JPH06138434A - Liquid crystal projector - Google Patents

Abstract

PURPOSE:To accurately display full color by controlling the pulse width of a driving pulse signal at every liquid crystal panel so that the transmissivity of the liquid crystal panels for respective colors R, G and B is uniform. CONSTITUTION:The pulse width of the driving pulse signal Yn of one common outputted from a driving signal generation circuit 34 is controlled so as to be made different at every LCD panel of each color in the display area of the same gradation. In the gradation display area where the contrast of blue is high, the pulse width of the driving pulse signal Yb outputted to the LCD panel for blue is set shorter than the pulse width of the driving pulse signals Yg and Yr outputted to other LCD panels for green and for red. In the gradation display area where the contrast of red is high, the pulse width of the driving pulse signal Yr outputted to the LCD panel for red is set shorter than the pulse width of other driving pulse signals Yg and Yb.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal projector, and more particularly to a liquid crystal projector having a liquid crystal panel for each of R, G and B colors.

[0002]

2. Description of the Related Art As a conventional liquid crystal projector, for example, there is a liquid crystal projector 1 in which liquid crystal panels are provided for R, G and B color signals as shown in FIG.

The liquid crystal projector 1 is driven by drive signals for R (red), G (green), and B (blue) that are input according to an input color video signal by a video signal processing circuit (not shown), LCD panel 2 for red, LCD panel 3 for green, and LCD for blue having color filters corresponding to the respective colors.
The panel 4, the light source 5, the blue light reflecting mirror 6 that reflects only the blue light of the light emitted from the light source 5 and transmits the green and red light, and the blue light reflected by the blue light reflecting mirror 6 A total reflection mirror 7 that totally reflects the light and makes it enter the LCD panel 4 for blue, and only a green light transmitted by the blue light reflection mirror 6 makes it enter the LCD panel 3 for green.
A green light reflection mirror 8 which transmits red light and makes it enter the red LCD panel 2, and a half mirror which transmits blue light which transmits the blue LCD panel 4 and reflects green light which transmits the green LCD panel 3. 9, a total reflection mirror 10 that totally reflects the red light transmitted through the red LCD panel 2, a blue light and a green light that are transmitted and reflected by the half mirror 9, and are reflected by the total reflection mirror 10. Half mirror 1 that transmits red light and makes it incident on the projection lens 12.
The projection lens 12 is configured to optically combine blue, green, and red lights received by the first and half mirrors 11 and project a full-color image on the screen 20.

Therefore, if the luminance of the red light, the green light and the blue light transmitted through the three red LCD panel 2, the green LCD panel 3 and the blue LCD panel 4 is not balanced, the correct "white" is obtained. , "Black" and "grey" cannot be displayed, the red LCD panel 2, the green LCD panel 3 and the blue LCD panel 4 are LCD panels formed of the same liquid crystal material.

[0005]

However, in order to project such a conventional full-color image, R, G, and B are projected.
In the liquid crystal projector in which the liquid crystal panels are provided for the respective color signals, the LCD panels formed of the same liquid crystal material are used, and the spectral characteristics thereof are almost the same, but as shown in FIG. The transmittances (or contrasts) of the LCD panels used in the wavelength regions of red, green, and red are very different, so the transmittances of the red LCD panel 2, the green LCD panel 3, and the blue LCD panel 4 are different. Balance is different when displaying, for example, "white" and "black", and the original "white" and "black" color displays are projected by combining the transmitted light of the three LCD panels. There is a problem in that the colors are not displayed in white and black.

That is, as shown in FIG. 8, three LCs are used.
The chromaticity when the gradation is changed from white to black by the color display that is synthesized and projected by the transmitted light of the D panel, originally, the data (dark scale) from white to black are all the same chromaticity ( x, y) = (0.3, 0.3), but as shown in the above figure, the LCD panel for blue is actually more than the LCD panel 2 for red and the LCD panel 3 for green. Four
Due to its low transmittance, the color display that should display bright white tends to be yellowish or the color display that should display dark black is displayed purple. However, there is a problem in that accurate full-color display cannot be performed.

Therefore, in the present invention, the pulse width of the drive pulse signal for driving the liquid crystal panel is set for each liquid crystal panel so that the transmittance of the liquid crystal panel provided for each color of R, G and B becomes uniform. An object of the present invention is to provide a liquid crystal projector that controls and accurately displays full color.

