Drive method of EL display panel

• US 8,063,855 B2
• Filed: 10/02/2007
• Issued: 11/22/2011
• Est. Priority Date: 04/26/2002
• Status: Active Grant

• Current Assignee: Japan Display Central Incorporated (Japan Display Incorporated)
• Original Assignee: Toshiba Matsushita Display Technology (Japan Display Incorporated)
• Inventors: Takahara, Hiroshi, Tsuge, Hitoshi
• Primary Examiner(s): Shalwala; Bipin
• Assistant Examiner(s): CHOWDHURY, AFROZA Y
• Application Number:
  US11/865,749
• Publication Number:
  US 20080084365A1
• Time in Patent Office: 1,512 Days
• Field of Search: 345/76, 345/204, 345/690
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/0408 Integration of the drivers onto the display substrate
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0452 Details of colour pixel setup, e.g. pixel composed of a red, a blue and two green components
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with 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 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2310/02 Addressing, scanning or driving the display screen or processing steps related thereto
• CPC Class Codes: G09G 2310/0218 with collection of electrodes in groups for n-dimensional addressing
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• 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 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2310/0283 Arrangement of drivers for different directions of scanning
• CPC Class Codes: G09G 2310/0297 Special arrangements with multiplexing or demultiplexing of display data in the drivers for data electrodes, in a pre-processing circuitry delivering display data to said drivers or in the matrix panel, e.g. multiplexing plural data signals to one D/A converter or demultiplexing the D/A converter output to multiple columns
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2320/0214 with crosstalk due to leakage current of pixel switch in active matrix panels
• CPC Class Codes: G09G 2320/0223 Compensation for problems related to R-C delay and attenuation in electrodes of matrix panels, e.g. in gate electrodes or on-substrate video signal electrodes
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• 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 2320/0606 : Manual adjustment
• CPC Class Codes: G09G 2320/0626 : for control of overall brightness
• CPC Class Codes: G09G 2320/066 : for control of contrast
• CPC Class Codes: G09G 2320/08 : Arrangements within a display terminal for setting, manually or automatically, display parameters of the display terminal
• CPC Class Codes: G09G 2330/02 : Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 2330/12 : Test circuits or failure detection circuits included in a display system, as permanent part thereof
• CPC Class Codes: G09G 3/006 : Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/20 : for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
• CPC Class Codes: G09G 3/2014 : by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/22 : using controlled light sources
• 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
• 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
• CPC Class Codes: H10K 50/844 : Encapsulations
• CPC Class Codes: H10K 50/846 : comprising getter material or desiccants
• CPC Class Codes: H10K 50/85 : Arrangements for extracting light from the devices
• CPC Class Codes: H10K 50/86 : Arrangements for improving contrast, e.g. preventing reflection of ambient light
• CPC Class Codes: H10K 50/87 : Arrangements for heating or cooling
• CPC Class Codes: H10K 59/12 : Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 59/131 : Interconnections, e.g. wiring lines or terminals
• CPC Class Codes: H10K 59/351 : comprising more than three subpixels, e.g. red-green-blue-white [RGBW]
• CPC Class Codes: H10K 59/353 : characterised by the geometrical arrangement of the RGB subpixels
• CPC Class Codes: H10K 59/88 : Dummy elements, i.e. elements having non-functional features
• CPC Class Codes: H10K 71/861 : Repairing

Abstract

A switching transistor is controlled to turn on or off depending on a turn-on voltage or a turn-off voltage applied to a gate signal line. A driver transistor is supplied with an image signal applied to a source signal line through a switching transistor. A voltage based on the supplied image signal is retained by a capacitor. The driver transistor supplies a light-emitting current to an EL element based on the voltage retained in the capacitor. A capacitor is formed between one terminal of the capacitor (that is, a gate terminal of the driver transistor) and a gate signal line. The capacitor causes the gate terminal voltage of the driver transistor to be varied depending on variation of the potential on the gate signal line.

Claims

1. An EL display apparatus comprising:

a display area in which pixels are arranged in a matrix, each of the pixels having an EL element;

source signal lines which transfer an image signal to the pixels;

gate signal lines;

a source driver circuit; and

a selection circuit;

wherein each of the pixels has;

a driver transistor which supplies an electric current to the EL element;

a first switching transistor which supplies the image signal applied to the source signal lines to the driver transistor;

a first capacitor connected to a gate terminal of the driver transistor, the first capacitor retaining a voltage which defines the electric current passing through the driver transistor; and

a second capacitor having a first terminal and a second terminal, said first terminal being connected to said gate signal line and said second terminal being connected to said gate terminal of the driver transistor,

wherein a gate terminal of the first switching transistor is connected to one of the gate signal lines, and

capacity of the second capacitor changes a potential on the gate terminal of the driver transistor depending on variation of a voltage applied to the one of the gate signal lines,

a change of said potential on the gate terminal of the driver transistor acts such that said driver transistor reduces said electric current supplied to said EL element,

said source driver outputs a signal from a signal output terminal,

said selection circuit has a plurality of groups, each one of said groups including one input terminal and a plurality of selection output terminals that can be connected with said one input terminal,

each one of said input terminals is connected with said signal output terminal of said source driver circuit, and each one of said selection output terminals is connected with each one of said source signal lines, and

said selection circuit selects one or more selection output terminals from said a plurality of selection output terminals and impresses said signal of said source driver circuit impressed to said input terminal of said selection circuit to said source signal line connected with said selected selection output terminal.

2. The EL display apparatus according to claim 1, further comprising a gate driver circuit which drives the gate signal lines,

wherein the gate driver circuit applies a voltage which causes the first switching transistor to turn on or off to the gate signal lines,

a first terminal of the second capacitor is connected to one of the gate signal lines connected to the gate terminal of the first switching transistor, and

a second terminal of the second capacitor is connected to the gate terminal of the driver transistor or one terminal of the first capacitor.

3. The EL display apparatus according to claim 1, further comprising a second switching transistor which causes a short-circuit between the gate terminal of the driver transistor and another terminal of the driver transistor,

wherein the second switching transistor has a multi-gate structure including dual gates or more.

4. The EL display apparatus according to claim 1, wherein a capacity of the second capacitor is smaller than a capacity of the first capacitor.

5. The EL display apparatus according to claim 1, wherein channel polarity of the driver transistor is the same as that of the first switching transistor.

6. The EL display apparatus according to claim 1, further comprising a third switching transistor in the pixel between the driver transistor and the EL element.

7. The EL display apparatus according to claim 1, further comprising a fourth switching transistor in the pixel,

wherein a first terminal of the fourth switching transistor is connected to the gate terminal of the driver transistor,

a second terminal of the fourth switching transistor is connected to an electrode or wire to which a predetermined voltage is applied, and

by operating the fourth switching transistor, the predetermined voltage is applied to the gate terminal of the driver transistor.

8. The EL display apparatus according to claim 1, wherein an encapsulation film is formed on an upper layer of an EL film constituting the EL element.

9. The EL display apparatus according to claim 1, further comprising a gate driver circuit which selects the gate signal lines,

wherein a control signal to the gate driver circuit is supplied from a source driver circuit.

10. The EL display apparatus according to claim 1, wherein at least a pixel having a first color and a pixel having a second color are arranged in a matrix in a display screen, and

a capacity of the second capacitor for the pixel having the first color is different from a capacity of the second capacitor for the pixel having the second color.

11. The EL display apparatus according to claim 1, wherein a film constituting the semiconductor for the transistors is formed in a laser anneal process in which striped laser shots are sequentially moved in parallel to a direction in which the source signal lines are formed.