Patent Application
20150145899
The present invention relates to a display device, and more specifically to a display device including an electrooptical element driven by current such as an organic EL (electroluminescent) element and a method of driving the same.
Organic EL display devices are known as thin profile, high image quality, and low power consumption display devices. The organic EL display device has formed therein a plurality of pixel circuits arranged in a matrix, the pixel circuits including organic EL elements, which are light-emitting electrooptical elements driven by current, driving transistors, and the like.
The organic EL elements have been known for having a decrease in light emitting efficiency due to deterioration over time, resulting in a decrease in light-emitting luminance.
In relation to the present invention, Patent Document 1 discloses a pixel circuit that compensates for increase in forward bias voltage resulting from deterioration over time of organic EL elements.
First, a scan wiring line Sj is selected and the transistor T11 turns ON, and a voltage based on the data signal fed from a data wiring line Di is written to the capacitor C11. Next, the selection of the scan wiring line Sj ends and the transistor T11 turns OFF, and control lines Vg13j and Vg15j are selected. As a result, the transistor T13 turns ON, and a drive current based on a voltage between source and gate of the transistor T12 is fed to the organic EL element OLED. Also, the transistor T15 turns ON, and the gate potential of the transistor T16 becomes equal to the anode potential of the organic EL element OLED based on the drive current. The anode potential Pi of the organic EL element OLED changes due to deterioration of the organic EL element OLED. Here, using the variable bias voltage source VS, a source potential Ps of the transistor T16 is set according to the following formula (1).
Ps=Pi−Vth (1)
Here, Vth represents a threshold voltage of the transistor T16.
By setting the source potential Ps of the transistor T16 according to formula (1), it is possible to extract the increase in forward bias voltage resulting from the deterioration of the organic EL element OLED as the source/drain current of the transistor T16. After the source/drain voltage of the transistor T16 is determined, the selection of the control line Vg15j ends and the transistor T15 turns OFF, and then the control line Vg14j is selected and the transistor T14 turns ON. Thus, the potential of the gate terminal of the transistor T12 decreases based on the source/drain current of the transistor T16. As a result, it is possible to perform luminance compensation based on the increase in forward bias voltage resulting from deterioration over time of the organic EL element OLED. Therefore, it is possible to mitigate a decrease in luminance of emitted light resulting from the deterioration over time of the organic EL elements OLED.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2005-258427
However, in the pixel circuit disclosed in Patent Document 1, when determining the source/drain current of the transistor T16, light is emitted from the organic EL element OLED. In other words, display is performed at a luminance based on the drive current prior to compensation according to the rise in forward bias voltage occurring. Thus, it is not possible to sufficiently mitigate a decrease in luminance of light emitted resulting from a deterioration over time of the electrooptical elements such as organic EL elements.
An object of the present invention is to provide a display device in which a decrease in luminance of emitted light resulting from deterioration over time of electrooptical elements such as organic EL elements is mitigated to a greater extent than in conventional devices, and a method of driving the same.
A first aspect of the present invention is an active matrix display device includes:
a plurality of data wiring lines supplying data signals;
a plurality of scan wiring lines that are each selectively driven;
a first power source line that supplies a first power source potential;
a second power source line that supplies a second power source potential;
a reverse bias control line that supplies a control potential at least during a first prescribed period; and
a plurality of pixel circuits provided at respective intersections between the plurality of data wiring lines and the plurality of scan wiring lines,
wherein each of the pixel circuits includes:
an electrooptical element provided between the first power source line and the second power source line;
a driving unit that controls a current flowing to the electrooptical element, the driving unit including a driving transistor provided between the first power source line and the second power source line and connected in series to the electrooptical element, and a driving capacitance unit that stores a drive voltage for controlling the driving transistor;
an input unit that supplies to the driving unit a voltage of the data signal supplied by a corresponding data wiring line in response to a corresponding scan wiring line being selected;
a compensation unit between the second power source line and the reverse bias control line, the compensation unit supplying to the driving capacitance unit a reverse direction current flowing through the electrooptical element; and
a light emission control transistor provided between the first power source line and the electrooptical element, the light emission control transistor being in an off state during a second prescribed period that includes the first prescribed period, and
wherein the driving unit determines the drive voltage based on at least a voltage of the data signal and the reverse direction current.
A second aspect of the present invention is the first aspect of the present invention,
wherein the driving unit determines the drive voltage based on at least a voltage of the data signal and a compensation voltage based on the reverse direction current.
A third aspect of the present invention is the second aspect of the present invention,
wherein the driving capacitance unit is provided between a control terminal and a first conductive terminal of the driving transistor and includes a first driving capacitance element to which the reverse direction current is supplied during the first prescribed period, and
wherein the driving unit is provided between the first conductive terminal and the first driving capacitance element of the driving transistor and further includes a transistor for controlling the application of the drive voltage, said transistor being off during the first prescribed period.
A fourth aspect of the present invention is the third aspect of the present invention,
wherein the input unit includes:
A fifth aspect of the present invention is the fourth aspect of the present invention,
wherein the compensation unit includes:
A sixth aspect of the present invention is the fifth aspect of the present invention, wherein the pixel circuits each further include a pre-processing unit that performs pre-processing on the drive voltage stored in the driving capacitance unit during a pre-processing period that is during the second prescribed period and before the first prescribed period.
A seventh aspect of the present invention is the sixth aspect of the present invention, wherein the pre-processing unit includes a first pre-processing transistor provided between terminals of the first driving capacitance element, the first pre-processing transistor being on during a first pre-processing period in the pre-processing period.
An eighth aspect of the present invention is the seventh aspect of the present invention,
wherein the driving capacitance unit further includes a second driving capacitance element provided between the first conductive terminal and a second conductive terminal of the driving transistor, and
wherein the pre-processing unit further includes a second pre-processing transistor provided between the control terminal and the second conductive terminal of the driving transistor, the second pre-processing transistor being on in a second pre-processing period during the pre-processing period and after the first pre-processing period.
A ninth aspect of the present invention is the eighth aspect of the present invention, wherein the first pre-processing transistor and the transistor for controlling the application of the drive voltage turn on during the second pre-processing period.
A tenth aspect of the present invention is the ninth aspect of the present invention, wherein the second transistor for supplying a reverse direction current and the transistor for controlling the application of the drive voltage turn on during the first pre-processing period.
An eleventh aspect of the present invention is the third aspect of the present invention, wherein the first conductive terminal of the driving transistor is located towards the first power source line.
A twelfth aspect of the present invention is the third aspect of the present invention, wherein the first conductive terminal of the driving transistor is located towards the second power source line.
A thirteenth aspect of the present invention is the first aspect of the present invention, wherein a conductive type of the driving transistor is of a p-channel type.
A fourteenth aspect of the present invention is the first aspect of the present invention, wherein a conductive type of the driving transistor is of an n-channel type.
A fifteenth aspect of the present invention is the first to fourteenth aspects of the present invention,
wherein the reverse bias control line supplies the control potential during the second prescribed period, and
wherein a control terminal of the light emission control transistor is connected to the reverse bias control line.
A sixteenth aspect of the present invention is a method of driving an active matrix display device including: a plurality of data wiring lines supplying data signals; a plurality of scan wiring lines that are each selectively driven; first power source lines that supply a first power source potential; second power source lines that supply a second power source potential; and a plurality of pixel circuits provided at respective intersections between the plurality of data wiring lines and the plurality of scan wiring lines, each of the pixel circuits including: an electrooptical element provided between the first power source line and the second power source line; and a driving unit that controls a current flowing to the electrooptical element, the driving unit having a driving transistor provided between the first power source line and the second power source line and connected in series to the electrooptical element, and a driving capacitance unit that stores a drive voltage for controlling the driving transistor, the method comprising:
supplying to the driving unit a voltage of the data signal supplied by a corresponding data wiring line in response to a corresponding scan wiring line being selected;
supplying to the driving capacitance unit a reverse direction signal flowing to the electrooptical element between the second power source line and a reverse bias control line that supplies a control potential at least during a first prescribed period;
determining the drive voltage based on at least a voltage of the data signal and the reverse direction current; and
controlling a light emission timing of the electrooptical element to block current flowing between the first power source line and the electrooptical element during a second prescribed period that includes the first prescribed period.
