconnected with the capacitive element C1 is electrically connected to the gate of the transistor Tr7. The transistor Tr5 is configured to establish and cut off electric connection between the high voltage line LH and the capacitive element C1, according to a control signal input into a control terminal AZ2. The gate of the transistor Tr5 is electrically connected to the control terminal AZ2. The source or the drain of the transistor Tr5 is electrically connected to the high voltage line LH. Of the source and the drain of the transistor Tr5, one that is a terminal unconnected with the high voltage line LH is electrically connected to the capacitive element C1.
The transistor Tr6 is configured to establish and cut off electric connection between the terminal A of the transistor Tr7 and the low voltage line LL, according to a potential difference Vgs6 (or a potential difference corresponding thereto) between the input voltage Vin, and the voltage VL of the low voltage line LL. The gate of the transistor Tr6 is electrically connected to the input terminal IN. The source or the drain of the transistor Tr6 is electrically connected to the low voltage line LL, and of the source and the drain of the transistor Tr6, one that is a terminal unconnected with the low voltage line LL is electrically connected to the terminal A of the transistor Tr7. In other words, the transistors Tr1, Tr3 and Tr6 are connected to the same voltage line (the low voltage line LL). Therefore, the terminal on the low voltage line LL side of the transistor Tr1, the terminal on the low voltage line LL side of the transistor Tr3 and the terminal on the low voltage line LL side of the transistor Tr6 are at the same potential. The transistor Tr7 is configured to establish and cut off electric connection between the high voltage line LH and one, which is a terminal unconnected with the low voltage line LL, of the source and the drain of the transistor Tr6, according to a potential difference Vgs7 (or a potential difference corresponding thereto) between the voltage Vs7 of the terminal unconnected with the capacitive element C1 of the source and the drain of the transistor Tr4 and a gate voltage Vg2 (the voltage Vs7 of the terminal A) of the transistor Tr2. The gate of the transistor Tr7 is electrically connected to the terminal unconnected with the capacitive element C1, which terminal is one of the source and the drain of the transistor Tr4. The source or the drain of the transistor Tr7 is electrically connected to the high voltage line LH, and of the source and the drain of the transistor Tr7, one that is the terminal (the terminal A) unconnected with the high voltage line LH is electrically connected to the terminal unconnected with the low voltage line LL, which terminal is one of the source and the drain of the transistor Tr6. In other words, the transistors Tr2, Tr5 and Tr7 are connected to the same voltage line (high voltage line LH). Therefore, the terminal on the high voltage line LH side of the transistor Tr2, the terminal on the high voltage line LH side of the transistor Tr5 and the terminal on the high voltage line LH side of the transistor Tr7 are at the same potential.
The low voltage line LL is equivalent to a specific example of “the first voltage line” according to the embodiment of the present invention. The high voltage line LH is equivalent to a specific example of “the second voltage line” according to the embodiment of the present invention.
The high voltage line LH is connected to a power source (not illustrated) that outputs a voltage (constant voltage) higher than the voltage VL of the low voltage line LL. The voltage of the high voltage line LH is Vdd at the time of driving the inverter circuit 1. On the other hand, the low voltage line LL is connected to a power source (not illustrated) that outputs a voltage (constant voltage) lower than a voltage VH of the high voltage line LH, and the voltage VL of the low voltage line LL is a voltage Vss (<Vdd) at the time of driving the inverter circuit 1.
The control terminal AZ1 is connected to a power source S1 (not illustrated) that outputs a predetermined pulse signal. The control terminal AZ2 is connected to a power source S2 (not illustrated) that outputs a predetermined pulse signal. The power source S1 is, for example, configured to output a high while a low is applied to the control terminal AZ2, as illustrated in Part (C) of FIG. 2. On the other hand, the power source S2 is, for example, configured to output a high while a low is applied to the control terminal AZ1, as illustrated in Part (B) of FIG. 2. In other words, the power source S1 and the power source S2 are configured to alternately output highs so that the transistors Tr4 and Tr5 are not in an ON state at the same time (namely, the transistors Tr4 and Tr5 are turned on and off alternately). The power source S1 is configured such that the output voltage of the power source S1 changes from low to high (in other words, the transistor Tr4 is turned on), in timing different from the timing in which the input voltage Vin rises. The power source S1 is, for example, configured such that the output voltage of the power source S1 changes from low to high immediately before the input voltage Vin drops.
The capacitive element C1 is inserted between the terminal unconnected with the high voltage line LH, which is one of the source and the drain of the transistor Tr5, and the low voltage line LL. The capacitive element C2 is inserted between the gate of the transistor Tr2 and the source of the transistor Tr2. The value of each of the capacitive element C1 and the capacitive element C2 is sufficiently larger than parasitic capacitances of the transistors Tr1 to Tr7. The value of the capacity of the capacitive element C1 is larger than the capacity of the capacitive element C2. When a falling voltage is input into the input terminal IN, and the transistor Tr3 is turned off, the value of the capacity of the capacitive element C1 becomes a value that makes it possible to charge the gate of the transistor Tr7 to a voltage of Vss+Vth7 or more. In addition, the Vth7 is a threshold voltage of the transistor Tr7.
Incidentally, in a relation with an inverter circuit in related art (the inverter circuit 200 in FIG. 17), the inverter circuit 1 is equivalent to a circuit in which a control element 10 and the capacitive element C2 are inserted between the transistors Tr1 and Tr2 in an output stage and the input terminal IN. Here, 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 a high voltage line LH2. The control element 10 further includes, for example, as illustrated in FIG. 1, the transistors Tr3 to Tr7 and the capacitive element C1.
