JPH05153530A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To reproduce a video image with fidelity by converting a television video signal into a picture element voltage whose hysteresis characteristic of a high polymer liquid crystal display panel is corrected based on digital voltage data resulting from A/D converting the video signal. CONSTITUTION:A video input signal V1 is inputted to a correction circuit 23 via an A/D converter 21 and a subtractor 26. An output of the circuit 23 is fed to the high polymer liquid crystal display panel ia a D/A converter 27 and an X driver 28 and fed to a delay circuit 25. Voltage data by one frame are stored tentatively in a memory 24 and the voltage data from the memory 24 are read in a succeeding input timing from the A/D converter 21. The circuit 23 extracts relevant correction voltage data from a data ROM 22 based on a difference voltage V being an output of the converter 21 and the circuit 25 and the data are outputted as digital picture element voltage data. Through the constitution above, the video image is reproduced with fidelity by writing the correction data for the hysteresis characteristic in the voltage - transmissivity characteristic of the panel and the correction data of the gamma characteristic to the ROM 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device using, for example, a polymer liquid crystal panel.

[0002]

2. Description of the Related Art Conventionally, a projection type liquid crystal display device is well known as a liquid crystal display device capable of displaying an image on a large screen and realizing it at a low price. The liquid crystal panel of the projection type liquid crystal display device which is currently mainstream is, for example, STN.
(Super Twisted Nematic) panel, etc., and since a deflector is used, the light transmittance is theoretically 50% or less.

In recent years, a liquid crystal panel (hereinafter referred to as a polymer liquid crystal panel) composed of a polymer / liquid crystal composite film capable of achieving a light transmittance of 80% or more has been devised. Since the panel does not use a deflecting plate, it is desired to be applied to a projection type liquid crystal display device.

Here, the polymer liquid crystal panel is shown in FIG.
As shown in (a) and (b), droplet-shaped liquid crystal domains 62 are dispersedly arranged in a polymer film 61, and electrodes 63 are arranged to face each other so as to sandwich the polymer film 61.

In this polymer liquid crystal panel, as shown in FIG. 4A, before applying a voltage to the electrode 63 (power SWOFF
(State) scatters light that is vertically incident on the polymer film 61, and as shown in FIG.
Due to N), the liquid crystal domains 62 are aligned in the direction of the electric field generated between the electrodes 63, and the refractive index of the light with the polymer film 61 is the same so that the entire panel is in a transparent state and transmits light. I'm doing it.

By the way, such a polymer liquid crystal panel has voltage-transmittance characteristics as shown in FIG. For example, when the voltage applied to the polymer liquid crystal panel is gradually increased, the transmittance of light passing through the polymer liquid crystal panel rises with a predetermined curve, and the voltage reaching the end point is lowered. Then, a so-called hysteresis characteristic occurs in which the transmittance changes with a curve different from that when the curve is raised. This hysteresis characteristic shows that the liquid crystal domain 62 has a central part and a peripheral part near the interface.
It is believed that this is caused by the different speeds of responding to the voltage. When this polymer liquid crystal panel is used in a projection type liquid crystal display device, as shown in FIG. 8, in order to set the brightness of the polymer liquid crystal panel as, for example, the transmittance T0, the pixel to be applied to the polymer liquid crystal panel is set. Let the voltage be V0 (point X). When the pixel voltage is raised and the same level of brightness (transmittance T0) is set again (point Y), it is necessary to drop the pixel voltage to V1 in accordance with the hysteresis characteristic, and the received TV signal is changed to the pixel voltage. It is difficult to perform such dimming control only by converting / amplifying to, and it is not possible to faithfully reproduce the image on the screen.

[0007]

As described above, in the conventional liquid crystal display device, it is difficult to control the dimming in accordance with the hysteresis characteristic peculiar to the polymer liquid crystal panel, and it is necessary to faithfully reproduce the image on the screen. There was a problem that I could not.

The present invention has been made to solve the above problems, and provides a liquid crystal display device capable of dimming control corresponding to a hysteresis characteristic peculiar to a polymer liquid crystal panel and realizing faithful image reproduction. The purpose is to do.

