JPH0444490A - Liquid crystal display device and liquid crystal projector - Google Patents

Abstract

PURPOSE:To improve the gradation near a white peak of a projected video by providing a liquid crystal panel corresponding to R, G, B lights as a light bulb, providing a liquid crystal panel acting as a white light bulb, synthesizing four units of projected lights and outputting the synthesized light. CONSTITUTION:A P wave transmitted through a polarized light beam splitter 8 is separated into R, G, B lights by dichroic mirrors 4a, 4b and made incident into liquid crystal panels 6R, 6B, 6G. On the other hand, an S wave separated by the splitter 8 is made incident in a liquid crystal panel 6W, from which a P wave is projected and is made incident in a polarized light beam splitter 9. Thus, the projected light from the panel 6W is synthesized with projected lights from the panels 6R, 6B, 6G at the splitter 9 and the synthesized light is projected onto a screen from a projection lens 7. Display with high accuracy is attained by adding a white light by RGB synthesis to the projected light and the gradation of the white level is reproduced with much accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device and a liquid crystal projector using the same.

[Summary of the Invention] The liquid crystal display device and the liquid crystal projector of the present invention are provided with a liquid crystal panel corresponding to R light, G light, and B light as a light valve, and a drive state is set according to the white luminance level of the video signal. , by providing a liquid crystal panel that functions as a white light valve and configuring the output light from the four units of liquid crystal panels to be combined and output, the gradation near the white peak of the output image can be reproduced well. This is what I did.

[Prior Art] FIG. 4 shows an example of a liquid crystal projector using a conventional three-panel liquid crystal display device.

1 is a metal halide lamp as a light source, 2 is a cut filter for infrared and ultraviolet rays, 3a to 3C are mirrors, 4a to 4d are dichroic mirrors that transmit only light of a specific wavelength, 5a to 5c are condenser lenses, 6
R, 6G, and 6B are respectively R light and G light valves.
A liquid crystal panel corresponds to light and B light, and 7 is a projection lens.

Light emitted from the metal halide lamp 1 and passed through the cut filter 2 is incident on a dichroic mirror 4a that reflects only the G light via a mirror 3a. The G light separated by the dichroic mirror 4a is incident on the liquid crystal panel 6G via the condenser lens 3b.

Further, the B light is reflected by the dichroic mirror 4b, and the B light and the R light are separated and enter the liquid crystal panels 6B and 6R via condenser lenses 5b and 5c, respectively.

Each of the liquid crystal panels 6G, 6B, and 6R is, for example, a TN mode transmissive liquid crystal in which horizontal and vertical electrodes are arranged to form a matrix of pixels, and an example of its structure is shown in FIG. , 6a and 6e are polarizing plates, 6b and 6d are transparent electrodes (and alignment films), and 6c is a liquid crystal. In other words, when no voltage is applied to the transparent electrodes 6b and 6d, only the P-polarized component of the incident light is transmitted through the polarizing plate 6a, but the plane of polarization is rotated by 90' by the liquid crystal 6c and reaches the polarizing plate 6e. Therefore, the light passes through the polarizing plate 6e.

However, when a sufficient voltage is applied to the transparent electrodes 6b and 6d, the molecules of the liquid crystal 6c align in the direction of the voltage and lose optical rotation, so that the light component that has passed through the polarizing plate 6a in that pixel is blocked by the polarizing plate 6e. (For normally white type and normally black type, the operation is opposite to the above). In other words, the transmittance is controlled by the applied voltage. Therefore, by controlling the transparent electrodes based on the R, G, and B drive signals E, E, E, each liquid crystal panel 6G, 6B.

The transmittance of the G light, B light, and R light incident on the 6R is controlled for each pixel, and an image corresponding to each color is obtained.

Light emitted from each liquid crystal panel 6G, 6B, 6R is combined by dichroic mirrors 4c, 4d, and projected as a color image onto a screen (not shown) via a projection lens 7.

[Problems to be Solved by the Invention] However, in a liquid crystal projector that utilizes the transmittance characteristics of such a liquid crystal panel, it is not possible to sufficiently increase the white peak brightness on the image compared to a projector using a CRT. Also, there was a problem in that the gradation in the white area could not be reproduced satisfactorily.

For example, in the case of a normally white type liquid crystal panel, the transmittance characteristic with respect to the applied voltage is shown as shown in FIG. 6(a), and this becomes a logarithmic graph as shown by the dotted line in FIG. 6(b). In other words, the transmittance from the black level (points E to D) to the midtone level (point C = around 70% transmittance) is approximately equal to the γ power of the applied voltage V shown by the solid line in FIG. 6(b). It is proportional, but it is not proportional after the 0 point, and it is particularly saturated from point B to point B (transmittance 90 to 100%).

Therefore, even if a driving voltage is applied to the liquid crystal panel using a video signal proportional to -Vγ, the gradation cannot be reproduced correctly in the area where the transmittance is 70% or more, that is, in the white area9 [Measures for solving the problem 1] The invention was made in view of these problems, and the invention is based on the R, G, and H drive signals.
In addition to the first, second, and third liquid crystal panels that are driven as B-light light valves.