The control element 10 is, for example, configured to charge the gate of the transistor Tr2 electrically connected to the terminal P3 to a voltage of Vss+Vth2 or more when a falling voltage is input into the terminal P1. Further, for example, the control element 10 is configured to cause the gate voltage Vg2 of the transistor Tr2 electrically connected to the terminal P3 to be a voltage of less than Vss+Vth2 when a rising voltage is input into the terminal P1. Incidentally, the description of the operation of the control element 10 will be provided with the following description of the operation of the inverter circuit 1.
[Operation]
Next, there will be described an example of the operation of the inverter circuit 1 with reference to FIG. 3 to FIG. 10. FIG. 3 is a waveform diagram illustrating an example of the operation of the inverter circuit 1. FIG. 4 through FIG. 10 are circuit diagrams illustrating an example of a series of operation of the inverter circuit 1.
First, as illustrated in FIG. 4, it is assumed that the input voltage Vin is low (Vss), the transistor Tr5 is on, and the transistor Tr4 is off. At the time, the transistors Tr1 and Tr3 are off, the capacitive element C1 is charged with Vdd, and a source voltage Vs5 of the transistor Tr5 is Vdd. Further, the gate voltage Vg2 of the transistor Tr2 is Vdd+ΔV. Here, ΔV is a value equal to or higher than the threshold voltage Vth2 of the transistor Tr2, and the transistor Tr2 is on. Therefore, at the time, in the output terminal OUT, Vdd is output as the output voltage Vout.
Subsequently, as illustrated in FIG. 5, in a state in which the input voltage Vin is low (Vss), the transistor Tr4 is turned on after the transistor Tr5 is turned off. In other words, the transistor Tr4 is turned on before the input voltage Vin changes from low (Vss) to high (Vdd). The gate voltage Vg2 of the transistor Tr2 is Vdd+ΔV before the transistor Tr4 is turned on. Therefore, even when the transistor Tr4 changes from OFF to ON, the transistor Tr2 maintains the ON state, and Vdd is maintained for the output voltage Vout as well.
Next, in a state in which the input voltage Vin is low (Vss), the transistor Tr5 is turned on after the transistor Tr4 is turned off. Similarly, when the transistor Tr4 is turned on (when the transistor Tr5 is turned off) after the transistors Tr4 and Tr5 repeat ON and OFF, the input voltage Vin changes from low (Vss) to high (Vdd) (FIG. 6). Then, the transistors Tr1, Tr3 and Tr6 are turned on, and the gates and the sources of the transistors Tr2 and Tr7 are charged to the voltage VL (=Vss) of the low voltage line LL. As a result, the transistor Tr2 is turned off, and in the output terminal OUT, Vss is output as the output voltage Vout. Further, when the transistor Tr4 is turned on, the capacitive element C1 charged with Vdd is connected to the low voltage line LL via the transistor Tr4. As a result, the voltage of the terminal (terminal B) on the transistor Tr5 side of the capacitive element C1 gradually decreases from Vdd and eventually becomes Vss.
Subsequently, in a state in which the input voltage Vin is high (Vdd), the transistor Tr5 is turned on after the transistor Tr4 is turned off. Similarly, when the transistor Tr4 is turned on (when the transistor Tr5 is off) after the transistors Tr4 and Tr5 repeat ON and OFF, the input voltage Vin changes from high (Vdd) to low (Vss). Then, the transistors Tr1, Tr3 and Tr6 are turned off.
Here, when the transistor Tr4 is turned on, the voltage (the voltage of the terminal B) of the capacitive element C1 gradually decreases from Vdd2 as described above (FIG. 7). Incidentally, VX in FIG. 7 is the voltage (the voltage of the terminal B) of the capacitive element C1 in a state immediately before the input voltage Vin changes from high (Vdd) to low (Vss). However, after the transistor Tr4 is turned on, the input voltage Vin changes from high (Vdd) to low (Vss), and the transistor Tr3 is turned off (FIG. 8). Therefore, the capacitive element C1 is connected to the gate of the transistor Tr7 via the transistor Tr4 and thus, the capacitive element C1 charges the gate of the transistor Tr7. As a result, each of the voltage of the capacitive element C1 and the gate voltage Vg2 of the transistor Tr2 becomes a voltage Vy.
At the time, in a case in which Vy is a value equal to or larger than the sum of the voltage (=Vss) of the low voltage line LL and the threshold voltage Vth7 of the transistor Tr7 (that is, Vss+Vth7), the transistor Tr7 is turned on, and a current flows in the transistor Tr7.
Here, the voltage Vy will be considered. It is assumed that parasitic capacitances of the transistors Tr1 through Tr7 are small enough to be ignored as compared with the capacitive element C1. At the time, Vy is expressed by an equation (1) using V.

Vy=VX  (1)

It is apparent from the equation (1) that Vy is determined without relying on the capacity of the capacitive element C1, and Vy always becomes VX.
The source of the transistor Tr7 and the gate of the transistor Tr2 are electrically connected to each other. Therefore, when a current flows in the transistor Tr7, the gate voltage Vg2 of the transistor Tr2 starts rising. After a lapse of a predetermined period of time, when the gate voltage Vg2 of the transistor Tr2 becomes Vs, +Vth2 or more, the transistor Tr2 is turned on and the output voltage Vout begins increasing gradually.