According to the first aspect of the present invention, the reverse direction current flowing in the electrooptical element (refers to the organic EL element below in the description of the effects of the invention) during reverse bias time is supplied to the driving capacitance unit, and the drive voltage is determined based on at least the voltages of the reverse direction current and the data signal. A forward direction current (drive current) based on this drive voltage is then supplied to the organic EL element. The reverse direction current becomes greater as deterioration over time of the organic EL element progresses. As a result, the drive current also attains a value based on the degree of progression over time of the organic EL element. As a result, luminance compensation occurs based on the progression over time of deterioration of the organic EL element. Furthermore, this luminance compensation occurs during the second prescribed period during which the organic EL element does not emit light. Therefore, prior to the luminance compensation being completed, the organic EL element does not emit light, and therefore, a decrease in luminance in emitted light due to deterioration over time of the organic EL element can be mitigated to a greater degree than in conventional devices.
According to the second aspect of the present invention, the compensation voltage based on the compensation current is supplied to the driving unit, and the drive voltage is determined based on at least the compensation voltage and the voltage of the data signal. A forward direction current (drive current) based on this drive voltage is then supplied to the organic EL element. The reverse direction current becomes greater as deterioration over time of the organic EL element progresses. Thus, the voltage based on the reverse direction current becomes greater as deterioration over time of the organic EL element progresses. As a result, the drive current also becomes larger as deterioration of the organic EL element progresses over time. As a result, effects similar to those of the first aspect of the present invention can be attained.
According to the third aspect of the present invention, the reverse direction current is supplied to the first driving capacitance element, and the application of the drive voltage is controlled by the transistor for controlling the application of the drive voltage, and thus, effects similar to those of the second aspect of the present invention can be attained.
According to a fourth aspect of the present invention, the input unit is realized by the input transistor and the input capacitance element. Thus, based on the selection timing for the scan wiring line, the voltage of the data signal can be supplied to the driving capacitance element through the input capacitance element.
According to the fifth aspect of the present invention, the compensation unit is realized by the first and second transistors for supplying a reverse direction current.
According to the sixth aspect of the present invention, it is possible to perform pre-processing on the drive voltage. Pre-processing includes initialization or threshold voltage compensation.
According to the seventh aspect of the present invention, during the first pre-processing period, both terminals of the first driving capacitance element are electrically connected to each other through the first pre-processing transistor. Thus, the voltage held in the first driving capacitance element is initialized to 0V. As a result, it is possible to reliably write the compensation voltage based on the reverse direction current to the first driving capacitance element.
According to the eight aspect of the present invention, during the second pre-processing period, the control terminal and the second conductive terminal of the driving transistor are electrically connected to each other through at least the second pre-processing transistor (form a diode connection). Thus, during the second pre-processing period, the threshold voltage of the driving transistor is written to the second driving capacitance element. As a result, it is possible to compensation for variation in the threshold voltage of the driving transistor using the threshold voltage.
According to the ninth aspect of the present invention, during the second pre-processing period, the second pre-processing transistor, the first pre-processing transistor, and the transistor for controlling the application of the drive voltage are turned ON, variation in threshold voltage in the driving transistor can be reliably compensated.
According to the tenth aspect of the present invention, during the first pre-processing period, the transistor for supplying the second reverse direction current, the transistor for controlling the application of the drive voltage, and the first pre-processing transistor cause the terminal of the second driving capacitance element to be electrically connected to the reverse bias control line. Thus, during the first pre-processing period, the voltage held in the second driving capacitance element is initialized to a value based on the control potential, which is a fixed potential. As a result, during the second pre-processing period, it is possible to stably write the threshold voltage of the driving transistor to the second driving capacitance element. Therefore, variation in the threshold voltage of the driving transistor can be stably compensated.
According to the eleventh aspect of the present invention, by providing a driving capacitance unit between the control terminal of the driving transistor and the first conductive terminal thereof towards the first power source line, it is possible to attain effects similar to those of the third aspect of the present invention.
According to the twelfth aspect of the present invention, by providing a driving capacitance unit between the control terminal of the driving transistor and the first conductive terminal thereof towards the second power source line, it is possible to attain effects similar to those of the third aspect of the present invention.
According to the thirteenth aspect of the present invention, it is possible to attain effects similar to those of the first aspect of the present invention using a p-channel type driving transistor.
According to the fourteenth aspect of the present invention, it is possible to attain effects similar to those of the first aspect of the present invention using an n-channel type driving transistor.
According to the fifteenth aspect of the present invention, components in the compensation unit and the light emission control transistor connected to the reverse bias control line can share a reverse bias control line. Thus, the number of lines can be reduced.
According to the sixteenth aspect of the present invention, in the method of driving the display device, effects similar to the first aspect of the present invention can be attained.
<0. Basic Study>
Before describing embodiments of the present invention, a basic study conducted by inventors of the present invention in order to solve the above-mentioned problems will be described. The inventors of the present invention fed a fixed current of 15 mA to an 8 mm2 organic EL element, and measured the luminance of the emitted light and the current during reverse bias (hereinafter referred to as “reverse bias current,” and assigned the reference character “Ioledr”) at respective elapsed times of 36 seconds, 3 minutes, 6 minutes, 12 minutes, 24 minutes, 1 hour, 2 hours, and 5 hours from start of fixed current feed. The reverse bias voltage was set at 2.8V.
As seen in
The transistors included in the pixel circuits of the respective embodiments are field effect transistors, and typically thin film transistors (sometimes abbreviated as “TFTs” below). Examples of transistors included in the pixel circuits are oxide TFTs in which the channel layer is made of an oxide semiconductor, a low temperature polysilicon TFT in which the channel layer is made of a low temperature polysilicon, and an amorphous silicon TFT in which the channel layer is made of amorphous silicon. An example of an oxide TFT is an indium gallium zinc oxide TFT in which the channel layer is made of InGaZnOx (indium gallium zinc oxide), which is an oxide semiconductor having indium (I), gallium (Ga), zinc (Zn), and oxygen (O) as main components. Oxide TFTs such as indium gallium zinc oxide TFTs are particularly suited to being used as the n-channel type transistor included in the pixel circuit. However, the present invention does not exclude the use of p-channel type oxide TFTs. Also, similar effects can be attained for oxide semiconductors other than indium gallium zinc oxide if the channel layer is made of an oxide semiconductor including at least one of indium, gallium, zinc, copper (Cu), silicon (Si), tin (Sn), aluminum (Al), calcium (Ca), germanium (Ge), and lead (Pb), for example. Of the transistors included in the pixel circuits of the respective embodiments, a first conductive terminal of the transistor T2 to be described later corresponds to the source terminal and the second conductive terminal corresponds to the drain terminal.
The oxide semiconductor layer included in the oxide TFT will be described here. The oxide semiconductor layer is an In—Ga—Zn—O type semiconductor layer, for example. The oxide semiconductor layer includes an In—Ga—Zn—O type semiconductor, for example. The In—Ga—Zn—O type semiconductor is a ternary oxide of indium (In), gallium (Ga), and zinc (Z). There is no special limitation on the ratio (composition ratio) of In, Ga, and Zn, and the ratio may be In:Ga:Zn=2:2:1, In:Ga:Zn=1:1:1, In:Ga:Zn=1:1:2, or the like, for example.
