Patent Grant
9208720
1. Field of the Invention
The present invention relates to an organic EL (electroluminescence) displaying apparatus.
2. Description of the Related Art
An organic EL displaying apparatus is constituted by arranging pixels each having an organic EL element on a substrate in a matrix form. In each pixel, the organic EL element is connected in series to a transistor for driving the organic EL element (hereinafter, called a driving transistor) and a power supply line for supplying power to the organic EL element. Here, Japanese Patent Application Laid-Open No. 2003-122301 discloses a constitution of achieving a satisfactory moving image displaying characteristic by further providing in series a transistor for controlling an emission period (hereinafter, called an emission period controlling transistor) between the power supply line and the organic EL element.
Further, since the organic EL displaying apparatus is a self-emitting displaying apparatus, there is an advantage capable of securing high contrast as compared with a liquid crystal displaying apparatus. Furthermore, several kinds of organic EL displaying apparatuses constituted so that a user can switch over a high-luminance displaying mode and a low-luminance displaying mode according to a kind of image data have been developed. Incidentally, there is a constitution of achieving a low-luminance display by lowering a peak value of luminance. However, since a current-luminance characteristic of the organic EL element is not linear, a complicated system is necessary to make a gamma characteristic constant between the high-luminance displaying mode and the low-luminance displaying mode. On the other hand, U.S. Pat. No. 6,583,775 discloses a constitution of achieving a low-luminance display by shortening an emission period without changing a peak vale of luminance from that in a high-luminance displaying mode.
However, in case of performing driving to control the emission period as disclosed in Japanese Patent Application Laid-Open No. 2003-122301, there is a case where a defective display occurs by a leak current at a time when an emission period controlling transistor is off, for the following reason.
In the driving to control the emission period, a desired gradation display is achieved by emission luminance of the organic EL element in the emission period. In the organic EL displaying apparatus of a voltage write driving type, a data voltage being gradation displaying data is input as a data signal from a data line to the driving transistor of each pixel. The data voltage to be input as the data signal has a voltage value between a minimum gradation displaying data voltage and a maximum gradation displaying data voltage, thereby performing the gradation display.
Further, an emission period and a non emission period are defined by on and off states of the emission period controlling transistor. When resistance at a time when the emission period controlling transistor is off is not sufficiently large, a leak current flows in the organic EL element even in the non emission period in the driving sequence, whereby the organic EL element emits light. When the emission luminance (also, merely called the luminance hereinafter) by the leak current is larger than the luminance in the emission period at the time of the minimum gradation display, light emission which is larger than the luminance in the emission period at the time of the minimum gradation display is superposed in the non emission period. Thus, there is a problem that a defective display such as a luminance variation, black floating at the time of the minimum gradation display, or the like occurs.
The above problem becomes more conspicuous in the constitution, as disclosed in U.S. Pat. No. 6,583,775, of achieving the low-luminance display by shortening the emission period, for the reason that a proportion of the non emission period in the one frame period becomes long. Thus, in this constitution, since a leak emission amount to be superposed further increases, the contrast deteriorates.
In consideration of the above-described conventional problem, the present invention aims to provide an organic EL displaying apparatus which suppresses a defective display caused by a leak current at a time when an emission period controlling transistor is off.
To achieve the above object, the present invention is directed to an organic EL displaying apparatus which is characterized by comprising: a plurality of pixels each of which includes an organic EL element, a driving transistor configured to supply a current according to potential of a gate electrode to the organic EL element, and an emission period controlling transistor connected in series to the organic EL element and the driving transistor and configured to control light emission of the organic EL element in response to a control signal; a data line configured to apply a data voltage according to gradation displaying data to the pixels; and a control line configured to supply the control signal to a gate electrode of the emission period controlling transistor, wherein, in a certain one of the pixels, a resistance Roff
According to the present invention, the luminance obtained by the leak current at the time when the emission period controlling transistor is off in a non emission period does not become larger than the luminance corresponding to the minimum gradation displaying data in an emission period. Therefore, it is possible to suppress that defective display such as a luminance variation, black floating at the time of the minimum gradation display, or the like occurs.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, organic EL displaying apparatuses according to preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, it should be noted that scale sizes of the respective drawings are different from the actuals because respective members in the drawings are properly enlarged and reduced to be easily recognized as necessary.
Further, the organic EL displaying apparatus 1 illustrated in
Furthermore, the organic EL displaying apparatus 1 illustrated in
The control signal is input from a driver IC or the like (not illustrated) to the row controlling circuit 11, and a plurality of control signals P1(1) to P1(m) and P2(1) to P2(m) for controlling the pixel circuits are output from the respective output terminals of the row controlling circuit 11. Here, the control signal P1 is input to the pixel circuit of each row through a control line 111, and the control signal P2 is input to the pixel circuit of each row through the control line 112. In
A video signal is input from the driver IC or the like (not illustrated) to the column controlling circuit 12, and a data voltage Vdata being the gradation displaying data (data signal) according to the video signal is output from each output terminal of the column controlling circuit. The data voltage Vdata output from the output terminal of the column controlling circuit 12 is input to the pixel circuit of each column through the data line 121, and has the voltage value between the minimum gradation displaying data voltage and the maximum gradation displaying data voltage, thereby performing the gradation display.
The pixel circuit illustrated in
It is preferable to provide the storage capacitor 15 as in the present embodiment, for the reason that it is possible to maintain the potential of the gate electrode of the driving transistor 162. Moreover, it is preferable to provide the control line 111 and the selecting transistor 161 as in the present embodiment, for the reason that it is possible to control the supplying of the data voltage by the control line 111 and the selecting transistor 161.
The driving transistor 162 may be an N-type transistor. In this case, it is desirable not to dispose the storage capacitor 15 between the power supply line 13 and the gate electrode of the driving transistor 162, but to dispose it between the grounding line 14 and the gate electrode of the driving transistor 162. Besides, each of the selecting transistor 161 and the emission period controlling transistor 163 may be a P-type transistor.
In the timing chart illustrated in
A period (A) is the program period at the one-prior row of the target row, and is also the period included in the period (D) in the one-prior frame of the target row. In the pixel circuit at the target row, a low-level signal is input to the control line 111, whereby the selecting transistor 161 is set to an off state. Consequently, the data voltage V(i−1) being the gradation displaying data at the one-prior row is not input to the pixel circuit at the i-th row being the target row.
In the period (B), a high-level signal is input to the control line 111 in the pixel circuit at the target row, whereby the selecting transistor 161 is set to an on state. Consequently, the data voltage V(i) being the gradation displaying data at the i-th row is input to the pixel circuit at the i-th row being the target row. Thus, an electric charge corresponding to the input data voltage V(i) is charged to the storage capacitor 15, whereby programming of the gradation displaying data is performed. Further, in this period, a low-level signal is input to the control line 112, whereby the emission period controlling transistor 163 is set to an off state. Consequently, a current is not supplied to the organic EL element 17, whereby the organic EL element 17 does not emit light.