Between the gate and the source of the transistor Tr2, the capacitive element C2 is connected. Therefore, due to bootstrap operation by the capacitive element C2, the gate voltage Vg2 of the transistor Tr2 also changes as a source voltage Vs2 of the transistor Tr2 changes. Here, when attention is paid to the gate and the source of the transistor Tr2, it is found that the gate voltage Vg2 of the transistor Tr2 rises due to the current of the transistor Tr7 and the rise in the source of the transistor Tr2. Therefore, because its transient is faster than that in a case of a rise only due to the current of the transistor Tr2, the voltage Vgs2 between the gate and the source of the transistor Tr2 gradually rises.
Here, a gate voltage Vg7 of the transistor Tr7 is Vy, and the transistor Tr4 between the gate of the transistor Tr7 and the low voltage line LL is on. Therefore, the capacitive element C1 is connected to the gate of the transistor Tr7 and thus, the gate voltage Vg7 of the transistor Tr7 hardly follows the change of the source voltage Vs7, and is approximately a value of Vy. As a result, the current from the transistor Tr7 becomes small as the gate voltage Vg2 of the transistor Tr2 rises. Eventually, when the voltage Vgs7 between the gate and the source of the transistor Tr7 becomes the threshold voltage Vth7 of the transistor Tr7, the current from the transistor Tr7 becomes considerably small, and due to the current from the transistor Tr7, the gate voltage Vg2 of the transistor Tr2 hardly increases. However, at the time, the transistor Tr2 is on, and the source voltage Vs2 (the output voltage Vout) of the transistor Tr2 continues rising and thus, the gate voltage Vg2 of the transistor Tr2 also keeps rising due to the bootstrap operation, and the transistor Tr7 is turned off completely.
At the time, when the voltage Vgs2 between the gate and the source of the transistor Tr2 is ΔV, and if ΔV is larger than the threshold voltage Vth2 of the transistor Tr2, Vdd is output to the outside as the output voltage Vout (FIG. 9).
Subsequently, the transistor Tr4 is turned off. Even if the transistor Tr4 is turned off, the transistor Tr7 also is turned off and thus, the gate voltage Vg2 of the transistor Tr2 is not affected. Therefore, the output of Vdd to the outside as the output voltage Vout continues. Further, after the transistor Tr4 is turned off, the transistor Tr5 is turned on again, and the source voltage Vs5 of the transistor Tr5 becomes an electric potential of Vdd.
When the transistor Tr4 is turned on after the transistor Tr5 is turned off, capacitive coupling occurs again, and the gate voltage Vg7 of the transistor Tr7 and the source voltage Vs5 of and the transistor Tr5 come to be at the same potential. When the voltage Vgs7 of the transistor Tr7 at the time is assumed to be Va, as illustrated in FIG. 10, the gate voltage Vg7 between the gate and the source of the transistor Tr7 is Va−Vdd−ΔV, and the transistor Tr7 still remains off. In addition, the voltage Vgs2 between the gate and the source of the transistor Tr2 continues to be ΔV and thus, Vdd is output to the outside as the output voltage Vout. By repeating these operations, the gate voltage Vg7 of the transistor Tr7 eventually becomes Vdd.
As described above, in the inverter circuit 1 of the present embodiment, the pulse signal (e.g., Part (B) of FIG. 2) whose signal waveform is approximately the inverse of the signal waveform (e.g., Part (A) of FIG. 2) of the pulse signal input into the input terminal IN is output from the output terminal OUT.
[Effect]
Incidentally, for example, the inverter circuit 200 as illustrated in FIG. 17 in related art has the single channel type of circuit configuration in which the two n-channel MOS transistors Tr1 and Tr2 are connected in series. In the inverter circuit 200, for example, as illustrated in FIG. 18, when the input voltage Vin is Vss, the output voltage Vout is Vdd−Vth2 without being Vdd. In other words, the threshold voltage Vth2 of the transistor Tr2 is included in the output voltage Vout, and the output voltage Vout is greatly affected by the variations of the threshold voltage Vth2 of the transistor Tr2.
Thus, for example, as illustrated in the inverter circuit 300 of FIG. 19, it is conceivable that the gate and the drain of the transistor. Tr2 may be electrically isolated from each other, and the gate may be connected to the high voltage wiring LH2 to which the voltage Vdd2 (≧Vdd+Vth2) higher than the voltage Vdd of the drain is applied. In addition, for example, it is conceivable to provide the bootstrap type of circuit configuration as indicated by the inverter circuit 400 in FIG. 20.
However, in the circuit in any of FIG. 17, FIG. 19 and FIG. 20, until the time when the input voltage Vin becomes high, namely when the output voltage Vout becomes low, a current (through current) flows from the high voltage wiring LH side to the low voltage wiring LL side via the transistors Tr1 and Tr2. As a result, the power consumption in the inverter circuit also becomes large. In addition, in the circuits of FIG. 17, FIG. 19 and FIG. 20, when, for example, the input voltage Vin is Vdd as indicated with the point surrounded by the broken line in Part (B) of FIG. 18, the output voltage Vout is not Vss, and the peak value of the output voltage Vout varies. Therefore, for example, when any of these inverter circuits is applied to a scanner in an organic electroluminescence display device employing an active matrix system, the threshold corrections and the mobility corrections of the drive transistors in the pixel circuits vary among the pixel circuits, and such variations result in variations in luminance.
