ACTIVE-MATRIX-TYPE LIGHT-EMITTING DEVICE, ELECTRONIC APPARATUS, AND PIXEL DRIVING METHOD FOR ACTIVE-MATRIX-TYPE LIGHT-EMITTING DEVICE

• US 20080036706A1
• Filed: 07/11/2007
• Published: 02/14/2008
• Est. Priority Date: 08/09/2006
• Status: Active Grant

• Current Assignee: Element Capital Commercial Company Pte. Ltd.
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: KITAZAWA, Takayuki
• Granted Patent: US 9,099,036 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0439 Pixel structures
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0838 with level shifting
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2300/0876 Supplementary capacities in pixels having special driving circuits and electrodes instead of being connected to common electrode or ground; Use of additional capacitively coupled compensation electrodes
• CPC Class Codes: G09G 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2310/0289 Details of voltage level shifters arranged for use in a driving circuit
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3266 Details of drivers for scan electrodes
• CPC Class Codes: G09G 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements

Abstract

An active-matrix-type light-emitting device includes: a pixel circuit including a light-emitting element, a driving transistor that drives the light-emitting element, a holding capacitor whose one end is connected to the driving transistor and which stores electric charges corresponding to written data, at least a control transistor that controls an operation associated with writing of data into the holding capacitor, and an emission control transistor; a first scanning line for controlling ON/OFF of the control transistor and a second scanning line for controlling ON/OFF of the emission control transistor; a data line through which the written data is transmitted to the pixel circuit; and a scanning line driving circuit which drives the first and second scanning lines and in which a current drive capability associated with the second scanning line is set to be lower than a current drive capability associated with the first scanning line.

Claims

1. An active-matrix-type light-emitting device comprising:

a pixel circuit including a light-emitting element, a driving transistor that drives the light-emitting element, a holding capacitor whose one end is connected to the driving transistor and which stores electric charges corresponding to written data, at least one control transistor that controls an operation associated with writing of data into the holding capacitor, and an emission control transistor provided between the light-emitting element and the driving transistor;

a first scanning line for controlling ON/OFF of the control transistor and a second scanning line for controlling ON/OFF of the emission control transistor;

a data line through which the written data is transmitted to the pixel circuit; and

a scanning line driving circuit which drives the first and second scanning lines and in which a current drive capability associated with the second scanning line is set to be lower than a current drive capability associated with the first scanning line.

2. The active-matrix-type light-emitting device according to claim 1,

wherein the scanning line driving circuit includes first and second output buffers for driving the first and second scanning lines, respectively, and

the size of a transistor included in the second output buffer is smaller than that of a transistor included in the first output buffer.

3. The active-matrix-type light-emitting device according to claim 2,

wherein the transistors included in the first and second output buffers are insulation gate type field effect transistors, and

the channel conductance (W/L) of the transistor included in the second output buffer is smaller than that of the transistor included in the first output buffer.

4. The active-matrix-type light-emitting device according to claim 1,

wherein the scanning line driving circuit includes first and second output buffers for driving the first and second scanning lines, respectively, and

a resistor is connected to an output end of the second output buffer in order to set a current drive capability associated with the second scanning line to be lower than a current drive capability associated with the first scanning line.

5. The active-matrix-type light-emitting device according to claim 1,

wherein the driving transistor is an insulation gate type field effect transistor, and

the current amount of a coupling current is reduced by decreasing a current drive capability associated with the second scanning line, such that unnecessary emission of the light-emitting element at the time of black display is suppressed, the coupling current being generated in a case when a changed component of an electric potential of the second scanning line leaks to the light-emitting element through a parasitic capacitance between a gate and a source of the emission control transistor when shifting the emission control transistor from an OFF state to an ON state by changing an electric potential of the second scanning line.

6. The active-matrix-type light-emitting device according to claim 1,

wherein the emission control transistor and the light-emitting element are disposed on a substrate so as to be close to each other.

7. The active-matrix-type light-emitting device according to claim 1,

wherein a current drive capability associated with the second scanning line is adjusted such that a period of time from the start of change of an electric potential of the second scanning line to convergence of the change is one horizontal synchronization period (1 H) or more.

8. The active-matrix-type light-emitting device according to claim 1,

wherein the control transistor driven through the first scanning line is a switching transistor connected between the data line and a common connection point between the holding capacitor and the driving transistor,

the switching transistor performs an ON/OFF operation at least once during one horizontal synchronization period (1 H), and

the emission control transistor driven through the second scanning line performs an ON/OFF operation at least once during a predetermined period within one vertical synchronization period (1 V).

9. The active-matrix-type light-emitting device according to claim 1,

wherein the pixel circuit is a pixel circuit using a current programming method, in which an emission gray scale of the light-emitting element is adjusted by controlling electric charges stored in the holding capacitor by means of a current flowing through the data line, or a pixel circuit using a voltage programming method, in which the emission gray scale of the light-emitting element is adjusted by controlling the electric charges stored in the holding capacitor by means of a voltage signal transmitted through the data line.

10. The active-matrix-type light-emitting device according to claim 1,

wherein the pixel circuit is a pixel circuit that uses a current programming method and has a circuit configuration for compensating for a change in a threshold voltage of an insulation gate type field effect transistor serving as the driving transistor,

the control transistor driven through the first scanning line is a write transistor having an end connected to the data line and the other end connected to an end of a coupling capacitor, and

the other end of the coupling capacitor is connected to a common connection point between the holding capacitor and the driving transistor.

11. The active-matrix-type light-emitting device according to claim 1,

wherein the light-emitting element is an organic electroluminescent element (organic EL element).

12. An electronic apparatus comprising the active-matrix-type light-emitting device according to claim 1.

13. The electronic apparatus according to claim 12,

wherein the active-matrix-type light-emitting device is used as a display device or a light source.

14. A pixel driving method for an active-matrix-type light-emitting device of performing ON/OFF driving for a control transistor and an emission control transistor through first and second scanning lines, respectively, in a pixel circuit including a light-emitting element, a driving transistor that drives the light-emitting element, a holding capacitor whose one end is connected to the driving transistor and which stores electric charges corresponding to written data, at least one control transistor that controls an operation associated with writing of data into the holding capacitor, and the emission control transistor provided between the light-emitting element and the driving transistor, the pixel driving method comprising:

setting a current drive capability associated with the second scanning line to be lower than a current drive capability associated with the first scanning line,

wherein a coupling current is reduced due to the setting, such that unnecessary emission of the light-emitting element at the time of black display is suppressed, the coupling current being generated in a case when a changed component of an electric potential of the second scanning line leaks to the light-emitting element through a parasitic capacitance between a gate and a source of the emission control transistor when shifting the emission control transistor from an OFF state to an ON state by changing an electric potential of the second scanning line.