TFTs having In—Ga—Zn—O type semiconductor layers have a high mobility (more than 20 times that of amorphous silicon TFTs) and a low leakage current (less than 1/100 of amorphous silicon TFTs), and thus, are well suited to being used as driving TFTs and switching TFTs in the pixel circuits. The use of TFTs having In—Ga—Zn—O type semiconductor layers can greatly reduce power consumption in display devices.
In—Ga—Zn—O type semiconductors may be amorphous, or may be crystalline, with crystalline portions included. It is preferable that crystalline In—Ga—Zn—O type semiconductors have the c axis oriented generally perpendicularly to the layer surface. Such a crystalline structure for an In—Ga—Zn—O type semiconductor is disclosed in Japanese Patent Application Laid-Open Publication No. 2012-134475, for example. All contents disclosed in Japanese Patent Application Laid-Open Publication No. 2012-134475 are incorporated by reference herein.
Another oxide semiconductor may be included in the oxide semiconductor layer instead of the In—Ga—Zn—O type semiconductor. For example, the oxide semiconductor layer may include a Zn—O type semiconductor (ZnO), an In—Zn—O type semiconductor (IZO (registered trademark)), a Zn—Ti—O type semiconductor (ZTO), a Cd—Ge—O type semiconductor, a Cd—Pb—O type semiconductor, CdO (cadmium oxide), an Mg—Zn—O type semiconductor, an In—Sn—Zn—O type semiconductor (In2O3-SnO2-ZnO), an In—Ga—Sn—O type semiconductor, or the like.
In the present specification, “a state in which component A is connected to component B” refers not only to a state in which the component A is directly and physically connected to component B, but also a case in which component A is connected to component B through another component. Also, “a state in which component C is provided between component A and component B” refers not only to a state in which the component C is directly and physically connected to component A and component B, but also a state in which component C is connected to component A and component B through other components. However, other components are limited to those that do not contradict with the concept of the present invention.
The display unit 10 is provided with an m number of data wiring lines Di (i=1 to m) and an n number of scan wiring lines Sj (j=1 to n) perpendicular therewith. The display unit 10 is also provided with an m×n number of pixel circuits 11 corresponding to the intersections of the m number of data wiring lines Di and the n number of scan wiring lines Sj. In
The display unit 10 is also provided with a power source line that supplies a high level power source potential Vdd (hereinafter referred to as the “high level power source line;” assigned the same reference character Vdd as the high level power source potential), a power source line that supplies a low level power source potential Vss (hereinafter referred to as the “low level power source line;” assigned the same reference character Vss as the low level power source potential), and a power source line that supplies a reverse bias power source potential Vr (hereinafter referred to as the “reverse bias power source line;” assigned the same reference character Vr as the reverse bias power source potential). The high level power source potential Vdd, the low level power source potential Vss, and the reverse bias power source potential Vr have a size relation indicated in formula (2) below:
Vdd>Vss>Vr (2)
The high level power source potential Vdd, the low level power source potential Vss, and the reverse bias power source potential Vr are supplied from a power source circuit that is not shown. The high level power source line Vdd, the low level power source line Vss, and the reverse bias power source line Vr are respectively connected to each pixel circuit 11 shared therebetween. In the present embodiment, the high level power source line Vdd is the first power source line, the low level power source line Vss is the second power source line, and the reverse bias power source line Vr is the reverse bias control line.
The display control circuit 20 outputs respective control signals to the data driver 30, the scan driver 40, and the group of selection drivers 50. More specifically, the display control circuit 20 outputs a data start pulse DSP, a data clock signal DCK, display data DA, and a latch pulse LP to the data driver 30. The display control circuit 20 outputs a scan start pulse SSP1 and a scan clock signal SCK1 to the scan driver 40. The display control circuit 20 outputs a selection start pulse SSP2 and a selection clock signal SCK2 to the group of selection drivers 50. The selection start pulse SSP2 in reality includes a plurality of start pulses. Similarly, the selection clock signal SCK2 includes a plurality of clock signals.
The data driver 30 includes an m-bit shift register, a sampling circuit, a latch circuit, an m number of D/A converters, and the like, which are not shown. The shift register has an m number of bistable circuits connected to each other in the vertical direction, and transmits the data start pulse DSP supplied to the shift register in the initial stage in synchronization with the data clock signal DCK, and outputs a sampling pulse from each stage. Display data DA is fed to the sampling circuit in synchronization with the output of the sampling pulse. The sampling circuit stores the display data DA according to the sampling pulse. When one row of display data DA is stored in the sampling circuit, the display control circuit 20 outputs a latch pulse LP to the latch circuit. When the latch circuit receives the latch pulse LP, it holds the display data stored in the sampling circuit. The D/A converters are provided for each of the m number of data lines Di, convert the display data DA held in the latch circuit to a data signal that is an analog signal, and feeds the obtained data signal to the m number of data wiring lines Di.
The scan driver 40 drives an n number of scan wiring lines Sj. The scan driver 40 includes a shift register, a buffer, and the like, which are not shown. The shift register sequentially transmits a scan start pulse SSP1 in synchronization with the scan clock signal SCK1. The scan signal outputted from respective steps of the shift register is fed to the corresponding scan wiring line through the buffer. As a result of an active scan signal (low level in the present embodiment), an m number of pixel circuits 11 connected to the scan wiring line Sj are simultaneously selected.
The group of selection drivers 50 drive an n number of control lines Vg4j, an n number of control lines Vg5j, an n number of control lines Vg6j, and an n number of control lines Vg7j. The group of selection drivers 50 are constituted of a plurality of selection drivers, and each selection driver controls one or more types of control lines. Each selection driver sequentially transmits a start pulse included in the selection start pulse SSP2 in synchronization with the timing of the selection clock signal SCK2. The selection signal outputted from respective steps of the shift register is fed to the corresponding control line through the buffer.
The transistor T1 functions as an input transistor. The transistor T2 functions as a driving transistor. The transistor T4 functions as a light emission control transistor. The transistor T5 functions as a first transistor for supplying a reverse direction current. The transistor T6 functions as a transistor for controlling the application of a drive voltage. The transistor T7 functions as a second transistor for supplying a reverse direction current. The capacitor C1 functions as an input capacitance element. The capacitor C3 functions as a first driving capacitance element.
The input unit 101 feeds to the driving unit 102 a data voltage based on the data wiring line fed by the corresponding data wiring line Di in response to the selection of the corresponding scan wiring line Sj. The gate terminal of the transistor T1 is connected to the scan wiring line Sj and a first conductive terminal of the transistor T1 is connected to the data wiring line Di. A first terminal of the capacitor C1 is connected to a second conductive terminal of the transistor T1.
The driving unit 102 controls a forward direction current (drive current) flowing through the organic EL element OLED. The driving capacitance unit 111 holds a drive voltage to be applied between the gate terminal and the first conductive terminal of the transistor T2. The drive voltage application control unit 112 controls the application of the drive voltage to the transistor T2. The gate terminal of the transistor T2 is connected to a second terminal of the capacitor C3, and the first conductive terminal of the transistor T2 is connected to the high level power source line Vdd. The gate terminal of the transistor T6 is connected to a control line Vg6j, and is provided between the first terminal of the capacitor C3 and the first conductive terminal of the transistor T2.
The light emission control unit 103 controls the timing at which the organic EL element OLED emits light, and, during a non-light emitting period LSP occurring later, stops the current (forward direction current) flowing between the high level power source line Vdd (first power source line) and the organic EL element OLED. In other words, during the non-light emitting period LSP, the organic EL element OLED is electrically disconnected from the transistor T2. The gate terminal of the transistor T4 is connected to the control line Vg4j, and the transistor T4 is provided between the second conductive terminal of the transistor T2 and the anode terminal of the organic EL element OLED.