Thus, for example, as indicated by an inverter circuit 500 in FIG. 21, it is conceivable that between the transistors Tr1 and Tr2 in the output stage and the input terminal IN, the capacitive elements C1 and C2 and the transistors Tr3 through Tr5 may be provided, and a control signal as illustrated in FIG. 22 may be input into the transistors Tr4 and Tr5. In the inverter circuit 500, there is almost no time period over which the transistor Tr1 and the transistor Tr2 are turned on at the same time. Therefore, almost no through current flows, and power consumption may be suppressed to a low level. In addition, in response to a fall in the input voltage Vin, the output voltage Vout becomes a voltage on a high voltage line VH1 side, and in response to a rise in the input voltage Vin, the output voltage Vout becomes a voltage on the low voltage line LL side. Therefore, there are no variations in the output voltage Vout, and variations in luminance from pixel to pixel may be reduced.
Incidentally, in the inverter circuit 500 of FIG. 21, the newly inserted transistor Tr5 is connected to a high voltage line LH2 to which a voltage higher than the high voltage line LH1 connected to the transistor Tr2 is applied. This is to enable turning on of the transistor Tr2 when the gate of the transistor Tr2 is charged by the capacitive element C1 charged with the voltage Vdd2. However, the voltage applied to the high voltage line LH2 is the voltage higher than the input voltage Vin. Therefore, when the withstand voltage of the inverter circuit 500 is made equal to the withstand voltage of the inverter circuit 200, yields may be reduced. Moreover, when the withstand voltage of the inverter circuit 500 is made higher than the withstand voltage of the inverter circuit 200, manufacturing cost may increase.
On the other hand, in the inverter circuit 1 of the present embodiment, between the gate of the transistor Tr7 and the low voltage line LL, 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, the transistors Tr1, Tr3 and Tr6 that perform on-off operation according to a potential difference between the input voltage Vin and the voltage VL of the low voltage line LL are provided, respectively. As a result, when the gate voltage of each of the transistors Tr1, Tr3 and Tr6 changes (falls) from high (Vdd) to low (Vss), on-resistance of each of the transistors Tr1, Tr3 and Tr6 gradually becomes large, and the time necessary to charge the gates and the sources of the transistors Tr2 and Tr7 to the voltage VL of the low voltage line LL becomes long. Further, when the gate voltage of each of the transistors Tr1, Tr3 and Tr6 changes (rises) from low (Vss) to high (Vdd), the on-resistance of each of the transistors Tr1, Tr3 and Tr6 gradually becomes small, and the time necessary to charge the gates and the sources of the transistors Tr2 and Tr7 to the voltage VL of the low voltage line LL becomes short. Furthermore, in the inverter circuit 1 of the present embodiment, when the input voltage Vin falls, the gate of the transistor Tr7 is charged to a voltage equal to or higher than the on-voltage of the transistor Tr7. As a result, when the falling voltage is input into the input terminal IN, the transistors Tr1, Tr3 and Tr6 are turned off, and immediately after that, the transistor Tr7 is turned on and further, the transistor Tr2 is turned on and thus, the output voltage Vout becomes the voltage on the high voltage line LH side. Moreover, when the input voltage Vin rises, the transistors Tr1, Tr3 and Tr6 are turned on, and immediately after that, the transistors Tr2 and Tr7 are turned off. As a result, the output voltage Vout becomes the voltage on the low voltage line LL side.
In this way, the inverter circuit 1 of the present embodiment is configured such that there are no time period over which the transistor Tr1 and the transistor Tr2 are turned on at the same time, time period over which the transistor Tr6 and the transistor Tr7 are turned on at the same time, and time period over which the transistors Tr3 to Tr5 are turned on at the same time. Therefore, there is almost no current (through current) that flows between the high voltage line VH and the low voltage line LL via the transistors Tr1 to Tr7. As a result, power consumption is allowed to be suppressed. In addition, in the inverter circuit 1, only a single voltage line is provided on each of the low voltage side and the high voltage side and thus, there is no need to increase the withstand voltage of the inverter circuit 1. Based upon the foregoing, in the present embodiment, it is possible to reduce the power consumption without increasing the withstand voltage.
<Modification>
In the embodiment described above, for example, as illustrated in FIG. 11 and FIG. 12, the transistor Tr4 may be turned off when the falling voltage is input into the input terminal IN, and the transistor Tr4 may be turned on after the falling voltage is input into the input terminal IN. In this case, it is possible to prevent the voltage (the source voltage of the transistor Tr5) of the capacitive element C1 from decreasing from Vdd2 by the transistor Tr3. As a result, it is possible to cause the inverter circuit 1 to operate at a high speed.
In addition, in the embodiment and the modification described above, for example, although not illustrated, it is possible to delete the capacitive element C2 in the inverter circuit 1. Even in this case, it is possible to cause the inverter circuit 1 to operate at a higher speed.
Further, in the embodiment and the modification described above, the transistors Tr1 to Tr7 are formed by the n-channel MOS TFTs, but may be formed by p-channel MOS TFTs, for example. In this case however, the high voltage line VH is replaced with the low voltage line LL, and the high voltage line VH is replaced with the low voltage line LL. Furthermore, a transient response when the transistors Tr1 to Tr7 change (rise) from low to high and a transient response when the transistors Tr1 to Tr7 change (drop) from high to low are reversed.
<Application Example>
FIG. 13 illustrates an example of the entire configuration of a display device 100 that is one of application examples of the inverter circuit 1 according to each of the above-described embodiment and the modifications. This display device 100 includes, for example, a display panel 110 (display section) and a driving circuit 120 (drive section).