In the period (C), a low-level signal is input to the control line 111 in the pixel circuit at the target row, whereby the selecting transistor 161 is set to an off state. Consequently, the data voltage V(i+1) being the gradation displaying data at the next target row is not input to the pixel circuit at the i-th row being the target row. Further, in this period, a high-level signal is input to the control line 112, whereby the emission period controlling transistor 163 is set to an on state. Consequently, the electric charge charged to the storage capacitor 15 in the period (B) and the current corresponding to the potential of the gate electrode of the driving transistor 162 are supplied to the organic EL element 17, whereby the organic EL element 17 emits light with the luminance of gradation according to the supplied current.
In the period (D), a low-level signal is input to the control line 112 in the pixel circuit at the target row, whereby the emission period controlling transistor 163 is set to an off state. Consequently, a current is not supplied to the organic EL element 17, whereby the organic EL element 17 does not emit light.
As described above, in the driving sequence of the organic EL displaying apparatus 1 according to the present embodiment, since the on state and the off state of the emission period controlling transistor 163 are controlled in response to the control signal P2 supplied on the control line 112, the emission period of the organic EL element 17 is controlled. Incidentally, in the present invention, driving for performing emission period controlling implies driving having a non emission period (period (D) in the above example) other than a period (period (B) in the above example) in which programming of a target row is performed in a driving sequence.
The first electrodes 171 are separately formed for the respective pixels. In
Although not illustrated, a sealing structure for protecting the organic EL element 17 from moisture and oxygen may be formed on the second electrode 173. As the sealing structure, it is possible to use a structure that a protection layer of a single layer or laminated plural layers is provided, a structure that a sealing member consisting of a glass substrate, a sealing cap or the like is provided, or a structure that the sealing member is provided on the protection layer.
The constitution of the organic EL displaying apparatus 1 illustrated in
Incidentally, a driving circuit which is suitably used in the organic EL displaying apparatus 1 in the present embodiment is constituted so as to satisfy the following expression (1) or (2) in the driving sequence as illustrated in
Roff
Ileak≦Ibk (2)
The symbol Roff
The symbol Ileak indicates the value of the leak current flowing in the organic EL element in a state that the data voltage (maximum gradation displaying data voltage) for flowing the current according to the maximum gradation in the organic EL element is applied to the gate electrode of the driving transistor 162 and in the non emission period in which the emission period controlling transistor 163 is off. The symbol Ibk indicates the value of the current flowing in the organic EL element in the state that the minimum gradation displaying data voltage is applied to the gate electrode of the driving transistor 162 and in the emission period in which the emission period controlling transistor 163 is on.
In the present embodiment, since the driving circuit satisfies the above expression (1) or (2), the emission luminance of the organic EL element by the leak current at the time when the emission period controlling transistor 163 is off is not larger than luminance (hereinafter, called minimum gradation luminance Lbk) corresponding to the minimum gradation displaying data in the emission period, even in case of performing the driving to control the emission period. Therefore, the light emission which is larger than the minimum gradation luminance in the emission period is not superposed in the non emission period, whereby it is possible to suppress that a luminance variation occurs.
Subsequently, the reason why the occurrence of the luminance variation can be suppressed by satisfying the above expression (1) or (2) will be described with reference to
More specifically, (1) of
It should be noted that, in the following description, the one frame period in which the minimum gradation displaying data is programmed in the program period of the target pixel may be called a minimum gradation displaying time, and the one frame period in which the maximum gradation displaying data is programmed in the program period of the target pixel may be called a maximum gradation displaying time.
The resistance between the source electrode and the drain electrode of the driving transistor 162 in the states of (1) and (2) of
In the state of (1) of
In the state of (2) of
In the state of (3) of
In the state of (4) of
Since the state of (1) of
Consequently, when the above expression (1) is satisfied, then the above expression (2) can be satisfied. Generally, a current-luminance characteristic of the organic EL element has a positive correlation. Therefore, when it can be confirmed that either the above expression (1) or (2) is satisfied in a certain pixel, it is said that the maximum gradation leak luminance Lleak is controlled to be equal to or smaller than the minimum gradation luminance Lbk in the relevant certain pixel. Incidentally, in a defective pixel which includes a defective transistor or the like produced in a manufacturing process, there is a case where either the above expression (1) or (2) is satisfied. However, in the present invention, the relevant defective pixel is not considered as the target, but only a normal pixel is considered as the target.
Here, the defective pixel will be defined as follows. That is, the same gradation displaying data is programmed to all the pixels within the displaying region, a proportion of the emission period in the periods other than the program period in the one frame period is set to t, and the organic EL displaying apparatus is driven so as to satisfy 0<t≦1. Here, average luminance in the one frame period of the average luminance in the displaying region obtained by measuring the luminance of the overall displaying region is set to Lmean. At this time, when the average luminance in the one frame period of a certain pixel is equal to or smaller than 0.8 Lmean or equal to or larger than 1.2 Lmean, the relevant certain pixel is defined as the defective pixel. This is because the pixel of which the luminance is within a range of 0.8 Lmean or smaller or a range of 1.2 Lmean or higher impairs uniformity in the displaying region. Namely, it should be noted that the normal pixel is the pixel which does not correspond to the defective pixel. Incidentally, it should be noted that the average luminance in the one frame period can be obtained by dividing the accumulated luminance in the one frame period by the time of the one frame period, and that the accumulated luminance is the value which is obtained by temporarily integrating the emission luminance of the organic EL element for the one frame period.
Incidentally, the luminance of the displaying region and the luminance of the pixel are measured in the following manner. Namely, a measuring range is first set on the overall displaying region or the partial pixel by using a luminance measuring unit. Then, when the organic EL displaying apparatus is driven in this state, the luminance on the overall displaying region or the partial pixel can be measured by the luminance measuring unit at each timing in the driving sequence or in the predetermined period. In any case, for example, a measuring unit in which a photosensor and an oscilloscope are mutually connected to each other can be used as the luminance measuring unit.
Concretely, the defective pixel includes a black-spot pixel in which the organic EL element does not emit light even in the emission period, a bright-spot pixel in which the organic EL element emits light with luminance (e.g., luminance equal to or higher than the maximum gradation luminance) higher than that of the normal pixel even at the minimum gradation displaying time or in the non emission period, and the like. In the black-spot pixel, when the maximum gradation displaying data is programmed as an example to all the pixels within the displaying region, the proportion t of the emission period in the periods other than the program period in the one frame period is set to 0.7, and the organic EL displaying apparatus is driven, then the luminance is equal to or smaller than 0.8 of the average luminance Lmean in the displaying region. Thus, the black-spot pixel corresponds to the defective pixel. Besides, in the bright-spot pixel, when the minimum gradation displaying data is programmed as an example to all the pixels within the displaying region, the proportion t of the emission period in the periods other than the program period in the one frame period is set to 0.7, and the organic EL displaying apparatus is driven, then the luminance is equal to or higher than 1.2 Lmean in the displaying region. Thus, the bright-spot pixel corresponds to the defective pixel.