The reverse direction current compensation unit 104 supplies to the capacitor C3 a compensation signal based on the reverse direction current Ioledr flowing through the organic EL element OLED. More specifically, the reverse direction current compensation unit 104 supplies to the capacitor C3 a voltage based on the reverse direction current Ioledr flowing through the organic EL element OLED. The gate terminal of the transistor T5 is connected to the control line Vg5j, and the transistor T5 is provided between the anode terminal of the organic EL element OLED and the first terminal of the capacitor C3. The gate terminal of the transistor T7 is connected to a control line Vg7j, and is provided between the second terminal of the capacitor C3 and the reverse bias power source line Vr.
At time t1a, the potential of the control line Vg4j changes from a low level to a high level. Thus, the transistor T4 turns OFF, and the second conductive terminal of the transistor T2 is electrically separated from the anode terminal of the organic EL element OLED. Thus, the organic EL element OLED stops emitting light.
At the time t1, the potential of the control line Vg6j changes from a low level to a high level, and the transistor T6 turns OFF. As a result, the first conductive terminal of the transistor T2 is electrically disconnected from the first terminal of the capacitor C3. Also, at the time t1, the potential of the control lines Vg5j and Vg7j changes from a high level to a low level, and thus, the transistors T5 and T7 turn ON. Therefore, the organic EL element OLED becomes reverse biased due to the low level power source potential Vss and the reverse bias power source potential Vr. As a result, the reverse direction current Ioledr flowing through the organic EL element OLED is fed to the capacitor C3. The reverse direction current Ioledr becomes a value based on the progression of deterioration of the organic EL element OLED as shown in the basic study. In other words, a voltage determined by the reverse direction current Ioledr based on the progression of deterioration of the organic EL element OLED (hereinafter referred to as the “reverse direction voltage” and assigned the reference character Voledr) is written to the capacitor C3. The reverse direction current Ioledr becomes greater as deterioration of the organic EL element progresses, and thus, the reverse direction voltage Voledr written to the capacitor C3 also becomes greater as deterioration of the organic EL element progresses. In this manner, in the present embodiment, the reverse direction voltage Voledr is fed to the driving unit 102 as the voltage based on the reverse direction current Ioledr. In the present embodiment and in the following embodiments, the reverse direction voltage Voledr corresponds to the compensation voltage based on the reverse direction current. Also, in the present embodiment and in the following embodiments, the reverse direction current compensation unit 104 supplying the reverse direction voltage Voledr to the driving unit 102 corresponds to the reverse direction current compensation unit 104 supplying the compensation signal based on the reverse direction current Ioledr to the driving unit 102.
At the time t2, the potential of the control lines Vg5j and Vg7j changes from a low level to a high level, and the transistors T5 and T7 turn OFF. Thus, reverse biasing of the organic EL element OLED ends. Also, at the time t2, the potential of the control line Vg6j changes from a high level to a low level, and thus, the transistor T6 turns ON. Thus, the capacitor C3 electrically connects the gate terminal and the first conductive terminal of the transistor T2. Also, at the time t2, the potential of the scan wiring line Sj changes from a high level to a low level, and thus, the transistor T1 turns ON. Therefore, the second terminal (gate potential of the transistor T2) of the capacitor C3 is boosted through the capacitor C1, and thus, “Vsig+Voledr” is written to the capacitor C3. Here, Vsig is the data signal voltage (hereinafter the “data voltage”). The data voltage Vsig is a negative voltage in the present embodiment and in Embodiments 2 to 5, and a positive voltage in Embodiments 6 and 7. It is preferable that the capacitance value of the capacitor C1 be sufficiently larger than the capacitance value of the capacitor C3. In the present embodiment, such boosting results in the data voltage Vsig being supplied to the driving unit 102.
Also, at the time t3, the potential of the scan wiring line Sj changes from a low level to a high level, and thus, the transistor T1 turns OFF. Therefore, the supplying of the data voltage Vsig to the driving unit 102 is stopped.
At the time t3a, the potential of the control line Vg4j changes from a high level to a low level, and thus, the transistor T4 turns ON. Therefore, a drive current I1 determined by formula (3) below is fed to the organic EL element OLED, and the organic EL element OLED emits light based on the value of the drive current I1.
I1=(β½)·(Vgs−VthT2)2 (3)
Here, β1 represents a constant, Vgs represents a source-gate voltage (drive voltage of the transistor T2, and VthT2 represents a threshold voltage of the transistor T2. Starting at time t3a, the first and second conductive terminals of the transistor T2 respectively function as the source terminal and the drain terminal. “Vsig+Voledr” is held in the capacitor C3 as described above; in other words, the drive voltage in the driving unit 102 is determined by the data voltage Vsig and the reverse direction voltage Voledr, and thus, formula (3) is replaced by formula (4) below.
I1=(β½)·(Vsig+Voledr−VthT2)2 (4)
In this manner, the drive current I1 is fixed by the drive voltage. The reverse direction voltage Voledr becomes larger as deterioration over time of the organic EL element OLED progresses, and thus, the drive current I1 shown in formula (4) also becomes larger as deterioration over time of the organic EL element OLED progresses. In the present embodiment and in respective embodiments below, the “reverse direction voltage Voledr becoming greater” refers to the absolute value of the reverse direction voltage Voledr becoming greater.
According to the present embodiment, the data voltage Vsig and the reverse direction current Ioledr flowing through the organic EL element OLED during reverse bias time are fed to the driving capacitance unit 111, and the drive voltage is determined by the data voltage Vsig and the voltage (compensation signal) based on the reverse direction current Ioledr. More specifically, the reverse direction voltage Voledr is written to the capacitor C3 (driving capacitance unit 111) connected to the control terminal and the first conductive terminal of the transistor T2. Then, as a result of the sum of the data voltage Vsig and the reverse direction voltage Voledr being written to the capacitor C3 through the capacitor C1 due to boosting, the drive voltage is determined as the sum of the data voltage Vsig and the reverse direction voltage Voledr. Then, the organic EL element OLED emits light according to the drive current I1, which is proportion to a value obtained by the difference between the drive voltage and the threshold voltage of the transistor T2 raised to the second power. The reverse direction voltage Voledr becomes larger as deterioration over time of the organic EL element OLED progresses, and thus, the drive current I1 also becomes larger as deterioration over time of the organic EL element OLED progresses. As a result, luminance compensation occurs based on the progression over time of deterioration of the organic EL element OLED. Furthermore, this luminance compensation occurs during the non-light emitting period LSP during which the organic EL element does not emit light. Therefore, prior to the luminance compensation being completed, the organic EL element OLED does not emit light, and therefore, a decrease in luminance in emitted light due to deterioration over time of the organic EL element can be mitigated to a greater degree than in conventional devices.
At time t1a, the potential of the control line Vg4j changes from the high level to the reverse bias power source potential Vr. Thus, the transistor T4 turns OFF, and the second conductive terminal of the transistor T2 is electrically separated from the anode terminal of the organic EL element OLED. Thus, the organic EL element OLED stops emitting light. During the non-light emitting period LSP, the reverse bias power source potential Vr is fed to the control line Vg4j, and thus, during the non-light emitting period LSP, an operation similar to that of Embodiment 1 occurs.
At the time t3a, the potential of the control line Vg4j changes from the reverse bias power source potential Vr to a high level, and thus, the transistor T4 turns ON. Therefore, the organic EL element OLED emits light according to the drive current I1 shown in the formula (4) above in a manner similar to that of Embodiment 1.
According to the present embodiment, the transistor T4 is of an n channel type, and by sharing the control line Vg4j between the gate terminal of the transistor T4 and the first conductive terminal of the transistor T7, the reverse bias power source line Vr of Embodiment 1 can be omitted.
