JPH04240979A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a projection picture with best contrast with respect to all projection angles of view (magnification) when a zoom projection lens and a swing optical system are adopted for the projection type liquid crystal display device. CONSTITUTION:Picture information is obtained from a light radiating from a projection light source 2 by a liquid crystal light bulb 3 and the light is modulated and projected with magnification on a screen 7 as a projected picture 8 via a zoom projection lens 5. In this case, a angle of view detection signal (a) corresponding to an angle of view theta of the zoom projection lens 5 is generated from an angle of view detector 6 and a video signal (b) is subjected to signal correction corresponding to the angle of view detection signal (a) by a correction control circuit 4 and the liquid crystal light bulb 3 is subjected to modulation control by a control signal C being an output of the correction control circuit 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to liquid crystal light valve drive control for a projection type liquid crystal display device.

0002

[Prior Art] Conventionally, drive control of a liquid crystal light valve is
It was common to perform fixed control at the best point of the liquid crystal light valve characteristics.

0003

[Problems to be Solved by the Invention] However, with the spread of projection type liquid crystal display devices and their improved performance, the use of tilt optical systems and zoom projection lenses has increased. On the other hand, in the conventional technology, the change in the angle of view (change in magnification) of the zoom lens does not result in the best clear viewing angle for all angles of view when considered from the perspective of the clear viewing angle of the liquid crystal light valve. This means that if the angle of view is changed using a zoom projection lens, there will be an angle of view at which the optimum contrast of the liquid crystal light valve cannot be obtained, which is a major factor in deteriorating image quality.

SUMMARY OF THE INVENTION The present invention aims to solve these problems and provides a projection type liquid crystal display device that can always reproduce an image with optimal contrast even when the angle of view (magnification) is changed using a zoom projection lens. There it is.

[0005]

[Means for Solving the Problems] A projection type liquid crystal display device of the present invention is a display device in which light from a projection light source is modulated by a liquid crystal light valve and projected onto a screen from a zoom projection lens, wherein The image of the zoom projection lens is provided with a view angle detector that detects the amount of change in the view angle, and a correction control circuit that corrects the driving voltage value of the liquid crystal light valve in accordance with the output of the view angle detector. The present invention is characterized in that the reference value of the drive voltage of the liquid crystal light valve and the video signal level are corrected in accordance with the angle change.

[0006]

Embodiment (Embodiment 1) FIG. 1 is a schematic diagram of an embodiment of the present invention. Here, the light emitted from the projection light source 2 supplied with voltage from the projection light source power supply 1 is modulated by obtaining image information by the liquid crystal light valve 3, and is enlarged and projected onto the screen 7 via the zoom projection lens 5. At this time, the liquid crystal light valve 3 changes the angle of view θ of the zoom projection lens 5.
This indicates that the view angle detection signal a, which is the output of the view angle detector 6 corresponding to , receives modulation control from the correction control circuit 4 using the control signal c obtained by correcting the video signal b.

FIG. 2 shows the relationship between the output angle α of the liquid crystal light valve at the maximum angle of view θw in this embodiment (configuration shown in FIG. 1), and FIG. 2 shows the optical relationship of the exit angle α' of the liquid crystal light valve at the minimum angle of view θn in .

These are based on the assumption that the projection distance L from the zoom projection lens 5 to the screen 7 is constant, and that the distance between the zoom projection lens 5 body and the liquid crystal light valve 3, that is, the flange back, is also fixed. When the angle of view of the projected image is widened, α is the largest, and when the angle of view of the projected image is narrowed, α' is the smallest. Hereinafter, FIGS. 2 and 3 will be explained in detail.

FIG. 2 shows a schematic configuration of this embodiment when the angle of view θw is the largest.

[0010] Here, A constituting the zoom projection lens 5
It can be said that the lens 9 and the B lens 10 are conceptually closest to the liquid crystal light valve 3. However, the angle of view θw is the largest, and the output angle α of the liquid crystal light valve 3 is also the largest.

A curve 11 (solid line) in FIG. 4 shows the relationship between the liquid crystal light valve drive voltage V and the liquid crystal light valve transmittance T at the output angle α at this time.

FIG. 3 schematically shows the configuration of this embodiment when the angle of view θn is the smallest.

Here, A constituting the zoom projection lens 5
Conceptually, the lens 9 and the B lens 10 can be said to be in a state farthest from the liquid crystal light valve 3. However, the angle of view θn is the smallest, and the output angle α' of the liquid crystal light valve 3 is also the smallest.

Curve 12 (broken line) in FIG. 4 shows the relationship between the liquid crystal light valve drive voltage V and the liquid crystal light valve transmittance T at the output angle α' at this time.

These characteristic curves (11 and 12) vary from (a) to (b) in FIG. 4 when the angle of view is wide (the magnification is large).
If the angle of view is narrow (low magnification), the driving voltage range for the liquid crystal light valve B shown in (c) to (d) in Figure 4 is the most appropriate driving voltage range. represents something.