(Display Panel 110)
The display panel 110 includes a display area 110A in which three kinds of organic EL elements 111R, 111G and 111B emitting mutually different colors are arranged two-dimensionally. The display area 110A is an area that displays an image by using light emitted from the organic EL elements 111R, 111G and 111B. The organic EL element 111R is an organic EL element that emits red light, the organic EL element 111G is an organic EL element that emits green light, and the organic EL element 111B is an organic EL element that emits blue light. Incidentally, in the following, the organic EL elements 111R, 111G and 111B will be collectively referred to as an organic EL element 111 as appropriate.
(Display Area 110A)
FIG. 14 illustrates an example of a circuit configuration within the display area 110A, together with an example of a write-line driving circuit 124 to be described later. Within the display area 110A, plural pixel circuits 112 respectively paired with the individual organic EL elements 111 are arranged two-dimensionally. In the present application example, a pair of the organic EL element 111 and the pixel circuit 112 configure one pixel 113. To be more specific, as illustrated in FIG. 12, a pair of the organic EL element 111R and the pixel circuit 112 configure one pixel 113R for red, a pair of the organic EL element 111G and the pixel circuit 112 configure one pixel 113G for green, and a pair of the organic EL element 111B and the pixel circuit 112 configure one pixel 113B for blue. Further, the adjacent three pixels 113R, 113G and 113B configure one display pixel 114.
Each of the pixel circuits 112 includes, for example, a drive transistor Tr100 that controls a current flowing in the organic EL element 111, a write transistor Tr200 that writes a voltage of a signal line DTL into the drive transistor Tr100, and a retention capacitor Cs, and thus each of the pixel circuits 112 has a 2Tr1C circuit configuration. The drive transistor Tr100 and the write transistor Tr200 are each formed by, for example, an n-channel MOS Thin Film Transistor (TFT). The drive transistor Tr100 or the write transistor Tr200 may be, for example, a p-channel MOS TFT.
In the display area 110A, plural write lines WSL (scanning line) are arranged in rows and plural signal lines DTL are arranged in columns. In the display area 110A, further, plural power-source lines PSL (member to which the source voltage is supplied) are arranged in rows along the write lines WSL. Near a cross-point between each signal line DTL and each write line WSL, one organic EL element 111 is provided. Each of the signal lines DTL is connected to an output end (not illustrated) of a signal-line driving circuit 123 to be described later, and to either of the drain electrode and the source electrode (not illustrated) of the write transistor Tr200. Each of the write lines WSL is connected to an output end (not illustrated) of the write-line driving circuit 124 to be described later and to the gate electrode (not illustrated) of the write transistor Tr200. Each of the power-source lines PSL is connected to an output end (not illustrated) of a power-source-line driving circuit 125 to be described later, and to either of the drain electrode and the source electrode (not illustrated) of the drive transistor Tr100. Of the drain electrode and the source electrode of the write transistor Tr200, one (not illustrated) that is not connected to the signal line DTL is connected to the gate electrode (not illustrated) of the drive transistor Tr100 and one end of the retention capacitor Cs. Of the drain electrode and the source electrode of the drive transistor Tr100, one (not illustrated) that is not connected to the power-source line PSL and the other end of the 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 within the drive circuit 120 will be described with reference to FIG. 13 and FIG. 14. The drive circuit 120 includes a timing generation circuit 121, a video signal processing circuit 122, the signal-line driving circuit 123, the write-line driving circuit 124 and the power-source-line driving circuit 125.
The timing generation circuit 121 performs control so that the video signal processing circuit 122, the signal-line driving circuit 123, the write-line driving circuit 124 and the power-source-line driving circuit 125 operate in an interlocking manner. For example, the timing generation circuit 121 is configured to output a control signal 121A to each of the above-described circuits, according to (in synchronization with) a synchronization signal 120B input externally.
The video signal processing circuit 122 makes a predetermined correction to a video signal 120A input externally, and outputs to the signal-line driving circuit 123 a video signal 122A after the correction. As the predetermined correction, there are, for example, a gamma correction and an overdrive correction.
The signal-line driving circuit 123 applies, according to (in synchronization with) the input of the control signal 121A, the video signal 122A (signal voltage Vsig) input from the video signal processing circuit 122, to each of the signal lines DTL, thereby performing writing into the pixel 113 targeted for selection. Incidentally, the writing refers to the application of a predetermined voltage to the gate of the drive transistor Tr100.
The signal-line driving circuit 123 is configured to include, for example, a shift resistor (not illustrated), and includes a buffer circuit (not illustrated) for each stage, corresponding to each column of the pixels 113. This signal-line driving circuit 123 is able to output two kinds of voltages (Vofs, Vsig) to each of the signal lines DTL, according to (in synchronization with) the input of the control signal 121A. Specifically, the signal-line driving circuit 123 supplies, via the signal line DTL connected to each of the pixels 113, the two kinds of voltages (Vofs, Vsig) sequentially to the pixel 113 selected by the write-line driving circuit 124.
Here, the offset voltage Vofs is a constant value without relying on the signal voltage Vsig. Further, the signal voltage Vsig is a value corresponding to the video signal 122A. A minimum voltage of the signal voltage Vsig is a value lower than the offset voltage Vofs, and a maximum voltage of the signal voltage Vsig is a value higher than the offset voltage Vofs.