[0009]

In order to achieve the above-mentioned object, the liquid crystal display device of the present invention is a liquid crystal display device having a polymer liquid crystal panel whose light transmittance is changed by applying a pixel voltage. First conversion means for converting a television video signal into digital voltage data, and new digital voltage data for correcting the hysteresis characteristic of the polymer liquid crystal panel based on the digital voltage data converted by the conversion means. Correction means to output,
The second conversion means for converting the new digital voltage data input from the correction means into the pixel voltage is provided.

[0010]

In the present invention, the television video signal is converted into digital voltage data by the first converting means, and this digital voltage data is inputted to the correcting means. The correction means outputs new digital voltage data for correcting the hysteresis characteristic of the polymer liquid crystal panel based on the digital voltage data to the second conversion means. The new digital voltage data input to the second conversion means is converted into a pixel voltage and applied to the polymer liquid crystal panel.

The corrected pixel voltage enables dimming control of the polymer liquid crystal panel, and as a result, faithful image reproduction of the television image signal is realized on the liquid crystal display device.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a projection type liquid crystal display device according to an embodiment of the present invention.

As shown in the figure, in this projection type liquid crystal display device, a light source 2 having a reflector 1, a polymer liquid crystal panel 3, a condenser lens 4, a diaphragm 5, a projection lens 6 and a screen 7 are on the optical axis. , A schlieren optical system arranged in, a antenna 8 for receiving a TV signal, a tuner 9 for demodulating the received TV signal into an analog video signal, and a video signal processing for displaying the analog video signal on the polymer liquid crystal panel 3. And a signal system such as a video signal processing circuit 10 that performs amplification and the like. This light source 2
A discharge lamp such as a metal halide having high efficiency, high brightness and high color rendering property is used for the.

As shown in FIG. 2, the polymer liquid crystal panel 3 includes a polymer / liquid crystal composite film 12 in which droplet-shaped liquid crystal domains 11 are dispersedly arranged, and the polymer / liquid crystal composite film 12 sandwiched therebetween. And an electrode portion 13 located opposite to the electrode portion 13. A plurality of pixels (not shown) are formed on one electrode portion 13. This polymer liquid crystal panel 3 is
The transmittance of light is changed by the pixel voltage applied to each pixel of the polymer / liquid crystal composite film 12, and the so-called dimming function of varying the amount of transmitted light passing through the polymer liquid crystal panel 3 is provided. There is.

Next, the configuration of the video signal processing circuit will be described with reference to FIG.

In the figure, 21 is a video signal input terminal V
An A / D converter having in, which converts an analog video signal input from this terminal into a digital video signal.
22 is a data ROM, which is the voltage of the polymer liquid crystal panel
Correction voltage data for correcting the hysteresis characteristic in the transmittance characteristic is written. 23 is a correction circuit,
Data ROM 2 according to the input digital video signal
The correction voltage data is extracted from 2 and this correction voltage data is newly output as a digital video signal. Reference numeral 24 denotes a memory, in which a digital video signal for one frame is temporarily stored as voltage data. A delay circuit 25 reads out and outputs voltage data in the memory 24 at the input timing of the digital video signal input from the A / D converter, and stores the newly input digital video signal in the memory 24. Reference numeral 26 denotes a subtractor, which compares the digital video signal for one frame output from the delay circuit 25 with a delay and the digital video signal for one frame from the A / D converter 21 to obtain the digital difference between them. The video signal is output to the correction circuit 23. A D / A converter 27 converts the digital video signal from the correction circuit 23 into an analog pixel voltage and outputs it. Reference numeral 28 denotes a signal line drive circuit (hereinafter, referred to as an X driver), which applies an input analog pixel voltage to each pixel of the polymer liquid crystal panel 3 to perform dimming control of transmitted light passing through each pixel. The image projected on the screen is reproduced by the amount of light transmission of each pixel of the polymer liquid crystal panel 3.

