JPH04268598A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To uniformize the brightness (contrast) on a screen without being affected by the angle of incidence of light on a light valve. CONSTITUTION:The light which is converged by a condenser lens 30 is made incident on the panel type light valve 31. In a figure, Po is light passing the center of the condenser lens 30 and Pa and Pa' are light beams passing points at distances from the center. Further, 32 is a projection lens and 33 is a screen. Then, Do is the light valve incidence position of Pi, Da is the incidence position of Da, and Da' is the incidence position of Pa'. The light valve 31 includes liquid crystal and the transmissivity of this liquid crystal is operated with a specific image signal DT to modulate light (including Po, Pa, and Pa'); and the modulated light beams Pmo, Pma, and Pma' are projected on the screen 33 to display an image. A data signal conversion part 34 includes a correction data holding part 35 which holds the transmissivity characteristic of the liquid crystal as correction data and a correcting circuit 36 which corrects input image data according to the correction data.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type liquid crystal display device, and more particularly to a projection type liquid crystal display device intended to achieve uniform brightness over the entire screen.

[0002] In recent years, as high-quality broadcasting such as satellite broadcasting and cable television has become commonplace, and as video sources such as movies have become easier to obtain, the need for high-quality, large-screen receivers has rapidly increased.

0003

2. Description of the Related Art A projection-type liquid crystal display device that enlarges and projects a liquid crystal display (LCD), a so-called liquid crystal projector, is attracting attention as a method for relatively easily obtaining a large screen.

[0004] Projection type liquid crystal display device (hereinafter referred to as projection type LCD)
) are (1) a large screen can be obtained even with a small LCD; (2)
) A resolution comparable to that of a direct-view type LCD can be obtained even with a small number of pixels, (3) There is no viewing angle problem, which is the biggest drawback of a direct-view type LCD (not only the contrast but also the color tone changes depending on the viewing angle). 4) CRT (cathode)
It has excellent features such as being smaller and lighter than the ray tube (ray tube) method, and eliminating the need for high-voltage circuits and convergence adjustment circuits.

FIG. 7 is a diagram showing the configuration of an optical system of a projection type LCD using a dichroic prism for color synthesis. In FIG. 7, light emitted from a lamp 10 is filtered by a filter 11 to remove unnecessary components in the infrared region and ultraviolet region, and then separated into red, blue, and green color components by two dichroic mirrors 12 and 13. Ru.

The blue light (B) is reflected by a mirror 14 and focused by a condenser lens 15, and then enters a blue light valve 16. After the green light (G) is focused by the condenser lens 17, the green light valve 1
The red light (R) is reflected by mirrors 19 and 20 and is focused by a condenser lens 21, and then enters a light valve 22 for red.

The light modulated by the three light valves 16, 18, and 22 with red, blue, and green image data is combined by a dichroic prism 23, and then transmitted through a projection lens 24 to a screen (not shown). z) projected onto the screen.

[0008] For the light valves 16, 18, and 22, active matrix type panels using TN crystals are used, for example, from the viewpoint of image quality.

[0009]

[Problems to be Solved by the Invention] However, in such conventional projection type liquid crystal display devices, the light is emitted onto the light valve through the condenser lens. The angle of light entering the bulb (incidence angle) differs between the center and the periphery of the light bulb, and as a result, the intensity of the light that passes through the liquid crystal becomes non-uniform in the plane direction, resulting in an increase in brightness (and contrast) on the screen. There was a problem that unevenness occurred.

To explain this in detail, in FIG.
o is light passing through the center of the condenser lens, and Pa is light passing through a point away from the center. Po enters the light valve almost straight, but Pa enters the light valve after being slightly refracted. Therefore, the incident angle θ of Po
The incident angle θa of Pa is always a small value with respect to the angle θa of Pa (approximately 90 degrees), and the value becomes smaller as it approaches the outer edge of the condenser lens. That is, the angle of incidence changes sharply toward the periphery of the light valve.

[0011] Here, when a predetermined voltage Von is applied to the liquid crystal, the transmittance becomes approximately 100% and light passes through the liquid crystal, while when a predetermined voltage Voff is applied, the transmittance becomes approximately 0% and light is blocked. In addition, in the case of multi-gradation (or multi-color) display,
The interval between Von and Voff is subdivided into several stages.

