Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2002-09-11
2004-08-10
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S045000, C345S077000, C315S159000, C315S169300
Reexamination Certificate
active
06774878
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive unit for a luminescence display panel employing, for example, organic El (electroluminescence) elements wherein the drive unit can switch between a normal scan mode in which all effective light-emitting elements in the luminescence display panel are repeatedly scanned to control light emission and a partial scan mode in which part of the effective light-emitting elements in the luminescence display panel are repeatedly scanned to control light emission, and more particularly to a drive unit for a luminescence display panel capable of achieving lower power consumption by extending the life of the light-emitting elements when the partial scan mode is selected.
2. Description of the Related Art
An organic EL display has been in practical use in some fields as a display in which a low power consumption, a high display quality, and a thin profile are possible in place of a liquid crystal display. This is because there is a background that a high efficiency and a long life by which a practical use can be endured are progressed by employing an organic compound by which an excellent light emission characteristic can be expected for a light emitting layer of EL elements employed for an EL display.
The organic EL element can be electrically expressed by an equivalent circuit as shown in FIG.
6
. That is, an organic EL element can be replaced by a structure composed of a parasitic capacitance compound C and a diode compound E which is connected in parallel to the capacitance compound, and the organic External light element is deemed as a capacitive light-emitting element. In the organic EL element, when a light emission drive voltage is applied, first, electrical charge corresponding to the capacitance of the element flows into an electrode as a displacement current and is stored therein. Then, when the electrical charge exceeds a predetermined voltage (light emission threshold value=Vth) inherent in the element, current begins to flow from the electrode (anode side of the diode element E) to an organic layer constituting the light emitting layer, and it can be deemed that light is emitted at an intensity proportional to the current.
FIG. 7
shows static light emission characteristics of such organic EL element. It can be seen from the drawing that in the organic EL element, in the case where the drive voltage (V) is at a light emission threshold voltage (Vth) or greater as shown in
FIG. 7A
, current (I) suddenly flows to cause light emission. In other words, if the drive voltage applied is at the light emission threshold voltage or lower, after charging for the parasitic capacitance, drive current hardly flows in the EL element, and thus the element does not emit light. In a light emittable region in which the drive voltage (V) is the light emission threshold voltage or greater, the EL element has a characteristic that the EL element emits light with a luminance (L) approximately proportional to the drive current (I) as shown in FIG.
7
B. Thus, an EL element has a luminance characteristic in which the greater the voltage (V) applied thereto, the greater the luminance (L) thereof in the light emittable region in which the drive voltage (V) is greater than the threshold voltage as shown in FIG.
7
C.
As a driving method for a display panel constituted by arranging such plurality of organic EL elements, a passive matrix driving method is known.
FIG. 8
shows an example of a passive matrix display panel and a drive unit therefor. In the passive matrix driving method, there are two driving methods for the organic EL elements, that is, cathode line scan/anode line drive and anode line scan/cathode line drive, and
FIG. 8
shows a feature of the former, the cathode line scan/anode line drive. That is, “n” pieces of anode lines A
1
to An are arranged as drive lines in a vertical direction, “m” pieces of cathode lines B
1
to Bm are arranged as scan lines in a horizontal direction, and organic EL elements E
11
to Enm are arranged at portions at which each line intersects (“n”דm” portions in total) to construct a display panel
1
.
The respective elements E
11
to Enm constituting pixels are arranged in the form of a lattice, and one ends (anode terminals of the diode elements EL of the equivalent circuit described above) are connected to the anode lines and the other ends (cathode terminals of the diode elements EL of the equivalent circuit described above) are connected to the cathode lines, corresponding to intersecting positions between the anode lines A
1
to An along the vertical direction and the cathode lines B
1
to Bm along the horizontal direction. The anode lines are connected to an anode line drive circuit
2
, and the cathode lines are connected to a cathode line scan circuit
3
so that the respective lines are driven thereby.
The cathode line scan circuit
3
is provided with scan switches SY
1
to SYm corresponding to the respective cathode scan lines B
1
to Bm to work so that either one of a reverse bias voltage VM from a reverse bias power supply circuit
5
(for example, 10 V) and the ground potential (0 V) is connected to a corresponding cathode scan line. The anode line drive circuit
2
is provided with drive sources I
1
to In supplying drive current to the respective EL elements via the respective anode lines and drive switches SX
1
to SXn, and the drive switches are controlled to be turned on so that current from the drive sources I
1
to In is supplied to the respective EL elements arranged corresponding to the cathode scan lines.
Thus, the drive sources are connected to desired anode drive lines while the cathode scan lines are scanned at a predetermined cycle so that the respective light-emitting elements are selectively caused to emit light. Although voltage sources such as constant voltage circuits can be employed as the drive sources, it is general to employ constant current sources as the drive sources because of the reasons that the voltage/luminance characteristic of an EL element is unstable with respect to temperature changes, the element is deteriorated by excess current, and the like although the current/luminance characteristic of an EL element is stable with respect to temperature changes.
The respective anode drive lines are further connected to a reset circuit
4
. This reset circuit
4
is provided with reset switches SR
1
to SRn provided for the respective anode drive lines, and these reset switches are turned on, so that the anode drive lines are set to the ground potential. Each of the anode line drive circuit
2
, the cathode line scan circuit
3
, and the reset circuit
4
is driven by a command signal brought from a light emission control section which is not shown.
That is, the light emission control section controls the anode line drive circuit
2
, the cathode line scan circuit
3
, and the reset circuit
4
so that an image corresponding to an image signal is shown according to the image signal. In this case, control is performed wherein the cathode line scan circuit
3
sequentially selects a cathode scan line corresponding to a horizontal scan period of image data by a command from the light emission control section to set it to the ground potential, and the scan switches SY
1
to SYm are switched so that other cathode scan lines are connected to the reverse bias power supply circuit
5
and the reverse bias voltage VM is applied thereto. The state shown in
FIG. 8
shows a state in which the first cathode scan line B
1
is scanned.
The reverse bias voltage VM is applied in order to charge the parasitic capacitance of driven EL elements which are connected to the intersections with the cathode line that has been selected for scanning and in order to prevent the EL elements connected to intersections between the driven anode lines and the cathode lines that have not been selected for scanning from emitting cross-talk light. This reverse bias voltage is generally set to a voltage approximately equal to the forward direction vo
Murakata Masaki
Yoshida Takayoshi
Hjerpe Richard
Nguyen Kimnhung
Tohoku Pioneer Corporation
Westerman Hattori Daniels & Adrian LLP
LandOfFree
Drive unit for a luminescence display panel does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Drive unit for a luminescence display panel, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Drive unit for a luminescence display panel will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3306699