Patent Application
20080291137
This application is based on, and claims priority from, Japanese Patent Application No. 2007-135856, filed on May 22, 2007, the contents of which are incorporated herein by reference.
The present invention relates to a driver device for an organic EL passive matrix device, and in particular, to a driver device having two row drivers, for an organic EL passive matrix device.
Organic EL devices are expected to be applied to next generation displays. A passive matrix system is one of driving systems to make an organic EL device to emit light. The system composes a matrix of electrode lines in rows and columns and drives organic EL elements (corresponding to pixels) arranged on points of intersection of the lines.
The minimum necessary voltage Vs of a power supply for driving the driver device 100 is represented by the equation (1).
V
s
=V
1
+V
2
+V
3
+V
cm
+V
4 (1)
where Vci (i=1, 2, . . . , m) is a voltage drop between a cathode terminal of the organic EL element i and an input terminal of the row driver 102 connected to the cathode terminal, and Vcm is a voltage drop from the cathode terminal of the organic EL elements arranged at m-th column. Power consumption P is a product of the voltage Vs and a current I that is a sum of the driving current I1, . . . , and Im.
The voltage drop Vci is generated by a resistance in the wiring (the cathode line) between the cathode terminal of the organic EL element at i-th column and the input terminal of the row driver 102 to which the cathode terminal is connected. The voltage drop Vci increases by shifting in the column direction (pixel direction) (in the direction from i=1 to m), as shown in
V
cm
=lr+2lr+3lr+ . . . +mlr (2)
When the power supply voltage Vs is applied, a reactive power is generated due to the difference of voltage in the column direction (pixel direction). The reactive power equals a product of the reactive voltage Vs shown in
In a 2.8 inch QVGA (240 RGB pixels×320 rows) for example, the resistance is about 100Ω provided the total length of the cathode line of each row is 45 mm and the thickness of the material of aluminum is 100 nm. When a current of 150 μA is fed to every pixel, the voltage drop Vcm is 5.7 V, the corresponding power equals 5.7 V×150 μA×240×3 (RGB), a half of which is a reactive power. Thus, there exists a problem of excessively large reactive power in a generally employed driver device in which the driving current is sunk by a single row driver.
The variation of wiring resistance in the pixel direction causes a problem of unevenness of luminance in addition to the problem of power. The variation in wire resistance causes variation in building-up characteristic at the pixels and variation in emitting time, resulting in the unevenness of luminance.
Japanese Unexamined Patent Application Publication No. H09-281928 discloses a technology to solve the problems of power consumption and uneven luminance by connecting a cathode scanning circuit, which is analogous to the row driver, to both terminals of a cathode line. Japanese Unexamined Patent Application Publication No. 2006-235162 also discloses a similar technology, in which a first and a second change-over mechanism of scanning lines are provided, the mechanism being analogous to the row driver, and a selected scanning line (analogous to the cathode line) is grounded to reduce unevenness of display due to the wiring resistance.
In a 2.8 inch QVGA (240 RGB pixels×320 rows) for example, the resistance is about 50Ω provided the total length in the half side of the cathode line is about 22.5 mm and the thickness of aluminum is 100 nm. When a current of 150 μA is fed to every pixel, the Vcm is 1.4 V and the corresponding power equals 1.4 V×150 μA×240×3 (RGB). The reactive power is reduced to ¼ as compared with the foregoing example. Since the voltage V4 in the row driver is halved, the power supply voltage can be further reduced. Thus, the reactive power and the power due to the cathode resistance are improved. With decrease in voltage variation in the column direction (pixel direction), variation in build-up characteristic also decreases to reduce unevenness in luminance.
Enlargement of display area raises a problem of increased power consumption in addition to the problem caused by the wiring resistance. Expanded display area shortens the time allowed to feed a current in each row. When a large-sized EL passive matrix device of 2.8 inch QVGA (240 RGB pixels×320 rows) for example, is driven by a set of a column driver and a row driver, a scanning period is 1/320. This requires increase in current in order to ensure desired luminance, causing increase in power consumption in the organic EL elements.
Japanese Unexamined Patent Application Publication No. 2006-047511 discloses that a driver device of a dual scanning system is employed in which two LSIs each integrating a column driver and a row driver on one chip with increase in the display area. By using two LSIs, the time allowed to feed current to each row can be doubled as compared with the case of one LSI, suppressing the current at a low level.
The conventional technologies as mentioned in the foregoing can mitigate, in some degree, the problems of the increase in power consumption and generation of uneven luminance due to enlargement of an organic EL passive matrix device. However, application to a large area display requires further improvement for solving such problems. Besides, the improvement is desired to be achieved at a low cost.
