US-20260128009-A1 - DISPLAY DEVICE, PIXEL CIRCUIT, AND METHOD FOR DRIVING PIXEL CIRCUIT

Abstract

In a pixel circuit 15 , a drive transistor T 4 has a drain connected to a power supply line ELVDD via a transistor T 6 , a source connected to an anode of an organic EL element OL via a transistor T 5 , and a gate connected to a reference voltage line Lref via a transistor T 3 and to the source via a capacitor C 1 . The anode is connected to a data signal line Dj via a transistor T 1 and to an initialization voltage line Lini via a transistor T 2 and to the source via the capacitor C 2 . The pixel circuit 15 is driven to sequentially perform initialization of the capacitors C 1 , C 2 , detection of a threshold voltage of the drive transistor T 4 , writing of a voltage according to a data signal D(j) subjected to threshold compensation into the capacitor C 1 , and lighting of the organic EL element OL according to the written voltage.

Inventors

• Ryo Yonebayashi

Assignees

• Sharp Display Technology Corporation

Dates

Publication Date

20260507

Application Date

20221130

Claims (12)

1. 1 . A display device comprising: a display portion including a plurality of pixel circuits, a high-voltage power supply line, a low-voltage power supply line, an initialization voltage line for supplying an initialization voltage determined in advance, and a reference voltage line for supplying a reference voltage determined in advance; and a drive circuit configured to drive the plurality of pixel circuits, wherein each of the pixel circuits includes a display element driven by a current, a drive transistor of an N-channel type, a write control switching element, an initialization switching element, a reference voltage supply control switching element, a first light emission control switching element, a second light emission control switching element, a first capacitor, and a second capacitor, the drive transistor has a drain terminal connected to the high-voltage power supply line via the second light emission control switching element, a gate terminal connected to the reference voltage line via the reference voltage supply control switching element, and a source terminal connected to the display element via the first light emission control switching element, the display element has a first terminal connected to the source terminal of the drive transistor via the first light emission control switching element and connected to the initialization voltage line via the initialization switching element, and a second terminal connected to the low-voltage power supply line, the first capacitor has a first electrode connected to the gate terminal of the drive transistor and a second electrode connected to the source terminal of the drive transistor, the second capacitor has a first electrode connected to the source terminal of the drive transistor, and a second electrode connected to the first terminal of the display element and configured to receive a data voltage to be written to the pixel circuit via the write control switching element, each of the pixel circuits is provided with an initialization period, a compensation period, a write period, and a light emission period, and the drive circuit controls ON and OFF of the write control switching element, the initialization switching element, the reference voltage supply control switching element, the first light emission control switching element, and the second light emission control switching element such that in each of the plurality of pixel circuits, in the initialization period, the first capacitor and the second capacitor are initialized such that a voltage for bringing the drive transistor to ON state is held in the first capacitor, in the compensation period, the voltage held in the first capacitor by initialization changes to a threshold voltage of the drive transistor, in the write period, the reference voltage is applied to the first electrode of the first capacitor in which the threshold voltage is held and the data voltage is applied to the second electrode of the second capacitor, so that a voltage corresponding to the data voltage is subjected to threshold compensation of the drive transistor and written to the first capacitor, and in the light emission period, a drive current corresponding to the voltage written to and held in the first capacitor is supplied to the display element.
2. 2 . The display device according to claim 1 , wherein the drive circuit drives the plurality of pixel circuits such that the write period for each of the pixel circuits partially overlaps with the write period for at least one other pixel circuit in which writing of the data voltage is started before the write period for the each of the pixel circuits.
3. 3 . The display device according to claim 1 , wherein the display portion further includes a plurality of data signal lines, a plurality of first scanning signal lines, a plurality of second scanning signal lines, a plurality of third scanning signal lines, a plurality of first light emission control lines, and a plurality of second light emission control lines, the write control switching element has a control terminal connected to one first scanning signal line of the plurality of first scanning signal lines, the initialization switching element has a control terminal connected to one second scanning signal line of the plurality of second scanning signal lines, the reference voltage supply control switching element has a control terminal connected to one third scanning signal line of the plurality of third scanning signal lines, the first light emission control switching element has a control terminal connected to one first light emission control line of the plurality of first light emission control lines, the second light emission control switching element has a control terminal connected to one second light emission control line of the plurality of second light emission control lines, the second electrode of the second capacitor is connected to one data signal line of the plurality of data signal lines via the write control switching element, and the drive circuit drives the plurality of first scanning