More specifically, the black-spot pixel is generated when short circuit between the first electrode and the second electrode, lack of the partial wiring in the circuit element layer, or the like occurs due to contamination of a foreign matter in the manufacturing process. Besides, the bright-spot pixel is generated when short circuit among the partial wirings in the circuit element layer, short circuit between the gate electrode and the activate layer, the source electrode or the drain electrode of the transistor, or the like occurs due to contamination of a foreign matter in the manufacturing process.
In the driving for the emission period control, the gradation display is performed based on the emission luminance of the organic EL element in the emission period (C), and each gradation is set as the luminance between the minimum gradation luminance and the maximum gradation luminance based thereon. Incidentally, in the driving for the emission period control, the average luminance obtained by dividing the accumulated luminance in the one frame period by the time of the one frame period is viewed as brightness by an observer. In the organic EL displaying apparatus 1 of the present embodiment, since the emitted light of the leak luminance larger than the minimum gradation luminance being the basis for setting the gradation in the non emission period (D) is not superposed on the emitted light in the emission period (C), it is possible to suppress a luminance variation at the maximum gradation displaying time.
Further, in the above description, only the minimum gradation luminance and the leak current flowing in the organic EL element in the period (D) in the case where the maximum gradation displaying data voltage is being applied to the gate electrode of the driving transistor 162 are compared with each other. In the case where the data voltage for displaying the gradation lower than the maximum gradation is being applied, the resistance between the source electrode and the drain electrode of the driving transistor 162 is larger than Rwh
As just described, in the present embodiment, even when the driving for the emission period control is performed, the leak luminance at the time when the emission period controlling transistor in the non emission period is off does not come to be larger than the minimum gradation luminance in the emission period. Therefore, it is possible to suppress that a luminance variation occurs.
A concrete example of the organic EL displaying apparatus 1 according to the first embodiment will be described hereinafter. Here, it should be noted that the present invention is not limited to the following examples. Moreover, it should be noted that the present invention is not limited by the polarities or the sizes of the transistors, the pixel arrangements, the pixel pitches, or the like, used in the following examples.
In this example, in the pixel circuit illustrated in
In this example, the two-dimensional arrangement of the pixels 100 illustrated in
The current value to be supplied to the organic EL element of each pixel in the emission period at the maximum gradation displaying time was set to 5×10−7 A, and the gradation displaying data was set so that the contrast in the case where the proportion t (0<t≦1) of the emission period in the periods other than the program period in the one frame period was 1 was 100000:1. Here, the contrast indicates the ratio of the accumulated luminance at the maximum gradation displaying time to the accumulated luminance at the minimum gradation displaying time, and such a definition will be available hereafter.
In this example, under such a design condition, the organic EL displaying apparatus 1 including the driving transistor 162 having its channel length L1 of 24 μm and its channel width W1 of 10 μm and the emission period controlling transistor 163 having its channel length L2 of 4 μm and its channel width W2 of 2.5 μm was manufactured in consideration of the above expression (1) or (2).
As illustrated in
The completed organic EL displaying apparatus 1 was driven according to the driving sequence condition illustrated in
Then, it was evaluated whether or not the completed organic EL displaying apparatus 1 satisfied the expression (2). More specifically, the current value flowing in the organic EL element 17 in a red pixel 100a (R) arbitrarily selected from among the pixels 100 in the displaying region 10 was measured. Since the same pixel circuit was used to all the pixels and driven in the same manner, the color of the pixel to be evaluated may be another color.
Here, a method of measuring the current value flowing in the organic EL element included in a pixel 100a will be described with reference to
First, as illustrated in
Subsequently, as illustrated in
First, the minimum gradation displaying data voltage was programmed to the pixel 100a (R) in the period (B) of
Subsequently, the maximum gradation displaying data voltage was programmed to the pixel 100a (R) in the period (B). Then, the voltage of 0V was applied as a low level signal to the control line 112 of the pixel 100a (R) in the period (D). At this time, when the current Ileak flowing in the organic EL element 17 of the pixel 100a (R) in the period (D) was measured, the current value of 5.4×10−13 A was obtained. Incidentally, the measuring timing may be set as arbitrary one timing in the period (D). Alternatively, the average current value in a predetermined period included in the period (D) may be set to Ileak.
As a result of the measurement, Ileak=5.4×10−13 A≦Ibk=5×10−12 A was obtained in the pixel 100a (R) included in the organic EL displaying apparatus 1 in this example, and this satisfied the above expression (2). Therefore, in the pixel 100a (R), even in case of performing the driving for controlling the emission period, the emission luminance of the organic EL element due to the leak current at the off time of the emission period controlling transistor 163 in the non emission period was not higher than the minimum gradation luminance in the emission period, whereby the occurrence of the luminance variation could be suppressed in the pixel 100a (R).
In the organic EL displaying apparatus 1 of the present embodiment, the current value flowing in the organic EL element 17 in each of other red pixels 100a (R) was measured in the same manner as described above, all the measured pixels satisfied the above expression (2). Since the pixel circuit same as that in the red pixel is used to the blue pixel and the green pixel, the occurrence of the luminance variation can be suppressed for the pixels of all the colors.
When the luminance of the organic EL element included in the pixel 100a (R) was measured actually, the maximum gradation leak luminance Lleak was smaller than the minimum gradation luminance Lbk. Subsequently, a method of measuring the luminance of the organic EL element included in a pixel 100a will be described. First, the range to be measured is set in the pixel 100a by using the luminance measuring unit. In this state, when the organic EL displaying apparatus 1 is driven according to the driving sequence illustrated in
Incidentally, the luminance may be measured before the second electrode 173a on the pixel 100a and the second electrode 173 on the pixels 100b are electrically separated from each other. Even in this case, when the organic EL displaying apparatus 1 is driven according to the driving sequence illustrated in
(Modification of Example 1)
This modification is different from Example 1 in the point that the current flowing in the organic EL element is not evaluated for each pixel but the current flowing in the organic EL element of the pixel 100 is evaluated for each row. More specifically, it is evaluated whether or not a sum total Ibk
Ileak
First, as well as Example 1, the organic EL displaying apparatus 1 was manufactured. Then, the wiring 190 including the power supply line 13 and the grounding line 14 of the manufactured organic EL displaying apparatus 1 was connected to a driving unit 19′ through the flexible printed substrate 191, as illustrated in
A method of measuring the sum total of the current values flowing in the organic EL elements of all the pixels within the displaying region in this modification will be described with reference to
As illustrated in
In this sum total measuring method, for all the rows, the minimum gradation displaying data voltage was programmed to each pixel included in each row in the period (B) of each row, and the voltage of 12V was applied as a high level signal to the control line 112 of each row in the period (C) of each row. At this time, when a sum total I1 of the current values flowing in the organic EL elements 17 of all the pixels 100 within the displaying region 10 in the period (C) at an arbitrarily selected measurement-target row (k-th row) was measured, the current value of 34.1×10−7 A was obtained. In this modification, k=50 was set. In any case, although k=50 was set, k may be a natural number which satisfies k≦480 in this modification. Incidentally, the measuring timing may be set as arbitrary one timing in the period (C) at the k-th row.