[0008]

The invention according to claim 1 is
A liquid crystal projector including a liquid crystal panel provided for each color of R, G, and B, and a drive circuit for controlling a pulse width of a drive pulse signal for driving each liquid crystal panel according to an input color video signal. In the invention, the drive circuit controls the pulse width of the drive pulse signal output to each of the liquid crystal panels so as to be different for each of the liquid crystal panels. A liquid crystal panel provided for each color of, and a drive circuit for controlling the pulse width of a drive pulse signal for driving each liquid crystal panel according to an input color video signal, Is configured so that the pulse width of the drive pulse signal output to each liquid crystal panel is different for each liquid crystal panel based on the difference between the predetermined brightness curve and the brightness curve of each color liquid crystal panel. It is characterized by controlling.

[0009]

According to the present invention, the pulse width of the drive pulse signal output to the liquid crystal panel for each color of R, G, B is controlled by the drive circuit so as to be different for each liquid crystal panel. .

Therefore, it is possible to control the transmittance between the R, G, and B liquid crystal panels to be uniform, to adjust the contrast for each color gradation, and to obtain a full-color image to be combined. A more accurate color can be displayed, and the full-color display capability of the liquid crystal projector can be improved.

According to the second aspect of the present invention, the driving circuit outputs to the respective liquid crystal panels based on the difference between the predetermined luminance curve and the luminance curves of the liquid crystal panels for the respective colors of R, G and B. The pulse width of the drive pulse signal is controlled to be different for each liquid crystal panel.

Therefore, it is possible to control the transmittance between the R, G, and B color liquid crystal panels to be uniform based on a predetermined brightness curve, and to adjust the contrast for each color gradation. , The combined full-color image can be displayed in more accurate colors, and the full-color display capability of the liquid crystal projector can be improved.

[0013]

EXAMPLES Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a video signal processing circuit 30 to which a drive circuit of a liquid crystal projector of the present invention is applied. The drive pulse signal, which will be described later, output from the video signal processing circuit 30 is output to the liquid crystal projector 1 shown in FIG. The description of the configuration of the liquid crystal projector 1 is omitted.

In FIG. 1, the video signal processing circuit 30 is
Decoder 31, counter 32, AND gate circuit 3
3, a drive signal generation circuit 34 and an A / D conversion circuit 35. 2A to 2M show examples of signals processed by the respective units in the drive signal generation circuit 34.

The decoder 31 generates a drive pulse signal for one common based on a clock signal (CK) and a reset signal (see FIG. 2A) input from the counter 32 based on the brightness characteristics of the LCD panel described later. A predetermined timing control signal for controlling the pulse width is output from the output terminal (instructing 7 gradations) to the AND gate circuit 33, and the AND gate circuit 33 determines the pulse width of the drive pulse signal. (See (b)) is output.

The counter 32 outputs to the decoder 31 a reset signal for dividing each common and a clock signal for dividing the number of gray levels within one common based on a clock signal and a reset signal input from a CPU (not shown). In addition,
The reset signal is also input to the drive signal generation circuit 34.

The drive signal generating circuit 34 includes binary counters 41a-41c and inverter circuits 42a-42.
c, OR circuits 43a to 43c, NAND circuit 44, NA
ND gate circuits 45a and 45b and level shifter 46
It is composed of

The binary counter 41a outputs the first clock signal x for pulse width setting (see FIG. 2C) based on the timing of the pulse width control signal PC input from the AND gate circuit 33 to the binary counter 41b.
To the OR circuit 43a, and the binary counter 41
b is the first input from the binary counter 41a
The second clock signal y (see FIG. 2 (d)) is output to the binary counter 41c and the OR circuit 43b based on the clock signal x of the binary counter 41c, and the binary counter 41c receives the second clock signal input from the binary counter 41b. A third clock signal z based on y (FIG. 2 (e)
Is output to the OR circuit 43c.

Each of the inverter circuits 42a to 42c has an A
Digital video data D input from the D / D conversion circuit 35
1 to D3 are inverted and output to the OR circuits 43a to 43c. Each of the OR circuits 43a to 43c has a logical sum of the first to third clock signals x, y and z input from the binary counters 41a to 41c and the digital video data D1 to D3 input from the inverter circuits 42a to 42c. The data is output to the NAND circuit 44. NAND circuit 44
Is the NAND circuit 45b for the exclusive OR data of the OR data input from the inverter circuits 42a to 42c.
Output to.