signal lines, the plurality of second scanning signal lines, the plurality of third scanning signal lines, the plurality of first light emission control lines, and the plurality of second light emission control lines, and drives the plurality of data signal lines in conjunction with driving of the plurality of first scanning signal lines such that in each of the pixel circuits, in the initialization period, the write control switching element and the second light emission control switching element are in OFF state, and the initialization switching element, the first light emission control switching element, and the reference voltage supply control switching element are in ON state, in the compensation period, the write control switching element and the first light emission control switching element are in OFF state, and the initialization switching element, the reference voltage supply control switching element, and the second light emission control switching element are in ON state, in the write period, the initialization switching element, the first light emission control switching element, and the second light emission control switching element are in OFF state, and the write control switching element and the reference voltage supply control switching element are in ON state, and in the light emission period, the write control switching element, the initialization switching element, and the reference voltage supply control switching element are in OFF state, and the first light emission control switching element and the second light emission control switching element are in ON state.
4. 4 . The display device according to claim 1 , wherein each of the pixel circuits further includes a current supply control switching element, the display portion further includes a plurality of data signal lines, a plurality of first scanning signal lines, a plurality of second scanning signal lines, a plurality of third scanning signal lines, and a plurality of light emission control lines, the write control switching element has a control terminal connected to one first scanning signal line of the plurality of first scanning signal lines, the initialization switching element has a control terminal connected to one second scanning signal line of the plurality of second scanning signal lines, the current supply control switching element has a control terminal connected to the one second scanning signal line, the reference voltage supply control switching element has a control terminal connected to one third scanning signal line of the plurality of third scanning signal lines, the second light emission control switching element has a control terminal connected to one light emission control line of the plurality of light emission control lines, the first light emission control switching element has a control terminal connected to another light emission control line of the plurality of light emission control lines, the another light emission control line transmitting a signal having a phase delayed from a phase of a signal transmitted by the one light emission control line, the second electrode of the second capacitor is connected to one data signal line of the plurality of data signal lines via the write control switching element, the drain terminal of the drive transistor is connected to the reference voltage line via the current supply control switching element, and the drive circuit drives the plurality of first scanning signal lines, the plurality of second scanning signal lines, the plurality of third scanning signal lines, and the plurality of light emission control lines and drives the plurality of data signal lines in conjunction with driving of the plurality of first scanning signal lines such that in each of the pixel circuits, in the initialization period, the write control switching element, the initialization switching element, the second light emission control switching element, and the current supply control switching element are in OFF state, and the first light emission control switching element and the reference voltage supply control switching element are in ON state, in the compensation period, the write control switching element, the first light emission control switching element, and the second light emission control switching element are in OFF state, and the initialization switching element, the reference voltage supply control switching element, and the current supply control switching element are in ON state, in the write period, the initialization switching element, the first light emission control switching element, the second light emission control switching element, and the current supply control switching element are in OFF state, and the write control switching element and the reference voltage supply control switching element are in ON state, and in the light emission period, the write control switching element, the initialization switching element, the reference voltage supply control switching element, and the current supply control switching element are in OFF state, and the first light emission control switching element and the second light emission control switching element are in ON state.
5. 5 . The display device according to claim 1 - or 2 , wherein the display portion further includes a plurality of data signal lines, a plurality of first scanning signal lines, a plurality of second scanning signal lines, and a plurality of light emission control lines, the reference voltage supply control switching element is an N-channel transistor or a P-channel transistor, and both the first light emission control switching element and the second light emission control switching element are transistors having conductivity types different from a conductivity type of the reference voltage supply control switching element, the write control switching element has a control terminal connected to one first scanning signal line of the plurality of first scanning signal lines, the initialization switching element has a control terminal connected to one second scanning signal line of the plurality of second scanning signal lines, the reference voltage supply control switching