Drive method of EL display apparatus

• US 7,924,248 B2
• Filed: 04/15/2010
• Issued: 04/12/2011
• Est. Priority Date: 04/26/2002
• Status: Expired due to Term

• Current Assignee: Japan Display Central Incorporated (Japan Display Incorporated)
• Original Assignee: Toshiba Matsushita Display Technology (Japan Display Incorporated)
• Inventors: Takahara, Hiroshi
• Primary Examiner(s): Shalwala; Bipin
• Assistant Examiner(s): Chowdhury; Afroza Y
• Application Number:
  US12/760,708
• Publication Number:
  US 20100265277A1
• Time in Patent Office: 362 Days
• Field of Search: 345/76, 345/690
• US Class Current: 345/76
• 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 2300/0842 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 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/0248 Precharge or discharge of column electrodes before or after applying exact column voltages
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• 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 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• 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 2320/0271 Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• 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

Abstract

To provide a drive method capable of maintaining gradation display performance regardless of screen display brightness.

Reference numeral 491R denotes a regulator used to control reference current for red (R). By adjusting a reference current for R linearly, it is possible to linearly vary a current flowing through a transistor 472a which constitutes a current mirror with a transistor 471R. This changes a current flowing through a transistor 472b which has received a current-based delivery from the transistor 472a in a transistor group 521a. This in turn causes changes to a transistor 473a in a transistor group 521b which constitutes a current mirror with the transistor 472b, resulting in changes to a transistor 473b which has received a current-based delivery from the transistor 473a. Thus, since drive current of the unit transistor 484 changes, programming current can be changed linearly. Reference numeral 491G denotes a regulator used to control reference current for green (G) and reference numeral 491B denotes a regulator used to control reference current for blue (B).

By adjusting 491R, 491G, and 491B, it is possible to adjust white balance easily and change screen brightness easily. Besides, gradation display performance is maintained at any screen brightness.

Claims

1. A drive method of an EL display apparatus that comprises a display screen in which a plurality of pixels each of which includes an EL element are formed in a matrix, the drive method comprising:

weighting a video signal with respect to a color of respective of the plurality of pixels, said video signal generating a signal which is to be impressed to the respective pixels of the EL display apparatus,

aggregating said weighted video signal, and

setting a maximum value of current that flows in the EL element of said pixel or a maximum value of emission brightness of the EL element of said pixel to a greater value according as a result of said aggregating of said weighted video signal gets smaller than a predetermined value.

2. The drive method of an EL display apparatus according to claim 1, wherein:

a multiplier of a gamma curve which converts input gradation data Di into output gradation data Do is defined as x,

said x of the multiplier of the gamma curve is set based on said result of said aggregating of said weighted video signal.

3. The drive method of an EL display apparatus according to claim 1, wherein:

when said result is smaller than said predetermined value, a time period for varying said maximum value of current that flows in the EL element of said pixel or said maximum value of emission brightness of the EL element of said pixel based on said result of said aggregating of said weighted video signal is a plurality of frame periods.

4. The drive method of an EL display apparatus according to claim 1, wherein:

displaying a non-display area on the display screen of the EL display apparatus, and shifting the non-display area on the display screen synchronizing with said one frame period by impressing a first voltage for supplying current to said EL element or a second voltage for intercepting the current flowing in said EL element to wiring that composes route where current of said EL element flows.

5. The drive method of an EL display apparatus according to claim 1, wherein:

a driver transistor for supplying current to said EL element is formed in said pixel of said EL display apparatus,

a switch transistor which is connected between a gate terminal and another terminal of said driver transistor is formed in said pixel of said EL display apparatus,

said driver transistor is a P-channel transistor, and

said switch transistor is a transistor having a multi-gate structure.

6. The drive method of an EL display apparatus according to claim 1, wherein, said EL display apparatus further comprises:

a source driver circuit that applies a video signal and,

a switch circuit arranged between an output terminal of said source driver circuit and source signal lines which said pixel is connected with, and

wherein, said switch circuit impresses image signal which is output from said output terminal of said source driver circuit to selected source signal line.

7. The drive method of an EL display apparatus according to claim 1, wherein said EL display apparatus further comprises:

a photo-sensor which detects a brightness of extraneous light, wherein

said maximum value of current that flows in the EL element or said maximum value of emission brightness of the EL element of said pixel is varied based on output of said photo-sensor.