NAND circuit 45a and NAND circuit 45
By inputting their outputs to one of the input terminals, b latches or updates the exclusive OR data input to the NAND circuit 45b at the timing of the reset signal input to the NAND circuit 45a and causes the level shifter 46 to perform the update. Output. The level shifter 46 is a NAND circuit 45b.
The exclusive OR data input from the above is converted into a drive pulse signal Yn (see FIGS. 2F to 2M) for controlling the grayscale display for one common based on the voltages V1 and V3 input from the outside. It outputs to the red LCD panel 2, the green liquid crystal panel 3 and the blue liquid crystal panel 4 in the conventional liquid crystal projector 1 shown in FIG.

The A / D conversion circuit 35 converts a video signal input through a connection terminal (not shown) or the like into digital video data D.
1 to D3 and output to the drive signal generation circuit 34.

Next, the operation of this embodiment will be described.

First, with reference to FIGS. 3 and 4, a description will be given of a problem of luminance balance which occurs between LCD panels when displaying a halftone in a conventional liquid crystal projector.

In a liquid crystal projector having three LCD panels for each color of R, G, and B, even if LCD panels of the respective colors have the same contrast characteristics, for example, as shown in FIG. In the display of the intermediate gradation, the change of the brightness (or gradation) of each color is not the same, that is, R, G, and
The brightness ratios of the B colors are different. FIG. 3 shows a case where the gradation display area is divided into 7 steps from 1 gradation to 7 gradations. In FIG. 3, the curve indicated by the chain line is
The brightness curve in which the value of (red brightness) × 3 is plotted, the curve indicated by the alternate long and short dash line is the brightness curve in which the value of (blue brightness) × 15 is plotted, and the curve indicated by the line is the green brightness curve. There is. For example, "black" from the first gradation to the third gradation
In the display area close to the color, the blue brightness is strong and the display is bluish. In the display area of the intermediate color between the third gradation and the fourth gradation, the red and blue luminances are slightly strong and the display is purpleish.
In the display region from the 4th gradation to the 4th gradation, which is close to the "white" color, the red brightness is strong and the display tends to be yellowish.

In the case of FIG. 3, an ND (Neutral Density) filter or the like is used when displaying "white" gradation in the upper right of the drawing.
Even if the color tone is corrected, the ratio of luminance in each gradation display area cannot be adjusted.

In order to solve this problem, as shown in FIG. 4, for example, liquid crystal applied to the LCD panel of each color for each gradation display area divided into 7 steps from 1 gradation to 7 gradations. If the applied voltage, that is, the drive pulse signal Yn output from the drive signal generation circuit 34 in the video signal processing circuit 30 of FIG. 1 is adjusted for each LCD panel of each color, the luminance ratio of each LCD panel is adjusted uniformly. It is possible to

Specifically, FIG. 4 shows an LCD of each color with each gradation on a curve similar to the brightness curve of each color shown in FIG.
A plot of the applied voltage applied to the panel is shown below. The applied voltage to the blue LCD panel is such that the brightness of blue decreases in the display regions of the first gradation to the fourth gradation with reference to the green brightness curve. The voltage (plot indicated by “△” in the figure) is lowered, and the applied voltage applied to the red LCD panel (in the figure, so that the brightness of red decreases in the display area of the 5th gradation to the 6th gradation). , The plot indicated by “□”) may be lowered. To this end, the pulse widths of the first to fourth gradations of the drive pulse signal Yn applied to the blue LCD panel 4 with respect to the green LCD panel 3 in the liquid crystal projector 1 shown in FIG. 6 are shortened. This is to set the pulse widths of the fifth to sixth gradations of the drive pulse signal Yn to be set and applied to the red LCD panel 2 to be short.

That is, in the present embodiment, as shown in FIG. 5, the pulse width of the drive pulse signal Yn of one common output from the drive signal generation circuit 34 within the display region of the same gradation is set for each color LCD panel. It is to control it differently. The change of the pulse width is determined by setting the signal output timing of the decoder 31 corresponding to each color. In FIG. 5, (a) is the drive pulse signal Yg applied to the green LCD panel 3, (b) is the drive pulse signal Yr applied to the red LCD panel 2, (c) is the blue LCD panel 4 Driving pulse signals Yb to be applied to the blue LCD panel 4 in the display regions of the first to fourth gradations on the LCD panel 4 for blue. The pulse width of the signal Yb is set shorter than the pulse widths of the other drive pulse signals Yg and Yr.

