Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1996-08-30
2001-02-13
Chow, Dennis-Doon (Department: 2775)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S212000, C345S210000, C345S095000, C323S267000
Reexamination Certificate
active
06188395
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power source circuit, a power source for driving a liquid crystal display, and a liquid crystal display device, and more particularly, to a new structure for a multiple output power source circuit which can supply a plurality of suitable electric potentials as a power source for driving the liquid crystal panel in a liquid crystal display device.
2. Description of Related Art
Conventionally, power source circuits which supply a plurality of electric potentials have been used for the driving circuit in liquid crystal panels, and one example of these power source circuits is disclosed in Japanese Laid-Open Patent Publication Hei 2-150819.
FIG. 11
shows the basic structure of this conventional power source circuit. In the liquid crystal panel
1
, a plurality of parallel segment electrodes SE
1
, SE
2
, . . . , (hereafter abbreviated as SEn) which extend in stripe form, and a plurality of parallel common electrodes CE
1
, CE
2
, . . . (hereafter abbreviated as CEn) which extend in a direction orthogonal to the segment electrodes, are provided in a state facing each other with an unrepresented liquid crystal layer interposed in between. The areas of the liquid crystal layer where these segment electrodes SEn and the common electrodes CEn cross comprise pixels, the optical state of which can change and which can be controlled to be dark or bright, and through the plurality of pixels, a desired display state can be reproduced over the liquid crystal panel as a whole.
When the attempt is made to display a desired picture image on the liquid crystal panel
1
, specific electric potentials are impressed for a specific length of time by a liquid crystal driving circuit in order to form the pixel state corresponding to the picture image display on the segment electrodes SEn and the common electrodes CEn, and through so-called time division driving, the state of each pixel is controlled, said pixels having a structure which is equivalent to a condenser with the liquid crystal layer interposed between electrodes.
The circuit shown in
FIG. 11
is a multiple output power source circuit which is used to supply the electric potentials V
0
, V
1
, V
2
, V
3
, V
4
and V
5
to the driving circuit of the liquid crystal panel
1
. In this circuit, first, using the high electric potential VDD, which is the power source electric potential that is supplied from the power source, and the low electric potential VEE as a base, the voltage is divided by voltage dividing resistors R
1
, R
2
, R
3
, R
4
and R
5
, to form intermediate electric potentials V
1
, V
2
, V
3
and V
4
. These intermediate electric potentials V
1
, V
2
, V
3
and V
4
are input into the noninverting input terminals of the operational amplifiers OP
1
, OP
2
, OP
3
and OP
4
which are formed inside the integrated circuit
2
. These operational amplifiers OP
1
, OP
2
, OP
3
and OP
4
are composed as voltage followers with the output terminals and inverting input terminals short circuited, and can supply the intermediate electric potentials V
1
, V
2
, V
3
and V
4
with low output impedance.
The output side of the operational amplifiers OP
1
, OP
2
, OP
3
and OP
4
are connected to resistors R
8
, R
9
, R
10
and R
11
, respectively, and the resistors R
8
through R
11
restrict the output current of the operational amplifiers OP
1
through OP
4
. In addition, after this, the top three electric potentials, out of the six electric potentials including the power source electric potential VDD and VEE, and the bottom three electric potentials are connected by condensers C
1
, C
2
, C
3
and C
4
between the respective electric potentials.
From the power source circuit thus formed, six output electric potentials V
0
to V
5
are output, with the power source electric potentials VDD as V
0
and VEE as V
5
. These output electric potentials V
0
through V
5
are impressed on the respective segment electrodes SEn and common electrodes CEn through the liquid crystal driving circuit which acts in accordance with the field signal corresponding to the picture image.
The voltage levels necessary when the liquid crystal panel is time division driven with high duty by the voltage averaging law are generally as shown in
FIG. 12
, and are the output electric potentials V
0
to V
5
having the relationships
V
0−
V
1=
V
1−
V
2=
V
2−
V
3=
V
3−
V
4=
V
4−
V
5 (1)
(here, V
0
>V
1
>V
2
>V
3
>V
4
>V
5
).
The signals which are applied to the segment electrodes SEn and the common electrodes CEn are, for example, as shown in FIG.
12
. In
FIG. 12
, the signal electric potential which is impressed on the segment electrodes SEn and is indicated by the dashed lines switches to either V
3
or V
5
within the interval of frame
0
(hereafter called Fr
0
) shown in
FIG. 12
, and in addition, switches to either V
0
or V
2
in the interval of frame
1
(hereafter called Fr
1
) shown in FIG.
12
. For example, the signal electric potential V
0
corresponds to the on state of the corresponding pixel region, and the signal electric potential V
2
corresponds to the off state. The switching state between the electric potential levels of the segment electrodes SEn changes depending on the pattern displayed.
On the other hand, the signal electric potential impressed on the common electrodes CEn is normally the non-selective state of V
4
in the interval of Fr
0
, and becomes the selective state of V
0
for only a specific interval. In addition, in the interval of Fr
1
, the electric potential is normally the non-selective state of V
1
, and becomes the selective state of V
5
for only a specific interval. The interval over which the common electrodes CEn achieve the selective state differs for each common electrode, and in general, the plurality of common electrodes CEn do not achieve the selective state simultaneously.
The intervals of Fr
0
and Fr
1
shown in
FIG. 12
alternatingly repeat, and through this the liquid crystal layer in the pixel areas undergoes alternating current driving, thereby preventing deterioration of the liquid crystal layer.
When the electric potential levels of these kinds of segment electrodes SEn and common electrodes CEn switches, the capacitance (composed of the segment electrode, the common electrode and the liquid crystal layer interposed therebetween) of the pixels which exist in plurality in the liquid crystal panel is charged and discharged, and consequently, an electric current is created between each of the electric potential levels of the output electric potentials V
0
through V
5
of the power source circuit through the liquid crystal panel. At this time, the switching of the electric potential level of the segment electrodes SEn is accomplished between V
0
and V
2
, or between V
3
and V
5
, and in addition, the majority of the common electrodes CEn are in a non-selective state, being the electric potential level of either V
1
or V
4
. Accordingly, the electric current accompanying the switching of the electric potential levels of the segment electrodes SEn primarily flows between V
0
, V
1
and V
2
, and between V
3
, V
4
and V
5
. In contrast to this, the common electrodes CEn are, as described above, for the most part in a non-selective state being the electric potential level of either V
1
or V
4
, but this becomes the electric potential level of V
0
or V
5
when the selective state is achieved. Accordingly, the electric current accompanying switching of the electric potential levels of the common electrodes primarily flows between V
0
, V
3
, V
4
and V
5
, and between V
0
, V
1
, V
2
and V
5
.
The current which is generated in the power source circuit created when the liquid crystal panel
1
is driven using this type of electric current, that is to say the above-described power source circuit, is supplied as a portion of the electric current which flows from the power source electric potential VDD to VEE. In other words, when considering,
Awad Amr
Chow Dennis-Doon
Oliff & Berridg,e PLC
Seiko Epson Corporation
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