FIG. 9 is a transmittance characteristic diagram of liquid crystal. In Figure 9, characteristic line A indicates that light is irradiated to the center of the light valve (
Transmittance curve when the incident angle is θo), characteristic line B is the irradiation of light to the peripheral part of the light valve (incident angle θa: θa<θo)
This is the transmittance curve when Looking at the change in transmittance between Von and Voff for these two curves, characteristic line A changes from approximately 100% to 0% with the maximum width, while characteristic line B changes by approximately 90%. from about 10% to number 1
It changes with a width of 0% less. This is because light is obliquely incident on the periphery of the light valve, which reduces or increases the amount of incident light.

[0013] This hinders the increase in the size of the light valve, and thus becomes an obstacle to achieving an even larger screen. Therefore, an object of the present invention is to make the brightness (and contrast) on the screen uniform without being affected by the angle of incidence of light on the light valve.

[0014]

[Means for Solving the Problems] FIG. 1 is a diagram showing the principle of the present invention. In this figure, light focused by a condenser lens 30 enters a panel-shaped light valve 31. Po is the light passing through the center of the condenser lens 30, Pa,
Pa' is light passing through a point away from the center. In addition, 32
is a projection lens, and 33 is a screen.

[0015] Here, the light valve incident position of Po is D
o.Similarly, the incident position of the light Pa is Da, and the incident position of the light Pa' is Da'. The light valve 31 includes a liquid crystal, modulates the light (including Po, Pa, and Pa') by manipulating the transmittance of the liquid crystal with a predetermined image signal DT, and modulates the modulated light Pmo.
, Pma, and Pma' are projected onto the screen 33 to display the image.

Reference numeral 34 denotes a data signal conversion section, and the data signal conversion section 34 includes a correction data holding section 35 that holds the transmittance characteristics of the liquid crystal as correction data, and a correction data holding section 35 that holds the transmittance characteristics of the liquid crystal as correction data, and a correction data holding section 35 that corrects the input image data based on the correction data. This includes a circuit 36.

[0017]

[Operation] In such a configuration, input image data is applied to the light valve 31 after being corrected based on the transmittance characteristics of the liquid crystal.

Therefore, even if the transmittance of the liquid crystal changes due to the influence of the incident angle, an image signal that has been corrected in advance to cancel out the change is provided, so the change in the transmittance can be suppressed, and the screen The display quality can be improved by uniformizing the brightness (and contrast) on the screen.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the drawings. 2 to 6 are diagrams showing an embodiment of a projection type liquid crystal display device according to the present invention. Note that since the optical system of this embodiment is the same as that of the conventional example, reference will be made to the conventional configuration (FIG. 7) as necessary.

First, the configuration will be explained. In Figure 2, 4
0 is a data signal conversion section, and 50 is a liquid crystal display section. The data conversion section 40 converts the data signal (image data) amplified by the amplifier section 61 into a digitized image signal using the A/D converter 41, and transfers this image signal to the conversion ROM group 42.
give to The conversion ROM group 42 includes a plurality of ROM1, RO
M2, . Further, the data conversion unit 40 encodes the outputs of counters 44 and 45 that count clock signals and horizontal synchronization signals (Hsync) using an encoder 46, and converts one ROM (ROM1, ROM
M2, . . . or ROMn) is generated.

Here, each ROM in the ROM group 42 is as follows:
Corresponds to each divided area of the display screen. FIG. 3(a) is a diagram showing an example of screen division. In this example, eight straight lines L1 to L8 are drawn from the corners of the screen toward the center of the screen, and two concentric circles L9 and L10 are further drawn. Each of the 17 regions B1 to B17 surrounded by these lines corresponds to each R
OM1, ROM2, . . . correspond to ROMn. ROM1
, ROM2, . . . ROMn store predetermined correction data, and this correction data is the transmittance characteristic of the liquid crystal panel (details will be described later).

On the other hand, the image signal from the data signal converter 40 is sent to the liquid crystal display section 50 after being subjected to alternating current processing (switching the polarity of the signal for each scanning line) in the inversion/non-inversion processing section 62. It will be done.

[0023] The liquid crystal display section 50 has a plurality of data buses DB.
a data-side driver 51 that sequentially selects a plurality of scan canvases SB and drives them with an image signal, and a scan-side driver 52 that sequentially selects a plurality of scan canvases SB and drives them with a predetermined voltage.
and a liquid crystal panel 53 in which data buses and scan canvases are arranged in a grid pattern and liquid crystal cells C are connected to the grid points (intersections).

When each lattice point is sequentially scanned in accordance with a predetermined scanning signal and an image signal is written into the liquid crystal cell for each lattice point, the transmittance of each lattice point changes in accordance with the write voltage. The liquid crystal panel 53 has a conventional light valve (
16, 18, and 22) in FIG. Therefore, the light irradiated onto the liquid crystal panel 53 passes through the dichroic prism (see reference numeral 23 in FIG. 7) or the projection lens (see numeral 23 in FIG. 7) in an amount corresponding to the transmittance of each grid point.
(see reference numeral 24), and then projected onto a screen.