Similarly, in the display area of the fourth to sixth gradations in the red LCD panel 2, the pulse width of the drive pulse signal Yr applied from the drive signal generation circuit 34 to the red LCD panel 2 is the same. However, other drive pulse signals Yg, Y
It is set shorter than the pulse width of b.

Therefore, in the graphs shown in FIGS. 3 and 4, the blue and red brightness curves can be brought close to the green brightness curve, and the gradation display in the display areas of the first to fourth gradations can be performed. The bluish display can be brought closer to the "black" or "gray" display. Similarly, the gradation display in the display regions of the 4th gradation to the 6th gradation of the graph is changed from the yellowish display to the "white" display. The display can be brought closer to the display, for example, the color display changing from “black” to “white” can be accurately reproduced on the screen, and the intermediate color of the full-color image projected from the liquid crystal projector 1 on the screen can be reproduced more accurately. Therefore, the full-color display capability of the liquid crystal projector can be improved.

[0032]

According to the first aspect of the present invention, the pulse width of the drive pulse signal output to the liquid crystal panel for each color of R, G, B by the drive circuit is controlled so as to be different for each liquid crystal panel. With such a configuration, it is possible to control the transmittance between the R, G, and B color liquid crystal panels to be uniform, to adjust the contrast for each color gradation, and to synthesize a full-color image. Can be displayed in a more accurate color, and the full color display capability of the liquid crystal projector can be improved.

According to the second aspect of the invention, the driving circuit outputs to each liquid crystal panel based on the difference between the predetermined brightness curve and the brightness curve of the liquid crystal panel for each of R, G and B. Since the pulse width of the drive pulse signal is controlled to be different for each liquid crystal panel, the transmittance between the R, G, and B color liquid crystal panels is made uniform based on a predetermined luminance curve. The liquid crystal projector can be controlled, the contrast can be adjusted for each color gradation, the combined full-color image can be displayed in more accurate colors, and the full-color display capability of the liquid crystal projector can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a video signal processing circuit to which a drive circuit of a liquid crystal projector of the present invention is applied.

FIG. 2 is a timing chart of signals processed by each unit in the video signal processing circuit of FIG.

FIG. 3 is a diagram showing a relationship between luminance and applied voltage in the R, G, and B liquid crystal panels.

FIG. 4 is a diagram showing the relationship between the brightness in the R, G, and B liquid crystal panel and the applied voltage applied by the drive signal generation circuit of FIG. 1.

5 is a diagram showing an example of drive pulse signals output from the drive signal generation circuit of FIG. 1 to the R, G, and B liquid crystal panels.

FIG. 6 is a configuration diagram of a main part of a conventional liquid crystal projector.

FIG. 7 is a diagram showing a spectral characteristic of a conventional liquid crystal.

FIG. 8 is a diagram showing changes in chromaticity when changing from white to black by three liquid crystal panels of R, G, and B.

[Explanation of symbols]

 1 liquid crystal panel 2 red LCD panel 3 green LCD panel 4 blue LCD panel 5 light source 5 6 blue light reflection mirror 7, 10 total reflection mirror 8 green light reflection mirror 9, 11 half mirror 12 projection lens 20 screen 30 video signal Processing circuit 31 Decoder 32 Counter 33 AND gate circuit 34 Drive signal generation circuit 35 A / D conversion circuit 41a to 41c Binary counter 42a to 42c Inverter circuit 43a to 43c OR circuit 44 NAND circuit 45a, 45b NAND gate circuit 46 Level shifter

Claims (2)

[Claims] 1. A liquid crystal panel provided for each color of R, G, B, and a drive circuit for controlling a pulse width of a drive pulse signal for driving each liquid crystal panel according to an input color video signal, In the liquid crystal projector including: the liquid crystal projector, wherein the drive circuit controls the pulse width of the drive pulse signal output to each of the liquid crystal panels to be different for each of the liquid crystal panels. 2. A liquid crystal panel provided for each color of R, G, B, and a drive circuit for controlling a pulse width of a drive pulse signal for driving each liquid crystal panel according to an input color video signal. In the liquid crystal projector comprising: the drive circuit, for each liquid crystal panel, a pulse width of a drive pulse signal output to each liquid crystal panel based on a difference between a predetermined brightness curve and a brightness curve of the liquid crystal panel of each color. A liquid crystal projector characterized in that it is controlled differently.