Patent Application
20210110773
The disclosure relates to a display device. In particular, it relates to a display device that includes a pixel circuit including an electro-optical element.
Organic EL display devices including pixel circuits including organic electro luminescence (hereinafter referred to as “EL”) elements have recently been coming into practical use. The pixel circuit of the organic EL display device includes not only the organic EL elements but also driving transistors, writing control transistors, and the like. Thin film transistors (hereinafter referred to as a “TFTs”) are used as these transistors. The organic EL elements are a type of electro-optical elements, and emit light of luminance in accordance with the amount of electric current that flows. Each of the driving transistors is arranged in series with the corresponding organic EL element, and regulates the amount of electric current that flows through the organic EL element.
The characteristics of the organic EL elements and the characteristics of the driving transistors vary from one element/transistor to another, and fluctuate over time. Hence, for the purpose of making the organic EL display device display images of high picture quality, it is necessary to compensate the variation and the fluctuation of the elements. There are two known methods of compensating the characteristics of the elements in the organic EL display device: compensation performed within the pixel circuit; and compensation performed outside the pixel circuit. In the former method, there may be a case where a process for initialize the voltage of the control terminal of the driving transistor to a predetermined level is performed before inputting a voltage (hereinafter referred to as the “data voltage”) into the pixel circuit in accordance with the image signal. In such a case, an initialization transistor is provided in the pixel circuit.
Many pixel circuits including organic EL elements have been proposed so far. For example, PTL 1 describes a pixel circuit 91 illustrated in
The pixel circuit 91 illustrated in
The pixel circuit 92 illustrated in
In the light emission period of the organic EL elements provided in the pixel circuit 91, a high-level voltage is applied to the scanning line Gi and the control line Pi to turn the TFT TR15 and the TFT TR13 off. In the display device of a related art, the high-level voltage applied to the scanning line Gi and the high-level voltage applied to the control line Pi are voltages of the same level. Hence, the off-current of the TFT TR13 may vary, resulting in a bright spot in the display screen (to be described in detail later).
In the light emission period of the organic EL elements provided in the pixel circuit 92, a high-level voltage is applied to the scanning lines Gi and Gi−1 to turn the TFT TR23 and the TFT TR25 off. In the display device of a related art, the high-level voltage applied to the scanning lines Gi and Gi−1 are voltages of the same level. Hence, the off-current of the TFT TR25 may vary, resulting in a bright spot in the display screen (to be described in detail later).
Accordingly, a challenge arises: providing a display device capable of suppressing the occurrence of bright spots on the display screen due to the variation of the off-current of the initialization transistor.
A solution to the challenge is provided, for example, by a display device including: a display portion including a plurality of scanning lines, a plurality of data lines, a plurality of control lines, and a plurality of pixel circuits; a scanning line drive circuit configured to drive the plurality of scanning lines; a data line drive circuit configured to drive the plurality of data lines; and a control line drive circuit configured to drive the plurality of control lines. In the display device, each of the plurality of pixel circuits includes an electro-optical element, a driving transistor, a writing control transistor, and an initialization transistor. The electro-optical element is disposed on a route connecting a first conductive member and a second conductive member and is configured to emit light of a luminance in accordance with an electric current flowing through the route. Both the first conductive member and the second conductive member are configured to supply a power source voltage. The driving transistor is disposed on the route in series with the electro-optical element and is configured to regulate an amount of the electric current flowing through the route. The writing control transistor includes: a first conduction terminal connected to a data line of the plurality of data lines; and a control terminal connected to a scanning line of the plurality of scanning lines. The initialization transistor includes: a first conduction terminal connected to a control terminal of the driving transistor; a second conduction terminal to which an initialization voltage is applied; and a control terminal connected to a first control line included in the plurality of control lines. The writing control transistor and the initialization transistor have the same polarity. An off-voltage to be given to the control terminal of the initialization transistor is closer to an on-voltage than an off-voltage to be given to the control terminal of the writing control transistor.
