Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-05-08
2001-03-27
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C345S102000, C345S103000, C396S292000
Reexamination Certificate
active
06208083
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a system and method for driving an organic EL display which is constructed using an organic compound and has applications in the fields of information display panels used on audio equipment, automotive measuring instrument panels, displays for displaying moving images and freeze-frame pictures, household electrical appliances, car and bicycle electrical equipment, etc.
DISCUSSION OF THE BACKGROUND
In recent years, an organic EL device has been intensively studied and put to practical use. The organic EL device is basically built up of a tin-doped indium oxide (ITO) or other transparent electrode, a triphenyldiamine (TPD) or other hole transporting layer laminated on the transparent electrode, an organic light emitting layer formed of a fluorescent material such as an aluminum quinolinol complex (Alq
3
) and laminated thereon, and a metal electrode (electron injecting electrode) provided on the organic light emitting layer and formed of a material having a low work function, for instance, Mg. Such a device now attracts attention as displays for use on household electrical appliances, car and bicycle electric equipment, etc., because a luminance of as high as several hundred to tens of thousands cd/m
2
is obtained at a voltage of about 10 V.
Such an organic EL device has a structure wherein an organic layer such as a light emitting layer is sandwiched between a scanning (common line) electrode that usually provides an electron injecting electrode and a data (segment line) electrode that usually provides a hole injecting electrode (transparent electrode), and formed on a transparent (glass) substrate. Electroluminescent displays are generally broken down into a matrix display wherein scanning electrodes and data electrodes are arranged in a matrix form to display information such as images and characters in the form of an assembly of dots (pixels), and a segment display comprising independently provided display units each having predetermined shape and size.
The segment type display may be driven in a static driving mode where the display units are independently driven. For the matrix display, on the other hand, a dynamic driving mode is used, wherein scanning lines and data lines are usually driven in a time division fashion.
When eyeing a certain scan line (electrode), the matrix display has such construction as shown in
FIG. 5
for instance. As depicted in
FIG. 5
, this matrix display may be considered as being built up of a switching element SW for driving the scanning line (connecting the scanning line to the ground side), a resistance (e.g., a pull-up or switch-on resistance) R for stabilizing the scanning line at a given (power source) potential when switching element SW is at rest, pixels D
1
, D
2
, D
3
, . . . or organic EL devices, capacitor components C
1
, C
2
, C
3
, . . . connected in parallel with one ends of associated pixels D
1
, D
2
, D
3
, . . . , and data lines (electrodes) connected to the other ends of pixels D
1
, D
2
, D
3
, . . . , which are not shown in FIG.
5
.
In this case, the organic EL devices or pixels are taken as being equivalent to diodes D
1
, D
2
, D
3
, . . . , as illustrated, with built-in capacitor components C
1
, C
2
, C
3
, . . . . When this display is driven in the time division mode, accordingly, a time constant given by each of capacitor components C
1
, C
2
, C
3
, . . . and the aforesaid resistance R gives rise to a delay time Td upon returning from a driving pulse Ton by the switching element as typically shown in FIG.
6
. This delay time Td is superposed on the driving pulse Ton of the next scan electrode. Although depending on data line conditions, the some pixels at the scanning electrode emits light for this delay time irrespective of being a non-selected pixel. This makes contrast worse or is perceived as anomalous light emission.
As shown in
FIG. 7
for instance, when a display having a certain number (n) of scanning lines is driven by driving each scanning lines
1
,
2
,
3
, . . . , n, a quiescent time Toff is provided between a certain scanning electrode driving pulse and the next scanning electron driving pulse, so that the delay time Td is absorbed thereby preventing a contrast lowering and anomalous light emission. It is here noted that a period Tr is a flyback or retrace time from the final scanning line n to the first scanning line
1
.
Incidentally, a display with a matrix portion
31
coexistent with a segment portion
32
is entrenched, as shown in
FIG. 8
as an example. When such a display is driven, these portions may be separately driven. However, if the matrix portion
31
and segment portion
32
can be driven by one single driving means, it is then possible to drive both efficiently with minimal hardware because, for control purposes, a controller, a driving circuit, etc. need be used, only one for each. In this case, the display is dynamically driven in a mixed matrix-and-segment form while one or more of scanning lines are assigned to the segment portion
32
with each segment selected by data line.
As can be seen from
FIG. 8
, however, the total area of each display device
32
a
corresponding to one line on the segment portion is usually much larger than the total area of each pixel
31
a
on one scanning line on the matrix portion
31
. This means that such a delay time as previously mentioned differs largely between both portions. Therefore, when the display is simply subjected to dynamic driving at an arbitrarily position (at the second line in the illustrated case) as shown in
FIG. 9
as an example, the delay time Td becomes long when the segment portion is driven, with the result that the segment portion emits light when the next line (the third line in the illustrated case) is driven. Consequently, this is perceived as an anomalous light emission phenomenon. It is here noted that while the delay time also occurs at the first line, this is within an allowable range because light is emitted at a contrast ratio of 1/100 or lower. On the other hand, light emitted at the second line is perceived as false light emission because the contrast ratio exceeds 1/100.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an organic EL display driving system which enables even a display with a mixed matrix-and-segment portion to be driven with neither a contrast lowering nor a false light emission phenomenon yet in simple construction.
When the display with a mixed matrix-and-segment portion is driven, the delay time due to a CR component in the driving circuit differs because there is an area difference between both portions, as already explained. For this reason, if the quiescent time corresponding to the matrix is set, it is then impossible to prevent a contrast lowering and an anomalous light emission phenomenon because the delay time at the segment portion is too long. If the quiescent time is set corresponding to the delay time at the segment portion, on the other hand, it is practically difficult to dynamically drive the matrix portion because the quiescent time becomes too long.
Regarding the means for driving such a display, usually, the feedback operation for driving the first driving line from the final driving line is often required to have some transition time. This feedback time is defined as a given non-selection time during which any of scanning and data lines is not driven. By making effective use of this non-selection time as a quiescent time for the segment portion, it is thus possible to prevent a contrast lowering and false light emission with high efficiency. In this regard, it is noted that all driving means have not always a flyback time. For this reason, driving means having no flyback time is provided with one or two or more dummy scanning lines. In this case, the flyback time is defined by a time during which one or more such scanning lines are driven. During flyback, data electrodes are in data-off states.
That is, the above object is achievable by the inventions defined
Furukawa Hirotada
Suzuki Mitsunari
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Philogene Haissa
TDK Corporation
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