Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-12-22
2004-08-24
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S085000
Reexamination Certificate
active
06781565
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an electro-optical device featuring reduced power consumption, a driving circuit and a driving method of the electro-optical device, and an electronic apparatus employing the electro-optical device as a display unit.
2. Description of the Related Art
A driving circuit of a conventional electro-optical device, such as a liquid crystal device, is constituted by a data line driving circuit, a scanning line driving circuit, etc. for supplying image signals, scanning signals, etc. at predetermined timings to data lines, scanning lines, etc. disposed in an image display region.
The data line driving circuit significantly differs in configuration, depending on whether input image signals are analog signals or digital signals. However, when display in a plurality of gray scales is performed, it is necessary to apply a voltage of an analog signal to a liquid crystal regardless of the type of an input image signal. Hence, if the input image signal is a digital signal, then the input image signal must be subjected to DA conversion so as to apply an analog signal voltage to the liquid crystal.
As a technique for the DA conversion, the PWM (Pulse Width Modulation) method is known.
FIG. 12
is a block diagram showing a configuration of a liquid crystal device to which the PWM method has been applied. As shown in
FIG. 12
, a liquid crystal device may be constructed by a data line driving circuit
130
′, a scanning line driving circuit
140
′, a group of switches
150
, and an image display region AA.
In the image display region AA, a plurality of scanning lines
112
are formed so that they are arranged in parallel in an X-direction, and a plurality of data lines
114
are formed in parallel in a Y-direction perpendicular thereto. Furthermore, at intersections of these scanning lines
112
and the data lines
114
, thin film transistors (hereinafter referred to as “TFTs”) serving as switches for controlling pixels are provided.
In this example, a gate electrode of a TFT
116
is connected to the scanning lines
112
, a source electrode of the TFT
116
is connected to the data lines
114
, and a drain electrode of the TFT
116
is connected to a pixel electrode
118
. Each of the pixels is constructed by the pixel electrode
118
, a common electrode formed on an opposing substrate, and a liquid crystal sandwiched between the two electrodes; hence, the pixels are arranged in a matrix pattern in association with the intersections of the scanning lines
112
and the data lines
114
. The data lines
114
oppose the common electrodes via the liquid crystal, and intersect with the scanning lines
112
, so that each data line
114
is accompanied with a parasitic capacitance.
The data line driving circuit
140
′ line-sequentially outputs selected signals corresponding to the data lines
114
, based on input image data D. The period during which the selected signals are set active is decided based on input image data values to be displayed at pixels corresponding to the selected signals. Lamp wave signals LS are supplied to input terminals of switches
151
making up the group of switches
150
, and output terminals thereof are connected to data lines
114
, selected signals being supplied to control terminals thereof. The switches
151
are configured so that they stay ON during a period in which selected signals stay active. Hence, the lamp wave signals LS are supplied to the data lines
114
only during a period corresponding to input image data values to be displayed at pixels. As a result, the lamp wave signals are written to the parasitic capacitors of the data lines
114
only during a period corresponding to input image data values. Furthermore, the scanning line driving circuit
130
′ generates scanning signals that become active for each horizontal scanning period and output the scanning signals to the scanning lines
112
.
In the configuration described above, if a certain scanning line
112
is selected by a scanning signal, then the TFT
116
connected to that scanning line
112
turns ON in the horizontal scanning period. At this time, the lamp wave signal LS is written to the parasitic capacitor of the data line
114
only for the period corresponding an input image data value; hence, a voltage based on the input image data value is applied to the pixel electrode
118
, and the applied voltage is held when the TFT
116
turns OFF. This makes it possible to display a gray scale based on a gray scale value indicated by input image data.
In the liquid crystal device set forth above, the lamp wave signals LS are written to the parasitic capacitors of the data lines
114
, and the voltages of the parasitic capacitors are captured into the pixels via the TFTs
116
. Therefore, the driving circuit for the lamp wave signals LS is required to have a sufficient driving capability for writing to the parasitic capacitors.
SUMMARY OF THE INVENTION
In the configuration of
FIG. 12
, even when the image display region AA is relatively small, a parasitic capacitance value of each of the data lines
114
is approximately 20 pF. In a liquid crystal device of a so-called XGA (1024 pixels×768 pixels) type, 1024 data lines are provided for each color of R, G, and B, so that a total parasitic capacitance value of the data lines
114
will be approximately 61 nF. If input image data includes 6 bits, then charging must be completed in a {fraction (1/64)} H period for the capacitance of 61 nF. This means that it is necessary to use a driving circuit capable of driving a heavy load for the driving circuit of the lamp wave signals LS, presenting a problem of an increased circuit scale. Furthermore, there has been a problem in that the driving circuit consumes more power to drive a heavier load.
The present invention has been accomplished at least in view of the above, and it is an object of the present invention to at least provide an electro-optical device featuring a reduced drive load, a driving circuit thereof, and an electronic apparatus employing the electro-optical device as its display unit.
A driving method for an electro-optical device in accordance with one exemplary embodiment of the present invention is intended for driving an electro-optical device equipped with a plurality of data lines, a plurality of scanning lines, pixel electrodes corresponding to intersections of the scanning lines and the data lines, and a plurality of signal supply lines corresponding to the scanning lines. The driving method may consist of the steps of: supplying scanning signals for sequentially selecting the scanning lines; sequentially supplying reference signals to the signal supply lines synchronously when the scanning signals become active; supplying pulse width modulation signals that are active only during a period corresponding to a gray scale value indicated by image data to the data lines; and capturing the reference signals from the signal supply lines corresponding to pixels and applying them to the pixel electrodes during a period in which the scanning lines and the data lines corresponding to the pixels simultaneously become active at the pixels corresponding to the intersections of the scanning lines and the data lines, while holding voltages of the pixel electrodes during a period in which either the scanning lines or the data lines corresponding to the pixels become inactive.
According to this exemplary embodiment, as soon as scanning signals are set active, the reference signals are sequentially supplied to the signal supply lines. Hence, a load on the driving circuit that drives the reference signals will be a parasitic capacitance on a single signal supply line, so that the load can be reduced. As a result, in the step for supplying reference signals, current consumption can be considerably reduced.
Furthermore, the electro-optical device in accordance with another exemplary embodiment the present invention is assumed to have an electro-optical material sandwiched between a pair of subs
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Dharia Prabodh M.
Mengistu Amare
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