8. The drive method of an EL display apparatus according to claim 1, wherein said display screen of said EL display apparatus has two or more color pixels, and

a pixel electrode area of at least one color pixel of said two or more color pixels is different from a pixel electrode area of another color pixel.

9. The drive method of an EL display apparatus according to claim 1, wherein said EL display apparatus further comprises:

a gate driver circuit having a P-channel transistor, wherein

a line of the pixels is selected by said gate driver circuit.

10. A drive method of an EL display apparatus that comprises a display screen in which a plurality of pixels each of which includes an EL element are formed in a matrix, the drive method comprising:

obtaining a value of current flowing in said display screen based on video data which is input in said EL display apparatus, wherein a value of current obtained in a first frame period is defined as a first value of current and a value of current obtained in a frame period other than said first frame period is defined as a second value of current,

setting a maximum value of current that flows in the EL element of said pixel or a maximum value of emission brightness of the EL element of said pixel when said obtained value of current is said first value of current more greatly than a maximum value of current that flows in the EL element of said pixel or a maximum value of emission brightness of the EL element of said pixel when said obtained value of current is said second value of current, in case that said first value of current is smaller than a predetermined value and is smaller than said second value of current.

11. The drive method of an EL display apparatus according to claim 10, wherein said EL display apparatus further comprises:

a source driver circuit for outputting video signal impressed to said pixels, and

a switch circuit which is connected between an output terminal of said source driver circuit and a source signal line which said pixels are connected with, wherein

a video signal output from said source driver circuit is impressed to select said source signal line by said switch circuit.

12. The drive method of an EL display apparatus according to claim 10, wherein said EL display apparatus further comprises:

a photo-sensor which detects a brightness of extraneous light, wherein

said maximum value of current that flows in the EL element or said maximum value of emission brightness of the EL element of said pixel is varied based on output of said photo-sensor.

13. The drive method of an EL display apparatus according to claim 10, wherein said display screen of said EL display apparatus includes two or more color pixels, and

a pixel electrode area of at least one color pixel of said two or more color pixels is different from a pixel electrode area of another color pixel.

14. The drive method of an EL display apparatus according to claim 10, wherein said EL display apparatus further comprises:

a gate driver circuit having a P-channel transistor, wherein

a line of the pixels is selected by said gate driver circuit.

15. A drive method of an EL display apparatus that comprises a display screen in which a plurality of pixels each of which includes an EL element and a driver transistor for supplying current to said EL element are formed in a matrix, wherein a multiplier of a gamma curve which converts input gradation data Di into output gradation data Do is defined as x,

the drive method comprising:

obtaining a value of aggregating video data based on video signal input to said EL display apparatus, wherein each of said aggregated values is defined as A and B respectively;

setting x of the multiplier of a gamma curve when said aggregated value is said B more greatly than x of the multiplier of a gamma curve when said aggregated value is said A, in case that said aggregated value B is greater than said aggregated value A; and

wherein when said aggregated value is said A, a current which is to flow in a first EL element corresponding to a first input gradation data D1 is defined as IA, and when said aggregated value is said B, a current which is to flow in said first EL element corresponding to said first input gradation data D1 is defined as IB,

setting said IA more greatly than said IB.

16. The drive method of an EL display apparatus according to claim 15, wherein a switch transistor which controls to turn on/off a current to be supplied to said EL element is formed in said pixel, and further comprising:

generating a non-display area and a display area on the display screen by controlling of said switch transistor.

17. The drive method of an EL display apparatus according to claim 15, further comprising:

setting a maximum value that flows in the EL element when said aggregated value is said A more greatly than a maximum value that flows in the EL element when said aggregated value is said B.

18. The drive method of an EL display apparatus according to claim 15, wherein a time period for varying said x of the multiplier of the gamma curve based on said aggregated value A to said x of the multiplier of the gamma curve based on said aggregated value B is a plurality of frame periods.

19. The drive method of an EL display apparatus according to claim 15, wherein said EL display apparatus further comprises:

a photo-sensor which detects a brightness of extraneous light, wherein

a value of said x of the multiplier of a gamma curve is set based on output of said photo-sensor.

20. The drive method of an EL display apparatus according to claim 15, wherein said display screen has two or more color pixels, and

a pixel electrode area of at least one color pixel of said two or more color pixels is different from a pixel electrode area of another color pixel.