Display device and method for driving same
An embodiment of the present invention realizes a display device equipped with a self light-emitting type display element driven by a current, by using a pixel circuit having a configuration simpler than a conventional configuration. A pixel circuit includes a driving transistor (T 1 ), an input transistor (T 2 ), a capacitor (Cst), and three organic EL elements (OLED(R), OLED(G), and OLED(B)). Cathode terminals of the organic EL elements (OLED(R), OLED(G), and OLED(B)) are respectively connected to low-level power supply lines (ELVSS(R), ELVSS(G), and ELVSS(B)). In such a configuration, in each sub-frame, only a low-level power supply voltage (ELVSS) corresponding to the sub-frame is set to a relatively low level, and the other low-level power supply voltages (ELVSS) are set to relatively high levels.
1. An active matrix-type display device configured to display a color image by dividing one frame period into a plurality of sub-frames and displaying a screen image of a different color for each of the sub-frames, the active matrix-type display device comprising:
a plurality of data lines;
a plurality of scanning signal lines disposed to be orthogonal to the plurality of data lines;
a plurality of pixel circuits provided corresponding to intersections of the plurality of data lines and the plurality of scanning signal lines;
a first power supply line configured to supply a constant voltage to the plurality of pixel circuits;
a plurality of second power supply lines configured to supply a relatively high-level first voltage and a relatively low-level second voltage to the plurality of pixel circuits, the plurality of second power supply lines corresponding, in a one-to-one manner, to the plurality of sub-frames included in the one frame period;
a data line drive circuit configured to apply a video signal to the plurality of data lines;
a scanning signal line drive circuit configured to apply a scanning signal to the plurality of scanning signal lines; and
a second power supply control unit configured to control a voltage to be given to the plurality of second power supply lines, wherein
the pixel circuit comprises:
a plurality of self light-emitting type electro-optical elements provided between each of the plurality of second power supply lines and the first power supply line, the plurality of self light-emitting type electro-optical elements corresponding, in a one-to-one manner, to the plurality of sub-frames included in the one frame period;
one first transistor that is provided to be in series with the plurality of electro-optical elements between the first power supply line and the plurality of second power supply lines, and that controls a driving current to be supplied to the plurality of electro-optical elements;
a second transistor that is provided between a control terminal of the first transistor and one of the data lines, and that electrically connects the control terminal of the first transistor and the data line when a scanning signal applied to a corresponding scanning signal line has been set active by the scanning signal line drive circuit; and
a capacitor provided between the control terminal of the first transistor and one conductive terminal of the first transistor, and
when any sub-frame included in the one frame period is assumed as a focused sub-frame, the second power supply control unit controls a voltage to be given to the plurality of second power supply lines such that, in the focused sub-frame, a voltage applied to an electro-optical element corresponding to the focused sub-frame becomes equal to or higher than a light emission threshold value and also a voltage applied to an electro-optical element other than the electro-optical element corresponding to the focused sub-frame becomes less than the light emission threshold value.
2. The display device according to claim 1 , wherein the data line drive circuit applies a voltage corresponding to a black color as the video signal to the plurality of data lines during a flyback period of each of the sub-frames, and
the scanning signal line drive circuit applies active scanning signals simultaneously to the plurality of scanning signal lines during a flyback period of each of the sub-frames.
3. The display device according to claim 1 , wherein a sub-frame appears 180 times or more during one second.
4. The display device according to claim 1 , wherein
a constant voltage given to the first power supply line is set to a higher level than that of the first voltage, and
the second power supply control unit controls a voltage to be given to the plurality of second power supply lines such that, in the focused sub-frame, the second voltage is given to a second power supply line corresponding to the focused sub-frame and also the first voltage is given to a second power supply line other than the second power supply line corresponding to the focused sub-frame.
5. The display device according to claim 1 , wherein the first transistor and the second transistor are thin-film transistors having a channel layer formed of an oxide semiconductor.
6. The display device according to claim 5 , wherein the oxide semiconductor is Indium Gallium Zinc Oxide including indium (In), gallium (Ga), zinc (Zn), and oxygen (O) as main components.
7. A method for driving an active matrix-type display device configured to display a color image by dividing one frame period into a plurality of sub-frames and displaying a screen image of a different color for each of the sub-frames, the active matrix-type display device comprising a plurality of data lines; a plurality of scanning signal lines disposed to be orthogonal to the plurality of data lines; a plurality of pixel circuits provided corresponding to intersections of the plurality of data lines and the plurality of scanning signal lines; a first power supply line configured to supply a constant voltage to the plurality of pixel circuits; and a plurality of second power supply lines configured to supply a relatively high-level first voltage and a relatively low-level second voltage to the plurality of pixel circuits, the plurality of second power supply lines corresponding, in a one-to-one manner, to the plurality of sub-frames included in the one frame period; the method comprising:
a data line driving step for applying a video signal to the plurality of data lines;
a scanning signal line driving step for applying a scanning signal to the plurality of scanning signal lines; and
a second power supply control step for controlling a voltage to be given to the plurality of second power supply lines, wherein
the pixel circuit comprises:
a plurality of self light-emitting type electro-optical elements provided between each of the plurality of second power supply lines and the first power supply line, the plurality of self light-emitting type electro-optical elements corresponding, in a one-to-one manner, to the plurality of sub-frames included in the one frame period,
one first transistor that is provided to be in series with the plurality of electro-optical elements between the first power supply line and the plurality of second power supply lines, and that controls a driving current to be supplied to the plurality of electro-optical elements,
a second transistor that is provided between a control terminal of the first transistor and one of the data lines, and that electrically connects the control terminal of the first transistor and the data line when a scanning signal applied to a corresponding scanning signal line has been set active in the scanning signal line driving step, and
a capacitor provided between the control terminal of the first transistor and one conductive terminal of the first transistor, and
when any sub-frame included in the one frame period is assumed as a focused sub-frame, in the second power supply control step, a voltage to be given to the plurality of second power supply lines is controlled such that, in the focused sub-frame, a voltage applied to an electro-optical element corresponding to the focused sub-frame becomes equal to or higher than a light emission threshold value and also a voltage applied to an electro-optical element other than the electro-optical element corresponding to the focused sub-frame becomes less than the light emission threshold value.