Therefore, the angle of view variable state of the zoom projection lens 5 is grasped by the angle of view detector 6, the liquid crystal light valve drive voltage range most suitable for the projection angle of view at that time is determined, and the liquid crystal light valve 3 is corrected and controlled. By doing so, the liquid crystal light valve 3 is provided with a video signal at the liquid crystal light valve operating point and operating region with the best contrast adapted to the change in the viewing angle (change in magnification).

FIG. 5 is a diagram showing a specific embodiment of the field angle detector 6 and correction control circuit of the present invention. Here, the A lens 9 and the B lens 10 (
In this embodiment, the optical or mechanical position (described in FIGS. 2 and 3) is detected by the volume VR that constitutes the angle of view detector 6.

First, among the lens groups constituting the zoom projection lens 5, the optical positions of the movable lens groups (represented by 9 and 10 in FIGS. 2 and 3) that vary and determine the angle of view (magnification) are as follows.
The information is transmitted to the volume VR that constitutes the angle of view detector 6 by a mechanical connection method using a gear or the like or an optical connection method using a photocoupler or the like. As a result, the angle of view detection signal a corresponding to the angle of view, that is, the projection magnification is obtained.

Next, the operational amplifier 101 and R1, R2,
A correction control circuit 4 constituted by an adder including R3 and R4 adds the angle of view detection signal a to the video signal b, and outputs a control signal c. Furthermore, the liquid crystal light valve 3 is driven by the phase inversion drive circuit 102 as a phase inversion signal.

During the above operation, the transmittance change curve shown in FIG. 4 is obtained by setting the constants R1 to R4 as the correction addition amount corresponding to the change in the angle of view (change in magnification) and at the same time determining the amplifier gain in the appropriate contrast region. The operating point corresponding to the movement of is determined.

Furthermore, due to the difference in the angle of view, the transmittance change curve (
In Fig. 4, it is simply expressed by the movement of the operating point).
It is also possible to consider a circuit configuration in which gamma correction is performed simultaneously by providing a table or the like and performing addition and subtraction together with the operating point movement amount in an arithmetic circuit (correction control circuit 4).

In this case, in a strict sense, the characteristics of the liquid crystal light valve 3 are also different in the vertical and horizontal directions, so the correction performance can be further improved by using a ROM table that takes into account positional changes.

Although this embodiment has been described using a tilting optical system in which the relationship between the angle of view and the bright viewing angle of the liquid crystal light valve is clear, the same operation and effect can be obtained without using the tilting optical system.

In addition, in this embodiment, the zoom projection lens 5 has been explained with a simple configuration consisting of two lenses, A lens and B lens, for convenience, but it is also possible to use a high-performance zoom projection lens 5 consisting of a multi-group lens including an aberration correction lens group, etc. Even for zoom lenses, the angle of view (magnification) of the lens group determines the change in angle of view (magnification).
The same operation can be obtained by transmitting the amount of change to the angle of view detector 6. Furthermore, by using an electric zoom system for the zoom projection lens 3 using a motor, etc., and detecting the amount of rotation of the motor by pulse counting, etc., electrical connection with the angle-of-view detector 6 is facilitated, and centralized control (angle-of-view) by the CPU is facilitated. It should be noted that detection) can also be easily realized.

[0025]

As described above, according to the present invention, there is provided a display device in which light from a projection light source is modulated by a liquid crystal light valve and projected onto a screen by a zoom projection lens. A view angle detector that detects the amount of change, and a correction control circuit that corrects the drive voltage value of the liquid crystal light valve in accordance with the output of the view angle detector, and the control circuit is configured to adjust the drive voltage value of the liquid crystal light valve according to the change in the view angle of the zoom projection lens. By correcting the reference value of the driving voltage of the liquid crystal light valve and the video signal level, the angle of view of the projected image (
A projection type liquid crystal display device that can regenerate and project an image with optimum contrast even when changing the magnification, regardless of the angular dependence of the appropriate clear viewing angle of the liquid crystal light valve is realized.

In particular, even with a liquid crystal light valve having a narrow optimum clear viewing angle, it is possible to use a projection lens with a large variable field angle range (zoom ratio), which has a great effect on improving display performance.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram of the operation at the maximum angle of view in one embodiment of the present invention.

FIG. 3 is an explanatory diagram of the operation at the minimum angle of view in one embodiment of the present invention.

FIG. 4 is a diagram showing the change in transmittance of a liquid crystal light valve in an embodiment of the present invention.

FIG. 5 is a specific configuration diagram of a view angle detector and a correction control circuit in an embodiment of the present invention.

[Explanation of symbols]

1 Power supply for projection light source 2. Projection light source 3.LCD light bulb 4 Correction control circuit 5 Zoom projection lens 6 View angle detector 7 Screen 8 Projected image 9 A lens 10 B lens

Claims (1)

[Claims] 1. A display device that modulates light from a projection light source using a liquid crystal light valve and projects the modulated light onto a screen from a zoom projection lens, the display device comprising: a view angle detector that detects an amount of change in the view angle of the zoom projection lens; A correction control circuit corrects the drive voltage value of the liquid crystal light valve in accordance with the output of the view angle detector, and adjusts a reference value of the drive voltage of the liquid crystal light valve in accordance with a change in the view angle of the zoom projection lens. and a projection type liquid crystal display device characterized by correcting the video signal level.