In this projection type liquid crystal display device, the light emitted from the light source 2 is collimated by the reflector 1 and is incident on the polymer liquid crystal panel 3.

On the other hand, the NTSC system television signal received by the antenna 8 is demodulated by the tuner 9 and interlaced analog video original signal (hereinafter referred to as analog video signal).
It becomes Vi1 and is input to the video signal processing circuit 10.

This analog video signal is input to the A / D converter 21 from the video signal input terminal Vin and converted into a digital video voltage Va1. This digital video voltage Va1
Is input to the subtractor 26. The first digital video voltage Va1 input to the subtractor 26 also passes through the correction circuit 23 as it is, and is output to the D / A converter 27 and the delay circuit 25 as the digital pixel voltage Vb1, and the D / A converter 2
The analog pixel voltage Vo1 is converted by 7 and output to the X driver 28. The analog pixel voltage Vo1 input to the X driver 28 is amplified by the X driver 28 and applied to the polymer liquid crystal panel 3.

Then, the above-mentioned polymer liquid crystal panel 3 is driven by the analog pixel voltage Vo1 applied to the polymer liquid crystal panel 3.
The parallel light incident on is transmitted through the polymer liquid crystal panel 3 as image light with its transmission amount controlled. This image light is
The light is condensed by the condenser lens 4 and passes through the diaphragm 5. In this diaphragm 5, scattered light in the transmitted light is blocked and image light with high contrast is generated. This image light is incident on the projection lens 6 and is enlarged by the projection lens 6 to form a large-screen image of the first frame on the screen 7.

On the other hand, the digital pixel voltage Vb1 input to the delay circuit 25 is temporarily stored in the memory for one frame as voltage data by the delay circuit 25.

Subsequently, when the next analog video signal Vi2 is input to the video signal input terminal Vin, converted into the digital video voltage Va2 by the A / D converter 21 and input to the subtractor 26, the delay is simultaneously performed. The circuit 25 is a memory 24
The digital pixel voltage Vb1 is output to the read subtractor 26 and the correction circuit 23.

Therefore, the subtracter 26 receives the digital video voltage Va2 and the digital video voltage Vb1. Then, the digital video voltages Vb1 and Va2 are subtracted from each other, and the difference digital video voltage ΔV is output to the correction circuit 23.

Since the digital video voltage ΔV from the subtractor 26 and the digital pixel voltage Vb1 from the delay circuit 25 are input to the correction circuit 23, corresponding correction voltage data is extracted from the data ROM 22 based on this. And is output as a digital pixel voltage Vb2. In this case, the correction circuit 23 determines the changing direction of the second input digital video voltage Va2 by the sign of ΔV (plus or minus), and according to the sign, the data RO
The corresponding correction voltage data is extracted from M22. The digital pixel voltage Vb2 is input to the D / A converter 27, converted into the analog pixel voltage Vo2, and output to the X driver 28.

The analog pixel voltage Vo2 input to the X driver 28 is amplified by the X driver 28 and applied to the polymer liquid crystal panel 3. After that, the image of the second frame is formed on the screen 7 as described above.

As described above, according to the projection type liquid crystal display device of this embodiment, as shown in FIG. 4, when the analog video signal is converted into the pixel voltage without correction and applied to the polymer liquid crystal panel 3, the input The transmittance for analog video signals
Although the hysteresis characteristic (dotted line) is shown, in the present embodiment, the voltage-transmittance characteristic can be drawn by the characteristic line A showing a predetermined rate of change with respect to the change of the input analog video signal.

For example, the transmittance T of the analog video signal Vi
After raising the analog video signal starting from o (point B) and returning the light transmittance to To after inputting the analog video signal Vi similar to the beginning, the polymer liquid crystal panel 3 is corrected. The applied pixel voltage Vo (point C) can be applied to control the light transmittance to To.

The present invention can be used not only for video reproduction of an NTSC system interlaced analog video original signal but also for video reproduction of a non-interlaced analog video original signal such as HDTV.