element has a control terminal connected to one light emission control line of the plurality of light emission control lines, the first light emission control switching element has a control terminal connected to the one light emission control line, the second light emission control switching element has a control terminal connected to another light emission control line of the plurality of light emission control lines, the another light emission control line transmitting a signal having a phase delayed from a phase of a signal transmitted by the one light emission control line, the second electrode of the second capacitor is connected to one data signal line of the plurality of data signal lines via the write control switching element, and the drive circuit drives the plurality of first scanning signal lines, the plurality of second scanning signal lines, and the plurality of light emission control lines and drives the plurality of data signal lines in conjunction with driving of the plurality of first scanning signal lines such that in each of the pixel circuits, the initialization period and the compensation period are integrated as an initialization/compensation period, and in the initialization/compensation period, the write control switching element and the first light emission control switching element are in OFF state, and the initialization switching element, the second light emission control switching element, and the reference voltage supply control switching element are in ON state, in the write period, the initialization switching element, the first light emission control switching element, and the second light emission control switching element are in OFF state, and the write control switching element and the reference voltage supply control switching element are in ON state, and in the light emission period, the write control switching element, the initialization switching element, and the reference voltage supply control switching element are in OFF state, and the first light emission control switching element and the second light emission control switching element are in ON state.
6. 6 . A pixel circuit included in a display portion provided in a display device, the pixel circuit comprising: a display element driven by a current; a drive transistor of an N-channel type; a write control switching element; an initialization switching element; a reference voltage supply control switching element; a first light emission control switching element; a second light emission control switching element; a first capacitor; and a second capacitor, wherein the display portion further includes a high-voltage power supply line, a low-voltage power supply line, an initialization voltage line for supplying an initialization voltage determined in advance, and a reference voltage line for supplying a reference voltage determined in advance, the drive transistor has a drain terminal connected to the high-voltage power supply line via the second light emission control switching element, a gate terminal connected to the reference voltage line via the reference voltage supply control switching element, and a source terminal connected to the display element via the first light emission control switching element, the display element has a first terminal connected to the source terminal of the drive transistor via the first light emission control switching element and connected to the initialization voltage line via the initialization switching element, and a second terminal connected to the low-voltage power supply line, the first capacitor has a first electrode connected to the gate terminal of the drive transistor and a second electrode connected to the source terminal of the drive transistor, and the second capacitor has a first electrode connected to the source terminal of the drive transistor, and a second electrode connected to the first terminal of the display element and configured to receive a data voltage to be written to the pixel circuit via the write control switching element.
7. 7 . The pixel circuit according to claim 6 , wherein the display portion further includes a plurality of data signal lines, a plurality of first scanning signal lines, a plurality of second scanning signal lines, a plurality of third scanning signal lines, a plurality of first light emission control lines, and a plurality of second light emission control lines, the write control switching element has a control terminal connected to one first scanning signal line of the plurality of first scanning signal lines, the initialization switching element has a control terminal connected to one second scanning signal line of the plurality of second scanning signal lines, the reference voltage supply control switching element has a control terminal connected to one third scanning signal line of the plurality of third scanning signal lines, the first light emission control switching element has a control terminal connected to one first light emission control line of the plurality of first light emission control lines, the second light emission control switching element has a control terminal connected to one second light emission control line of the plurality of second light emission control lines, and the second electrode of the second capacitor is connected to one data signal line of the plurality of data signal lines via the write control switching element.