Another solution to the challenge is provided by a display device driving method for driving a display device including the above-described display portion. The display device driving method includes: driving the plurality of scanning lines; driving the plurality of data lines; and driving the plurality of control lines. The writing control transistor and the initialization transistor have the same polarity. An off-voltage to be given to the control terminal of the initialization transistor is closer to an on-voltage than an off-voltage to be given to the control terminal of the writing control transistor.
According to the display device and the method of driving the display device, an off-voltage to be given to the control terminal of the initialization transistor is closer to an on-voltage than an off-voltage to be given to the control terminal of the writing control transistor. Hence, the voltage between the gate and the source (gate-source voltage) at the time when the initialization transistor is in the off state becomes lower than otherwise, the variation in the off-current of the initialization transistor is suppressed, and the occurrence of bright spots on the display screen is suppressed.
Display devices according to some embodiments will be described below with reference to the drawings. The display device according to each of the embodiments is an organic EL display device equipped with pixel circuits each of which includes an organic EL element. The organic EL element is a kind of electro-optical elements, and is also referred to as an organic light emitting diode, or an OLED. In the following description, the horizontal direction in the drawings is referred to as the “row direction”, and the vertical direction in the drawings is referred to as the “column direction”. In addition, each of the letters m and n represents an integer that is equal to or larger than 2, the letter i represents an integer that is equal to or larger than 1 and is equal to or smaller than m, and the letter j represents an integer that is equal to or larger than 1 and is equal to or smaller than n.
The display portion 11 includes: m scanning lines G1 to Gm; n data lines S1 to Sn; 3m control lines E1 to Em, P1 to Pm, and Q1 to Qm; and (m×n) pixel circuits 15. The scanning lines G1 to Gm extend in the row direction, and are arranged in parallel to one another. The data lines S1 to Sn extend in the column direction, and are arranged in parallel to one another and orthogonally to the scanning lines G1 to Gm. The scanning lines G1 to Gm and the data lines S1 to Sn intersect at (m×n) locations. The (m×n) pixel circuits 15 are arranged in a 2D manner and correspond to the intersection points of the scanning line G1 to Gm and the data lines S1 to Sn. The control lines E1 to Em, P1 to Pm, and Q1 to Qm are arranged in parallel to the scanning lines G1 to Gm. To each of the pixel circuits 15, three different voltages (i.e., a high-level power source voltage ELVDD, a low-level power source voltage ELVSS, and an initialization voltage VINIT) are fixedly supplied by use of an unillustrated wiring line or electrode. The following description assumes that the high-level power source voltage ELVDD is supplied through a high-level power-source voltage wiring line and that the low-level power source voltage ELVSS is supplied through a common electrode.
The display control circuit 12 outputs a control signal CS1 to the scanning line/control line drive circuit 13, and also outputs both a control signal CS2 and an image signal X1 to the data line drive circuit 14. Based on the control signal CS1, the scanning line/control line drive circuit 13 drives the scanning lines G1 to Gm and the control lines E1 to Em, P1 to Pm, and Q1 to Qm. Based on both the control signal CS2 and the image signal X1, the data line drive circuit 14 drives the data line S1 to Sn. To be more specific, in the ith line period, the scanning line/control line drive circuit 13 applies an on-voltage (a voltage to turn the TFT on, in this case, a low-level voltage) to the ith scanning line Gi, and also applies an off-voltage (a voltage to turn the TFT off, in this case a high-level voltage) to the other (m−1) scanning lines. Hence, in the ith line period, the pixel circuits 15 in the ith row are selected in a batch manner. Based on the control signal CS2, the data line drive circuit 14 applies n data voltages in accordance with the image signal X1 to the data lines S1 to Sn. Hence, in the ith line period, n data voltages are inputted into their corresponding pixel circuits 15 in the ith row.