The pre-processing unit 105 performs pre-processing of the drive voltage held in the driving capacitance unit 111 during a pre-processing period PP during the non-light emitting period LSP and prior to the reverse direction compensation period ICP. The pre-processing unit 105 includes an initializing unit 121. The initializing unit 121 corresponds to the first pre-processing unit.
The initializing unit 121 includes one transistor T8. The transistor T8 is of a p channel type. The transistor T8 functions as a first pre-processing transistor. The initializing unit 121 causes a short-circuit between the first terminal and the second terminal of the capacitor C3 during an initializing period IP to be described below during the pre-processing period PP. The gate terminal of the transistor T8 is connected to a control line Vg8j, and the transistor T8 is provided between the first terminal and the second terminal of the capacitor C3. The connective relations of other components within the pixel circuit 11 and between components are similar to those of Embodiment 1, and thus, descriptions thereof are omitted.
At the time t1, the potential of the control line Vg6j changes from a low level to a high level, and the transistor T6 turns OFF. As a result, the first conductive terminal of the transistor T2 is electrically disconnected from the first terminal of the capacitor C3. Also, at the time t1, the potential of the control line Vg8j changes from a high level to a low level, and thus, the transistor T8 turns ON. Thus, short-circuiting occurs between the first terminal and the second terminal of the capacitor C3, and the electric charge stored in the capacitor C3 is erased (the holding voltage is initialized to 0V).
At the time t2, the potential of the control line Vg8j changes from a low level to a high level, and the transistor T8 turns OFF. Thus, the initialization of the holding voltage of the capacitor C3 is completed.
According to the present embodiment, the transistor T8, which is ON during the initializing period IP, is provided between the first terminal and the second terminal of the capacitor C3, and thus, during the initializing period IP, the first terminal and the second terminal of the capacitor C3 are electrically connected to each other. Thus, the holding voltage of the capacitor C3 is initialized to 0V. As a result, during the reverse direction compensation period ICP, it is possible to reliably write to the capacitor C3 the reverse direction voltage Voledr based on the reverse direction current Ioledr.
The capacitor C2 is provided between the first conductive terminal of the transistor T2 and the first conductive terminal of the transistor T6. The capacitor C2 functions as a second driving capacitance element.
The threshold voltage compensation unit 122 includes one transistor T3. The transistor T3 is of a p channel type. The transistor T3 functions as a second pre-processing transistor. The threshold voltage compensation unit 122, the initializing unit 121, and the drive voltage application control unit 112 operate together during a threshold voltage compensation period TCP during the pre-processing period PP and after the initializing period IP, thereby causing a short-circuit between the second conductive terminal and the gate terminal of the transistor T2. The gate terminal of the transistor T3 is connected to the control line Vg3j, and the transistor T3 is provided between the first conductive terminal of the transistor T6 (one end of the drive voltage application control unit 112 towards the capacitor C2) and the second conductive terminal of the transistor T2. The threshold voltage compensation unit 122 corresponds to the second pre-processing unit.
The initializing unit 121, the reverse direction current compensation unit 104, and the drive voltage application control unit 112 of the present embodiment operate together during the initializing period IP, thereby causing a short-circuit between the first terminal of the capacitor C2 and the reverse bias power source line Vr. The connective relations of other components within the pixel circuit 11 and between components are similar to those of Embodiment 3, and thus, descriptions thereof are omitted.
During the time t1, the potential of the control line Vg6j is maintained at a low level, and thus, the transistor T6 is ON. Also, at the time t1, the potential of the control lines Vg7j and Vg8j changes from a high level to a low level, and thus, the transistors T7 and T8 respectively turn ON. Thus, the first terminal and the second terminal of the capacitor C3 are electrically connected to each other, and the voltage held in the capacitor C3 is initialized to 0V. Also, as a result of the first terminal of the capacitor C2 and the reverse bias power source line Vr being electrically connected to each other, the voltage held in the capacitor C2 is initialized to the potential difference between the high level power source potential Vdd and the reverse bias power source potential Vr, which are both fixed potentials. Initialization of the voltage held in the capacitor C3 to 0V may be performed alone in the initializing period IP.
At the time t2, the potential of the control line Vg7j changes from a low level to a high level, and the transistor T7 turns OFF. As a result, the gate terminal of the transistor T2 and the reverse bias power source line Vr are electrically disconnected from each other. Also, at the time t2, the potential of the control line Vg3j changes from a high level to a low level, and thus, the transistor T3 turns ON. As a result, the gate terminal and the second conductive terminal of the transistor T2 are electrically connected to each other through the transistors T3 and T6 (forming a diode connection).). As a result, during the threshold voltage compensation period TCP at the time t2 to t3, a voltage based on the threshold voltage VthT2 of the transistor T2 is written to the capacitor C2. Below, for ease of description, it is assumed that the threshold voltage VthT2 of the transistor T2 is written to the capacitor C2. As a result of the initialization above, a voltage having a larger absolute value than the threshold voltage VthT2 is stored in the capacitor C2 immediately before the time t2.
At the time t3, the potential of the control lines Vg3j, Vg6j, and Vg8j changes from a low level to a high level, and the transistors T3, T6, and T8 turn OFF. As a result, the writing of the threshold voltage VthT2 of the transistor T2 to the capacitor C2 is completed. Also, at the time t3, the potential of the control lines Vg5j and Vg7j changes from a high level to a low level, and thus, the transistors T5 and T7 turn ON. Therefore, the organic EL element OLED becomes reverse biased due to the low level power source potential Vss and the reverse bias power source potential Vr. As a result, the reverse direction current Ioledr flowing through the organic EL element OLED is fed to the capacitor C3. As a result, similar to Embodiment 1, a reverse direction voltage Voledr is written to the capacitor C3.
At the time t4, the potential of the control lines Vg5j and Vg7j changes from a low level to a high level, and the transistors T5 and T7 turn OFF. Thus, reverse biasing of the organic EL element OLED ends. Also, at the time t4, the potential of the control line Vg6j changes from a high level to a low level, and thus, the transistor T6 turns ON. As a result, the capacitors C2 and C3 are connected in series, and the voltage held in the entire driving capacitance unit 111 becomes “VthT2+Voledr.”
Also, at the time t5, the potential of the scan wiring line Sj changes from a high level to a low level, and thus, the transistor T1 turns ON. At this time, as a result of the above-mentioned boosting through C1, the voltage held in the entire driving capacitance unit 111 becomes “Vsig+VthT2+Voledr.” It is preferable that the capacitance value of the capacitor C1 be sufficiently larger than the capacitance values of the capacitors C2 and C3.
Also, at the time t6, the potential of the scan wiring line Sj changes from a low level to a high level, and thus, the transistor T1 turns OFF. Therefore, the supplying of the data voltage Vsig to the driving unit 102 is stopped.
At the time t6a, the potential of the control line Vg4j changes from a high level to a low level, and thus, the transistor T4 turns ON. The entire driving capacitance unit 111 holds a voltage of “Vsig+VthT2+Voledr,” or in other words, the drive voltage is determined by the data voltage Vsig in the driving unit 102, the threshold voltage VthT2 of the transistor T2, and the reverse direction voltage Voledr, and thus, in the present embodiment, the drive current I1 according to the following formula (5) is fed to the organic EL element OLED.
I1=(β½)·(Vsig+Voledr)2 (5)
Unlike the formula (4), the threshold voltage VthT2 is absent in formula (5). Thus, variation in the threshold voltage VthT2 of the transistor T2 is compensated.