Moreover, in the period (B) of each row, the maximum gradation displaying data voltage was programmed to each pixel included in the k-th row, and the minimum gradation displaying data voltage was programmed to each pixel included in each of all the rows other than the k-th row. Then, in the period (D) of each row, the voltage of 0V was applied as a low level signal to the control line 112 of each row. At this time, when a sum total I2 of the current values flowing in the organic EL elements 17 of all the pixels 100 within the displaying region 10 in the period (D) at the k-th row was measured, the current value of 34.0×10−7 A was obtained. Incidentally, the measuring timing may be set as arbitrary one timing in the period (D) at the k-th row.
Therefore, sum total I2=34.0×10−7 A≦sum total I1=34.1×10−7 A was obtained in this modification.
Here, the sum total of the currents flowing in the respective pixels included in all the rows other than the k-th row at the I1 measuring time is equal to that at the I2 measuring time, a difference between the sum totals I1 and I2 of the current values corresponds to a difference between the sum total Ibk
Therefore, the relation of the expression (2)′ was satisfied in this modification. When the sum total Ibk
Further, the evaluation may be performed to the plurality of continuous rows by performing the same measurement. More specifically, it is evaluated whether or not a sum total Ibk
Ileak
By the measuring method like this, it is possible to enlarge the value of the difference between these two currents and thus make the magnitude relation comparison easy.
A method of measuring the difference between the sum totals of the currents Ibk and Ileak for the continuous q rows, in the same manner as that of measuring the difference for the one row, will be described. Namely, for all the rows, the minimum gradation displaying data voltage is programmed to each pixel included in each row in the period (B) of each row in the driving sequence, and a high level signal is applied to the control line 112 of each row in the period (C) of each row. At this time, a sum total I1′ of the current values flowing in the organic EL elements 17 of all the pixels 100 within the displaying region 10 is measured for the arbitrarily selected measurement-target continuous rows from the k-th row to the (k+q−1)-th row at arbitrary timing in the period in which the high level signal is being applied to the control lines 112 of all of these rows.
Further, in the period (B) of each row, the maximum gradation displaying data voltage is programmed to each pixel of each of the plurality of measurement-target continuous rows from the k-th row to the (k+q−1)-th row, and the minimum gradation displaying data voltage is programmed to each pixel of each of all the rows other than the rows from the k-th row to the (k+q−1)-th row. Then, in the period (D) of each row, a low level signal is applied to the control line 112 of each pixel of each row. At this time, a sum total I2′ of the current values flowing in the organic EL elements 17 of all the pixels 100 within the displaying region 10 is measured at arbitrary timing in the period in which the low level signal is being applied to the control lines 112 of all the continuous rows from the k-th row to the (k+q−1)-th row.
A difference between the sum totals I1′ and I2′ of the current values thus measured corresponds to a difference between the sum total Ibk
By doing so, the difference between the sum total of the current Ibk and the sum total of the current Ileak of the q rows can be measured.
Incidentally, with respect to the above-described continuous q rows from the k-th row to the (k+q−1)-th row, the period in which the high level signal is being applied to the control lines 112 of all of these rows is present in a case where the following expression (3) is satisfied.
q/m<t (3)
Further, with respect to the continuous q rows from the k-th row to the (k+q−1)-th row, the period in which the low level signal is being applied to the control lines 112 of all of these rows is present in a case where the following expression (4) is satisfied.
q/m<(1−t) (4)
Here, in the expressions (3) and (4), m is a natural number indicating the number of all the rows within the displaying region of the organic EL displaying apparatus, and q is a natural number indicating the number q of the plurality of continuous rows for which the difference between the sum total of the current Ibk and the sum total of the current Ileak respectively flowing in the organic EL element 17 is measured. Moreover, t is a real number indicating the proportion t (0<t≦1) of the emission period in the periods other than the program period in the one frame period.
For the organic EL displaying apparatus 1 as well as Example 1, q=100 was set, and the difference between the sum total of the current Ibk and the sum total of the current Ileak of the 100 rows from the arbitrarily selected k-th (=50) row was measured by the above-described method. The manufactured organic EL displaying apparatus 1 has m=480, and q=100 and t=0.7 here. Thus, the above expressions (3) and (4) are satisfied. Consequently, the period in which the high level signal is being applied to the control lines 112 of all of the continuous q rows from the k-th row to the (k+q−1)-th row and the period in which the low level signal is being applied to the control lines 112 of all of these rows are present. Incidentally, the high level signal to be applied to the control line 112 in the period (C) of each row was set to 12V, and the low level signal to be applied to the control line 112 in the period (D) of each row was set to 0V. At this time, the sum total I1′ of the currents Ibk flowing in the organic EL elements 17 of all the pixels 100 within the displaying region 10 was 36.6×10−7 A, and the sum total I2′ of the currents Ileak flowing in the organic EL elements 17 of all the pixels 100 within the displaying region 10 was 28.0×10−7 A. Therefore, in this modification, the sum total Ibk
Further, the sum total Ibk
Incidentally, the average luminance, for each row or the plurality of rows, of the luminance of the organic EL element included in each pixel can be likewise measured by setting the measuring range of the luminance measuring unit to each row or the plurality of rows in the luminance measuring method in Example 1.
This comparative example is an example that the selecting transistor 161 is an N-type transistor, the driving transistor 162 is a P-type transistor, and the emission period controlling transistor 163 is an N-type transistor. The organic EL displaying apparatus including the driving transistor 162 having its channel length of 24 μm and its channel width of 10 μm and the emission period controlling transistor 163 having its channel length of 4 μm and its channel width of 25 μm was manufactured. The wiring connection construction and the like of the organic EL displaying apparatus in this comparative example are the same as those of the organic EL displaying apparatus in Example 1 except for the emission period controlling transistor 163.
The organic EL displaying apparatus was driven according to the same driving sequence condition as that in Example 1, and the current value flowing in an organic EL element 17 of a red pixel 100a′ (R) (not illustrated) arbitrarily selected from the plurality of pixels 100 within the displaying region 10 was measured in the method described in Example 1. More specifically, when the current Ibk flowing in the organic EL element 17 of the pixel 100a′ (R) in the period (C) was measured, the current value of 5×10−12 A was obtained. Moreover, when the current Ileak flowing in the organic EL element 17 of the pixel 100a′ (R) in the period (D) was measured, the current value of 5.8×10−12 A was obtained.
In the organic EL displaying apparatus of this comparative example, the current Ileak was large as compared with Example 1 due to the size of the emission period controlling transistor 163 different from that in Example 1, whereby the above expression (2) was not satisfied in the pixel 100a′ (R). Moreover, when the current value flowing in the organic EL element 17 was measured for other plurality of pixels 100 (R) in the same manner as that described above in the organic EL displaying apparatus of this comparative example, the above expression (2) was not satisfied in all of the measured pixels.