The first liquid crystal panel includes a fourth liquid crystal panel whose drive state is set according to the image brightness level and is driven as a white light valve. The liquid crystal display device is configured to include an output combining means for combining and outputting the output lights of the second, third, and fourth liquid crystal panels. Further, a liquid crystal projector is constructed using the liquid crystal display device.

[Operation] By combining the light emitted by the fourth liquid crystal panel, which serves as a white light valve, with the light emitted from each of the R, G, and B liquid crystal panels, it is possible to obtain a high-brightness image. Therefore, if the fourth liquid crystal panel is driven with a predetermined drive voltage when the image is in the white region, it is possible to obtain good gradation in the white region, and also to increase the white peak brightness. It can be expressed as a brightness image.

[Embodiment] FIG. 1 shows a projection optical system of an embodiment of a liquid crystal display device of the present invention as a liquid crystal projector. The same reference numerals as in FIG. 4 indicate the same parts.

3d is a mirror, 5d is a condenser lens, 6W is a liquid crystal panel driven as a white light valve, and 8.9 is a polarizing beam splitter.

In this embodiment, the metal halide lamp 1 emits light,
From the light whose infrared rays and ultraviolet rays have been cut by the cut filter 2, the S polarized component (S wave) is deflected by the polarizing beam splitter 8, and only the P polarized component (P wave) is transmitted. The transmitted P wave is passed through dichroic mirror 4
The light is separated into R light, B light, and G light by a and 4b, and is incident on liquid crystal panels 6R, 6B, and 6G, respectively. The light emitted as S waves from the liquid crystal panels 6R, 6B, and 6G is combined by the dichroic mirrors 4c and 4d, and enters the polarizing beam splitter 9.

On the other hand, the S wave separated by the polarizing beam splitter 8 is incident on the liquid crystal panel 6W via the mirror 3d and the condenser lens 5d, and is emitted from the liquid crystal panel 6w as a P wave and is incident on the polarizing beam splitter 9. Therefore, the light emitted from the liquid crystal panel 6w is combined with the light emitted from the liquid crystal panels 6R, 6B, and 6G at the polarizing beam splitter 9, and is projected onto the screen through the projection lens 7.

In this way, by adding white light to the emitted light resulting from RGB synthesis, a display with higher brightness becomes possible, and as a result, the gradation of white color can also be reproduced more precisely.

Here, the liquid crystal panel 6W has a luminance signal (E,=0.30
E , +0.59E , +0.11E , No video display will be performed for the

Furthermore, the image display is not performed for a video signal that is high brightness but not white (for example, a signal in which only the B component is high brightness, a light blue color, etc.).

Therefore, for example, (transmittance of liquid crystal panel 6R) = (transmittance of liquid crystal panel 6B) = (transmittance of liquid crystal panel 6G) 2
In the case of 70% (completely E, I=EG=E, ≧70%IR
E) White light is transmitted only through the liquid crystal panel 6w at a predetermined transmittance depending on the brightness level. below,
A setting example will be described.

It is assumed that each of the liquid crystal panels 6R, 6B, 6G, and 6W is a normally white type having the transmittance characteristics shown in FIG.
Too much transmittance 100%, V2O transmittance 90%...
In the liquid crystal panels 6R, 6B, and 6G, the signal voltages E*, Ea, and EB of R, G, and B are respectively set to
When the signal voltage is Eb, the drive voltage V too is set so that the transmittance is 100%, and when the signal voltage is Eb, the drive voltage V 90 is set so that the transmittance is 90%. It is assumed that the drive conditions are set so that voltage V is applied.

At this time, in the liquid crystal panel 6W, the luminance signal voltage E is a driving voltage v1° at which the transmittance is 100% when the signal voltage is Ea, as shown in FIG. However, when the signal voltage is Eb, the drive voltage v7 at which the transmittance becomes 70%
Further, when the signal voltage is Ec, the drive voltage (■) makes the transmittance 0%. The drive conditions are set so that the voltage is applied to each pixel electrode.

Therefore, for example, in the liquid crystal panels 6R, 6B, and tjG, the R, G, and B video signals Ea, Ea, and Ea are respectively E.
When the level is at point C, a driving voltage V, which obtains a transmittance of 70% (voltage which obtains point C) is applied, but at this time, in the liquid crystal panel 6W, the luminance signal E, is at the level of Ec. Even if the driving voltage V gets one point. is applied,
In addition, R, G, B in the liquid crystal panels 6R, 6B, and 6G.
When the video signals ER, E, , E are at the level of Eb and a driving voltage of ■9° (voltage to obtain point B) that obtains 90% transmittance is applied, point H is applied to the liquid crystal panel 6W. A driving voltage V7° is applied to obtain the following.

Then, only when a white image is obtained by the liquid crystal panels 6R, 6B, 6G, white light of a predetermined brightness is emitted from the liquid crystal panel 6W and combined by the polarizing beam splitter 9, This will push the brightness of the white light obtained from this to even higher brightness.