Here, since the projection type LCD enlarges the liquid crystal panel and projects it onto the screen, the liquid crystal panel 5
There is a one-to-one correspondence between the shape of No. 3 and the screen shape on the screen. Therefore, each area B1 to B17 that was divided into screens earlier is
It is also each divided area of the liquid crystal panel 53.

That is, the transmittance characteristic data of the liquid crystal stored in each of ROM1 to ROMn is stored in the liquid crystal panel 5.
This is transmittance characteristic data for each region in No. 3, and the degree of change in transmittance due to the influence of the incident angle is grasped and stored for each region.

FIG. 3(b) shows the correction data (transmittance characteristic data for each region) stored in each ROM1 to ROMn.
FIG. In this diagram, B1, B2, B5
, B6, B9, B10, B11, B14, and B15, its size is expressed as height H.
It is expressed as. The amount of correction is larger at the periphery than at the center of the screen (area B9). This is because the degree of change in transmittance due to the influence of the incident angle is greater in the peripheral area than in the central area.

FIG. 4 is a diagram showing an example of image signal correction in an arbitrary area (Bx). In FIG. 4, Von is a voltage value corresponding to the white level (100% transmittance) in the image signal, and Voff is a voltage value corresponding to the black level (0% transmittance).

If no correction is performed, a change in transmittance occurs due to the influence of the incident angle depending on the position on the liquid crystal panel where the region Bx exists.

In order to cancel the change in transmittance, voltages ΔVon and ΔVoff of a certain magnitude are set to Von and Vof, respectively.
Just add it to f (see the following formula ■■) Von+ΔVon →Von' ...■Voff+
ΔVoff→Voff'...■ That is, the magnitudes of ΔVon and ΔVoff may be determined for each region, and data representing these magnitudes may be used as correction data for each region.

The specific procedure for setting the correction data is, for example, to obtain the voltage-transmittance characteristics for each area of the liquid crystal panel,
The extent to which each of these area characteristics deviates from the voltage-transmittance characteristics of a reference area (for example, the central area) is determined. Then, a voltage correction amount that can cancel out this deviation is determined and stored in each ROM as correction data.

Therefore, according to this embodiment, since the correction data for each area of the liquid crystal panel 53 is stored inside the conversion ROM group 42, no matter which position of the liquid crystal panel 53 the light is incident on, that position can be detected. The included region correction data allows the image signal to be appropriately corrected. As a result, changes in transmittance due to the influence of the incident angle can be canceled out (or suppressed), the brightness (and contrast) on the screen can be made uniform, and display quality can be improved.

Note that the method of region division is not limited to the above example, and various methods can be considered. For example, as shown in FIG. 5, the screen may be divided into squares. Further, in the above embodiment, the image signal is corrected by digital processing, but it is of course possible to perform the correction in an analog manner. For example, as shown in FIG. 6, the pedestal voltage and amplification factor of the image signal may be changed as appropriate by controlling the values of the feedback resistors Rf and Ro of the OP amplifier according to the display position on the screen. good.

[0034]

According to the present invention, since the image signal is corrected according to the transmittance characteristics of the liquid crystal, the brightness on the screen ( and contrast) can be made uniform.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is a configuration diagram of an embodiment.

FIG. 3 is a screen division diagram and a schematic diagram of correction data for each division area in one embodiment.

FIG. 4 is an image signal correction diagram of one embodiment.

FIG. 5 is another screen split diagram of one embodiment.

FIG. 6 is an analog circuit diagram of one embodiment.

FIG. 7 is a configuration diagram of an optical system common to a conventional example and an embodiment.

FIG. 8 is a diagram illustrating a main part of an optical system for explaining the angle of incidence.

FIG. 9 is a characteristic diagram for explaining changes in transmittance.

[Explanation of symbols]

30: Condenser lens 31: Light bulb 33: Screen 34: Data signal conversion section 35: Correction data holding section 36: Correction circuit

Claims (1)

[Claims] 1. Light focused by a condenser lens is irradiated onto a panel-shaped light valve, and the light is modulated by manipulating the transmittance of the liquid crystal of the light valve with a predetermined image signal, and the modulated light is A projection type liquid crystal display device that displays an image by projecting it onto a screen, wherein the liquid crystal transmittance characteristic is maintained and the image signal is corrected according to the transmittance characteristic. .