When the currents Ileak and Ibk do not satisfy the above expression (2), it can be said that the emission luminance (leak luminance) of the organic EL element due to the leak current in the non emission period of the period (D) is larger than the minimum gradation luminance in the emission period. In the driving for the emission period control, the gradation display is performed based on the emission luminance of the organic EL element in the emission period. Consequently, in the pixel in which the leak luminance is larger than the minimum gradation luminance, the emitted light of the organic EL element at the leak luminance larger than the minimum gradation luminance being the basis of the gradation setting in the non emission period is superposed to the emitted light in the emission period. Actually, the gradation display could not be performed correctly in this pixel, and the luminance variation occurred.
In the organic El displaying apparatus according to the first embodiment, another concrete example different from Example 1 will be described. The organic EL displaying apparatus in this example is the same as the organic EL displaying apparatus in Example 1 except that the polarities of the selecting transistor 161 and the emission period controlling transistor 163 in the pixel are the P type and the contrast is set to 10000:1.
In the pixel circuit constitution illustrated in
The manufactured organic EL displaying apparatus was driven according to the driving sequence condition illustrated in
In the period (B), the minimum gradation displaying data voltage was programmed to the pixel 100a (R). Then, in the period (C), the voltage of 0V was applied as a low level signal to the control line 112 connected to the pixel 100a (R). At this time, the current Ibk flowing in the organic EL element 17 of the pixel 100a (R) was measured in the period (C), the current value of 5×10−11 A was obtained. Moreover, in the period (B), the maximum gradation displaying data voltage was programmed to the pixel 100a (R). Then, in the period (D), the voltage of 12V was applied as a high level signal to the control line 112 connected to the pixel 100a (R). At this time, the current Ileak flowing in the organic EL element 17 of the pixel 100a (R) was measured in the period (D), the current value of 2.0×10−11 A was obtained.
Therefore, in the organic EL displaying apparatus in this example, the above expression (2) was satisfied in the pixel 100a (R). Consequently, the emission luminance of the organic EL element by the leak current at the time when the emission period controlling transistor 163 in the non emission period was off was not larger than the minimum gradation luminance in the emission period, even in case of performing the driving to control the emission period. Thus, the occurrence of the luminance variation in the pixel 100a (R) could be suppressed.
Subsequently, a more appropriate constitution in the organic EL displaying apparatus of the first embodiment which can switch over a high-luminance displaying mode and a low-luminance displaying mode to each other by changing the length of the emission period (C) using the emission period controlling transistor will be described.
In the organic EL displaying apparatus of this example, the mode switchover is performed by changing the length of the emission period, without changing the peak value of the luminance in the emission period between the high-luminance displaying mode and the low-luminance displaying mode. More specifically, the low-luminance displaying mode is achieved by shortening the emission period. In this case, as the proportion of the non emission period in the one frame period is prolonged by shortening the emission period, the luminance variation due to the superposition of the leak luminance in the non emission period becomes more conspicuous. Moreover, since the superposed leak luminance increases, a problem of deterioration of the contrast occurs.
Hereinafter, the deterioration of the contrast will be described in detail. Here, as described above, the contrast indicates the ratio between the accumulated luminance at the maximum gradation displaying time and the accumulated luminance at the minimum gradation displaying time.
In the one frame period, the proportion of the emission period in the periods other than the program period is defined as t (0<t≦1). With respect to the organic EL displaying apparatus which has the same constitution but of which the value of t has been changed, degree of the deterioration of the contract in case of t<1 in regard to the contrast in case of t=1 will be concretely described. Since the power supply voltage (i.e., the voltage between the power supply line potential Vcc and the grounding line potential Vocom) is common to these organic EL displaying apparatuses respectively having the different values of t, the emission luminance corresponds to the current value by the current-luminance characteristic of the organic EL element. Moreover, in the current and voltage regions within the range used in this example, since the current-luminance characteristic of the organic EL element is approximately linear, the accumulated luminance ratio indicating the contrast and a total current-carrying amount ratio are approximately coincident with each other. Consequently, in what follows, the degree of the deterioration of the contrast in case of t<1 in regard to the contrast in case of t=1 will be described by using the ratio between the total current-carrying amount to the organic EL element at the maximum gradation displaying time and the total current-carrying amount to the organic EL element at the minimum gradation displaying time. Moreover, in the driving sequence illustrated in
When the total current-carrying amounts to the organic EL element in the one frame period at the maximum gradation displaying time and the minimum gradation displaying time are respectively represented by Swh and Sbk, Swh and Sbk are respectively represented by the following expressions (5) and (6).
Swh=Iwh×t+Ileak×(1−t) (5)
Sbk=Ibk×t+Ibk
It should be noted that the definitions of Iwh, Ibk, Ileak, Ibk
Here, the organic EL displaying apparatus having Iwh of 5×10−7 A and Ibk of 5×10−12 A, manufactured in Example 1, is considered. The contrast in case of t=1 in this apparatus is Swh/Sbk=Iwh/Ibk=100000, from the above expressions (5) and (6).
On the other hand, the approximate values of the contrasts in a case where the values of Ileak and t are changed are represented by Table 1 below. Here, Ileak and the resistance Roff
Vcc−Vocom=(Rwh
It should be noted that the expression (7) is the relational expression of the voltage drop on the wiring route between the power supply line and the grounding line in the pixel circuit in the non emission period at the maximum gradation displaying time in the state (4) of
In t<1, even if Ileak has any value, the contrast deteriorates due to the superposition of the leak current at the non emission time, as compared with t=1. However, in consideration of human sensitivity (visibility), it is desirable to have the contrast equal to or higher than 70% of the contrast in t=1. Therefore, it can be understood from Table 1 that it is desirably for Ileak to have a value equal to or lower than 1×10−12 A in t=0.5, have a value equal to or lower than 5×10−13 A in t=0.25, and have a value equal to or lower than 1×10−13 A in t=0.05. In t=0.7, it is possible for the organic EL displaying apparatus satisfying the above expression (2) to secure the contrast equal to or higher than 70%. This can be expressed by the following expression (8). Namely, when the organic EL displaying apparatus in the first embodiment is set to have the constitution that the high-luminance displaying mode and the low-luminance displaying mode can be switched over by a user according to a kind of image data, it is desirable that the value of Ileak satisfies the relation of the following expression (8), in regard to the proportion t (0<t≦1) of the emission period in the one frame period.
{Iwh×t+Ileak×(1−t)}/{Ibk×t+Ibk
In this way, even when the low-luminance display is performed by shortening the emission period in the organic EL displaying apparatus in the first embodiment, it is possible to achieve the high-contrast and satisfactory display. Thus, it is more preferable. Incidentally, Swh and Sbk can be measured for the one frame period by using the current measuring method described in Example 1 or Modification of Example 1. Also, Iwh, Ileak, Ibk and Ibk
Initially, the constitution of the organic EL displaying apparatus and the driving sequence will be described. Here, in the organic EL displaying apparatus of the present embodiment, the parts same as or corresponding to those in the organic EL displaying apparatus of the first embodiment illustrated in
A plurality of control signals P1(1) to P1(m), P2(1) to P2(m), and P3(1) to P3(m) for controlling the operations of the pixel circuits are output from the respective output terminals of the row controlling circuit 11. Here, the control signal P1 is input to the pixel circuit of each row through a control line 111, the control signal P2 is input to the pixel circuit of each row through a control line 112, and the control signal P3 is input to the pixel circuit of each row through a control line 113. In
A video signal is input from the driver IC or the like (not illustrated) to the column controlling circuit 12, and a data voltage Vdata being the gradation displaying data (data signal) according to the video signal is output from each output terminal of the column controlling circuit. Moreover, a reference voltage Vsl is output from each output terminal. The data voltage Vdata and the reference voltage Vsl output from the output terminal of the column controlling circuit 12 are input to the pixel circuit of each column through a data line 121. Here, the data line 121 for supplying the data voltage may be provided separately from a reference voltage line for supplying the reference voltage, and the wiring connections of these lines may be switched over.