In this case, when the luminance of the combined white light is converted into the transmittance shown in FIG. 2(a), it becomes as shown by the dotted line in FIG. 2(d). In other words, the white peak luminance can be approximately doubled.

In addition, when the characteristic in Figure 2 (d) is converted into a logarithmic graph, it is shown as in Figure 2 (e), and it is proportional to Vγ up to a higher brightness region (point B + H), and therefore -Vγ When a driving voltage is applied to a liquid crystal panel using a proportional video signal, gradation can be more accurately reproduced in a high-brightness white area.

Therefore, in the liquid crystal projector of this embodiment, it is also possible to display a subtitle or the like on a white image using a high-intensity white signal, for example.

Note that the liquid crystal panel 6W is driven only when E, l=E, =E, ≧70% IRE, but E R= E
It may be driven even when a=E a≧70% IRE. However, it is clearly E.

If ≠EC, if E6≠E8, or if E8≠E8
In this case, do not drive it. If you do this,
For color image parts other than white, LCD panel 6W
Since white light is not synthesized from the emitted light, there is no decrease in color saturation and color reproducibility can be maintained.

Note that it goes without saying that similar effects can be obtained even when a normally black type liquid crystal panel is used.

By the way, since the liquid crystal panel has a structure that cuts either the S wave or the P wave when it is incident, in the case of the conventional three-panel liquid crystal projector as shown in FIG.
When entering each liquid crystal panel, only half of the emitted light components of the metal halide lamp are used as projection light, but in the case of this embodiment, the S wave and P wave are separated in advance by the deflection beam splitter 8. , one side is made incident on the liquid crystal panel 6W, so that the emitted light component of the metal halide lamp 1 can be effectively utilized.

FIG. 3 shows another embodiment of the present invention, in which dichroic mirrors 4a, 4b, mirrors 3f, 3g, and 3h transmit R light, G light, and B light to liquid crystal panels 6R, 6B, respectively.
, 6G, and the liquid crystal panels 6R, 6B.
, 6G output light is combined by a prism 10. In this case as well, the same effect as in the embodiment shown in FIG. 1 can be obtained by combining the white light emitted from the liquid crystal panel 6W.

In yet another embodiment, it may be possible to separate the R, G, and B lights using a prism, without using a dichroic mirror.

In each of the above embodiments, a dedicated light source may be provided for the liquid crystal panel 6W.

Furthermore, R, G, and B liquid crystal panels are provided corresponding to the liquid crystal panel 6W in each of the above embodiments (that is, six units of liquid crystal panels in total are provided), and these are used as a white light valve. It is also conceivable to improve the brightness of color images.

Incidentally, although the above embodiments have been explained in the case of a liquid crystal projector, it goes without saying that similar effects can be obtained even if the liquid crystal display device is configured as a non-projection type liquid crystal display device.

[Effects of the Invention] As explained above, in the liquid crystal display device and liquid crystal projector of the present invention, the light emitted from the fourth liquid crystal panel driven as a white light valve is By configuring it so that it can be combined with the output light of the second and third liquid crystal panels and output, it is possible to increase the white peak brightness by almost twice, and also increase the image level in the white area. This has the effect of making it possible to reproduce tonality more accurately.

! l! ! Figure 3 is an optical block diagram showing another embodiment of the present invention, Figure 4 is an optical block diagram of a conventional liquid crystal projector, Figure 5 is a structural diagram of a liquid crystal panel, and Figures 6 (a) and (b) are transmission diagrams. FIG. 3 is an explanatory diagram of the relationship between the ratio and the applied voltage.

1 is a metal halide lamp, 2 is a cut filter, 38
~3h is a mirror, 4a~4d are dichroic mirrors,
5a to 5c are condenser lenses, 6R, 6B, 6G, 6
W is a liquid crystal panel, 7 is a projection lens, 8.9 is a polarizing beam splitter, and 10 is a prism.

[Brief explanation of drawings]

FIG. 1 is an optical block diagram showing an embodiment of the present invention. FIGS. 2(a) to (e) are explanatory diagrams of the relationship between the transmittance of the liquid crystal panel and the applied voltage. B. (PSIL) Procedural amendment (voluntary) July 24, 1990

Claims (2)

[Claims] (1) R light, G light based on R, G, B drive signals
The first and second light valves are driven as light and B light valves.
, a third liquid crystal panel, a fourth liquid crystal panel driven as a white light valve according to the image brightness level, and the output light of the first, second, third, and fourth liquid crystal panels are combined and output. A liquid crystal display device characterized in that it is equipped with an emission combining means. (2) R light, G light based on R, G, B drive signals
The first and second light valves are driven as light and B light valves.
, a third liquid crystal panel, a fourth liquid crystal panel driven as a white light valve according to the image brightness level, and the output light of the first, second, third, and fourth liquid crystal panels are combined and output. and a projection lens that projects the output lights of the first, second, third, and fourth liquid crystal panels onto a screen, which are synthesized by the output combination means. .