El display panel and el display apparatus comprising it

• US 20050057580A1
• Filed: 09/20/2002
• Published: 03/17/2005
• Est. Priority Date: 09/25/2001
• Status: Abandoned Application

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Yamano, Atsuhiro, Takahara, Hiroshi, Tsuge, Hitoshi
• Application Number:
  US10/490,645
• Publication Number:
  US 20050057580A1
• Time in Patent Office: Days
• US Class Current: 345/690
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• 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 2310/0205 Simultaneous scanning of several lines in flat panels
• CPC Class Codes: G09G 2310/0218 with collection of electrodes in groups for n-dimensional addressing
• 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 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• CPC Class Codes: G09G 2310/0267 Details of drivers for scan electrodes, other than drivers for liquid crystal, plasma or OLED displays
• 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 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 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• 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 59/12 : Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 59/351 : comprising more than three subpixels, e.g. red-green-blue-white [RGBW]

Abstract

In a source driver (14) provided in an electroluminescent (EL) display device of the present invention, the gate voltage of a first-stage current source formed by a transistor (631) is applied to the gate of a transistor (632a) which is a second-stage current source situated next to the transistor (631) and, as a result, a current flowing through the transistor (632a) is transferred to a transistor (632b) which is a second-stage current source. In addition, the gate voltage of the transistor (632b) is applied to the gate of a transistor (633a) which is a third-stage current source situated next to the transistor (632b) and, as a result, a current flowing through the transistor (633a) is transferred to a transistor (633b) which is a third-stage current source. The gate of the transistor (633b) is provided with a large number of current sources (634) corresponding to the number of bits required.

Claims

1. An electroluminescent (EL) display device comprising:

a plurality of source signal lines;

a plurality of EL elemental devices, each capable of the emission of light at a brightness corresponding to a current supplied via said source signal line; and

a source driver which supplies a current corresponding to a gray scale of an image to said EL elemental device via said source signal line,

said source driver comprising;

reference signal generating means which generates reference signals,

a first current source which outputs a reference signal generated by said reference signal generating means in electric current form, and

a plurality of second current sources provided in association with said source signal lines, each of said plurality of second current sources being configured such that a reference signal outputted by said first current source is transferred in voltage form,

wherein a current according to said image gray scale is generated by the use of a reference signal held by each of said second current sources.

2. The EL display device as set forth in claim 1,

wherein a plurality of unit transistors, each of said unit transistors being so configured as to output said reference signal in electric current form when selected, are connected to each of said second current sources,

wherein said source driver is so configured as to select one or more of said unit transistors according to said image gray scale, and

wherein said EL display device is configured such that both a relational expression of 40≦

K/(St)^1/2 and a relational expression of St≦

300, where K indicates the number of representable gray scales and St (square micrometers) indicates the size of said unit transistor, are satisfied.

3. The EL display device as set forth in claim 1, wherein said plural second current sources are formed in a region the area of which does not exceed 2 square millimeters.

4. The EL display device as set forth in claim 1, wherein said source driver is provided with a light shielding film for preventing said first and second current sources from being illuminated with rays of light emitted from said EL elemental device.

8. Electronic equipment which is provided with an EL display device as set forth in claim 2 and which is so configured as to output an image signal to said EL display device.

5. An electroluminescent (EL) display device comprising:

a plurality of source signal lines;

a plurality of EL elemental devices, each capable of the emission of light at a brightness corresponding to a current supplied via said source signal line; and

a source driver which supplies a current corresponding to a gray scale of an image to said EL elemental device via said source signal line,

said source driver comprising;

a first current output circuit, made up of a plurality of unit transistors each operable to output a first unit current, for outputting to said EL elemental device a desired current by the combination of said first unit currents, and

a second current output circuit, made up of a plurality of unit transistors each operable to output a second unit current greater than said first unit current, for outputting to said EL elemental device a desired current by the combination of said second unit currents,

wherein, when a gray scale to be displayed is lower than a predetermined gray scale, said first current output circuit is so operated as to output a corresponding current for said gray scale to be displayed, while, when a gray scale to be displayed is higher than said predetermined gray scale, said second current output circuit is so operated as to output a corresponding current for said gray scale to be displayed, and wherein said EL display device is configured such that said first current output circuit outputs a given current.