The pixel circuit illustrated in
Here, each of the selecting transistor 161, the emission period controlling transistor 163 and the erasing transistor 264 is an N-type transistor, and the driving transistor 162 is a P-type transistor. The selecting transistor 161 is disposed so that its gate electrode is connected to the control line 111, its drain electrode is connected to the data line 121, and its source electrode is connected to the storage capacitor 15. The erasing transistor 264 is disposed so that its gate electrode is connected to the control line 113, one of its source and drain electrodes is connected to the gate electrode of the driving transistor 162, and the other of its source and drain electrodes is connected to the drain electrode of the driving transistor 162 and the drain electrode of the emission period controlling transistor 163. The driving transistor 162 is disposed so that its source electrode is connected to a power supply line 13, and its drain electrode is connected to one of the source and drain electrodes of the erasing transistor 264 and the drain electrode of the emission period controlling transistor 163. The emission period controlling transistor 163 is disposed so that its gate electrode is connected to the control line 112, and its source electrode is connected to the anode of the organic EL element 17. The cathode of the organic EL element 17 is connected to a grounding line 14. The storage capacitor 15 is disposed among the selecting transistor 161, the gate electrode of the driving transistor 162, and one of the source and drain electrodes of the erasing transistor 264.
It is preferable to provide the storage capacitor 15 as in the present embodiment, for the reason that it is possible to maintain the potential of the gate electrode of the driving transistor 162. Further, it is preferable to provide the control line 111 and the selecting transistor 161 as in the present embodiment, for the reason that it is possible to control the supplying of the data voltage by the control line 111 and the selecting transistor 161. Furthermore, it is preferable to provide the control line 113 and the erasing transistor 264 as in the present embodiment, for the reason that it is possible to reduce an adverse effect of variation of a threshold voltage of the driving transistor on the displaying characteristic by the control line 113 and the erasing transistor 264.
Each of the driving transistor 162, the emission period controlling transistor 163 and the erasing transistor 264 may be a P-type transistor.
In the timing chart illustrated in
After the pixels of all the rows were programmed in the program period, the pixels of all the rows simultaneously emit light in the emission period, and simultaneously black out in the non emission period. Here, the emission period is the period in which the organic EL elements of the pixels of all the rows including the pixel of the target row emit light, and the non emission period is the period in which the organic EL elements of the pixels of all the rows including the pixel of the target row are controlled not to emit light. The emission period and the non emission period are defined by on and off states of the emission period controlling transistor. Incidentally, a ratio of the emission period and the non emission period subsequent to the program period in the one frame period may arbitrarily be set. In the drawing, symbols V(i−1), V(i) and V(i+1) indicate the data voltages Vdata to be input respectively to the pixel circuits at the (i−1)-th row (one-prior row of target row), the i-th row (target row) and the (i+1)-th row (one-posterior row of target row) in the one frame period, on the target column.
(A) Another-Row Program Period (Prior to Target Row)
In this period, a low-level signal is input to each of the control lines 111 and 113 in the pixel circuit at the target row, whereby each of the selecting transistor 161 and the erasing transistor 264 is set to an off state. Consequently, the data voltage V(i−1) being the gradation displaying data at the one-prior row is not input to the pixel circuit at the i-th row being the target row. During this period, in the pixel at the target row, the gradation displaying data programmed in the immediately previous frame period is held in the storage capacitor 15 until the program period of the target row starts. At this time, the off state of the emission period controlling transistor 163 is maintained.
(B) Discharge Period
In this period, a high-level signal is input to each of the control lines 111 to 113 in the pixel circuit at the target row, whereby each of the selecting transistor 161, the erasing transistor 264 and the emission period controlling transistor 163 is set to an on state. Consequently, the data voltage V(i) being the gradation displaying data of the target row is set to the data line 121, and the data voltage V(i) is input to the side of the data line 121 of the storage capacitor 15. Moreover, each of the erasing transistor 264 and the emission period controlling transistor 163 comes to an on state. Thus, the gate electrode of the driving transistor 162 and the grounding line 14 are connected to each other through the organic EL element 17. Consequently, the potential of the gate electrode of the driving transistor 162 comes to have a potential close to grounding line potential Vocom irrespective of the potential in the immediately preceding state, and the driving transistor 162 comes to an on state.
(C) Program Period
In this period, a low-level signal is input to the control line 112, whereby the emission period controlling transistor 163 is set to an off state. Consequently, a current flows from the drain electrode to the gate electrode in the driving transistor 162, whereby the gate-source voltage of the driving transistor 162 comes close to a threshold voltage of the driving transistor 162. The gate voltage of the driving transistor 162 at this time is input to the side of the storage capacitor 15 which is connected to the gate electrode of the driving transistor. Moreover, the data voltage V(i) being the gradation displaying data of the corresponding row is still set to the data line 121 from the period (B), and the data voltage V(i) is input to the side of the data line 121 of the storage capacitor 15. Consequently, an electric charge corresponding to a voltage of a difference between the gate voltage of the driving transistor 162 and the data voltage V(i) is charged to the storage capacitor 15, whereby the gradation displaying data voltage is programmed.
(D) Another-Row Program Period (Posterior Row of Target Row)
In this period, a low-level signal is input to each of the control lines 111 and 113, whereby each of the selecting transistor 161 and the erasing transistor 264 is set to an off state. Consequently, even when the voltage of the data line 121 changes to the data voltage V(i+1) being the gradation displaying data concerning the posterior row, the electric charge charged to the storage capacitor 15 in the period (C) is held. The pixel of the target row is on standby with this state until the program of another row is completed. At this time, the off state of the emission period controlling transistor 163 is maintained.
(E) Emission Period
In this period, a high-level signal is input to the control lines 111 of all the rows, whereby the selecting transistors 161 included in the pixel circuits of all the rows are set to an on state. Then, a reference voltage Vsl is set to the data lines of all the columns. Consequently, the reference voltage Vsl is input to the side of the data line 121 of the storage capacitor 15. Since the erasing transistor 264 is in an off state in this period, the electric charge charged to the storage capacitor 15 in the period (C) is held. Therefore, the gate voltage of the driving transistor 162 changes by a difference between the data voltage V(i) and the reference voltage Vsl.
After then, a high-level signal is input to the control line 111 in the period (E) and the period (F), and a low-level signal is input to the control line 113 in the period (E) and the period (F). Consequently, the on state of the selecting transistor 161 and the off state of the erasing transistor 264 are maintained in the period (E) and the period (F), whereby the gate voltage of the driving transistor 162 is maintained constant during these periods.
