Liquid crystal cells – elements and systems – Liquid crystal system – Projector including liquid crystal cell
Reexamination Certificate
1998-09-30
2001-03-20
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Projector including liquid crystal cell
C349S095000, C349S187000
Reexamination Certificate
active
06204895
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a projection-type display device using a light collecting plate, and more specifically to a display panel associated with the light collecting plate in a predetermined positional relationship and a position adjusting method for the display panel.
Hitherto, many types of liquid crystal display panels have been proposed. The most commonly used type of liquid crystal display panel is one that has a layer of liquid crystal represented by twisted nematic liquid crystal. With this type of liquid crystal display panel, display is achieved by controlling the twist of liquid crystal molecular orientation to determine the optical rotatory power of light that passes through the liquid crystal layer. Stated in more detail, the operating principle consists in the control of light transmission to the image observed surface side of the liquid crystal display panel by employing the birefringence or optical rotatory power of light in the liquid crystal layer and the linear polarization characteristics of the polarizing plates.
The liquid crystal display panel has thin film transistors (hereinafter referred to as TFTS) each formed for the purpose of switching a voltage applied to the liquid crystal within an associated pixel. The TFTs made of amorphous silicon or polysilicon have been manufactured or are now under development. Among them, the polysilicon-based TFTs have advantages resulting from the mobility in polysilicon. That is, in the first place, since the polysilicon is high in mobility, the amount of charge that can be flowed into each TFT per unit time can be increased. Therefore, the TFT size can be reduced and, as a result, the pixel aperture ratio can be increased. Second, a circuitry of driving the switching TFTs can be formed on the same substrate using polysilicon. Accordingly, the necessity of driver ICs serving as the driving circuitry and the mounting step therefor is eliminated, reducing the manufacturing cost. Further, it is possible to reduce the width of the frame portion outside the display area, which will be required in a future liquid crystal display panel. Because of the aforementioned advantages, attention has been paid to the polysilicon-based TFTs as a key technology.
A liquid crystal display panel containing the driving circuitry formed of such polysilicon TFTs has been developed and manufactured as a display element for a video projector or a video camera monitor because it provides a small, high-definition display panel.
In order to attain high brightness, the video projector generally employs a three-panel scheme of displaying a color image with three liquid crystal display panels for red, green and blue (hereinafter referred to as R, G, and B, respectively) which are three primary colors of light. On the other hand, the video camera monitor employs a single-panel scheme of displaying a color image with a single liquid crystal display panel having a color filter. In addition, a low-brightness projector has been manufactured by diverting the single liquid crystal display panel for the video camera monitor to projection.
However, the liquid crystal display panel for the single-panel scheme requires three times as many pixels as that for the three-panel scheme. When the display panel for the single-panel scheme is formed in the same size as that for the three-panel scheme, the aperture ratio thereof is lowered due to the required number of pixels. In addition, there is loss of light due to the color filter. Therefore, it is difficult to implement a high-brightness projector. For this reason, the three-panel scheme is mainly employed in the conventional projector. However, it difficult to reduce the manufacturing cost since three display panels and an optical separation and collection system are required in the three-panel scheme.
In view of a reduction in the manufacturing cost, attention has been paid on new types of single-panel projectors. In particular, a single-panel projector that uses dichroic mirrors for performing deflection and color separation and a liquid crystal display panel having a microlens light collecting plate, and a single-panel projector that uses a liquid crystal display panel having a hologram optical element plate for performing color separation and light collection are being developed actively.
FIG. 14
schematically illustrates the operating principle of a liquid crystal projector that requires no color filter, and
FIG. 15
illustrates the paths of light incident on a set of RGB pixels in the liquid crystal projector. As shown in
FIG. 14
, a microlens light collecting plate
102
is mounted on the light receiving surface of a liquid crystal display panel
104
, which is composed of an array substrate
105
having TFTs formed thereon and a counter substrate
106
opposed to the array substrate. The light collecting plate
102
has an array of microlenses
102
L each assigned to a corresponding set of RGB pixels on the liquid crystal display panel. By dichroic mirrors
103
, white light emitted from a light source is separated into collimated color component rays
110
,
111
, and
112
of RGB and deflected to the light collecting plate
102
at different incident angles. Each microlens focuses the color component rays
110
,
111
, and
112
of RGB onto the apertures
107
,
108
, and
109
of corresponding RGB pixels in the liquid crystal display panel. Accordingly, the apertures
107
,
108
and
109
of RGB pixels can receive the color component rays
110
,
111
, and
112
, respectively. The color component rays
110
,
111
and
112
are transmitted through the apertures
107
,
108
and
109
and emitted therefrom as outgoing rays
115
,
116
and
117
. In this manner, color display can be performed without using a color filter. It thus follows that there is no loss of light due to the color filter. Therefore, the dimensions and the cost of the optical system can be reduced.
In the display device using such a microlens or hologram optical element plate, each microlens or hologram optical element must be precisely aligned with a corresponding set of color pixels of the liquid crystal display panel. To reduce loss of light, the precision of the alignment must be increased as the pixels of the liquid crystal display panel are downsized. This is particularly important to the above-described display device with no color filter. Conventionally, there is an attempt to adjust the positional relationship between the microlenses and the color pixels of the liquid crystal display panel by observing a moire pattern. However, in such a moire-based alignment method, it is difficult to secure the precision of alignment enough to cope with the downsizing of pixels. In addition, this method cannot determine the center of each microlens and which one of the color pixels opposes the center of the microlens. Accordingly, the method is not applicable to the above-described single-panel display device with no color filter.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a display panel which can improve the precision in positional adjustment of aligning the focal spots of lenses of a light collecting plate with pixel electrodes thereof, and a position adjusting method for the display panel.
According to the present invention there is provided a display panel to be fixed to a light collecting plate having a plurality of lenses, the display panel comprising: a matrix array of pixel electrodes opposed to the lenses of the light collecting plate; a plurality of electrode wiring lines formed along rows and columns of the pixel electrodes; a driver circuit formed outside a display area corresponding to the matrix array of the pixel electrodes, for driving the pixel electrodes via the electrode wirings; and a plurality of alignment marks for positional adjustment of aligning the focal spots of the lenses with the pixel electrodes; wherein the alignment marks are arranged to be opposed to the lenses and separated from the display area by a distance corresponding t
Nakamura Hiroki
Nakamura Takafumi
Watanabe Yoshihiro
Kabushiki Kaisha Toshiba
Parker Kenneth
Qi Mike
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