# US 7,411,586 B2 · Light emitting device, method of driving a light emitting device, element substrate, and electronic equipment

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- Number: US 7,411,586 B2
- Document ID: US7411586B2
- Status: Granted
- Kind: B2
- Application number: 11/382,085
- Filed: 2006-05-08
- Published: 2006-11-16
- Granted: 2008-08-12
- Earliest claimed: 2001-08-29
- Assignees: Semiconductor Energy Laboratory Co., Ltd.
- Inventors: Hajime Kimura
- Web page: https://patentgrep.com/patent/US7411586B2

## CPC

- G09G 3/2022: {using sub-frames}
- G09G 3/3208: organic, e.g. using organic light-emitting diodes [OLED]
- G09G 3/3225: using an active matrix
- G09G 3/3241: the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
- 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
- H10D 30/0314: {of lateral top-gate TFTs comprising only a single gate}
- H10D 30/0321: {comprising silicon, e.g. amorphous silicon or polysilicon}
- H10D 30/6715: {characterised by the doping profiles, e.g. having lightly-doped source or drain extensions}
- H10D 30/673: {characterised by the shapes, relative sizes or dispositions of the gate electrodes}
- H10D 30/6739: {Conductor-insulator-semiconductor electrodes}
- G09G 2300/0814: used for selection purposes, e.g. logical AND for partial update
- G09G 2300/0842: forming a memory circuit, e.g. a dynamic memory with one capacitor
- G09G 2300/0861: with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
- G09G 2310/061: for resetting or blanking
- G09G 2320/0233: Improving the luminance or brightness uniformity across the screen
- H10D 30/6721: {having lightly-doped extensions consisting of multiple lightly doped zones or having non-homogeneous dopant distributions, e.g. graded LDD}
- H10D 86/00: Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates
- H10D 86/40: characterised by multiple TFTs
- H10D 86/60: wherein the TFTs are in active matrices
- H10K 59/12: Active-matrix OLED [AMOLED] displays
- H10K 59/871: {Self-supporting sealing arrangements}
- H10K 59/873: {Encapsulations}
- H10K 59/874: {including getter material or desiccant}
- G09G: ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION (arrangements for transferring data between digital computers and displays G06F3/14; static indicating arrangements comprising an association of a number of separate sources or light control cells G09F9/00; static indicating arrangements comprising integral associations of a number of light sources H01J, H01K, H10H, H05B33/12; scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission, details thereof H04N1/00)
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
- H10K: ORGANIC ELECTRIC SOLID-STATE DEVICES

## Abstract

A display device capable of obtaining a constant luminance without being influenced by temperature change is provided as well as a method of driving the display device. A current mirror circuit composed of a first transistor and a second transistor is provided in each pixel. The first transistor and second transistor of the current mirror circuit are connected such that their drain currents are kept almost equal irrespective of the level of load resistance. By controlling the OLED drive current using the current mirror circuit, a change in OLED drive current due to fluctuation in characteristics between transistors is avoided and a constant luminance is obtained without being influenced by temperature change.

## Claims

### Claim 1

A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a light emitting element, a power supply line, and a signal line,
wherein the first transistor and the second transistor are connected to each other at their gates,
wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a source of the first transistor,
wherein the fourth transistor has a source and a drain one of which is connected to the gates of the first and second transistors and the other of which is connected to the power supply line,
wherein the fifth transistor has a source and a drain one of which is connected to the source of the first transistor and the other of which is connected to a pixel electrode of the light emitting element,
wherein the sixth transistor has a source and a drain one of which is connected to a source of the second transistor and the other of which is connected to the pixel electrode of the light emitting element, and
wherein a gate of the fifth transistor and a gate of the sixth transistor are connected to each other.

### Claim 2 (depends on 1)

A light emitting device according to claim 1, wherein the fifth transistor and the sixth transistor have the same polarity.

### Claim 3 (depends on 1)

A light emitting device according to claim 1, wherein the first transistor and the second transistor have the same polarity.

### Claim 4 (depends on 1)

Electronic equipment comprising a light emitting device of claim 1.

### Claim 5

A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a light emitting element, a power supply line, and a signal line,
wherein a source of the first transistor and a source of the second transistor are both connected to the power supply line,
wherein the first transistor and the second transistor are connected to each other at their gates,
wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a drain of the first transistor,
wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor or to the signal line and the other of which is connected to the gates of the first and second transistors,
wherein the fifth transistor has a source and a drain one of which is connected to a drain of the sixth transistor and the other of which is connected to a drain of the second transistor,
wherein a gate of the sixth transistor is connected to the gates of the first and second transistors,
wherein a source of the sixth transistor is connected to the drain of the first transistor, and
wherein the drain of the second transistor is connected to a pixel electrode of the light emitting element.