Moreover, in this period, a high-level signal is input to the control line 112, whereby the emission period controlling transistor 163 is set to an on state. Consequently, a current according to the potential of the gate electrode of the driving transistor 162 is supplied to the organic EL element 17, whereby the organic EL element 17 emits light with the gradation luminance according to the supplied current.
(F) Non Emission Period
In this period, a low-level signal is input to the control lines 112 of all the rows, whereby the emission period controlling transistor 163 is set to an off state. Consequently, the organic EL element 17 does not emit light in this period.
As just described, in the driving sequence of the organic EL displaying apparatus 1 of the present embodiment, the on state and the off state of the emission period controlling transistor 163 are controlled in response to the control signal P2 of the control line 112, whereby the emission period of the organic EL element 17 is controlled.
In the present embodiment, to suppress that a luminance variation occurs due to the current Ileak in the non emission period, the emission period controlling transistor 163 and the driving transistor 162 are constituted so that the resistances of them satisfy the expression (1) and the currents values Ileak and Ibk satisfy the expression (2) in the above driving sequence. Here, the respective definitions of the resistance Roff
Hereinafter, a comparative example of the present embodiment will be described. Here, this comparative example is equivalent to a case where, in the same constitution as that of the organic EL displaying apparatus in the present embodiment, there are one or a plurality of pixels not satisfying the above expressions (1) and (2) due to different sizes or the like of the emission period controlling transistor 163.
In the pixel in which the resistances of the emission period controlling transistor 163 and the driving transistor 162 and the current values Ileak and Ibk do not satisfy the expressions (1) and (2), it can be said that the emission luminance (leak luminance) of the organic EL element by the leak current in the non emission period (F) is larger than the minimum gradation luminance in the emission period of the period (E). Further, the emission luminance (leak luminance) of the organic EL element by the leak current in the period (D) in the program period is sometimes larger than the minimum gradation luminance in the emission period of the period (E). More specifically, when the combined resistance of the resistances Rgray
Moreover, in the organic EL displaying apparatus in the comparative example of the present embodiment, there is a case where a problem of contrast deterioration due to occurrence of following black floating in addition to the luminance variation occurs. This problem will be described with reference to
More specifically, (1) of
Since the selecting transistor 161 and the erasing transistor 264 are in an off state in the period (D) in the driving sequence, the electric charge charged to the storage capacitor 15 in the period (C) is held. Since this is the electric charge corresponding to the gate voltage of the driving transistor 162 at the time when the gate-source voltage of the driving transistor 162 comes close to the threshold voltage of the driving transistor 162 in the period (C), the driving transistor 162 does not come to be completely in the off state in the period (D) irrespective of the gradation displaying data voltage set to the data line 121 in the program period (C). Namely, the driving transistor is in an intermediate state between the on state and the off state.
Resistance between the source and drain electrodes of the driving transistor 162 in this state is represented by Rgray
In the organic EL displaying apparatus 1 of the present embodiment, since it is constructed that the resistances of the emission period controlling transistor 163 and the driving transistor 162 satisfy the expression (1), it is possible to control the emission luminance of the organic EL element to be equal to or smaller than the minimum gradation luminance even in the state (1) of
On the other hand, in the organic EL displaying apparatus of the comparative example in the present embodiment, the pixel in which the resistances of the emission period controlling transistor 163 and the driving transistor 162 do not satisfy the expression (1) is present, and there is a case where the current Ileak2 comes to be larger than the current Ibk in this pixel. More specifically, when the combined resistance of the resistances Rgray
Incidentally, to evaluate whether or not the displaying apparatus according to the second embodiment has been manufactured, there are following ways. Namely, in case of evaluating the current flowing in the organic EL element for each pixel, it only has to measure the current values Ileak and Ibk by using the current measuring method described in Example 1. Further, in the displaying apparatus according to the second embodiment, the pixels of all the rows concurrently emit light in the emission period, and concurrently stop emitting light in the non emission period. In the displaying apparatus of performing the driving operation like this, it only has to measure the sum total of the current values Ileak and the sum total of the current values Ibk respectively flowing in the organic EL elements of the pixels included in all the rows in the displaying region, by using the current measuring method described in Modification of Example 1.
In the first embodiment, the organic EL displaying apparatus in which the emission period controlling transistor is constituted by the single transistor has been described. In the present embodiment, the organic EL displaying apparatus has the emission period controlling transistor in which the two transistors are connected in series by means of their source or drain electrodes, and the common control line is provided to the gate electrodes of these two transistors.
In the organic EL displaying apparatus of the present embodiment, an off resistance Roff
In the present embodiment, since the emission period controlling transistor 163 is constituted by the plurality of transistors 163A and 163B, it is possible to have the following effect.
Generally, there is a case where an off resistance of a transistor becomes small due to influence of static electricity occurred in a manufacturing process of the transistor, carrier transportation occurred through a level of crystal grain boundary when an edge of the gate electrode and the crystal grain boundary of the active layer are coincident, or the like. When the emission period controlling transistor 163 is constituted by a single transistor, there is a case where a defective pixel is generated due to such adverse effects. On the other hand, when the emission period controlling transistor 163 is constituted by the plurality of transistors as in the present embodiment, even if the off resistance of one transistor becomes small due to the above adverse effects, the combined resistance of the off resistances of the one transistor and the other transistor may satisfy the expression (1). Therefore, it is possible to more definitely achieve the organic EL displaying apparatus which satisfies the expression (1). Consequently, the current values Ileak and Ibk satisfy the expression (2), and it is thus possible to suppress occurrence of a luminance variation.
The emission period controlling transistor 163 may be constituted to have three or more transistors mutually connected in series and a control line common to these transistors. As the number of the transistors, connected in series, of constituting the emission period controlling transistor 163 increases, it is possible to further improve the effect of suppressing the occurrence of the luminance variation.
A concrete example of the organic EL displaying apparatus 1 according to Example 3 will be described hereinafter.
In this example, in the pixel circuit illustrated in
In the manufactured organic EL displaying apparatus, the proportion t (0<t≦1) of the emission period in the periods other than the program period in the one frame period was set to 0.7, a voltage of 9.5V was applied as the power supply line voltage (i.e., the voltage between the power supply line potential Vcc and the grounding line potential Vocom), and one gradation displaying data on the low gradation side in the intermediate gradation displaying data was programmed to all the pixels and driven in the driving sequence illustrated in
In the driving, the number of the manufactured organic EL displaying apparatuses including the defective pixels having the luminance higher than the peripheral pixels and thus being viewed, and having the luminance equal to or higher than 1.2 Lmean of average luminance Lmean in the displaying region was zero. Subsequently, the arbitrary ten organic EL displaying apparatuses were selected from the 100 organic EL displaying apparatuses, and the selected apparatuses were driven according to the driving sequence condition illustrated in
Also, for each of the remaining nine organic EL displaying apparatuses in the arbitrarily selected ten organic EL displaying apparatuses, when the current values flowing in the organic EL elements 17 of the plurality of pixels 100 (R) in the displaying region were measured in the same manner, the relation of the expression (2) was satisfied for all the measured pixels in all the organic EL displaying apparatuses.