For example, in the data ROM 22, the correction voltage data for correcting the hysteresis characteristic in the voltage-transmittance characteristic of the polymer liquid crystal panel 3 and the correction voltage data for correcting the γ characteristic are written. The γ characteristic is an input / output characteristic of a television image signal, which is used to determine a numerical value for expanding or compressing the brightness of a CRT (CRT), and to reproduce a faithful color image by a color CRT. It is necessary to set the total γ value including transmission and reception to 1.

Normal television broadcasting is transmitted in consideration of γ = 2.2 of the grid voltage-beam current characteristic as shown in FIG. 5, and it is faithful to display this on a polymer liquid crystal panel having different γ characteristics. Color reproduction cannot be performed. Therefore, it is necessary to perform characteristic correction according to the γ characteristic of the polymer liquid crystal panel used.

The memory has a capacity capable of temporarily storing digital video signals for two fields. Further, the delay circuit reads out and outputs the digital video signal for two fields of the memory 24 at the input timing of the digital video signal for the next two fields from the A / D converter 21.

In this case, the HDT received by the antenna 8
The V system television signal is demodulated by the tuner 9 and becomes a non-interlaced analog video original signal (hereinafter referred to as an analog video signal) Vi1 which is input to the video signal processing circuit 10. Then, in the video signal processing circuit 10, the same video signal processing as in the above-described embodiment is performed. The video signal processing at this time is performed for every two fields of the video signal.

As described above, according to this embodiment, the polymer liquid crystal panel including the CRT γ characteristic for every two fields per screen with respect to the non-interlaced analog video original signal input to the video signal processing circuit 10. Since the pixel voltage output to 3 is corrected, the number of scanning lines is twice that of the NTSC system.
It is possible to display a TV image signal of a TV system or the like on the polymer liquid crystal panel 3 in a good color and to realize a good image reproduction on the screen.

In this embodiment, the data ROM is
As shown in FIG. 4, the correction voltage data was written so as to draw a characteristic line A that overlaps the voltage rising curve of the hysteresis characteristic. However, in addition to this, various characteristic lines such as the voltage falling curve and the curve passing through the center of the hysteresis characteristic line are written. It is also possible to write the correction voltage data so that

[0036]

As described above, according to the liquid crystal display device of the present invention, the television signal is corrected by the correction means,
Since the display of the polymer liquid crystal panel is controlled by the corrected pixel voltage, the hysteresis characteristic peculiar to the polymer liquid crystal panel is corrected, and the faithful image reproduction of the television signal can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a projection type liquid crystal display device of an embodiment according to the present invention.

2 is a cross-sectional view showing a polymer liquid crystal panel of the embodiment of FIG.

FIG. 3 is a diagram showing a configuration of a video signal processing circuit of the embodiment of FIG.

FIG. 4 is a voltage-transmission characteristic diagram of the embodiment of FIG.

FIG. 5 is a diagram showing a grid voltage-beam current characteristic of a CRT.

FIG. 6 is a diagram showing a light transmission principle of a polymer liquid crystal panel.

7 is a voltage-transmittance characteristic diagram of the polymer liquid crystal panel of FIG.

8 is a voltage-transmission characteristic diagram of a conventional projection type liquid crystal display device using the polymer liquid crystal panel of FIG.

[Explanation of symbols]

 3 ……………… Polymer LCD panel 8 ……………… Antenna 9 ………… Tuner 10 ………… Video signal processing circuit 21 ………… A / D converter 22… ………… Data ROM 23 ………… Correction circuit 24 ………… Memory 25 ………… Delay circuit 26 ……………… Subtractor 27 ……………… D / A conversion 28 …… ……… X driver

Claims (1)

[Claims] 1. A liquid crystal display device having a polymer liquid crystal panel in which the transmittance of light is changed by applying a pixel voltage, wherein a television video signal is converted into digital voltage data.
Conversion means, correction means for outputting new digital voltage data for correcting the hysteresis characteristic of the polymer liquid crystal panel on the basis of the digital voltage data converted by the conversion means, and input by this correction means. 2. A liquid crystal display device comprising: a second conversion means for converting new digital voltage data into the pixel voltage.