Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-04-10
2004-01-06
Liang, Regina (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S100000
Reexamination Certificate
active
06674422
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention generally relates to a method for driving an electro-optical panel, a data line driving circuit thereof, an electro-optical apparatus, and electronic equipment.
2. Description of Related Art
Generally, an image display portion of a liquid crystal display apparatus includes an element substrate, an opposing substrate, and liquid crystal enclosed in a gap defined between these substrates. A plurality of scanning lines, a plurality of data lines, transistors provided correspondingly to the intersections of the scanning lines and the data lines, and pixel electrodes are formed on the element substrate. On the other hand, a common electrode is formed on the opposing substrate. Further, thin film transistors (hereunder referred to as “TFTs”) are used as the transistors.
Each TFT has a gate connected to a scanning line, a source connected to a data line, and a drain connected to a pixel electrode.
Generally, a method for driving this image display portion includes simultaneously turning on a plurality of TFTs by selecting scanning lines with predetermined timing, and then applying a voltage of each of the data lines to the pixel electrodes simultaneously. In this case, voltages corresponding to image data are supplied to the data lines, respectively. The transmittance of the liquid crystal is controlled according to the voltage applied between the pixel electrode and the common electrode. This enables gray scale display according to the values of image data.
The relationship between the voltage applied to the liquid crystal and the transmittance thereof (hereunder referred to as “V-T characteristic”) is not a linear relation but a non-linear relation. Therefore, it is necessary to perform an operation of making the quantity of change in transmittance of the liquid crystal uniform, correspondingly to each gray scale level of image data. In the present application, this operation is referred to as a &ggr;-correction.
FIG. 17
is a block diagram illustrating a data line driving circuit for driving one data line, and peripheral circuits thereof. As shown in this figure, the data line driving circuit includes a first latch circuit
921
, a second latch circuit
922
, and a DA converter
93
. Further, a controller
6
and a &ggr;-correction circuit
91
are provided at a preceding stage of this data line driving circuit.
The controller
6
generates 6-bit image data DA. The &ggr;-correction circuit
91
performs &ggr;-correction on the image data DA and generates 8-bit image data DB (D&ggr;1, D&ggr;2, . . . , D&ggr;8). Incidentally, the &ggr;-correction circuit
91
includes a RAM or a ROM, in which a table for performing &ggr;-correction is stored. Data stored in this table is determined according to the input-output characteristic of the DA converter
93
, and the transmittance-applied-voltage characteristic of the liquid crystal.
The DA converter
93
is a capacitance division DA converter using switches and capacitors. The DA converter
93
has 8 parallel-placed capacitive devices
941
to
948
. If “C” represents the value of capacity of the capacitive device
941
, then the capacitive devices
942
,
943
, . . . ,
948
are selected so that the values of these capacitive devices are
2
C,
4
C, . . . , and
128
C, respectively.
Further, data line capacitance
940
is parasitic on a data line
99
. In
FIG. 17
, the value of this parasitic capacitance is indicated by Cs. A voltage Vcom at a terminal, which is at the side opposite to the data line
99
, of an equivalent capacitor having capacitance equal to the data line capacitance
940
is applied to the common electrode placed on the opposing substrate.
Two reference voltages Va and Vb are supplied to the DA converter
93
. One terminal of each of the capacitive devices
941
to
948
is connected to a supply terminal Ta for supplying the reference voltage Va. On the other hand, the other terminal of each of the capacitive devices
941
to
948
is connected to the supply terminal Ta through a corresponding one of reset switches
951
to
958
. When the switches
951
to
958
are on, both terminals of each of the capacitive devices
941
to
948
are short-circuited, so that the charged electricity of the capacitive devices
941
to
948
is discharged therefrom. Further, a reset switch
910
is connected to between a terminal for supplying the other reference voltage Vb and the data line
99
. When this switch
910
is on, the electric potential of the data line
99
is reset to a level corresponding to the voltage Vb.
Additionally, each of switches
961
to
968
, which is adapted to be on or off according to the value of a corresponding one of data D&ggr;1 to D&ggr;8, is provided between the data line
99
and a corresponding one of the capacitive devices
941
to
948
. When switches
961
to
968
are selectively turned on, the capacitive devices connected to the switches, which are turned on, are parallel-connected to one another. Thus, a voltage corresponding to image data DB is applied to the data line
99
.
Meanwhile, in recent years, liquid crystal exhibiting a nearly linear V-T characteristic has been developed by improving the composition thereof. It has been known that, especially, in the case of certain TN (Twisted Nematic) liquid crystal, as shown in a graph of
FIG. 18
, the V-T characteristic thereof almost rectilinearly (or linearly) changes at the white side, while such a characteristic thereof curvedly (or non-linearly) changes at the black side.
When the liquid crystal whose V-T characteristic having both of a linear portion and a non-linear portion is driven, it is considered that the liquid crystal is driven by assuming that the V-T characteristic thereof linearly changes. In this case, although the &ggr;-correction circuit
91
can be omitted, the gray scale level of an actually displayed image is higher than that of an original image to be displayed, because the relation between the transmittance and the applied voltage is actually a non-linear relation at the black side. Thus, this conventional liquid crystal has a drawback in that the original image cannot be displayed with proper gray scale levels at the black side. Additionally, this conventional liquid crystal has other drawbacks in that the contrast ratio of a display using this liquid crystal is decreased, and that the picture quality thereof is degraded.
Conversely, in the case of performing &ggr;-correction by using the &ggr;-correction circuit
91
, none of such drawbacks occur, because preliminarily &ggr;-corrected image data is supplied to the data line driving circuit. However, a primary part of the &ggr;-correction circuit
91
includes the RAM or ROM, as described above. Moreover, peripheral circuits, such as a read circuit, are necessary. Thus, such a conventional liquid crystal display unit has a drawback in that when the &ggr;-correction circuit
91
is used, the cost and power-consumption thereof are increased.
SUMMARY OF THE INVENTION
The present invention is accomplished in view of the aforementioned circumstances. Accordingly, an object of the present invention is to provide a data line driving circuit of an electro-optical panel, which has a circuit having a small occupied area and can be driven with low power consumption, and to provide a driving method therefor, and to provide an electro-optical apparatus, and to provide electronic equipment.
To achieve the foregoing object, according to an aspect of the present invention, there is provided a method for driving an electro-optical panel on the precondition that this method is used in an electro-optical panel having an electro-optical material, whose transmittance-applied-voltage characteristic has a linear portion and a non-linear portion, a plurality of scanning lines, a plurality of data lines, switching devices provided correspondingly to intersections between the scanning lines and the data lines, and pixel electrodes provided correspondingly thereto. This method includes the step of determining, according t
Liang Regina
Seiko Epson Corporation
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