Display device

• US 6,404,137 B1
• Filed: 09/01/2000
• Issued: 06/11/2002
• Est. Priority Date: 09/03/1999
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Shodo, Kenzo
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Vu, Jimmy T.
• Application Number:
  US09/654,068
• Time in Patent Office: 648 Days
• Field of Search: 315/169.1, 315/169.2, 315/169.3, 345/99, 345/39, 345/46, 345/48, 345/55, 313/581, 313/585
• US Class Current: 315/169.1
• 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 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 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2360/148 the light being detected by light detection means within each pixel
• CPC Class Codes: G09G 3/30 using electroluminescent panels
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

A combination of a light emitting element and a light receiving element for monitoring the amount of light emitted from the light emitting element are provided. Also, a control circuit is added for controlling the amount of light emitted from the light emitting element in response to an output of the light receiving element. As their combination constitutes a pixel, a plurality of the pixels are arrayed in a matrix form. With the light emitting elements connected to a line for switching on and off the elements, a resultant display device enables to render the pixels uniform in the luminance. As a result, each pixel can emit a desired level of the illumination determined by an input signal regardless of discrete emission characteristics of the pixel, whereby a reproduced image is free from color blurs and creates highly explicit steps of gradation.

Claims

1. A display device comprising:

a light emitting element;

a light receiving element for monitoring the amount of light emitted from said light emitting element; and

a control circuit for controlling the amount of light emitted from said light emitting element according to an output of said light receiving element;

wherein a plurality of sets of said light emitting elements and said light receiving elements are provided so that each set of said plurality of sets constitutes a pixel in a display, and wherein in each of said pixels the amount of light emitted from said light emitting elements is favorably adjusted.

2. A display device according to claim 1, wherein said control circuit comprises:

a comparator circuit for comparing between a voltage of the output of said light receiving element and a voltage of the input signal; and

a driver MOS transistor for driving said light emitting element;

wherein an output of said comparator circuit as a driver signal being fed to the gate of said driver MOS transistor for determining a driving voltage to said light emitting element.

3. A display device according to claim 2, wherein a plurality of pixels are arrayed in a matrix form, each pixels comprising a group of said light emitting element, said light receiving element, and said driver MOS transistor, the gate of said driver MOS transistor of each pixel being connected to a capacitor for holding a gate voltage of said driver MOS transistor, each pixel also including a control terminal for controlling simultaneously the action of a first switching element for switching on and off said driver signal fed to the gate of said driver MOS transistor and the action of a second switching element for switching on and off the output of said light receiving element fed to said comparator circuit, whereby the light amount of said light emitting element of each pixel can be adjusted by the selecting action of said control terminal.

4. A display device according to claim 2, wherein said driver MOS transistor and said light emitting element are connected in series between the power source voltage and the ground so:

that the driver power to said light emitting element can be adjusted by said driver signal fed to the gate of said driver MOS transistor.

5. A display device according to claim 3, wherein said first and second switching elements comprise MOS transistors of which the gates are connected to a select line so that said first and second switching elements can simultaneously be controlled from the select line.

6. A display device according to claim 3, wherein while said first switching element of each of said pixels aligned in a column or a row is connected at one end to a driver line, said second switching element of each of said pixels alligned in a column or a row is connected at one end to a monitor line, and said control terminal of each of said pixels aligned in a row or a column is connected to a select line, a first shift register is provided for sequentially scanning the columns or rows of said driver line and said monitor line and a second shift register is provided for sequentially scanning the rows or columns of said select line, whereby a desired pixel can be selected.

7. A display device according to claim 3, wherein a plurality of groups are arrayed in a matrix form in a semiconductor substrate, each of said groups constituting said pixel, and comprising said light receiving element, driver MOS transistor, said capacitor, said first switching element, and said second switching element, and a plurality of light emitting elements, each of which is said light emitting element, are arrayed in a matrix form, said light emitting element provided as associated with said each group on said semiconductor substrate and arranged for emitting light from upper and lower surfaces.

8. A display device according to claim 7, wherein said light emitting element comprises an organic EL element.

9. A display device according to claim 8, wherein said light emitting element is formed by depositing transparent electrode layers and organic layers on said semiconductor substrate and separating said layers to pieces by etching.