For the remaining 90 organic EL displaying apparatuses, when the sum total of the currents flowing in the organic EL elements included in the respective pixels was evaluated for each row in the method described in Modification of Example 1, the expression (2)′ was satisfied for all the measured rows in all the organic EL displaying apparatuses.
In the organic EL displaying apparatus in this example, the expression (2) was satisfied for the pixel 100a (R). For this reason, in the pixel 100a (R), the emission luminance of the organic EL element 17 by the leak current at the off time of the emission period controlling transistor 163 in the non emission period is not larger than the minimum gradation luminance in the emission period even when the driving for controlling the emission period is performed. Therefore, since the same pixel circuit is formed not only for the pixel 100a (R) but also for other color pixels, it is possible to suppress the occurrence of the luminance variation for the pixels of all the colors. Moreover, since the expression (2)′ was satisfied in the organic EL displaying apparatus in this example, it was possible to suppress the luminance variation of the average luminance for each row.
As a comparative example, the 100 organic EL displaying apparatuses each having the constitution of Example 1 that the emission period controlling transistor 163 was constituted by the single transistor were manufactured. In the manufactured organic EL displaying apparatus, the proportion t (0<t≦1) of the emission period in the periods other than the program period in the one frame period was set to 0.7, a voltage of 9.5V was applied as the power supply line voltage (i.e., the voltage between the power supply line potential Vcc and the grounding line potential Vocom), and the intermediate gradation displaying data same as that in Example 3 was programmed to all the pixels and driven in the driving sequence illustrated in
With respect to the organic EL displaying apparatus including the pixel having the higher luminance than that of the peripheral pixels and thus being visible, when the current flowing in the organic EL element of the relevant pixel in the non emission period (D) was evaluated by the method described in Example 1 in the state that the maximum gradation displaying data voltage was applied to the gate electrode of the driving transistor, the current of 5.0×10−10 A to 6.0×10−9 A was obtained. When the luminance of the relevant pixel was measured by setting the measuring range of the luminance measuring unit to the relevant pixel, the luminance was equal to or higher than 1.2 Lmean of the average luminance Lmean in the displaying region. The relevant pixel is the defective pixel in which the off resistance of the transistor became small due to the influence of the static electricity occurred in the manufacturing process of the transistor, the carrier transportation occurred through the level of the crystal grain boundary when the edge of the gate electrode and the crystal grain boundary of the active layer are coincident, or the like.
With respect to the remaining 85 organic EL displaying apparatuses other than the 15 organic EL displaying apparatuses each including the defective pixel, when the sum total of the currents flowing in the organic EL element included in each pixel was evaluated for each row in the method described in Modification of Example 1, the expression (2)′ was satisfied for all the measured rows in all the organic EL displaying apparatuses.
As just described, since the emission period controlling transistor is constituted by the plurality of transistors connected in series, the defectiveness caused in the transistor manufacturing process and the like can be reduced. Thus, it is possible to more definitely satisfy the above expression (1), i.e., the above expression (2) or the above expression (2)′.
In the present embodiment, the organic EL displaying apparatus 1 of the first embodiment has been modified by the constitution of the emission period controlling transistor in which the two transistors are connected in series by means of their source or drain electrodes and the common control line is provided to the gate electrodes of these two transistors. It should be noted that this constitution is also applicable to the second embodiment. That is, the organic EL displaying apparatus of the second embodiment may be modified by the constitution of the emission period controlling transistor in which two transistors are connected in series by means of their source or drain electrodes and a common control line is provided to the gate electrodes of these two transistors. Also in such a case, it is possible to have the effect same as that in the present embodiment.
While the present invention has been described with reference to the exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2010-261242, filed Nov. 24, 2010 and Japanese Patent Application No. 2011-247715, filed Nov. 11, 2011, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-261242 | Nov 2010 | JP | national |
| 2011-247715 | Nov 2011 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6583775 | Sekiya et al. | Jun 2003 | B1 |
| 6950081 | Akimoto et al. | Sep 2005 | B2 |
| 7259735 | Kasai | Aug 2007 | B2 |
| 7834827 | Miyake et al. | Nov 2010 | B2 |
| 7999768 | Kim et al. | Aug 2011 | B2 |
| 7999770 | Kasai | Aug 2011 | B2 |
| 8624807 | Miyake et al. | Jan 2014 | B2 |
| 8659519 | Abe et al. | Feb 2014 | B2 |
| 20030067424 | Akimoto et al. | Apr 2003 | A1 |
| 20040150595 | Kasai | Aug 2004 | A1 |
| 20060022900 | Miyake et al. | Feb 2006 | A1 |
| 20070091029 | Uchino et al. | Apr 2007 | A1 |
| 20070257867 | Kasai | Nov 2007 | A1 |
| 20070257868 | Kasai | Nov 2007 | A1 |
| 20080001974 | Kim et al. | Jan 2008 | A1 |
| 20080036706 | Kitazawa | Feb 2008 | A1 |
| 20080204435 | Miyamoto | Aug 2008 | A1 |
| 20090102761 | Akimoto et al. | Apr 2009 | A1 |
| 20090135111 | Yamamoto et al. | May 2009 | A1 |
| 20100053041 | Abe et al. | Mar 2010 | A1 |
| 20100253666 | Yamamoto | Oct 2010 | A1 |
| 20110057925 | Miyake et al. | Mar 2011 | A1 |
| 20110227908 | Choi | Sep 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 1506931 | Jun 2004 | CN |
| 1728218 | Feb 2006 | CN |
| 101097684 | Jan 2008 | CN |
| 101123065 | Feb 2008 | CN |
| 2002-149112 | May 2002 | JP |
| 2003-122301 | Apr 2003 | JP |
| 2003-122304 | Apr 2003 | JP |
| 2007-241009 | Sep 2007 | JP |
| 201011719 | Mar 2010 | TW |
| Entry |
|---|
| U.S. Appl. No. 13/286,406, filed Nov. 11, 2011. |
| U.S. Appl. No. 13/299,940, filed Nov. 18, 2011. |
| U.S. Appl. No. 13/302,047, filed Nov. 22, 2011. |
| U.S. Appl. No. 13/296,547, filed Nov. 15, 2011. |
| Taiwanese Office Action issued in counterpart application No. 100142902 dated Jan. 28, 2014, along with its English-language translation—12 pages. |
| Chinese Office Action issued in counterpart application No. 201110377025.X dated Dec. 16, 2013, along with its English-language translation—17 pages. |
| Chinese Office Action issued in counterpart application No. 201110377025.X dated Jul. 17, 2014, along with its English-language translation—17 pages. |
| Japanese Office Action issued in corresponding application No. 2011-247715 dated Sep. 15, 2015—6 pages with partial English translation. |
| Number | Date | Country | |
|---|---|---|---|
| 20120127221 A1 | May 2012 | US |