8. 8 . The pixel circuit according to claim 6 , further comprising a current supply control switching element, wherein the display portion further includes a plurality of data signal lines, a plurality of first scanning signal lines, a plurality of second scanning signal lines, a plurality of third scanning signal lines, and a plurality of light emission control lines, the write control switching element has a control terminal connected to one first scanning signal line of the plurality of first scanning signal lines, the initialization switching element has a control terminal connected to one second scanning signal line of the plurality of second scanning signal lines, the current supply control switching element has a control terminal connected to the one second scanning signal line, the reference voltage supply control switching element has a control terminal connected to one third scanning signal line of the plurality of third scanning signal lines, the second light emission control switching element has a control terminal connected to one light emission control line of the plurality of light emission control lines, the first light emission control switching element has a control terminal connected to another light emission control line of the plurality of light emission control lines, the another light emission control line transmitting a signal having a phase delayed from a phase of a signal transmitted by the one light emission control line, the drain terminal of the drive transistor is connected to the reference voltage line via the current supply control switching element, and the second electrode of the second capacitor is connected to one data signal line of the plurality of data signal lines via the write control switching element.
9. 9 . The pixel circuit according to claim 6 , wherein the display portion further includes a plurality of data signal lines, a plurality of first scanning signal lines, a plurality of second scanning signal lines, and a plurality of light emission control lines, the reference voltage supply control switching element is an N-channel transistor or a P-channel transistor, and both the first light emission control switching element and the second light emission control switching element are transistors having conductivity types different from a conductivity type of the reference voltage supply control switching element, the write control switching element has a control terminal connected to one first scanning signal line of the plurality of first scanning signal lines, the initialization switching element has a control terminal connected to one second scanning signal line of the plurality of second scanning signal lines, the reference voltage supply control switching element has a control terminal connected to one light emission control line of the plurality of light emission control lines, the first light emission control switching element has a control terminal connected to the one light emission control line, the second light emission control switching element has a control terminal connected to another light emission control line of the plurality of light emission control lines, the another light emission control line transmitting a signal having a phase delayed from a phase of a signal transmitted by the one light emission control line, and the second electrode of the second capacitor is connected to one data signal line of the plurality of data signal lines via the write control switching element.
10. 10 . The pixel circuit according to claim 6 , wherein the drive transistor is a thin film transistor in which a channel layer is formed of an oxide semiconductor.
11. 11 . A method for driving a pixel circuit included in a display portion provided in a display device, wherein the pixel circuit includes a display element driven by a current, a drive transistor of an N-channel type, a write control switching element, an initialization switching element, a reference voltage supply control switching element, a first light emission control switching element, a second light emission control switching element, a first capacitor, and a second capacitor, the display portion further includes a high-voltage power supply line, a low-voltage power supply line, an initialization voltage line for supplying an initialization voltage determined in advance, and a reference voltage line for supplying a reference voltage determined in advance, the drive transistor has a drain terminal connected to the high-voltage power supply line via the second light emission control switching element, a gate terminal connected to the reference voltage line via the reference voltage supply control switching element, and a source terminal connected to the display element via the first light emission control switching element, the display element has a first terminal connected to the source terminal of the drive transistor via the first light emission control switching element and connected to the initialization voltage line via the initialization switching element, and a second terminal connected to the low-voltage power supply line, the first capacitor has a first electrode connected to the gate terminal of the drive transistor and a second electrode connected to the source terminal of the drive transistor, the second capacitor has a first electrode connected to the source terminal of the drive transistor, and a second electrode connected to the first terminal of the display element and configured to receive a data voltage to be written to the pixel circuit via the write control switching element, and the method comprises: initializing the first capacitor and the second capacitor such that a voltage for bringing the drive transistor to ON state is held in the first capacitor; performing a threshold detection by changing the voltage held in the first capacitor as a result of initializing the first capacitor and the second capacitor, to a threshold voltage of the drive transistor; writing a voltage corresponding to the data voltage to the first capacitor by applying the reference voltage to the first electrode of the first capacitor in which the threshold voltage is held in as a result of the threshold detection-step and applying the data voltage to the second electrode of the second capacitor; and performing a light emission by supplying a drive current corresponding to the voltage written to and held in the first capacitor as a result of writing the voltage corresponding to the data voltage, to the display element.
12. 12 . The method according to claim 11 , wherein in writing the voltage corresponding to the data voltage, the pixel circuit is driven such that a period for writing the data voltage to the pixel circuit partially overlaps with a period for writing the data voltage to at least one other pixel circuit in which writing of the data voltage is started before the period for writing the data voltage to the pixel circuit.

