JPH0617980B2 - Projection liquid crystal display - Google Patents

Description

TECHNICAL FIELD The present invention relates to a projection type liquid crystal display device.

[Prior Art] Conventionally, as a projection type liquid crystal display device, Japanese Patent Laid-Open No. 60-291
There is one disclosed in Japanese Patent No. This uses three liquid crystal panels with red, green, and blue pixels formed, provides a light source for each liquid crystal panel, and combines the light transmitted through each liquid crystal panel with a semi-transmissive mirror or a semi-transmissive prism. Then, the image is displayed on the screen.

[Problems to be Solved by the Invention] In the above, three light sources are required, the light utilization efficiency is poor, and variations occur due to deterioration of the lamps, and there is a drawback that the image quality deteriorates. Moreover, since three lamps and three liquid crystal panels are used, the overall configuration is large. In addition, different semi-transmissive mirrors or semi-transmissive prisms must be used, resulting in an increase in manufacturing cost.

The present invention provides a projection type liquid crystal display device which requires only one light source and can be miniaturized.

[Means for Solving Problems] In the present invention, one light source and light from this light source are separated by being reflected or transmitted by an optical filter according to color.
A liquid crystal light valve in which pixels of colors corresponding to the respective lights are formed is provided on the optical path of the separated light, and the light transmitted through the liquid crystal light valves is combined by the second optical filter to form an image on the screen. It is designed to be projected.

[Embodiment] In FIG. 1, 1 is a halogen lamp and 2 is a concave lens, which constitute a light source for parallel rays.
Reference numerals 3 and 4 are dichroic mirrors that form an optical filter, both of which reflect green and transmit red and blue.
The mirror 3 is for separating light, and the mirror 4 is for combining light. 5 and 6 are the first and second liquid crystal light valves, respectively, and the liquid crystal light valve 5 is
Prism 5a, 5a, green filter 5b, polarizing plate 5c,
5c and liquid crystal panel 5d, liquid crystal light valve
6 is composed of a prism 6a, 6b, the polarizing plate 6b, 6b and the liquid crystal panel 6d having a red and blue filter 6c.
Reference numerals 7 and 8 are mirrors for making the light transmitted through the dichroic mirror 3 into light in the opposite direction and transmitting it through the liquid crystal light valve 6 . 9 is a condenser lens, 10 is a projection zoom lens, and 11 is a screen.

FIG. 2 shows a state in which the liquid crystal light valve 6 is viewed from the side. The lower prism 6a in the figure is for allowing light to enter the liquid crystal panel 6d at a predetermined angle, while the upper prism 6a is transparent. It is for making the light parallel to the incident light. The prism 5a of the liquid crystal light valve 5 is similar to this.

The reason why the angle of the incident light to the liquid crystal panel is adjusted by the prism in this way will be described later.

Next, the operation will be described. The light from the halogen lamp 1 is converted into parallel rays by the concave lens 2 and supplied to the dichroic mirror 3. Dichroic mirror 3
The light transmitted through is reflected by the mirrors 7 and 8 and supplied to the liquid crystal light valve 6 .

On the other hand, the light reflected by the dichroic mirror 3 is supplied to the liquid crystal light valve 5 .

The light transmitted through the liquid crystal light valves 5 and 6 is combined by the dichroic mirror 4, condensed by the condenser lens 9, and then projected onto the screen 11 via the zoom lens 9.

In this way, only one light source is required, and the lights that pass through the dichroic mirrors 3 and 4 are parallel to each other, so that the overall size of the device can be reduced. Further, the same dichroic mirror can be used for the two dichroic mirrors, which is advantageous in terms of cost.

Here, the meaning of using a prism for the liquid crystal light valve will be described. In the liquid crystal panel using the TN type liquid crystal, the relationship between the incident angle of light and the contrast is as follows.

In FIG. 3, when the alignment direction of the liquid crystal panel is the direction of arrow A, the relationship between the viewing angle θ centered on the axis X perpendicular to the panel surface and the contrast is as shown in FIG. . In the figure, C represents contrast. From this figure, the angle φ from the alignment axis Y is 135 degrees, and θ = 10
It can be seen that the azimuth of degree can maximize the contrast. This azimuth is determined by the tilt angle of the alignment, the cross angle, the dielectric anisotropy, etc., but θ = 3 to 1
It is included in the range of 5 degrees.

Therefore, the prism 6a is used so that the angle of the incident light on the liquid crystal panel 6d falls within the above range to obtain the maximum contrast.

Next, a method of driving the liquid crystal panels 5d and 6d will be described. The liquid crystal usually has a noticeable flicker unless it is driven at 40 Hz or higher. 60 for NTSC television broadcasting
Since it is a field and 30 frame transmission system, when an TFT active matrix panel is used as the liquid crystal panel and this is driven by field alternating current, the liquid crystal is substantially 30
The cycle decreases to Hz drive. That is, as shown in FIG. 5A, the polarity applied to the source line is inverted for each field, but this cycle becomes 30 Hz. Then, as shown in FIG. 5B, a wave is formed in the light intensity and flicker occurs.