According to the present embodiment, the transistor T3 and the capacitor C2, which turn ON in the threshold voltage compensation period TCP are provided, and during the threshold voltage compensation period TCP, the transistors T6 and T8 turn ON. As a result, during the threshold voltage compensation period, the gate terminal and the second conductive terminal of the transistor T2 are electrically connected to each other through the transistors T3, T6, and T8 (forming a diode connection).). As a result, during the threshold voltage compensation period TCP, the threshold voltage VthT2 of the transistor T2 is written to the capacitor C2. Therefore, the threshold voltage VthT2 of the transistor T2 held in the capacitor C2 is used to compensate for the variation in the threshold voltage VthT2 of the transistor T2.
Also, according to the present embodiment, during the initializing period IP, the transistors T6 and T7 are turned ON in addition to the transistor T8. Thus, the first terminal of the capacitor C2 and the reverse bias power source line Vr are electrically connected to each other through the transistors T6 to T8. As a result, the voltage held in the capacitor C2 is initialized to the potential difference of the high level power source potential Vdd and the reverse bias power source potential Vr, which are fixed potentials during the initializing period IP. Therefore, during the threshold voltage compensation period TCP, it is possible to stably write the threshold voltage VthT2 of the transistor T2 to the capacitor C2, and thus, it is possible to stably compensate for the variation in the threshold voltage VthT2 of the transistor T2.
Vr>Vdd>Vss (6)
The gate terminal of the transistor T2 is connected to a second terminal of the capacitor C3, and the second conductive terminal of the transistor T2 is connected to the low level power source line Vss. The gate terminal of the transistor T4 is connected to the control line Vg4j, and the transistor T4 is provided between the first conductive terminal of the transistor T2 and the cathode terminal of the organic EL element OLED. The gate terminal of the transistor T5 is connected to the control line Vg5j, and the transistor T5 is provided between the cathode terminal of the organic EL element OLED and the second terminal of the capacitor C3. The gate terminal of the transistor T6 is connected to a control line Vg6j, and is provided between the first terminal of the capacitor C3 and the first conductive terminal of the transistor T2. The gate terminal of the transistor T7 is connected to a control line Vg7j, and is provided between the first terminal of the capacitor C3 and the reverse bias power source line Vr. The connective relations of the input unit 101 are similar to those of Embodiment 1, and thus, descriptions thereof are omitted.
At time t1a, the potential of the control line Vg4j changes from a low level to a high level. Thus, the transistor T4 turns OFF, and the first conductive terminal of the transistor T2 is electrically separated from the cathode terminal of the organic EL element OLED. Thus, the organic EL element OLED stops emitting light.
At the time t1, the potential of the control line Vg6j changes from a low level to a high level, and the transistor T6 turns OFF. As a result, the first conductive terminal of the transistor T2 is electrically disconnected from the first terminal of the capacitor C3. Also, at the time t1, the potential of the control lines Vg5j and Vg7j changes from a high level to a low level, and thus, the transistors T5 and T7 turn ON. Therefore, the organic EL element OLED becomes reverse biased due to the reverse bias power source potential Vr and the high level power source potential Vdd. As a result, similar to Embodiment 1, a reverse direction voltage Voledr is written to the capacitor C3.
At the time t2, the potential of the control line Vg5j changes from a low level to a high level, and the transistor T5 turns OFF. Thus, reverse biasing of the organic EL element OLED ends. By maintaining the transistor T7 in the ON state, the reverse bias power source potential Vr is applied to the first terminal of the capacitor C3. Also, at the time t2, the potential of the scan wiring line Sj changes from a high level to a low level, and thus, the transistor T1 turns ON. Therefore, the second terminal (gate potential of the transistor T2) of the capacitor C3 is boosted through the capacitor C1, and thus, “Vsig+Voledr” is written to the capacitor C3 in a manner similar to Embodiment 1.
Also, at the time t3, the potential of the control line Vg6j changes from a high level to a low level, and thus, the transistor T6 turns ON. Thus, the capacitor C3 electrically connects the gate terminal and the first conductive terminal of the transistor T2. Also, at the time t3, the potential of the control line Vg7j changes from a low level to a high level, and the transistor T7 turns ON. As a result, the first terminal of the capacitor C3 and the reverse bias power source line Vr are electrically disconnected from each other. Also, at the time t3, the potential of the scan wiring line Sj changes from a low level to a high level, and thus, the transistor T1 turns OFF. Therefore, the supplying of the data voltage Vsig to the driving unit 102 is stopped.
At the time t3a, the potential of the control line Vg4j changes from a high level to a low level, and thus, the transistor T4 turns ON. As a result, in a manner similar to Embodiment 1, the organic EL element OLED is lit according to the value of the drive current I1, which becomes larger as deterioration of the organic EL element OLED progresses over time.
According to the present embodiment, effects similar to Embodiment 1 can be attained using the high level power source potential Vdd, the low level power source potential Vss, and the reverse bias power source potential Vr determined in the formula (6) above.
The gate terminal of the transistor T2 is connected to a second terminal of the capacitor C3, and the second conductive terminal of the transistor T2 is connected to the high level power source line Vdd. The gate terminal of the transistor T4 is connected to the control line Vg4j, and the transistor T4 is provided between the first conductive terminal of the transistor T2 and the anode terminal of the organic EL element OLED. The gate terminal of the transistor T5 is connected to the control line Vg5j, and the transistor T5 is provided between the anode terminal of the organic EL element OLED and the second terminal of the capacitor C3. The gate terminal of the transistor T7 is connected to a control line Vg7j, and is provided between the first terminal of the capacitor C3 and the reverse bias power source line Vr. The connective relations of the input unit 101 are similar to those of Embodiment 1, and thus, descriptions thereof are omitted.
At time t1a, the potential of the control line Vg4j changes from a high level to a low level. Thus, the transistor T4 turns OFF, and the first conductive terminal of the transistor T2 is electrically separated from the anode terminal of the organic EL element OLED. Thus, the organic EL element OLED stops emitting light.
Also, at the time t1, the potential of the control line Vg6j changes from a high level to a low level, and thus, the transistor T7 turns OFF. As a result, the first conductive terminal of the transistor T2 is electrically disconnected from the first terminal of the capacitor C3. Also, at the time t1, the potential of the control lines Vg5j and Vg7j changes from a low level to a high level, and thus, the transistors T5 and T7 turn ON. Therefore, the organic EL element OLED becomes reverse biased due to the low level power source potential Vss and the reverse bias power source potential Vr. As a result, similar to Embodiment 1, a reverse direction voltage Voledr is written to the capacitor C3.
Also, at the time t2, the potential of the control line Vg5j changes from a high level to a low level, and thus, the transistor T5 turns OFF. Thus, reverse biasing of the organic EL element OLED ends. By maintaining the transistor T7 in the ON state, the reverse bias power source potential Vr is applied to the first terminal of the capacitor C3. Also, at the time t2, the potential of the scan wiring line Sj changes from a low level to a high level, and thus, the transistor T1 turns ON. Therefore, the second terminal (gate potential of the transistor T2) of the capacitor C3 is boosted through the capacitor C1, and thus, “Vsig+Voledr” is written to the capacitor C3 in a manner similar to Embodiment 1.
At the time t3, the potential of the control line Vg6j changes from a low level to a high level, and the transistor T6 turns ON. Thus, the capacitor C3 electrically connects the gate terminal and the first conductive terminal of the transistor T2. Also, at the time t3, the potential of the control line Vg7j changes from a high level to a low level, and thus, the transistor T7 turns OFF. As a result, the first terminal of the capacitor C3 and the reverse bias power source line Vr are electrically disconnected from each other. Also, at the time t3, the potential of the scan wiring line Sj changes from a high level to a low level, and thus, the transistor T1 turns OFF. Therefore, the supplying of the data voltage Vsig to the driving unit 102 is stopped.
At the time t3a, the potential of the control line Vg4j changes from a low level to a high level, and the transistor T4 turns ON. As a result, in a manner similar to Embodiment 1, the organic EL element OLED is lit according to the value of the drive current I1, which becomes larger as deterioration of the organic EL element OLED progresses over time.