Description

TECHNICAL FIELD The present disclosure relates to a display device, and particularly to a current drive type display device including a display element driven by a current, such as an organic electroluminescence (EL) display device, a pixel circuit used in the display device, and a method for driving the pixel circuit. BACKGROUND ART In recent years, an organic EL display device including a pixel circuit provided with an organic EL element (also referred to as an organic light emitting diode (OLED)) has been put into practical use, the organic EL display device being also referred to as an “OLED display device”. The pixel circuit of the organic EL display device includes a drive transistor, a write control transistor, a holding capacitor, and the like in addition to the organic EL element. A thin film transistor is used for the drive transistor and the write control transistor, the holding capacitor is connected to a gate terminal of the drive transistor, and a voltage (specifically, a voltage indicating a gradation value of a pixel to be formed in the pixel circuit, and hereinafter referred to as a “data voltage”) corresponding to a data signal representing an image to be displayed is applied to the holding capacitor from a drive circuit via a data signal line. The organic EL element is a self-luminous display element that emits light with luminance corresponding to a current flowing through the organic EL element. The drive transistor is provided in series with the organic EL element, and controls a current flowing through the organic EL element in accordance with a voltage held in the holding capacitor. Variations and shifts occur in the characteristics of the organic EL element and the drive transistor. Therefore, in order to perform high image quality display in the organic EL display device, it is necessary to compensate for variations and shifts in characteristics of these elements. As for the device, method organic EL display a of compensating characteristics of these elements inside a pixel circuit and a method of compensating characteristics of these elements outside the pixel circuit are known. As a pixel circuit corresponding to the former method, there is known a pixel circuit configured to initialize a voltage of a gate terminal of a drive transistor, that is, a voltage held in a holding capacitor, and then charge the holding capacitor with a data voltage via the drive transistor in a diode-connected state. Inside of such a pixel circuit, variations and shifts in the threshold voltage of the drive transistor are compensated for (hereinafter, this compensation for variations and shifts in the threshold voltage is referred to as “threshold compensation”). As an organic EL display device of a system of performing threshold compensation in a pixel circuit (hereinafter referred to as an “internal compensation system”), there is also known an organic EL display device including a pixel circuit that performs internal compensation in a configuration different from a configuration of an organic EL display device using a pixel circuit configured to charge a holding capacitor with a data voltage via a drive transistor in a diode-connected state as described above (hereinafter referred to as an “internal compensation type pixel circuit based on diode connection”). For example, as illustrated in FIG. 20, in a pixel circuit 101 in an organic EL display device described in Patent Document 1, a capacitor C111 corresponding to the holding capacitor is connected between a gate terminal and a source terminal of a drive transistor 111, a capacitor C112 is provided in series with the capacitor C111, and one end of the capacitor C112 is connected to a gate of the drive transistor 111. In the internal compensation type pixel circuit based on diode connection, as described above, after initialization of the holding capacitor, the holding capacitor is charged with the data voltage via the drive transistor in the diode-connection state, and thus, the data voltage subjected to threshold compensation is written in the holding capacitor. On the other hand, in the pixel circuit in the organic EL display device described in Patent Document 1, after the capacitors C111 and C112 are initialized, an operation of holding a threshold voltage Vth of the drive transistor 111 in the capacitor C111 for threshold compensation is performed, and thereafter, a data signal is applied to the other end of the capacitor C112, and thus, a voltage corresponding to the voltage of the data signal is subjected to threshold compensation and written in the capacitor C111. CITATION LIST Patent Documents [Patent Document 1] JP 2004-361640 A[Patent Document 2] JP 2021-510207 A[Patent Document 3] WO 2008/152793 SUMMARY Technical Problem In the internal compensation type pixel circuit based on the diode connection, threshold compensation of the drive transistor is performed simultaneously when the data voltage is written to the holding capacitor. In th