The present invention provides a driver device for an organic EL passive matrix device that achieves reduction of power consumption and suppression of unevenness in luminance in the organic EL passive matrix device at a low cost.
Specifically, a driver device for an organic EL passive matrix device is provided that has a plurality of anode lines and a plurality of cathode lines arranged in a matrix form and organic EL elements arranged at points of intersection of the lines. The driver device comprises a column driver connecting to one end of the plurality of anode lines and, first and second row drivers, one of the row drivers connecting to an end of the plurality of cathode lines and the other of the row drivers connecting to the other end of the plurality of cathode lines. The column driver feeds current through selected anode line of the plurality of anode lines. The first and second row drivers sink the current fed by the column driver through selected cathode lines of the plurality of cathode lines. The column driver, the first row driver, and the second row driver are integrated in a single integrated circuit (IC).
The column driver is preferably disposed in a vicinity of a peripheral side of the IC, and the first row driver is disposed in the vicinity of one peripheral side adjacent to the peripheral side at which the column driver is disposed, and the second row driver is disposed in a vicinity of another peripheral side adjacent to the peripheral side at which the column driver is disposed.
The column driver is preferrably disposed in a vicinity of a peripheral side of the IC, and the first row driver is angled and disposed in a vicinity of the column driver and in a vicinity of one peripheral side adjacent to the peripheral side at which the column driver is disposed, and the second row driver is angled and disposed in a vicinity of the column driver and in a vicinity of another peripheral side adjacent to the peripheral side at which the column driver is disposed.
The driver device preferably includes two partial driver devices each being any one of the driver devices for an organic EL passive matrix device and disposed at each end region of the anode lines of the organic EL passive matrix device, and the two partial driver devices being connected through a wire and operated in synchronism with each other, and sharing the driving function on the organic EL passive matrix device.
Further, the organic EL passive matrix device preferably has pixels at least 240 RGB pixels×at least 320 rows.
The present invention provides such a driver device for an organic EL passive matrix device that achieves reduction in power consumption and suppression of uneven luminance by providing two row drivers at both ends of cathode lines, at a low cost by virtue of packaging a column driver and two row drivers in a single IC.
The invention will be described with reference to certain preferred embodiments and the accompanying drawings wherein:
The power supply/control signal input 505 accepts a power and a control signal from outside and feeds the power and the signal to the column driver 501, the first row driver 502, the second row driver 503, and the memory 504. The power and the signal are, for example, a power supply voltage Vs for the column driver 501 and write-in display data for the memory 504.
The driver device of this embodiment example is featured by that a column driver 501 and row drivers 502 and 503 are packaged in a single IC in the arrangement as shown in
As described above, a driver device of this first embodiment example (including the modification) achieves reduction in power consumption and suppression of uneven luminance by providing two row drivers at both ends of the cathode lines, at a low cost by virtue of packaging a column driver and two row drivers in a single IC.
The power supply/control signal inputs 715 and 725 accept a power and a control signal from outside and feeds the power and the signal to the column drivers 715 and 725, respectively. Driver device 710 includes two row drivers 712 and 713. Likewise, driver device 720 includes two row drivers 722 and 723. In addition, the power and signal are fed to the column drivers 711,721, row drivers 712,713 and the memory 714 and 724
In the case of a large-sized organic EL passive matrix device such as a 2.8 inch QVGA (240 RGB pixels×320 rows), a scanning period becomes 1/320 and current has to be increased in the conventional devices. However, the separated driving in two sections as in the invention elongates the scanning period from 1/320 to 1/160. As a result, the driving current for the organic EL elements can be halved to reduce the power consumption to a half or less as compared with the conventional devices, yet ensuring necessary luminance. Moreover, the voltage drop due to anode resistance and power consumption are also reduced.
Meanwhile, the anode resistance is due to a transparent electrode material such as indium-zinc ozide (IZO). In the case of a 2.8 inch device, the resistance is about 12 kΩ assuming the length of the anode line of 60 mm and the thickness of IZO of 440 nm. Feeding a current of 150 μA, the voltage drop V2 due to the anode resistance amounts-up to 1.8 V (12 kΩ×0.15 mA). When divided into two sections, this value can be halved.
In order to make the two separated areas into one picture, the two ICs are connected through the connector 730 and the upper and lower sections are synchronized in the row direction (scanning direction) using the column (pixel) data in each section to display the organic EL passive matrix device.
As described above, a driver device of this second embodiment example, in which first and second partial driver devices each having two row drivers are provided at both ends of anode lines of the organic EL passive matrix device, and drives the organic EL passive matrix device separately. As a result, further reduction in power consumption is achieved.
The invention has been described with reference to certain preferred embodiments thereof. It will be understood, however, that modifications and variations are possible within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-135856 | May 2007 | JP | national |
