Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-04-05
2002-08-13
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
Reexamination Certificate
active
06433485
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a testing apparatus and method of an organic light emitting diode (hereinafter referred to as OLED) array. More specifically, it relates to the testing apparatus and method of checking for defective pixel units of an active matrix OLED panel.
2. Description of the Related Art
Newly developed flat-plane displays, succeeding cathode ray tube (CRT) displays and liquid crystal displays (LCDs), are OLED displays. OLED displays have the advantages of self-emitting light, high luminance, wide viewing angle, and a simple fabricating process, etc., therefore hold appeal for researchers lately. An OLED emits light by using an organic light-emitting layer disposed between the anode and cathode thereof. The organic light-emitting layer is composed of dyes or high polymers.
FIG. 1
shows the schematic structure of a general OLED in a cross-sectional view. As depicted in
FIG. 1
, numeral
1
shows a substrate which generally is made of glass material and serves as an emitting plane. Numeral
3
shows an anode layer which is transparent and made of metal oxide such as ITO (indium tin oxide) with good conductivity and is also pervious to light. Numeral
5
shows an organic layer supposed to have highly efficient fluorescence. Numeral
7
shows a cathode layer generally made of a metallic alloy. Physically, respectively connecting the anode layer
3
and cathode layer
7
to a positive electrode and negative electrode is equivalent to injecting holes and electrons into the organic layer
5
. After the holes and electrons overcome the respective energy gaps, excitons are generated in the organic layer
5
. The excitons decay from an excited state to a fundamental state, thereby radiating light for releasing energy. The anode layer
3
and substrate
1
are transparent and the light radiates along the arrow direction as depicted in FIG.
1
.
In general, OLED displays include two driving types: passive matrix and active matrix. In a passive matrix OLED display, an organic layer is deposited between cathode electrode lines and anode electrode lines, wherein the cathode electrode lines are perpendicular to the anode electrode lines, thereby forming an array of OLEDS. Furthermore, switches corresponding to the OLED circuit are used to control the light emission of OLEDS.
FIG. 2
shows the circuit diagram of a conventional passive matrix OLED display. In
FIG. 2
, OLED panel
9
comprises cathode electrode lines
10
perpendicular to anode electrode lines
12
. The diode at the cross section of any cathode electrode line
10
and any anode line
12
represents a corresponding pixel unit
20
. Anode electrode lines
12
couples current sources
14
via switches
18
and cathode electrode lines
10
are coupled to a ground via switches
16
. In practical operation, the scan lines corresponding to the cathode electrode lines
10
are sequentially turned on, i.e. the corresponding switches
16
are conducted, to be grounded. Further, each of the pixel units
20
can be selectively lit by controlling the switches
18
. To the passive matrix OLED, its simple structure is the main advantage favorable to fabricating cost and benefit. However, the passive matrix OLED operates under short-pulse mode, therefore requiring higher operating voltage. Also, the passive matrix OLED has a low efficiency of light emission.
In an active matrix OLED display, each of the OLEDs is coupled with an independently connected driving circuit.
FIG. 3
shows the circuit diagram of a conventional active matrix OLED display. In
FIG. 3
, numeral
50
means a switching TFT (thin-film transistor), numeral
52
means a storage capacitor, numeral
54
means a driving TFT, and numeral
56
means an OLED. In addition, numeral
30
means a signal line, numeral
40
means a scan line, numeral
32
means a power supply line, numeral
42
means a capacitor line, and numeral
44
means a common line.
The gate and source of the switching TFT
50
respectively connect to the scan line
40
and the signal line
30
. The drain of the switching TFT
50
connects to the storage capacitor
52
. A scan signal is provided via the scan line
40
to control the state of the switching TFT
50
. When the switching TFT
50
is in conducted state (or turned on), logic signals at the signal line
30
are transmitted to node A. In addition, the other terminal of the storage capacitor
52
connects to the capacitor line
42
. Generally every capacitor line
42
of all pixel units in an OLED panel is commonly connected. The logic signal at node A is coupled to the gate of the driving TFT
54
, and the source and drain of the driving TFT
54
respectively connect to the power supply line
32
and the anode of the OLED
56
. The cathode of the OLED
56
connects to common line
44
. When the logic signal at node A turns on the driving TFT
54
, the path from the power supply line
32
, driving TFT
54
, OLED
56
to common line
44
forms a loop and the OLED
56
emits light. When the driving TFT
54
is not in a conducted state (turned off), OLED will not emit light. In addition, generally every power supply line
32
and common line
44
of all pixel units in the OLED panel are respectively connected together; wherein the power supply line
32
couples to a positive voltage, and the common line
44
is grounded.
As described above, the driving TFT structure of the active matrix OLED is partially similar with that of a LCD panel, for example the switching TFT
50
and the storage capacitor
52
. However, the pixel unit structures of the OLED and LCD are different. Therefore, the conventional apparatus for testing the LCD panel is not appropriate for the OLED panel.
FIG. 4
shows a conventional testing scheme for an active matrix LCD panel. In
FIG. 4
, numeral
62
and
60
mean a control transistor and storage capacitor corresponding to a pixel unit and the gate of the control transistor connects to a scan line
72
. Numeral
74
means a testing point, the input position of image signals. Testing apparatus comprises a switch
65
, a voltage source
69
, and a judging device
67
. The switch
65
controls the selection of connecting the judging device
67
or voltage source
69
to the testing point
74
. The way of testing is described as follows. First, the switch
65
is switched to couple the voltage source
69
to the storage capacitor
60
so as to store charge in the storage capacitor
60
(i.e. node A′). Next, hold the charge stored in the storage capacitor
60
for a period of time, and then switch the switch
65
to the judging device
67
. The judging device
67
reads out (detects) the charge stored in the storage capacitor and determines whether the pixel unit is perfect or defective.
Accordingly, it is not able to completely test a general OLED pixel unit by virtue of the testing scheme for a conventional active matrix LCD panel as shown in FIG.
4
. The reason is that the testing scheme cannot be applied to test the driving TFT
54
and OLED
56
depicted in FIG.
3
.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an apparatus and method of testing an OLED array (or panel), capable of completely finding out whether the pixel units in the OLED array are perfect or defective.
The present invention achieves the above-indicated objects by providing a method of testing an OLED array, which has a plurality of pixel units and each of the pixel units comprises a commonly shared power supply line and a commonly shared common line. First, a current meter and a voltage source are provided and connected in serial between the common line and power supply line. Then, a first logic value (for example, logic “1”) is sequentially written to the pixel units and first current readings corresponding to the written pixel units are taken by virtue of the current meter. Finally, whether or not the pixel units are defective is determined according to the first current readings corresponding to the written pixel units; further, w
Chen Yeong-E
Tai Ya-Hsiang
Birch & Stewart Kolasch & Birch, LLP
Industrial Technology Research Institute
Minh A D
Wong Don
LandOfFree
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