### Claim 6 (depends on 5)

A light emitting device according to claim 5, wherein the first transistor and the second transistor have the same polarity.

### Claim 7 (depends on 5)

Electronic equipment comprising a light emitting device of claim 5.

### Claim 8

A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a light emitting element, a power supply line, and a signal line,
wherein a source of the first transistor and a source of the second transistor are both connected to the power supply line,
wherein the first transistor and the second transistor are connected to each other at their gates,
wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a drain of the first transistor,
wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor or to the signal line and the other of which is connected to the gates of the first and second transistors,
wherein the fifth transistor has a source and a drain one of which is connected to a drain of the first transistor and the other of which is connected to a source of the sixth transistor,
wherein a gate of the sixth transistor is connected to the gates of the first and second transistors,
wherein a drain of the sixth transistor is connected to the drain of the second transistor, and
wherein the drain of the second transistor is connected to a pixel electrode of the light emitting element.

### Claim 9 (depends on 8)

A light emitting device according to claim 8, wherein the first transistor and the second transistor have the same polarity.

### Claim 10 (depends on 8)

Electronic equipment comprising a light emitting device of claim 8.

### Claim 11

A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a light emitting element, a power supply line, and a signal line,
wherein the first transistor and the second transistor are connected to each other at their gates,
wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a drain of the first transistor,
wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor or to the signal line and the other of which is connected to the gates of the first and second transistors,
wherein the fifth transistor has a source and a drain one of which is connected to a drain of the second transistor and the other of which is connected to a drain of the first transistor, and
wherein the sources of the first and second transistors are connected to a pixel electrode of the light emitting element.

### Claim 12 (depends on 11)

A light emitting device according to claim 11, wherein the first transistor and the second transistor have the same polarity.

### Claim 13 (depends on 11)

Electronic equipment comprising a light emitting device of claim 11.

### Claim 14

A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a light emitting element, a power supply line, and a signal line,
wherein the first transistor and the second transistor are connected to each other at their gates,
wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a drain of the first transistor,
wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor or to the signal line and the other of which is connected to the gates of the first and second transistors,
wherein the fifth transistor has a source and a drain one of which is connected to a drain of the second transistor and the other of which is connected to a drain of the sixth transistor,
wherein the source of the sixth transistor is connected to the drain of the first transistor, and
wherein the sources of the first and second transistors are connected to a pixel electrode of the light emitting element.

### Claim 15 (depends on 14)

A light emitting device according to claim 14, wherein the first transistor and the second transistor have the same polarity.

### Claim 16 (depends on 14)

Electronic equipment comprising a light emitting device of claim 14.

### Claim 17

A light emitting device having a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a light emitting element, a power supply line, and a signal line,
wherein the first transistor and the second transistor are connected to each other at their gates,
wherein the third transistor has a source and a drain one of which is connected to the signal line and the other of which is connected to a source of the first transistor,
wherein the fourth transistor has a source and a drain one of which is connected to the drain of the first transistor and the other of which is connected to the gates of the first and second transistors,
wherein the fifth transistor has a source and a drain one of which is connected to the source of the first transistor and the other of which is connected to a source of the second transistor,
wherein the drains of the first and second transistors are connected to the power supply line, and
wherein the source of the second transistor is connected to a pixel electrode of the light emitting element.

### Claim 18 (depends on 17)

A light emitting device according to claim 17 further comprising a sixth transistor, wherein the sixth transistor has a source and a drain one of which is connected to the source of the second transistor and the other of which is connected to the source of the first transistor.

### Claim 19 (depends on 17)

A light emitting device according to claim 17 further comprising a sixth transistor, wherein the sixth transistor has a source and a drain one of which is connected to the source of the second transistor and the other of which is connected to the source of the first transistor, and
wherein a gate of the fifth transistor and a gate of the sixth transistor are connected to each other.

### Claim 20 (depends on 17)

A light emitting device according to claim 17, wherein the first transistor and the second transistor have the same polarity.

### Claim 21 (depends on 17)

Electronic equipment comprising a light emitting device of claim 17.

### Claim 22

A method of driving a light emitting device that has a plurality of pixels each including a light emitting device,
wherein, in a first period, a current determined by a video signal is supplied to the pixels, and first means of each of the pixels converts the supplied current into a voltage to supply a first current to the light emitting element in an amount according to the voltage converted, and
wherein, in a second period, the first means of each of the pixels supplies a third current to the light emitting element in an amount according to the voltage converted, and second means of each of the pixels supplies a second current to the light emitting element in an amount according to the voltage converted.