According to the present embodiment, it is possible to attain effects similar to those of Embodiment 1 using an n channel type transistor.
The gate terminal of the transistor T2 is connected to a second terminal of the capacitor C3, and the first conductive terminal of the transistor T2 is connected to the low level power source line Vss. The gate terminal of the transistor T4 is connected to the control line Vg4j, and the transistor T4 is provided between the second conductive terminal of the transistor T2 and the cathode terminal of the organic EL element OLED. The gate terminal of the transistor T5 is connected to the control line Vg5j, and the transistor T5 is provided between the cathode terminal of the organic EL element OLED and the first terminal of the capacitor C3. The gate terminal of the transistor T6 is connected to a control line Vg6j, and is provided between the first terminal of the capacitor C3 and the first conductive terminal of the transistor T2. The gate terminal of the transistor T7 is connected to a control line Vg7j, and is provided between the second terminal of the capacitor C3 and the reverse bias power source line Vr. The connective relations of the input unit 101 are similar to those of Embodiment 1, and thus, descriptions thereof are omitted.
At time t1a, the potential of the control line Vg4j changes from a high level to a low level. Thus, the transistor T4 turns OFF, and the second conductive terminal of the transistor T2 is electrically separated from the cathode terminal of the organic EL element OLED. Thus, the organic EL element OLED stops emitting light. The operation during the time t2 to t3a is similar to that of Embodiment 6, and thus, descriptions thereof are omitted.
Also, at the time t1, the potential of the control line Vg6j changes from a high level to a low level, and thus, the transistor T7 turns OFF. As a result, the first conductive terminal of the transistor T2 is electrically disconnected from the first terminal of the capacitor C3. Also, at the time t1, the potential of the control lines Vg5j and Vg7j changes from a low level to a high level, and thus, the transistors T5 and T7 turn ON. Therefore, the organic EL element OLED becomes reverse biased due to the reverse bias power source potential Vr and the high level power source potential Vdd. As a result, similar to Embodiment 1, a reverse direction voltage Voledr is written to the capacitor C3.
According to the present embodiment, effects similar to Embodiment 1 can be attained using the high level power source potential Vdd, the low level power source potential Vss, and the reverse bias power source potential Vr, determined in the formula (6) above, and additionally, an n-channel transistor.
The present invention is not limited to the embodiments above, and it is possible to provide various modifications within a range that does not deviate from the gist of the present invention. For example, in the respective embodiments, the voltage corresponding to the initial value of the reverse direction current Ioledr shown in
In Embodiments 3 to 5, the transistor T4 may be of an n-channel type similar to Embodiment 2, with the control line Vg4j being shared between the gate terminal of the transistor T4 and the first conductive terminal of the transistor T7. Also, in Embodiment 6 and 7, the transistor T4 may be of the p-channel type with the control line Vg4j being shared between the gate terminal of the transistor T4 and the first conductive terminal of the transistor T7.
In Embodiments 5 to 7, initialization and/or threshold voltage compensation may be performed. In such a case, at least the threshold voltage compensation unit 122 (transistor T3) is provided between the gate terminal and the second conductive terminal of the transistor T2.
In Embodiments 1 to 3 and 6, the position where the transistor T4 is provided may be modified to be between the high level power source line Vdd (first power source line) and the transistor T2. In Embodiments 5 and 7, the position where the transistor T4 is provided may be modified to between the low level power source line Vss (first power source line) and the transistor T2.
An active matrix display device includes:
a plurality of data wiring lines supplying data signals;
a plurality of scan wiring lines that are each selectively driven;
a first power source line that supplies a first power source potential;
a second power source line that supplies a second power source potential;
a reverse bias control line that supplies a control potential at least during a first prescribed period; and
a plurality of pixel circuits provided at respective intersections between the plurality of data wiring lines and the plurality of scan wiring lines,
wherein each of the pixel circuits includes:
an electrooptical element provided between the first power source line and the second power source line;
a driving unit that controls a current flowing to the electrooptical element, the driving unit including a driving transistor provided between the first power source line and the second power source line and connected in series to the electrooptical element, and a driving capacitance unit that stores a drive voltage for controlling the driving transistor;
an input unit that supplies to the driving unit a voltage of the data signal supplied by a corresponding data wiring line in response to a corresponding scan wiring line being selected;
a compensation unit between the second power source line and the reverse bias control line, the compensation unit supplying to the driving capacitance unit a reverse direction current flowing through the electrooptical element; and
a light emission control transistor provided between the first power source line and the electrooptical element, the light emission control transistor being in an off state during a second prescribed period that includes the first prescribed period, and
wherein the driving unit determines the drive voltage based on at least a voltage of the data signal and the reverse direction current.
According to the display device disclosed in Additional Note A1, the reverse direction current flowing through the electrooptical element (hereinafter referred to as the organic EL element in the additional note descriptions) during reverse bias time is supplied to the driving capacitance unit, and the drive voltage is determined based on the voltage of at least the reverse direction current and the data signal. A forward direction current (drive current) based on this drive voltage is then supplied to the organic EL element. The reverse direction current becomes greater as deterioration over time of the organic EL element progresses. As a result, the drive current also attains a value based on the degree of progression over time of the organic EL element. As a result, luminance compensation occurs based on the progression over time of deterioration of the organic EL element. Furthermore, this luminance compensation occurs during the second prescribed period during which the organic EL element does not emit light. Therefore, prior to the luminance compensation being completed, the organic EL element does not emit light, and therefore, a decrease in luminance in emitted light due to deterioration over time of the organic EL element can be mitigated to a greater degree than in conventional devices.
In the display device according to Additional Note A1,
the second power source potential is lower than the first power source potential, and
the control potential is lower than the second power source potential.
According to such a display device disclosed in Additional Note A2, effects similar to the display device disclosed in Additional Note A1 can be attained by causing a forward direction current (drive current) to flow from the first power source line towards the second power source line, and a reverse direction current to flow from the second power source line towards the reverse bias control line.
In the display device according to Additional Note A1,
the second power source potential is higher than the first power source potential, and
the control potential is higher than the second power source potential.
According to such a display device disclosed in Additional Note A3, effects similar to the display device disclosed in Additional Note A1 can be attained by causing a forward direction current (drive current) to flow from the second power source line towards the first power source line, and a reverse direction current to flow from the reverse bias control line towards the second power source line.
An active matrix display device includes:
a plurality of data wiring lines supplying data signals;
a plurality of scan wiring lines that are each selectively driven;
a first power source line that supplies a first power source potential;
a second power source line that supplies a second power source potential;
a reverse bias control line that supplies a control potential at least during a first prescribed period; and
a plurality of pixel circuits provided at respective intersections between the plurality of data wiring lines and the plurality of scan wiring lines,
wherein each of the pixel circuits includes:
an electrooptical element provided between the first power source line and the second power source line;
a driving unit that controls a current flowing to the electrooptical element, the driving unit including a driving transistor provided between the first power source line and the second power source line and connected in series to the electrooptical element;
an input unit that supplies to the driving unit a voltage of the data signal supplied by a corresponding data wiring line in response to a corresponding scan wiring line being selected;
a compensation unit between the second power source line and the reverse bias control line, the first compensation unit supplying to the driving unit a compensation signal based on a reverse direction current flowing through the electrooptical element; and
a light emission control unit that controls a light emission timing of the electrooptical element such that current is prevented from flowing between the first power source line and the electrooptical element during a second prescribed period that includes the first prescribed period, and
wherein the driving unit determines a drive voltage for controlling the driving transistor in accordance with at least a voltage of the data signal and the compensation signal.