Note that each of the TFTs included in the pixel circuit 15 may be an amorphous silicon transistor including a channel layer made from an amorphous silicon, a low-temperature polysilicon transistor including a channel layer made from a low-temperature polysilicon, or an oxide semiconductor transistor including a channel layer made from an oxide semiconductor. The oxide semiconductor may be, for example, indium gallium zinc oxide (also referred to as “IGZO”). Each of the TFTs included in the pixel circuit 15 may be a TFT of the top-gate type or a TFT of the bottom-gate type.
The source terminal of the TFT M16 and a first one of the electrodes of the capacitor C1 (the upper-side electrode one in
The organic EL element L1 is disposed on the route connecting the first and the second conductive members (i.e., the high-level power-source voltage wiring line 16 and the common electrode 17) configured to supply their respective power source voltages. The organic EL element L1 thus functions as an electro-optical element configured to emit light of luminance in accordance with the amount of electric current that flows through the route. The TFT M11 is disposed on the route in series with the electro-optical element, and functions as a driving transistor configured to regulate the amount of electric current flowing through the route. The TFT M15 functions as a writing control transistor whose first conduction terminal is connected to the data line Sj and whose control terminal is connected to the scanning line Gi. The TFT M13 functions as an initialization transistor whose first conduction terminal is connected to the control terminal of the driving transistor, whose second conduction terminal is applied with the initialization voltage VINIT, and whose control terminal is connected to a first control line (i.e., the control line Pi). The writing control transistor and the initialization transistor have the same polarity.
The first conduction terminal of the driving transistor is connected to the second conduction terminal of the writing control transistor. The TFT M12 functions as a threshold compensation transistor whose first conduction terminal is connected to the second conduction terminal of the driving transistor, whose second conduction terminal is connected to the control terminal of the driving transistor, and whose control terminal is connected to the scanning line Gi. The TFT M16 functions as a first light-emission control transistor whose first conduction terminal is connected to the first conductive member, whose second conduction terminal is connected to the first conduction terminal of the driving transistor, and whose control terminal is connected to a light-emission control line (i.e., control line Ei). The TFT M14 functions as a second light-emission control transistor whose first conduction terminal is connected to the second conduction terminal of the driving transistor, whose second conduction terminal is connected to a first one of the terminals of the electro-optical circuit, and whose control terminal is connected to the light-emission control line. The capacitor C1 is disposed between the first conductive member and the control terminal of the driving transistor. The TFT M17 functions as a second initialization transistor whose first conduction terminal is connected to a first one of the terminals of the electro-optical circuit, whose second conduction terminal is applied with the initialization voltage, and whose control terminal is connected to a second control line (i.e., the control line Qi).
Hereinafter, the signal on the scanning line Gi is referred to as a “scanning signal Gi”, and the signals on the control lines Ei, Pi, and Qi are referred to as “control signals Ei, Pi, and Qi”, respectively. As illustrated in
Prior to the time t11, the scanning signal Gi and the control signals Pi and Qi are at the high level, whereas the control signal Ei is at the low level. Hence, the TFTs M14 and M16 are in the ON state, whereas the TFTs M12, M13, M15, and M17 are in the OFF state. During the above-described period, in a case where the TFT M11 has a gate-source voltage of not higher than the threshold voltage, a current flows from the high-level power-source voltage wiring line 16 to the common electrode 17 through the TFTs M16, M11, and M14 as well as through the organic EL element L1. Hence, the organic EL element L1 emits light of the luminance in accordance with the electric current that flows.
At the time t11, the control signal Ei is switched to the high level. In response to the switching, the TFTs M14 and M16 are turned OFF. Hence, from the time t11 onwards, no electric current flows through the organic EL element L1, and thus the organic EL element L1 emits no light at all.
Then at the time t12, the control signal Pi is switched to the low level. In response to the switching, the TFT M13 is turned ON. Hence, the gate voltage of the TFT M11 is initialized to the initialization voltage VINIT. The initialization voltage VINIT is set to a low enough level to allow the TFT M11 to be turned ON immediately after the switching of the scanning signal Gi to the low level.