Furthermore, in the case of frame AC drive, half of that is 15
Since it becomes Hz drive, flicker is very noticeable, which is a big problem in practical use.

Therefore, in this example, the liquid crystal panels 5d and 6d are driven with their polarities inverted as shown in FIG. According to this, since the light intensity waves are 180 degrees out of phase with each other on the liquid crystal panels 5d and 6d as shown in FIG. 6C and both are superposed, the period of the light intensity waves on the entire screen is half that of the conventional one. It will be. Therefore, in the case of field driving, the frequency is apparently 60 Hz, and flicker is hardly noticeable.

Next, the arrangement of pixels in the liquid crystal panels 5d and 6d will be described. In the liquid crystal panel 6d, it is most preferable in terms of color mixing that the blue and red pixels are arranged in a zigzag pattern as shown in FIG. Further, as shown in FIG. 8, the green pixels of the liquid crystal panel 5d and the red and blue pixels of the liquid crystal panel 6d can be combined by shifting by 1/2 pixel in each of the vertical and horizontal directions. It is effective in improving the uniformity.

In the above example, the polarizing plates are provided before and after each liquid crystal panel, but instead of this, the lens 2 and the dichroic mirror 3 are provided.
May be provided between the lens 9 and the dichroic mirror 4. In this case, the number of polarizing plates is the smallest. The polarizing plate between the lens 9 and the dichroic mirror 4 may be provided on the front surface of the screen 11.

The light valve 6 may be provided between the mirrors 7 and 8 or between the dichroic mirror 3 and the mirror 7.

Furthermore, in the above example, as the dichroic mirror, the one that most easily manufactures reflects green and transmits red and blue is used, but it is not limited to this, and any one of red, blue, and green is reflected, and the remaining What is necessary is that it can pass through. in this case,
It is necessary for each liquid crystal panel to form pixels of a color corresponding to the color of incident light. However, regarding the spectral characteristics of the halogen lamp, since red is the strongest, it is effective to form the red pixel on the same light valve as the blue or green pixel in order to improve the light utilization rate.

[Effects of the Invention] According to the present invention, the light from the light source and the projected light are parallel to each other, so that the entire apparatus can be configured compactly, and since only one light source is required, the cost is structurally reduced. Is also advantageous and the adjustment of the light source is easy. Furthermore, since only two optical filters such as expensive dichroic mirrors are required, the cost is low and the same first and second optical filters can be used, which is advantageous in terms of cost and assembly process. It will be

Further, as an application aspect, when two apparatuses are arranged side by side to project a stereoscopic image, it is advantageous in terms of space to narrow the distance between the two apparatuses.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention, FIG. 2 is a side view showing a part of FIG. 1 extracted, and FIG. 3 shows an azimuth of light incident on a liquid crystal panel. Explanatory diagram, FIG. 4 is an explanatory diagram showing the viewing angle characteristics of the liquid crystal, FIG. 5 is a waveform diagram showing the polarity and light intensity of the voltage applied to the pixel, and FIG. 6 is a pixel in one embodiment of the present invention. FIG. 7 is a waveform diagram showing a voltage applied to the substrate and light intensity, FIG. 7 is an explanatory diagram showing an arrangement example of pixels, and FIG. 8 is an explanatory diagram showing an example of a state in which pixels of each liquid crystal panel are combined. 1 ... Halogen lamp 3,4 ...... Dichroic mirror 5 , 6 ...... Liquid crystal light valve 7,8 ...... Mirror

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-179723 (JP, A) JP-A-60-107625 (JP, A) Actual development 59-87022 (JP, U)

Claims (2)

[Claims] 1. A light source for generating parallel rays and a red light provided at a predetermined angle with respect to light from the light source,
A first optical filter that transmits either green or blue and reflects the rest; an optical reflection system that reflects light that has passed through the first optical filter in a direction opposite to that of the first optical filter; A second optical filter that combines the light reflected by the optical filter and the light reflected by the optical reflection system to generate light that is parallel and opposite to the light from the light source; A first liquid crystal light valve provided between the second optical filters and having pixels of a color corresponding to the light reflected by the first optical filter, the first optical filter, the optical reflection system, and the first optical filter. A second liquid crystal light valve provided on the optical path between the two optical filters and having pixels of a color corresponding to the light transmitted through the first optical filter, and composed by the second optical filter. Light Projection type liquid crystal display device, characterized in that the projection on the lean. 2. The projection type liquid crystal display device according to claim 1, wherein the first optical filter and the second optical filter reflect green and transmit red and blue.