The write-line driving circuit 124 is configured to include, for example, a shift resistor (not illustrated), and includes a buffer circuit 5 for each stage, corresponding to each row of the pixels 113. The buffer circuit 5 is configured to include plural inverter circuits 1 described above, and outputs, from an output end, a pulse signal approximately in the same phase as a pulse signal input into an input end. The write-line driving circuit 124 outputs two kinds of voltages (Vdd, Vss) to each of the write lines WSL, according to (in synchronization with) the input of the control signal 121A. Specifically, the write-line driving circuit 124 supplies, via the write line WSL connected to each of the pixels 113, the two kinds of voltages (Vdd, Vss) to the pixel 113 targeted for driving, and thereby controls the write transistor Tr200.
Here, the voltage Vdd is a value equal to or higher than an on-voltage of the write transistor Tr200. Vdd is the value of a voltage output from the write-line driving circuit 124 at the time of extinction or at the time of a threshold correction to be described later. Vss is a value lower than the on-voltage of the write transistor Tr200, and also lower than Vdd.
The power-source-line driving circuit 125 is configured to include, for example, a shift resistor (not illustrated), and includes, for example, a buffer circuit (not illustrated) for each stage, corresponding to each row of the pixels 113. This power-source-line driving circuit 125 outputs two kinds of voltages (VccH, VccL) according to (in synchronization with) the input of the control signal 121A. Specifically, the power-source-line driving circuit 125 supplies, via the power-source line PSL connected to each of the pixels 113, the two kinds of voltages (VccH, VccL) to the pixel 113 targeted for driving, and thereby controls the light emission and extinction of the organic EL element 111.
Here, the voltage VccL is a value lower than a voltage (Vc1+Vca) that is the sum of a threshold voltage Vc1 of the organic EL element 111 and a voltage Vca of the cathode of the organic EL element 111. Further, the voltage VccH is a value equal to or higher than the voltage (Vc1+Vca).
Next, an example of the operation (operation from extinction to light emission) of the display device 100 according to the present application example will be described. In the present application example, in order that even when the threshold voltage Vth and the mobility μ of the drive transistor Tr100 change over time, light emission luminance of the organic EL element 111 remains constant without being affected by these changes, correction operation for the change of the threshold voltage Vth and the mobility μ is incorporated.
FIG. 15 illustrates an example of the waveform of a voltage applied to the pixel circuit 112 and an example of the change in each of the gate voltage Vg and the source voltage Vs of the drive transistor Tr100. In Part (A) of FIG. 15, there is illustrated a state in which the signal voltage Vsig and the offset voltage Vofs are applied to the signal line DTL. In Part (B) of FIG. 15, there is illustrated a state in which the voltage Vdd for turning on the write transistor Tr200 and the voltage Vss for turning off the write transistor Tr200 are applied to the write line WSL. In Part (C) of FIG. 15, there is illustrated a state in which the voltage VccH and the voltage VccL are applied to the power-source line PSL. Further, in Part (D) and Part (E) of FIG. 15, there is illustrated a state in which the gate voltage Vg and the source voltage Vs of the drive transistor Tr100 change over time in response to the application of the voltages to the power-source line PSL, the signal line DTL and the write line WSL.
(Vth Correction Preparation Period)
First, a Preparation for the Vth Correction is Made. Specifically, when the voltage of the write line WSL is Voff, and the voltage of the power-source line PSL is VccH (in other words, when the organic EL element 111 is emitting light), the power-source-line driving circuit 125 reduces the voltage of the power-source line PSL from VccH to VccL (T1). Then, the source voltage Vs becomes VccL, and the organic EL element 111 stops emitting the light. Subsequently, when the voltage of the signal line DTL is Vofs, the write-line driving circuit 124 increases the voltage of the write line WSL from Voff to Von, so that the gate of the drive transistor Tr100 becomes Vofs.
(First Vth Correction Period)
Next, the correction of Vth is performed. Specifically, while the write transistor Tr200 is on, and the voltage of the signal line DTL is Vofs, the power-source-line driving circuit 125 increases the voltage of the power-source line PSL from VccL to VccH (T2). Then, a current Ids flows between the drain and the source of the drive transistor Tr100, and the source voltage Vs rises. Subsequently, before the signal-line driving circuit 123 switches the voltage of the signal line DTL from Vofs to Vsig, the write-line driving circuit 124 reduces the voltage of the write line WSL from Von to Voff(T3). Then, the gate of the drive transistor Tr100 enters a floating state, and the correction of Vth stops.
(First Vth Correction Stop Period)
In a period during which the Vth correction is stopped, in, for example, other row (pixel) different from the row (pixel) to which the previous correction is made, the voltage of the signal line DTL is sampled. At the time, in the row (pixel) to which the previous correction is made, the source voltage Vs is lower than Vofs−Vth. Therefore, during the Vth correction stop period, in the row (pixel) to which the previous correction is made, the current Ids flows between the drain and the source of the drive transistor Tr100, the source voltage Vs rises, and the gate voltage Vg also rises due to coupling via the retention capacitor Cs, as well.
(Second Vth Correction Period)
Next, the Vth correction is made again. Specifically, when the voltage of the signal line DTL is Vofs and the Vth correction is possible, the write-line driving circuit 124 increases the voltage of the write line WSL from Voff to Von, thereby causing the gate of the drive transistor Tr100 to be Vofs (T4). At the time, when the source voltage Vs is lower than Vofs−Vth (when the Vth correction is not completed yet), the current Ids flows between the drain and the source of the drive transistor Tr100, until the drive transistor Tr100 is cut off (until a between-gate-and-source voltage Vgs becomes Vth). Subsequently, before the signal-line driving circuit 123 switches the voltage of the signal line DTL from Vofs to Vsig, the write-line driving circuit 124 reduces the voltage of the write line WSL from Von to Voff (T5). Then, the gate of the drive transistor Tr100 enters a floating state and thus, it is possible to keep the between-gate-and-source voltage Vgs constant, regardless of the magnitude of the voltage of the signal line DTL.
Incidentally, during this Vth correction period, when the retention capacitor Cs is charged to Vth, and the between-gate-and-source voltage Vgs becomes Vth, the drive circuit 120 finishes the Vth correction. However, when the between-gate-and-source voltage Vgs does not reach Vth, the drive circuit 120 repeats the Vth correction and the Vth correction stop, until the between-gate-and-source voltage Vgs reaches Vth.
(Writing and μ Correction Period)
After the Vth correction stop period ends, the writing and the μ correction are performed. Specifically, while the voltage of the signal line DTL is Vsig, the write-line driving circuit 124 increases the voltage of the write line WSL from Voff to Von (T6), and connects the gate of the drive transistor Tr100 to the signal line DTL. Then, the gate voltage Vg of the drive transistor Tr100 becomes the voltage Vsig of the signal line DTL. At the time, an anode voltage of the organic EL element 111 is still smaller than the threshold voltage Ve1 of the organic EL element 111 at this stage, and the organic EL element 111 is cut off. Therefore, the current Ids flows in an element capacitance (not illustrated) of the organic EL element 111 and thereby the element capacitance is charged and thus, the source voltage Vs rises by ΔVy, and the between-gate-and-source voltage Vg, soon becomes Vsig+Vth−ΔVy. In this way, the μ correction is performed concurrently with the writing. Here, the larger the mobility μ of the drive transistor Tr100 is, the larger ΔVy is. Therefore, by reducing the between-gate-and-source voltage Vg, by ΔVy before light emission, variations in the mobility μ among the pixels 113 are removed.
(Light Emission Period)
Lastly, the write-line driving circuit 124 reduces the voltage of the write line WSL from Von to Voff (T7). Then, the gate of the drive transistor Tr100 enters a floating state, the current Ids flows between the drain and the source of the drive transistor Tr100, and the source voltage Vs rises. As a result, a voltage equal to or higher than the threshold voltage Ve1 is applied to the organic EL element 111, and the organic EL element 111 emits light of desired luminance.
In the display device 100 of the present application example, as described above, the pixel circuit 112 is subjected to on-off control in each pixel 113, and the driving current is fed into the organic EL element 111 of each pixel 113, so that holes and electrons recombine and thereby emission of light occurs, and this light is extracted to the outside. As a result, an image is displayed in the display area 110A of the display panel 110.
Incidentally, in the present application example, for example, the buffer circuit 5 in the write-line driving circuit 124 is configured to include the plural inverter circuits 1. Therefore, there is almost no through current that flows in the buffer circuit 5 and thus, the power consumption of the buffer circuit 5 may be suppressed. In addition, since there are few variations in the output voltages of the buffer circuits 5, it is possible to reduce the variations among the pixel circuits 112, in terms of the threshold correction and the mobility correction of the drive transistor Tr100 within the pixel circuit 112, and moreover, variations in luminance among the pixels 113 may be reduced.
Further, in the inverter circuit 1, only a single voltage line is provided on each of the low voltage side and the high voltage side and thus, there is no need to increase the withstand voltage of the inverter circuit 1 and also, it is possible to minimize an occupied area and thus, a narrower frame is realized.
The present invention has been described by using the embodiment, the modifications and the application example, but the present invention is not limited to the embodiment and like and may be variously modified.
For example, in the embodiment and the modifications described above, only a single voltage line is provided on each of the low voltage side and the high voltage side. However, for example, a voltage line connected to at least one of plural transistors on the high voltage side and a voltage line connected to other transistors on the high voltage side may not be a common line. Similarly, for example, a voltage line connected to at least one of plural transistors on the low voltage side and a voltage line connected to other transistors on the low voltage side may not be a common line.
For example, in the above-described application example, the inverter circuit 1 according to the above-described embodiment is used in the output stage of the write-line driving circuit 124. However, this inverter circuit 1 may be used in an output stage of the power-source-line driving circuit 125, instead of being used in the output stage of the write-line driving circuit 124, or may be used in the output stage of the power-source-line driving circuit 125 in conjunction with the output stage of the write-line driving circuit 124.
The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2010-085492 filed in the Japan Patent Office on Apr. 1, 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, a fifth transistor, a sixth transistor and a seventh transistor each having channels of same conduction type;
a first capacitive element; and
an input terminal and an output terminal,
wherein the first transistor makes or breaks electric 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 electric connection between a second voltage line and the output terminal, in response to a potential difference between a voltage of a first terminal that is a source or a drain of the seventh transistor and a voltage of the output terminal or a potential difference corresponding thereto,
the third transistor makes or breaks electric connection between a gate of the seventh transistor and the third voltage line, in response to a potential difference between the voltage of the input terminal and a voltage of a third voltage line or a potential difference corresponding thereto,
the fourth transistor makes or breaks electric connection between the first capacitive element and the gate of the seventh transistor, in response to a first control signal inputted into a gate of the fourth transistor,
the fifth transistor makes or breaks electric connection between the first capacitive element and a fourth voltage line, in response to a second control signal inputted into a gate of the fifth transistor,
the sixth transistor makes or breaks electric connection between the first terminal and the fifth voltage line, in response to a potential difference between the voltage of the input terminal and a voltage of a fifth voltage line or a potential difference corresponding thereto,
the seventh transistor makes or breaks electric connection between the first terminal and a sixth voltage line, in response to a potential difference between a gate voltage of the seventh transistor and a gate voltage of the second transistor or a potential difference corresponding thereto, and
the first capacitive element is inserted between a drain or a source of the fifth transistor and a seventh voltage line.

