Drive method of EL display panel

• US 7,777,698 B2
• Filed: 03/06/2003
• Issued: 08/17/2010
• 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:
  US10/511,447
• Publication Number:
  US 20050168491A1
• Time in Patent Office: 2,721 Days
• Field of Search: 345/690, 345/76, 345/204
• 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

In order to charge and discharge parasitic capacitance of a source signal line sufficiently and program a predetermined current value into a pixel transistor, it is necessary to output a relatively large current from the source driver circuit. However, if such a large current is passed through the source signal line, the value of this current is programmed into the pixel, causing a larger than desired current to flow through an EL element. For example, if a 10 times larger current is used for programming, a 10 times larger current flows through the EL element, and thus the EL element illuminates 10 times more brightly. To obtain predetermined emission brightness, the time during which the current flows through the EL element can be reduced to 1/10 of one frame (1 F). This way, the parasitic capacitance of the source signal line can be charged and discharged sufficiently and the predetermined emission brightness can be obtained.

Claims

1. A drive method for an EL display panel that has a display screen in which pixels are formed in a matrix state, the EL display panel comprising:

EL elements arranged in a matrix;

driver transistors which supply current to be passed through the EL elements;

a first condenser having a first terminal and a second terminal;

first switching elements placed in current paths of the EL elements;

a switching transistor which is connected between a gate terminal and another terminal of said driver transistor; and

a gate driver circuit which turns on and off the first switching elements for control;

wherein;

said first terminal of the condenser is connected to said gate terminal of the driver transistor,

said second terminal of the first condenser is connected to an electrode to which a predetermined voltage is impressed,

said switching transistor has a multi-gate structure,

the gate driver circuit generates a plurality of stripe non-display areas on said display screen of the EL display panel by controlling the first switching elements in an off-state two or more times during one frame period,

the gate driver circuit moves the plurality of stripe non-display areas in a scanning direction of the gate driver circuit at a cycle of one frame period, and

an operation for retaining an image signal applied to each pixel is executed only once during the one frame period.

3. The drive method for the EL display panel according to claim 1,

wherein the first switching elements are turned off periodically during one frame period.

4. The drive method for the EL display panel according to claim 1, wherein the gate driver circuit is formed in a same process as the driver transistors.

5. The drive method for the EL display panel according to claim 1, wherein the gate driver circuit is constructed of P-channel transistors.

6. The drive method for the EL display panel according to claim 1, wherein the driver transistors are P-channel transistors.

8. The drive method for the EL display panel according to claim 1, wherein brightness of the display screen is varied or controlled by varying proportion of the non-display area to a display area of the display screen.

2. A drive method for an EL display panel that has a display screen in which pixels are formed in a matrix state, the EL display panel comprising:

EL elements arranged in a matrix;

driver transistors which supply current to be passed through the EL elements;

a first condenser having a first terminal and a second terminal;

first switching elements placed in current paths of the EL elements;

a switching transistor which is connected between a gate terminal and another terminal of said driver transistor; and

a gate driver circuit which selects pixel rows of the EL display panel in sequence;

wherein,

said first terminal of the condenser is connected to said gate terminal of the driver transistor,

said second terminal of the condenser is connected to an electrode to which a predetermined voltage is impressed,

said switching transistor has a multi-gate structure,

a start pulse to be input into the gate driver circuit is controlled to turn on and off said first switching element,

a plurality of stripe non-display areas on said display screen of the EL display panel are generated and the plurality of stripe non-display areas are moved in a scanning direction of the gate driver circuit at a cycle of one frame period; and

an operation for retaining an image signal applied to each pixel is executed only once during the one frame period.

7. The drive method for the EL display panel according to claim 2, wherein the driver transistors are P-channel transistors.

9. The drive method for the EL display panel according to claim 2, wherein brightness of the display screen is varied or controlled by varying proportion of the non-display area to a display area of the display screen.

10. The drive method for the EL display panel according to claim 2, wherein the gate driver circuit is formed with P-channel transistors.

11. An EL display panel that has a display screen in which pixels are formed in matrix state, comprising:

a gate driver circuit which selects a line of the pixels of said display screen; and

a source driver circuit which supplies an image signal that is to be impressed to said pixels;

wherein,

each said pixel has an EL element, a driver transistor which supplies current to the EL element, a first switching element and a second switching element,

said gate driver circuit turns on said second switching element to impress a first voltage to a selected line of the pixels,

said gate driver circuit turns on said first switching element to impress said image signal to said line of the pixels,

said image signal is impressed to said line of the pixels after said first voltage is impressed to said line of the pixels,

said line of the pixels to which said first voltage was impressed becomes a non-display area until said image signal is impressed to said line of the pixels, and

said non-display area is moved in a scanning direction of said gate driver circuit at a cycle of frame period.

12. The EL display panel according to claim 11, further comprising:

a condenser that is formed in said pixel, wherein

said condenser has a first terminal and a second terminal,

a switching element comprising a switching transistor,

said first terminal of said condenser is connected with a gate terminal of said switching transistor, and said second terminal of said condenser is connected with a gate terminal of said driver transistor.

13. The EL display panel according to claim 11, wherein

after said second switching element of the pixel is turned on and said first voltage is impressed to said pixel, and

after a plurality of horizontal scanning periods, said first switching element of the pixel is turned on to impress said image signal to said pixel.

14. The EL display panel according to claim 11, further comprising:

a selection circuit formed on an output side of said source driver circuit, wherein

said source driver circuit 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 a source signal line for transmitting the image signal to said pixel, and

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

15. The EL display panel according to claim 11, wherein

said each pixel further has a third switching element which short-circuits a gate terminal and the other terminal of said driver transistor, and

said third switching element is a transistor having a multi-gate structure.

16. The EL display panel according to claim 11, further comprising:

a detection unit which detects a brightness of extraneous light.

17. The EL display panel according to claim 11, wherein a control signal for said gate driver circuit is supplied from said source driver circuit.

18. The EL display panel according to claim 11, wherein a said first switching element is a transistor having a multi-gate structure.

19. The EL display panel according to claim 11, wherein

said each pixel includes a first color pixel and a second color pixel,

a size of said first color pixel is different from a size of said second color pixel.