JP2803675B2 - LCD projection display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal cell for a light valve.
The present invention relates to a rear projection type liquid crystal projection display device used as a device.

BACKGROUND ART In a display device of this type, a driving method of a liquid crystal cell includes:
The adoption of an active matrix system in which a non-linear element such as a thin film transistor is incorporated in each pixel increases the amount of display information, and thus, there is a device that can display a TV image. However, in an active matrix type liquid crystal cell, since the non-linear element portion for driving the liquid crystal and the pixel electrode portion are opaque, when enlarged and projected on a transmissive screen, the shadow of this electrode portion is displayed on the screen. Will be projected.

On the other hand, as a transmissive screen, as shown in FIG. 2, a two-panel screen combining a Fresnel lens 6 and a lenticular lens 7 is generally used. However, when the image of the active matrix type liquid crystal cell is enlarged and projected on the transmission type screen including the lenticular lens, the shadow of the electrode portion of the liquid crystal cell is projected on the screen as described above. There is a problem that a beat is generated due to the pitch of the image and the pitch of the lenticular lens of the screen, resulting in so-called moire fringes, which significantly reduces the image quality.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points,
It is an object of the present invention to provide a liquid crystal projection display device capable of preventing occurrence of moiré fringes.

In the liquid crystal projection display device according to the present invention, a phase grating having a plurality of ridges arranged in parallel with each other in a direction perpendicular to the optical axis is provided between the liquid crystal cell and the transmission screen, and a plurality of ridges are provided. The extending direction matches the ridge direction of the lenticular lens of the transmission screen.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS.

In FIG. 1, reference numeral 1 denotes an active matrix type liquid crystal cell. Light emitted from a light source 2 is converted into parallel light by a condenser lens 3 and irradiated to the liquid crystal cell 1. After being transmitted through the liquid crystal cell 1, the irradiation light is applied to the transmission screen 6 via the rectangular wave phase grating 4 and the magnifying projection lens 5.

As shown in FIG. 2, a two-screen screen combining a Fresnel lens 11 and a lenticular lens 12 is used as the transmission screen 6. In this two-panel type screen, the lenticular lens 12 is arranged on the incident surface side, so that it is possible to widen the angle and reduce the color shift. An image with good contrast can be obtained even under illumination. Further, the concentric Fresnel lens 11 macroscopically converges light toward the observer in front, and the diffusion layer 14 can obtain appropriate vertical directional characteristics.

The rectangular wave phase grating 4 is formed similarly to the phase grating disclosed in Japanese Patent Publication No. 49-20105, and functions as an optical low-pass filter. That is, as shown in FIG. 3, the rectangular wave phase grating 4 is
And a grid portion 16 composed of a plurality of ridges formed on one main surface of the substrate portion 15 in parallel with each other. This rectangular wave phase grating 4 is such that the main surface of the substrate portion 15 is perpendicular to the optical axis, and the extending direction of the plurality of ridges forming the grating portion 16 matches the ridge direction of the lenticular lens 12. Are located in

Here, the width in the direction perpendicular to the optical axis of each of the plurality of protrusions forming the lattice portion 16 is a, the pitch of the plurality of protrusions is p, and the optical axis direction of each of the plurality of protrusions is , That is, the optical height of the grating portion 16 is denoted by δ. At this time, if the following equation is satisfied, the performance of the rectangular wave phase grating 4 as a low-pass filter is within a practically acceptable range.

cosδ ≧ −1 (1) p / a ≧ 2 (2) cosδ ≧ 1-0.35p / a (3) cosδ ≧ 1-0.65p / a (4) The liquid crystal cell 1 When the distance between one principal surface of the substrate portion 15 of the rectangular wave phase grating 4 and 1 is 1, the cut-off spatial frequency Sc of the rectangular wave phase grating 4 is expressed by the following equation.

Sc = a / lλ (5) where λ is the wavelength of the irradiation light.

Since the spatial frequency of the image projected on the lenticular lens 12 is lower than the cut-off spatial frequency Sc, this cut-off spatial frequency Sc is projected on the spatial frequency corresponding to the pitch of the electrodes of the liquid crystal cell 1 and on the liquid crystal surface of the liquid crystal cell 1. The spatial frequency of the intensity distribution of the light emitted from the lenticular lens 12 is set to a value lower than one of the spatial frequencies corresponding to the pitch of the lenticular lens 12, so that the spatial frequency of the light A component corresponding to the pitch of the electrodes of the liquid crystal cell 1 in the intensity distribution of light emitted from the lenticular lens 12 and being lower than one of the corresponding spatial frequency and the spatial frequency corresponding to the pitch of the lenticular lens 12 Prevents the occurrence of moire fringes caused by the difference in spatial frequency between components corresponding to the pitch of lens 12. You can do it.

FIG. 4 is a block diagram showing another embodiment of the present invention,
Each component is configured in the same manner as the first device, except that the rectangular wave phase grating 4 is disposed between the magnifying projection lens 5 and the transmission screen 6.