Then at the time t13, the control signal Pi is switched to the high level. In response to the switching, the TFT M13 is turned OFF. Hence, from the time t13 onwards, no initialization voltage VINIT is applied to the gate terminal of the TFT M11.
Then at the time t14, the scanning signal Gi and the control signal Qi are switched to the low level. In response to the switching, the TFTs M12, M15, and M17 are turned ON. From the time t14 onwards, the gate terminal and the drain terminal of the TFT M11 are electrically connected to each other through the TFT M12 that is in the ON state. Hence, the TFT M11 is in a diode-connected state. Consequently, an electric current flows from the data line Sj to the gate terminal of the TFT M11, through the TFTs M15, M11, and M12. The gate voltage of the TFT M11 is raised by this electric current. Once the gate-source voltage of the TFT M11 reaches the threshold voltage of the TFT M11, no electric current flows. The gate voltage of the TFT M11 a sufficient time after the time t14 is represented by (Vd−|Vth_M11|), where Vth_M11(<0) is the threshold voltage of the TFT M11, and Vd is the voltage of the data line Sj during the compensation period. In addition, as the TFT M17 is turned ON at the time t14, the voltage of the anode terminal of the organic EL element L1 is initialized to the initialization voltage VINIT.
Then at the time t15, the scanning signal Gi and the control signal Qi are switched to the high level. In response to the switching, the TFTs M12, M15, and M17 are turned OFF. From the time t15 onwards, the capacitor C1 keeps the inter-electrode voltage (ELVDD−Vd+|Vth_M11|). In addition, no initialization voltage VINIT is applied to the anode terminal of the organic EL element L1 any longer.
Then at the time t16, the control signal Ei is switched to the low level. In response to the switching, the TFT M14 and M16 are turned ON. From the time t16 onwards, an electric current flows from the high-level power-source voltage wiring line 16 to the common electrode 17 through the TFTs M16, M11, and M14 and through the organic EL element L1. The gate-source voltage Vgs of the TFT M11 is kept at (ELVDD−Vd+|Vth_M11|) by the operation of the capacitor C1. Hence, the electric current I1 that flows from the time t16 onwards is given by Equation (1) below with a constant K:
I1=K(Vgs−|Vth_M11|)2=K(ELVDD−Vd)2 (1)
Hence, from the time t16 onwards, the organic EL element L1 emits light of luminance in accordance with the data voltage Vd inputted into the pixel circuit 15 irrespective of the threshold voltage Vth_M11 of the TFT M11.
Hereinafter, the high-level voltage to be applied to the scanning lines G1 to Gm is denoted by G_H, whereas the high-level voltage to be applied to the control lines P1 to Pm is denoted by P_H. In the display device 10, the high-level voltage P_H is set to a value that is lower than the high-level voltage G_H (P_H<G_H). To put it differently, in comparison to the off-voltage G_H to be given to the control terminal of the writing control transistor (i.e., TFT M15), the off-voltage P_H to be given to the control terminal of the initialization transistor (i.e., TFT M13) is set relatively close to the on-voltage (i.e., low-level voltage).
The high-level voltage P_H is set, for example, so that the difference between the high-level voltage P_H and the on-voltage corresponds to the average value of the threshold voltages Vth_M11 of all the TFT M11 included in the display portion 11. For example, the difference between the high-level voltage P_H and the on-voltage is set to substantially the same as the average value of the threshold voltages Vth_M11 of all the TFTs M11 included in the display portion 11. The threshold voltage Vth_M11 has an absolute value of, for example, approximately from 3 to 8 V.
An effect that the display device 10 of the present embodiment has is described below by comparing the display device 10 with a display device with the two high-level voltages P_H and the G_H being at the same level (hereinafter, referred to as a “known display device”). For both the known display device and the display device 10, the condition for turning OFF the TFT M15 is given by Relationship (2) below, and the condition for turning OFF the TFT M13 is given by Relationship (3) below:
G_H−max(ELVDD,Vd)>Vth_M15 (2)
P_H−Vn11>Vth_M13 (3)
In Relationships (2) and (3) above, Vn11 is the voltage of the node N11, Vth_M13 is the threshold voltage of the TFT M13, and Vth_M15 is the threshold voltage of the TFT M15.
During the compensation period, the TFT M11 is in the diode-connected state. Hence, the gate voltage of the TFT M11 during the compensation period is given by Equation (4) below:
Vn11=Vd−|Vth_M11| (4)
In the case of the known display device, the two high-level voltages are equal to each other (i.e., P_H=G_H). Hence, in a case where the threshold voltage Vth_M13 of the TFT M13 and the threshold voltage Vth_M15 of the TFT M15 are approximately equal to each other, the gate-source voltage at the time of being turned OFF is higher for the TFT M13 than for the TFT M15. Hence, the off current for the TFT M13 is more likely to vary. Consequently, bright spots may occur in the display screen.
In contrast, in the case of the display device 10 the two high-level voltages have a relation of P_H<G_H. Hence, even in a case where the threshold voltage Vth_M13 of the TFT M13 and the threshold voltage Vth_M15 of the TFT M15 are approximately equal to each other, the gate-source voltage of the TFT M13 at the time of being turned OFF is reduced and thus the variation in the off-current for the TFT M13 is suppressed. Hence, the display device 10 according to the present embodiment reduces the variation in the off-current for the initialization transistor (i.e., TFT M13) configured to initialize the voltage of the control terminal of the driving transistor (i.e., gate terminal of the TFT M11), and thus suppresses the occurrence of bright spots on the display screen.
In addition, as the pixel circuit 15 includes the TFT M17, the voltage of the anode terminal of the organic EL element L1 is initialized by use of the initialization voltage VINIT to be applied to the gate terminal of the TFT M11. Note that a display device according to a modified example of the present embodiment may be provided as a display device including a pixel circuit obtained by removing the TFT M17 from the pixel circuit 15.
The display portion 21 includes: m scanning lines G1 to Gm; n data lines S1 to Sn; m control lines P1 to Pm; and (m×n) pixel circuits 25. The scanning lines G1 to Gm, the data lines S1 to Sn, the control lines P1 to Pm, and the (m×n) pixel circuits 25 are arranged in the same patterns as the patterns in the first embodiment. As in the first embodiment, three different voltages ELVDD, ELVSS, and VINIT are fixedly supplied to each of the pixel circuits 25. The scanning line/control line drive circuit 23 is a combination circuit that combines a scanning line drive circuit and a control line drive circuit. Based on the control signal CS1, the scanning line/control line drive circuit 23 drives the scanning lines G1 to Gm and the control lines P1 to Pm.
The source terminal of the TFT M21 and a first one of the electrodes of the capacitor C2 (the upper-side electrode one in
The organic EL element L2 is disposed on the route connecting the first and the second conductive members (i.e., the high-level power-source voltage wiring line 16 and the common electrode 17) configured to supply their respective power source voltages. The organic EL element L2 thus functions as an electro-optical element configured to emit light of luminance in accordance with the amount of electric current that flows through the route. The TFT M21 is disposed on the route in series with the electro-optical circuit, and functions as a driving transistor configured to regulate the amount of electric current flowing through the route. The TFT M23 functions as a writing control transistor whose first conduction terminal is connected to the data line Sj and whose control terminal is connected to the scanning line Gi. The TFT M25 functions as an initialization transistor whose first conduction terminal is connected to the control terminal of the driving transistor, whose second conduction terminal is applied with the initialization voltage VINIT, and whose control terminal is connected to a first control line (i.e., the control line Pi). The writing control transistor and the initialization transistor have the same polarity.
The driving transistor includes a first conduction terminal connected to the first conductive member. TFT M22 functions as a threshold compensation transistor whose first conduction terminal is connected to the second conduction terminal of the writing control transistor, whose second conduction terminal and whose control terminal are connected to the control terminal of the driving transistor. The TFT M24 functions as a light-emission control transistor whose first conduction terminal is connected to the second conduction terminal of the driving transistor, whose second conduction terminal is connected to a first one of the terminals of the electro-optical circuit, and that is complementarily conducted to the initialization transistor. The capacitor C2 is disposed between the first conductive member and the control terminal of the driving transistor.
As illustrated in
Prior to the time t21, the scanning signal Gi and the control signal Pi are at the high level. Hence, the TFTs M23 and M25 are in the OFF state, whereas the TFT M24 is in the ON state. During the above-described period, in a case where the TFT M21 has a gate-source voltage of not higher than the threshold voltage, a current flows from the high-level power-source voltage wiring line 16 to the common electrode 17 through the TFTs M21 and M24 as well as through the organic EL element L2. Hence, the organic EL element L2 emits light of the luminance in accordance with the electric current that flows.
At the time t21, the control signal Pi is switched to the low level. In response to the switching, the TFT M24 is turned OFF and the TFT M25 is turned ON. Hence, from the time t21 onwards, no electric current flows through the organic EL element L2, and thus the organic EL element L2 emits no light at all. Hence, the gate voltage of the TFT M21 is initialized to the initialization voltage VINIT.
Then at the time t22, the control signal Pi is switched to the high level. In response to the switching, the TFT M24 is turned ON and the TFT M25 is turned OFF. Hence, from the time t22 onwards, no initialization voltage VINIT is applied to the gate terminal of the TFT M21. In addition, as in the period before the time t21, in a case where the TFT M21 has a gate-source voltage that is not higher than the threshold voltage, an electric current flows through the organic EL element L2 and makes the organic EL element L2 emit light.
Then at the time t23, the scanning signal Gi is switched to the low level. In response to the switching, the TFT M23 is turned ON. Consequently, an electric current flows from the data line Sj to the gate terminals of the TFTs M21 and M22 through the TFTs M23 and M22. The gate voltages of the TFTs M21 and M22 are raised by this electric current. Once the gate-source voltage of the TFT M22 reaches the threshold voltage of the TFT M22, no electric current flows.
The gate voltages of the TFTs M21 and M22 a sufficient time after the time t23 is represented by (Vd−|Vth_M22|), where Vth_M21 (<0) is the threshold voltage of the TFT M21, and, Vth_M22 (<0) is the threshold voltage of the TFT M22, and Vd is the data voltage during the writing period.
Then at the time t24, the scanning signal Gi is switched to the high level. In response to the switching, the TFT M23 is turned OFF. From the time t24 onwards, the capacitor C2 keeps the inter-electrode voltage (ELVDD−Vd+|Vth_M22|). In addition, an electric current flows from the high-level power-source voltage wiring line 16 to the common electrode 17 through the TFTs M21 and M24 as well as through the organic EL element L2. The gate-source voltage Vgs of the TFT M21 is kept at (ELVDD−Vd+|Vth_M22|) by the operation of the capacitor C2. Hence, the electric current I2 that flows from the time t24 onwards is given by Equation (5) below with a constant K:
I2=K(Vgs−|Vth_M21|)2=K(ELVDD−Vd+|Vth_M22|−|Vth_M21|)2 (5)
Assuming that the threshold voltage Vth_M21 of the TFT M21 is equal to the threshold voltage Vth_M22 of the TFT M22, Equation (6) below is derived from the equation (5):
I2=K(ELVDD−Vd)2 (6)
Hence, from the time t24 onwards, the organic EL element L2 emits light of luminance in accordance with the data voltage Vd inputted into the pixel circuit 25 irrespective of the threshold voltage Vth_M21 of the TFT M21.
