Display apparatus and driving method thereof

• US 7,474,285 B2
• Filed: 05/16/2003
• Issued: 01/06/2009
• Est. Priority Date: 05/17/2002
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Kimura, Hajime
• Primary Examiner(s): Lefkowitz; Sumati
• Assistant Examiner(s): Kumar; Srilakshmi K
• Application Number:
  US10/438,821
• Publication Number:
  US 20030214466A1
• Time in Patent Office: 2,062 Days
• Field of Search: 345/39, 345/77, 345/82, 345/90, 327/108, 327/563, 348/647, 706/33
• US Class Current: 345/77
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: 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
• CPC Class Codes: G09G 2300/0885 Pixel comprising a non-linear two-terminal element alone in series with each display pixel element
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: 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
• CPC Class Codes: G09G 3/325 the data current flowing through the driving transistor during a setting phase, e.g. by using a switch for connecting the driving transistor to the data driver

Abstract

This invention provides a display apparatus in which it is possible to have a light emitting element emitted light with constant luminance without coming under the influence of deterioration over time, and it is possible to realize accurate gray scale express, and yet, it is possible to speed up writing of a signal current to each pixel, and influence of noise of a leak current etc. is suppressed, and a driving method thereof. A plurality of pairs of switch parts and current source circuits are disposed in each pixel. Switching of each of a plurality of the switch parts is controlled by a digital video signal. When the switch part is turned on, by a current supplied from the current source circuit making a pair with the switch part, the light emitting element emits light. A current which is supplied from one current source circuit to the light emitting element is constant. A value of a current flowing through the light emitting element is comparable to a value of added currents which are supplied to the light emitting element from respective all current source circuits making pairs with the switch parts which are in the conductive states.

Claims

1. A display device comprising;

a power supply line; and

a pixel comprising;

a first current source circuit and a second current source circuit; and

a first switch part electrically connected to the first current source circuit in series and a second switch part electrically connected to the second current source circuit in series,

wherein each of the first current source circuit and the second current source circuit comprises

a first transistor and a second transistor,

wherein the power supply line and the light emitting element are electrically connected through the first switch part and the first current source circuit, and

wherein the power supply line and the light emitting element are electrically connected through the second switch part and the second current source circuit.

2. A display device comprising:

a power supply line; and

a pixel comprising;

a first current source circuit and a second current source circuit; and

a first switch part electrically connected to the first current source circuit in series and a second switch part electrically connected to the second current source circuit in series,

wherein the power supply line and the light emitting element are electrically connected through the first switch part and the first current source circuit,

wherein the power supply line and the light emitting element are electrically connected through the second switch part and the second current source circuit, and

wherein each of the first current source circuit and the second current source circuit comprises;

a first transistor wherein a gate and a drain are connected;

a second transistor;

a first unit adapted to selectively input a control current as a drain current of the first transistor;

a second unit adapted to hold a gate voltage of the first transistor;

a third unit adapted to select a connection of a gate of the second transistor and the drain of the first transistor; and

a fourth unit adapted to set a drain current of the second transistor as an output current and wherein the second transistor has a gate voltage which is the same as the gate voltage of the first transistor.

3. The display device as set forth in claim 2, wherein current values of the output currents of the first current source circuit and the second current source circuit are set at values which differ.

4. The display device as set forth in claim 2, wherein current values of the control currents which are inputted to the first current source circuit and the second current source circuit are set at values which differ.

7. The display device as set forth in claim 3, wherein current values of the control currents which are inputted to the first current source circuit and the second current source circuit are set at values which differ.

5. A display device comprising:

a power supply line; and

a pixel comprising;

a first current source circuit and a second current source circuit; and

a first switch part electrically connected to the first current source circuit in series and a second switch part electrically connected to the second current source circuit in series,

wherein the power supply line and the light emitting element are electrically connected through the first switch part and the first current source circuit,

wherein the power supply line and the light emitting element are electrically connected through a second switch part and the second current source circuit,

wherein the first current source circuit comprises;

a first transistor wherein a gate and a drain are connected;

a second transistor;

a first unit adapted to selectively input a control current as a drain current of the first transistor;

a second unit adapted to hold a gate voltage of the first transistor;

a third unit adapted to select a connection of the gate and the drain of the first transistor; and

a fourth unit adapted to set a drain current of the second transistor as an output current and wherein the second transistor has a gate voltage which is the same as the gate voltage of the first transistor, and

wherein the second current source circuit comprises;

a third transistor wherein a gate and a drain are connected;

a fourth transistor;

a fifth unit adapted to selectively input the control current as a drain current of the third transistor;

a sixth unit adapted to hold a gate voltage of the third transistor;

a seventh unit adapted to select a connection of the gate of the third transistor and the gate of the fourth transistor; and

an eighth unit adapted to set a drain current of the fourth transistor as an output current and wherein the fourth transistor has a gate voltage which is the same as the gate voltage of the third transistor.

6. The display device as set forth in claim 5, wherein current values of the output currents of the first current source circuit and the second current source circuit are set at values which differ.