According to such a display device disclosed in Additional Note B1, the compensation signal based on the reverse direction current flowing to the electrooptical element (organic EL element) during reverse bias time is supplied to the driving unit, and the drive voltage is determined by the voltages of at least the compensation signal and the data signal. A forward direction current (drive current) based on this drive voltage is then supplied to the organic EL element. The reverse direction current becomes greater as deterioration over time of the organic EL element progresses. Thus, the compensation signal also attains a value based on the degree of progression over time of deterioration of the organic EL element. As a result, the drive current also attains a value based on the degree of progression over time of the organic EL element. As a result, luminance compensation occurs based on the progression over time of deterioration of the organic EL element. Furthermore, this luminance compensation occurs during the second prescribed period during which the organic EL element does not emit light. Therefore, prior to the luminance compensation being completed, the organic EL element does not emit light, and therefore, a decrease in luminance in emitted light due to deterioration over time of the organic EL element can be mitigated to a greater degree than in conventional devices.
In the display device according to Additional Note B1,
the compensation signal is at a compensation voltage based on the reverse direction current, and
the driving unit determines the drive voltage based on at least a voltage of the data signal and the compensation voltage.
According to such a display device disclosed in Additional Note B2, the compensation voltage based on the reverse direction current is supplied to the driving unit, and the drive voltage is determined based on at least the compensation voltage and the voltage of the data signal. A forward direction current (drive current) based on this drive voltage is then supplied to the organic EL element. The reverse direction current becomes greater as deterioration over time of the organic EL element progresses. Thus, the compensation voltage based on the reverse direction current becomes greater as deterioration over time of the organic EL element progresses. As a result, the drive current also becomes larger as deterioration of the organic EL element progresses over time. As a result effects similar to the display device disclosed in Additional Note B1 can be attained.
In the display device according to Additional Note B2,
the driving unit includes a driving capacitance unit that is provided between a control terminal and a first conductive terminal of the driving transistor and that stores the drive voltage,
the input unit supplies a voltage of the data signal to the driving capacitance unit, and
the compensation unit supplies the compensation voltage to the driving capacitance unit during at least a portion of the first prescribed period.
According to the display device disclosed in Additional Note B3, the drive voltage can be determined using the compensation voltage supplied to the driving capacitance unit.
In the display device according to Additional Note B3,
the compensation unit supplies the reverse direction current to the driving capacitance unit during the first prescribed period, and
the input unit includes an input capacitance element and supplies a voltage of the data signal to the driving capacitance unit through the input capacitance element.
According to the display device disclosed in Additional Note B4, when a reverse direction current is supplied to the driving capacitance unit, the voltage of the data signal is supplied to the driving capacitance unit through the input capacitance element, and thus, the drive voltage can be determined by at least the compensation voltage and the voltage of the data signal. In this manner, it is possible to perform luminance compensation based on the degree of progression of deterioration of the organic EL element.
In the display device according to Additional Note B4,
the driving capacitance unit includes a first driving capacitance element to which the reverse direction current is supplied during the first prescribed period, and
the driving unit further includes a drive voltage application control unit that controls the application of the drive voltage to the driving transistor.
According to the display device disclosed in Additional Note B5, by supplying the reverse direction current to the first driving capacitance element to control the application of the drive voltage using the drive voltage application control unit, luminance compensation based on the degree of progression of deterioration of the organic EL element can be performed.
In the display device according to Additional Note B5, the pixel circuits each further include a pre-processing unit that performs pre-processing on the drive voltage stored in the driving capacitance unit during a pre-processing period that is during the second prescribed period and before the first prescribed period.
According to such a display device disclosed in Additional Note B6, it is possible to perform pre-processing on the drive voltage. Pre-processing includes initialization or threshold voltage compensation.
In the display device according to Additional Note B6, the pre-processing unit includes a first pre-processing unit that causes a short-circuit between both terminals of the first driving capacitance element during a first pre-processing period during the pre-processing period.
According to the display device disclosed in Additional Note B7, by the first pre-processing unit, both terminals of the first driving capacitance element can be electrically connected to each other during the first pre-processing period. Thus, the voltage held in the first driving capacitance element is initialized to 0V. As a result, it is possible to reliably write the compensation voltage to the first driving capacitance element.
In the display device according to Additional Note B7,
the driving capacitance unit further includes a second driving capacitance element provided between the first conductive terminal and a second conductive terminal of the driving transistor,
the pre-processing unit further includes a second pre-processing unit provided between the control terminal and the second conductive terminal of the driving transistor, and
at least the second pre-processing unit causes a short-circuit between the control terminal and the second conductive terminal of the driving transistor during a second pre-processing period during the pre-processing period and after the first pre-processing period.
According to the display device disclosed in Additional Note B8, the control terminal and the second conductive terminal of the driving transistor can be electrically connected to each other (form a diode connection) during the second pre-processing period using at least the second pre-processing unit. Thus, during the second pre-processing period, the threshold voltage of the driving transistor is written to the second driving capacitance element. As a result, it is possible to compensation for variation in the threshold voltage of the driving transistor using the threshold voltage.
In the display device according to Additional Note B8, at least one of the first pre-processing unit, the compensation unit, and the drive voltage application control unit causes a short-circuit between the terminal of the second driving capacitance element and the reverse bias control line.
According to the display device disclosed in Additional Note B9, during the first pre-processing period, a terminal of the second driving capacitance element and the reverse bias control line are electrically connected to each other by at least one of the first pre-processing unit, the compensation unit, and the drive voltage application control unit. Thus, during the first pre-processing period, the voltage held in the second driving capacitance element is initialized to a value based on the control potential. As a result, during the second pre-processing period, it is possible to stably write the threshold voltage of the driving transistor to the second driving capacitance element. Therefore, variation in the threshold voltage of the driving transistor can be stably compensated.
In the display device according to any one of Additional Notes B1 to B9,
the reverse bias control line supplies the control potential during the second prescribed period, and
the light emission control unit is controlled by the reverse bias control line and blocks a current flowing between the first power source line and the electrooptical element when the control potential is supplied to the control line.
According to such a display device disclosed in Additional Note B10, the reverse bias control line is shared between the components in the compensation unit connected to the reverse bias control line and the light emission control unit. Thus, the number of lines can be reduced.
In a method of driving an active matrix display device including: a plurality of data wiring lines supplying data signals; a plurality of scan wiring lines that are each selectively driven; first power source lines that supply a first power source potential; second power source lines that supply a second power source potential; and a plurality of pixel circuits provided at respective intersections between the plurality of data wiring lines and the plurality of scan wiring lines, each of the pixel circuits including: an electrooptical element provided between the first power source line and the second power source line; and a driving unit that controls a current flowing to the electrooptical element, the driving unit having a driving transistor provided between the first power source line and the second power source line and connected in series to the electrooptical element, and a driving capacitance unit that stores a drive voltage for controlling the driving transistor, the method includes:
supplying to the driving unit a voltage of the data signal supplied by a corresponding data wiring line in response to a corresponding scan wiring line being selected;
supplying to the driving unit a compensation signal based on a reverse direction current flowing to the electrooptical element between the second power source line and a reverse bias control line that supplies a control potential at least during a first prescribed period;
determining a drive voltage for controlling the driving transistor by at least a voltage of the data signal and the compensation signal; and
controlling a light emission timing of the electrooptical element to block current flowing between the first power source line and the electrooptical element during a second prescribed period that includes the first prescribed period.
According to such a method for driving a display device disclosed in Additional Note B11, effects similar to the display device disclosed in Additional Note B1 can be attained.
The display device of the present invention has the characteristic of being able to mitigate a decrease in luminance resulting from deterioration over time of the electrooptical element, and thus, it is possible to use the present invention in various types of display devices including electrooptical elements such as organic EL displays.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-123295 | May 2012 | JP | national |
| 2012-256088 | Nov 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/062587 | 4/30/2013 | WO | 00 |