In this configuration, if the distance between one principal surface of the substrate portion 15 of the rectangular wave phase grating 4 and the transmission screen 6 is l ′,
The cut-off spatial frequency Sc of the rectangular wave phase grating 4 is represented by the following equation.

Sc = a / l′ λ (6) Accordingly, in the apparatus shown in FIG. 4, the cut-off spatial frequency Sc represented by the equation (6) is set to the spatial frequency corresponding to the electrode pitch of the liquid crystal cell 1 and the liquid crystal cell. By setting the spatial frequency to a value lower than one of the spatial frequencies corresponding to the pitch of the lenticular lens 12 projected on the liquid crystal surface, the occurrence of moiré fringes can be prevented as in the apparatus of FIG. .

FIG. 5 is a block diagram showing still another embodiment of the present invention. Irradiation light emitted from a light source 21 is converted into parallel light by a reflector 22, and then enters a dichroic mirror 23. The dichroic mirror 23 is formed so as to selectively reflect only the blue component of the irradiation light. The blue component is separated from the irradiation light by the dichroic mirror 23, reflected by the reflection mirror 24, and then
Dichroic prism through 25 and rectangular wave phase grating 26
It is incident on 27.

On the other hand, the component transmitted through the dichroic mirror 23 enters the dichroic mirror 29. The dichroic mirror 29 is formed so as to selectively reflect only the green component of the irradiation light. The green component is separated from the irradiation light by the dichroic mirror 29 and is incident on the dichroic prism 27 via the liquid crystal cell 30 and the rectangular wave phase grating 31.

The component transmitted through the dichroic mirror 29, that is, the red component is reflected by the reflection mirrors 32 and 33, and then enters the dichroic prism 27 via the liquid crystal cell 34 and the rectangular wave phase grating 35.

In the dichroic prism 27, the blue component is reflected by the reflection surface 27a, and the green component is reflected by the reflection surfaces 27a and 27b.
, And the red component is reflected by the reflection surface 27b.
Each of the blue, green, and red components is incident on the magnifying projection lens 37 by the dichroic prism 27. Each of the blue, green, and red components is irradiated on the transmission screen 38 by the magnifying projection lens 37, and a color image is formed.

In the above configuration, like the device of FIG.
The generation of moire fringes for each of the green and red components can be prevented, and a good color image can be obtained.

In the above embodiment, the rectangular wave phase grating 4 is provided between the liquid crystal cell 4 and the magnifying projection lens 5 and between the magnifying projection lens 5 and the transmissive screen 6. It may be formed on the pupil of the projection lens 5.
However, in that case, assuming that the focal length of the magnifying projection lens 5 is f, the cut-off spatial frequency Sc of the rectangular wave phase grating 4 is expressed by the following equation.

Sc = a / fλ (7) Effects of the Invention As described in detail above, in the liquid crystal projection display device according to the present invention, the liquid crystal cell and the transmission screen are arranged parallel to each other in a direction perpendicular to the optical axis. A phase grating having a plurality of ridges is provided, and the extending direction of the plurality of ridges is made to coincide with the ridge direction of the lenticular lens of the transmission screen. Therefore, in the liquid crystal projection display according to the present invention, the spatial frequency of the intensity distribution of the light emitted from the lenticular lens by the phase grating is changed by the spatial frequency corresponding to the pitch of the electrodes of the liquid crystal cell and the spatial frequency corresponding to the pitch of the lenticular lens. The frequency can be lower than any one of the frequencies, and the spatial frequency between the component corresponding to the pitch of the electrode of the liquid crystal cell and the component corresponding to the pitch of the lenticular lens 12 of the intensity distribution of the light emitted from the lenticular lens. Moire fringes caused by the difference can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a schematic perspective view showing the configuration of a transmission screen,
FIG. 4 is a sectional view showing a shape of a rectangular wave phase grating, FIG. 4 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a block diagram showing still another embodiment of the present invention. Explanation of reference numerals of main parts 1 ... liquid crystal cell 2 ... light source 4 ... rectangular wave phase grating 6 ... screen

Claims (2)

(57) [Claims] 1. A liquid crystal projection display device which irradiates an active matrix liquid crystal cell with light from a light source and enlarges and projects the light passing through the liquid crystal cell onto a transmission screen including a lenticular lens. A phase grating having a plurality of ridges arranged in parallel to each other in a direction perpendicular to the optical axis between the expression screens, wherein the extending direction of the plurality of ridges coincides with the ridge direction of the lenticular lens. A liquid crystal projection display device. 2. A cut-off spatial frequency of the phase grating is set to a value lower than one of a spatial frequency corresponding to a pitch of an electrode of the liquid crystal cell and a spatial frequency corresponding to a pitch of the lenticular lens. The liquid crystal projection display device according to claim 1, wherein: