Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2002-09-24
2004-05-25
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169300, C315S169200, C345S082000
Reexamination Certificate
active
06741037
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the priority benefit of Taiwan application serial no. 91116536, filed Jul. 25, 2002.
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to the driving circuit of a display. More particularly, the present invention relates to the driving circuit of a display for preventing electrostatic discharge.
2. Description of Related Art
People are always interested in watching recorded images and movies. Ever since the invention of the cathode ray tube (CRT), television has become commercialized and television sets are owned by almost every family. With rapid progress in manufacturing techniques, the CRT has been used in many applications including the desktop monitor of a personal computer. However, due to radiation hazards and bulkiness of the electron gun, CRT display is heavy and hard to streamline into a flat panel.
Because of intrinsic bulkiness, researchers are now developing more slim-line displays. The so-called “flat panel displays” now includes liquid crystal displays (LCDs), field emission displays (FEDs), organic light-emitting diode (OLED) displays and plasma display panel (PDP) displays.
The organic light-emitting diode (OLED) is also known as an organic electroluminescence display (OELD) due to its self-illuminating character. OLED is driven by a low DC voltage and has properties including high brightness level, high energy efficiency, high contrast values as well as slimness and being lightweight. Moreover, the display is able to emit light of a range of colors from the three primary colors red (R), green (G) and blue (B) to white light. Hence, OLED is considered to be the display panel of the next generation. Aside from having high resolution and light just like the LCD and having self-illuminating capacity, a quick response and a low energy consumption just like the LED, OLED also has other advantages including a wide viewing angle, good color contrast and a low production cost. Thus, OLED is often used in LCD or as a background light source for indicator panels, mobile phones, digital cameras and personal digital assistants (PDA).
According to the type of driver selected to drive the OLED, the OLED can be divided into passive matrix driven or active matrix driven type. Passive matrix OLED has the advantage of structural simplicity and a low production cost. However, the passive matrix OLED has a relative low resolution rendering it unsuitable for producing high-quality images. Moreover, the passive matrix OLED consumes a lot of power, has a shorter working life and sub-optimal displaying capacity. Although the active matrix OLED is slightly more expensive to produce, it can be assembled to form a huge screen, aside from having a large viewing angle, the capacity for producing high brightness level and a quick response.
According to the driving method, a flat display panel is also divided into a voltage-driven type or a current-driven type. The pixel circuit of a conventional voltage-driven type of active matrix OLED is shown in FIG.
1
. As shown in
FIG. 1
, the pixel circuit
10
includes a driving circuit
102
and an OLED (
104
). The driving circuit
102
further includes a thin film transistor TFT
1
(
106
), a storage capacitor C (
108
) and a second thin film transistor TFT
2
(
110
). The drain terminal of the transistor TFT
1
(
106
) is coupled to a data line. The gate terminal of the transistor TFT
1
(
106
) is coupled to a scanning line. The drain terminal of the transistor TFT
1
(
106
) is coupled to a first terminal of the capacitor C (
108
) and the gate terminal of the transistor TFT
2
(
110
). The second terminal of the capacitor C (
108
) is connected to a voltage source V
ss
(a common negative source line of the panel). The voltage source V
ss
is at a negative voltage or a ground potential. The drain terminal of the transistor TFT
2
(
110
) is connected to another voltage source V
dd
(a common positive voltage line of the panel). The voltage source V
dd
is at a positive voltage. The source terminal of the transistor TFT
2
(
110
) is coupled to the second terminal of the capacitor C (
108
) and the anode (also known as indium-tin-oxide, ITO) of the OLED (
104
). The cathode of the OLED (
104
) is coupled to the voltage source V
ss
. With this type of design, the anode of the OLED in each pixel is separate and independent. Hence, each pixel
10
is linked to other pixels through the common voltage source V
dd
only when the transistor TFT
2
(
110
) conducts. Because of this, static charges produced during the fabrication process are concentrated within individual pixels rather than distributing evenly to all pixels. Consequently, electrostatic discharge (ESD) of individual pixels may subsequently occur and damage the pixels. Ultimately, these pixels may fail to light up creating the so-called defect points. In general, tens and sometimes of point defects are found within an area 50 cm
2
of a display panel. When a large number of point defects appear on a display panel, quality of the image produced by the display will be greatly compromised.
SUMMARY OF INVENTION
Accordingly, one object of the present invention is to provide a driving circuit for a display that can prevent electrostatic discharge. By connecting the anodes of light-emitting device in every pair of neighboring pixels with a high resistant resistor (the value of the resistance depends on material constituting the light-emitting diode and size of each pixel), electric charge produced during fabrication is distributed evenly to all the pixels. Since electric charges no longer accumulate at the anode of the light-emitting device, point defects in the display is greatly reduced.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a driving circuit of a display for preventing electrostatic discharge. The driving circuit drives a first light-emitting device and a second light-emitting device. The first light-emitting device has an anode and a cathode. Similarly, the second light-emitting device has an anode and a cathode. A major aspect of this invention is the connection of the anode of the first light-emitting device with the anode of the second light-emitting device through a high resistant resistor. The resistance of the resistor must be greater than the internal resistance of the first light-emitting device and the internal resistance of the second light-emitting device.
In one preferred embodiment of this invention, the display is an active matrix organic electroluminescence display.
In another preferred embodiment of this invention, the first light-emitting device and the second light-emitting device are organic light-emitting diodes or polymeric light-emitting diodes.
This invention also provides a display capable of preventing electrostatic discharge. The display includes a plurality of pixels with each pixel having a light-emitting device. One major aspect of the display is that the each pair of neighboring anodes of the light-emitting device is connected together through a high resistant resistor. The resistance of the resistor must be greater than the internal resistance of the light-emitting diode.
In brief, the anode of each pair of neighboring pixels in a display is connected together through a high resistant resistor (the resistance of the resistor depends on the material constituting the light-emitting device and size of the pixel) in this invention. Hence, any static electric charges produced during fabrication are evenly distributed to all the pixels. Ultimately, electric charges no longer accumulate at the anode of the light-emitting device, thereby reducing overall number of point defects in the display.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 4899086 (1990-02-01), Hirata et al.
patent: 5177405
Au Optronics Corporation
Dinh Trinh Vo
J. C. Patents
Wong Don
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