6. The EL display device as set forth in claim 5, wherein the magnitude of said second current is not less than four times nor more than eight times the magnitude of said first current.

7. The EL display device as set forth in claim 5, wherein said source driver is provided with a light shielding film for preventing said first and second current output circuits from being illuminated with rays of light emitted from said EL elemental device.

9. An electroluminescent (EL) display device comprising:

a display region in which EL elemental devices are arranged in a matrix, and

a source driver which supplies in electric current form a video signal to said EL elemental device,

said source driver comprising;

reference current generating means which generates a reference current,

a first current source which is fed a reference current from said reference current generating means and which outputs a first current corresponding to said reference current,

a second current source which is fed a first current outputted from said first current source and which outputs a second current corresponding to said first current,

a third current source which is fed a second current outputted from said second current source and which outputs a third current corresponding to said second current, and

a plurality of unit current sources each of which is fed a third current outputted from said third current source, and outputs to said EL elemental device a unit current corresponding to said third current in response to input image data.

10. An electroluminescent (EL) display device comprising:

a display region in which EL elemental devices are arranged in a matrix, and

a source driver which supplies in electric current form a video signal to said EL elemental device,

wherein said source driver has a plurality of unit transistors,

wherein said unit transistor is so configured as to output, when selected, a unit current corresponding to the magnitude of an input video signal, and

wherein said EL display device is configured such that both a relational expression of 40≦

K(St)^1/2 and a relational expression of St≦

300, where K indicates the number of representable gray scales and St (square micrometers) indicates the size of said unit transistor, are satisfied.

11. An electroluminescent (EL) display device comprising:

a display region in which EL elemental devices are arranged in a matrix, and

a source driver which supplies in electric current form a video signal to said EL elemental device,

wherein said source driver has a transistor group made up of a first transistor and a plurality of second transistors in current-mirror connection with said first transistor, and

wherein said transistor group is formed in a region the area of which does not exceed 2 square millimeters.

12. The EL display device as set forth in claim 11,

wherein said first transistor is made up of a plurality of unit transistors, and

wherein said plural unit transistors are formed in a region the area of which does not exceed 2 square millimeters.

13. An electroluminescent (EL) display device comprising:

a display region in which pixels each having a respective EL elemental device are arranged in a matrix, and

a transistor elemental device formed in said pixel,

a gate driver for the ON/OFF control of said transistor elemental device, and

a source driver for supplying a video signal to said transistor elemental device,

wherein said gate driver is formed by a P channel transistor,

wherein said transistor formed in said pixel is a P channel transistor, and

wherein said source driver is formed by a semiconductor chip.

15. The EL display device as set forth in either claim 13 or claim 14, wherein said source driver outputs a video signal in electric current form.

16. The EL display device as set forth in either claim 13 or claim 14, wherein said gate driver performs shifting operations by four clock signals.

14. An electroluminescent (EL) display device comprising:

a display region in which an EL elemental device, a drive transistor, a first switching elemental device which establishes a path between said drive transistor and said EL elemental device, and a second switching elemental device which establishes a path between said drive transistor and a source signal line,

a first gate driver for the ON/OFF control of said first switching elemental device,

a second gate driver for the ON/OFF control of said second switching elemental device, and

a source driver which applies a video signal to said transistor elemental device,

wherein said gate driver is formed by a P channel transistor,

wherein a transistor formed in a pixel and said switching elemental devices are P channel transistor elemental devices, and,

wherein said source driver is formed by a semiconductor chip.