### Claim 23

A method of driving a light emitting device with one frame period having a first period and a second period,
wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates and a constant voltage is applied to sources of the first and second transistors,
wherein, in the first period, the gate of the first transistor is connected to a drain of the first transistor and a drain of the second transistor is connected to a pixel electrode of a light emitting element, and
wherein, in the second period, the drains of the first and second transistors are connected to the pixel electrode of the light emitting element and the gate of the first transistor is disconnected from the drain of the first transistor.

### Claim 24 (depends on 23)

A method of driving a light emitting device according to claim 23, wherein the amount of drain current of the first transistor is controlled in the first period to thereby control the luminance of the light emitting element in the second period.

### Claim 25 (depends on 23)

A light emitting device according to claim 23, wherein the first transistor and the second transistor have the same polarity.

### Claim 26

A method of driving a light emitting device with one frame period having a first period and a second period,
wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, a source of the first transistor and a source of the second transistor are connected to each other, and a constant voltage is applied to a drain of the first transistor,
wherein, in the first period, a drain of the second transistor is set to a floating state, and the gate of the first transistor is connected to the drain of the first transistor, and
wherein, in the second period, the constant voltage is applied to the drain of the second transistor, the gate of the first transistor is disconnected from the drain of the first transistor, and the sources of the first and second transistors are connected to a pixel electrode of a light emitting element.

### Claim 27 (depends on 26)

A method of driving a light emitting device according to claim 26, wherein the amount of drain current of the first transistor is controlled in the first period to thereby control the luminance of the light emitting element in the second period.

### Claim 28 (depends on 26)

A light emitting device according to claim 26, wherein the first transistor and the second transistor have the same polarity.

### Claim 29

A method of driving a light emitting device with one frame period having a first period and a second period,
wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, a drain of the first transistor and a drain of the second transistor are connected to each other, and a constant voltage is applied to the drains of the first and second transistors,
wherein, in the first period, the gates of the first and second transistors are connected to the drains of the first and second transistors, and
wherein, in the second period, sources of the first and second transistors are connected to a pixel electrode of a light emitting element.

### Claim 30 (depends on 29)

A method of driving a light emitting device according to claim 29, wherein the amount of drain current of the first transistor is controlled in the first period to thereby control the luminance of the light emitting element in the second period.

### Claim 31 (depends on 29)

A light emitting device according to claim 29, wherein the first transistor and the second transistor have the same polarity.

### Claim 32

A method of driving a light emitting device with one frame period having a first period and a second period,
wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, and a source of the first transistor and a source of the second transistor are connected to each other,
wherein, in the first period, a constant voltage is applied to the gate and drain of the first transistor, a drain of the second transistor is set to a floating state, and a drain current of the first transistor is controlled by a constant current source, and
wherein, in the second period, the gate of the first transistor is disconnected from the drain of the first transistor, a constant voltage is applied to the drains of the first and second transistors, and a drain current of the first transistor and a drain current of the second transistor both flow into a light emitting element.

### Claim 33

A method of driving a light emitting device with one frame period having a first period and a second period,
wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, and a drain of the first transistor and a drain of the second transistor are connected to each other,
wherein, in the first period, a constant voltage is applied to the gates of the first and second transistors and to the drains of the first and second transistors, and a drain current of the first transistor is controlled by a constant current source, and
wherein, in the second period, the gate of the first transistor is disconnected from the drain of the first transistor, the gate of the second transistor is disconnected from the drain of the second transistor, a constant voltage is applied to the drains of the first and second transistors, and a drain current of the first transistor and a drain current of the second transistor both flow into a light emitting element.

### Claim 34

A method of driving a light emitting device with one frame period having a first period and a second period,
wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, and a constant voltage is applied to sources of the first and second transistors,
wherein, in the first period, the gate of the first transistor is connected to a drain of the first transistor, a drain of the second transistor is connected to a pixel electrode of a light emitting element, and a drain current of the first transistor is controlled by a constant current source, and
wherein, in the second period, the gates of the first and second transistors are connected to a gate of a third transistor of the light emitting device, the first transistor and the third transistor have the same amount of drain current, and a drain current of the second transistor and a drain current of the third transistor both flow into the light emitting element.

### Claim 35

A method of driving a light emitting device with one frame period having a first period and a second period,
wherein, in the first and second periods, a first transistor and second transistor of the light emitting device are connected to each other at their gates, and a source of the first transistor and a source of the second transistor are both connected to a pixel electrode of a light emitting element,
wherein, in the first period, the gate of the first transistor is connected to a drain of the first transistor, a constant voltage is applied to a drain of the second transistor, and a drain current of the first transistor is controlled by a constant current source, and
wherein, in the second period, the gates of the first and second transistors are connected to a gate of a third transistor of the light emitting device, the drain of the first transistor is connected to a source of the third transistor, a constant voltage is applied to a drain of the third transistor and to the drain of the second transistor, and a drain current of the second transistor and a drain current of the third transistor both flow into the light emitting element.