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

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

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

5. The inverter circuit according to claim 4, wherein the first, third, sixth and seventh voltage lines are maintained at the same potential.

6. The inverter circuit according to claim 5, wherein the second, fourth and fifth voltage lines are connected to a power source that outputs a voltage higher than voltages of the first, third, sixth and the seventh voltage lines.

7. The inverter circuit according to claim 6, wherein the fourth and fifth transistors are turned on and off alternately so as to prevent the fourth and fifth transistors from simultaneously staying in ON-state.

8. The inverter circuit according to claim 7, wherein the fourth transistor is turned on before a voltage of the input terminal falls.

9. The inverter circuit according to claim 7, wherein the fourth transistor is turned on after the voltage of the input terminal falls.

10. A display device having 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 rows and columns, and the drive section including a plurality of inverter circuits each provided for each of 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, a fifth transistor, a sixth transistor and a seventh transistor each having channels of same conduction type;
a first capacitive element; and
an input terminal and an output terminal,
wherein the first transistor makes or breaks electric 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 electric connection between a second voltage line and the output terminal, in response to a potential difference between a voltage of a first terminal that is a source or a drain of the seventh transistor and a voltage of the output terminal or a potential difference corresponding thereto,
the third transistor makes or breaks electric connection between a gate of the seventh transistor and the third voltage line, in response to a potential difference between the voltage of the input terminal and a voltage of a third voltage line or a potential difference corresponding thereto,
the fourth transistor makes or breaks electric connection between the first capacitive element and the gate of the seventh transistor, in response to a first control signal inputted into a gate of the fourth transistor,
the fifth transistor makes or breaks electric connection between the first capacitive element and a fourth voltage line, in response to a second control signal inputted into a gate of the fifth transistor,
the sixth transistor makes or breaks electric connection between the first terminal and the fifth voltage line, in response to a potential difference between the voltage of the input terminal and a voltage of a fifth voltage line or a potential difference corresponding thereto,
the seventh transistor makes or breaks electric connection between the first terminal and a sixth voltage line, in response to a potential difference between a gate voltage of the seventh transistor and a gate voltage of the second transistor or a potential difference corresponding thereto, and
the first capacitive element is inserted between a drain or a source of the fifth transistor and a seventh voltage line.

11. A display device having 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 rows and columns, and the drive section including a plurality of inverter circuits each provided for each of 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, a fifth transistor, a sixth transistor and a seventh transistor each having channels of same conduction type;
a first capacitive element; and
an input terminal and an output terminal,
wherein a gate of the first transistor is electrically connected to the input terminal, 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 seventh 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 seventh 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,
a gate of the sixth transistor is electrically connected to the input terminal, one terminal of a drain and a source of the sixth transistor is electrically connected to a fifth voltage line, and the other terminal of the sixth transistor is electrically connected to the gate of the second transistor,
one terminal of a drain and a source of the seventh transistor is electrically connected to a sixth voltage line, and the other terminal of the seventh transistor is electrically connected to the gate of the second transistor, and
the first capacitive element is inserted between the other terminal of the fifth transistor and a seventh voltage line.

12. An inverter circuit, comprising:
a set of transistors each having channels of same conduction type including a first transistor, a second transistor, a third transistor, a fourth transistor, and a fifth transistor;
a first capacitive element; and
an input terminal,
wherein the first transistor makes or breaks an electric connection between a gate of the fifth transistor and a first voltage line, in response to a voltage of the input terminal applied to a gate of the first transistor,
wherein the second transistor makes or breaks an electric connection between the first capacitive element and the gate of the fifth transistor, in response to a first control signal applied to a gate of the second transistor,
wherein the third transistor makes or breaks an electric connection between the first capacitive element and a second voltage line, in response to a second control signal applied to a gate of the third transistor,
wherein the fourth transistor makes or breaks an electric connection between a first current terminal of the fifth transistor and the first voltage line, in response to the voltage of the input terminal applied to a gate of the fourth transistor, and
wherein the fifth transistor makes or breaks an electric connection between the first terminal of the fifth transistor and a fourth voltage line, in response to a voltage applied to the gate of the fifth transistor.

13. An inverter circuit, comprising:
a set of transistors each having channels of same conduction type including a first transistor, a second transistor, a third transistor, a fourth transistor, and a fifth transistor;
a first capacitive element; and
an input terminal,
wherein a gate of the first transistor is electrically connected to the input terminal, a first current terminal of the first transistor is electrically connected to a first voltage line, and a second current terminal of the first transistor is electrically connected to a gate of the fifth transistor,
wherein a gate of the second transistor is supplied with a first control signal and a first current terminal of the second transistor is electrically connected to the gate of the fifth transistor,
wherein a gate of the third transistor is supplied with a second control signal, a first current terminal of the third transistor is electrically connected to a second voltage line, and a second current terminal of the third transistor is electrically connected to a second current terminal of the second transistor,
wherein a gate of the fourth transistor is electrically connected to the input terminal, a first current terminal of the fourth transistor is electrically connected to the first voltage line, and a second current terminal of the fourth transistor is electrically connected to a first current terminal of the fifth transistor, and
a second current terminal of the fifth transistor is electrically connected to a third voltage line.