In the display device 20, as in the case of the first embodiment, the high-level voltage P_H is set to a value that is lower than the high-level voltage G_H (P_H<G_H). To put it differently, in comparison to the off-voltage G_H to be given to the control terminal of the writing control transistor (i.e., TFT M23), the off-voltage P_H to be given to the control terminal of the initialization transistor (i.e., TFT M25) is set relatively close to the on-voltage (i.e., low-level voltage).
Hence, as in the case of the first embodiment, the display device 20 according to the present embodiment reduces the variation in the off-current for the initialization transistor (i.e., TFT M25) configured to initialize the voltage of the control terminal of the driving transistor (i.e., gate terminal of the TFT M21), and thus suppresses the occurrence of bright spots on the display screen.
The display portion 31 includes: m scanning lines G1 to Gm; n data lines S1 to Sn; 2m control lines E1 to Em and P1 to Pm; and (m×n) pixel circuits 35. The scanning lines G1 to Gm, the data lines S1 to Sn, the control lines E1 to Em and P1 to Pm, and the (m×n) pixel circuits 35 are arranged in the same patterns as the patterns in the first embodiment. As in the first and second embodiments, three different voltages ELVDD, ELVSS, and VINIT are fixedly supplied to each of the pixel circuits 35. The scanning line/control line drive circuit 33 is a combination circuit that combines a scanning line drive circuit and a control line drive circuit. Based on the control signal CS1, the scanning line/control line drive circuit 33 drives the scanning lines G1 to Gm and the control lines E1 to Em and P1 to Pm.
The pixel circuit 35 includes: an organic EL element L2; five TFTs M21 to M25; and a capacitor C2. The pixel circuit 35 is connected to the scanning line Gi, the control lines Ei and Pi, and the data line Sj. The gate terminal of the TFT M24 is not connected to the control line Pi but is connected to the control line Ei.
In the display device 30, as in the case of the first and second embodiments, the high-level voltage P_H is set to a value that is lower than the high-level voltage G_H (P_H<G_H). Hence, as in the case of the first and second embodiments, the display device 30 according to the present embodiment reduces the variation in the off-current for the initialization transistor (i.e., TFT M25) configured to initialize the voltage of the control terminal of the driving transistor (i.e., gate terminal of the TFT M21), and thus suppresses the occurrence of bright spots on the display screen.
In addition, in the display device 30, the high-level voltage P_H to be applied to the control line P1 to Pm is set to a value that is lower than the high-level voltage to be applied to the control line E1 to Em (hereinafter denoted by E_H) (P_H<E_H). Hence, the display device 30 according to the present embodiment maintains the on-voltage of the TFT M24 even when the high-level voltage P_H is lowered.
Various modifications can be made to the display devices according to the first to third embodiments. The description in each of the first to third embodiments is based on a display device including a pixel circuit with a particular configuration, but a display device may include a different pixel circuit from the one described thus far as long as the pixel circuit includes an organic EL element, a driving transistor, a writing control transistor, and an initialization transistor. As in the cases of the first to third embodiments, in a case where the driving transistor and the writing control transistor are P-channel transistors, the high-level voltage to be given to the control terminal of the initialization transistor is set to a value that is lower than the high-level voltage to be given to the control terminal of the writing control transistor. In a case where the initialization transistor and the writing control transistor are N-channel transistors, the low-level voltage to be given to the control terminal of the initialization transistor is set to a value that is higher than the low-level voltage to be given to the control terminal of the writing control transistor. Such display devices have similar effects to the effects that the display devices according to the first to third embodiments have.
In addition, the description in each of the first to third embodiments is based on a case where an organic EL display device that includes a pixel circuit including an organic EL element (organic light emitting diode) is an exemplar display device that includes a pixel circuit including an electro-optical circuit. It is, however, allowable to configure, in a similar manner, an inorganic EL display device that includes a pixel circuit including an inorganic light emitting diode or a quantum-dot light emitting diode (QLED) display device that includes a pixel circuit including a quantum-dot light emitting diode.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/034024 | 9/21/2017 | WO | 00 |
