JPH11119689A - Video display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the contrast of a video from being lowered by unnecessary light such as scattered light caused in a writing optical system and to display the bright video by changing the threshold value of a modulation element for modulating writing light. SOLUTION: A video signal 27 from a video signal processor 26 is inputted to both of a CRT 14 being the video light generation device and an integration circuit 28. Besides, an output from the integration circuit 28 is inputted to a driving controller 29 driving a reset pulse generation circuit 11. By the controller 29, the voltage of the writing term of a reset pulse is decided and the generation circuit 11 is driven. Therefore, the voltage of the writing term of the reset pulse, that means, the voltage applied on the liquid crystal layer of a liquid crystal light valve 12 in the writing term is changed and the threshold value for modulating the writing light is changed. In such a way, the device is controlled so that the threshold value of the light valve 12 for modulating the writing light is changed in order to hardly receive the effect of the unnecessary light such as scattered light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device for a projection display.

[0002]

2. Description of the Related Art In recent years, a projection type display, particularly an image display device using a liquid crystal light valve as a light writing type modulation element has been receiving attention.

An optical writing type liquid crystal light valve is a device that plays a central role in an image projection system in which reading light whose intensity is modulated by writing light is reflected by a reflection layer in the light valve and projected. An image display device using a liquid crystal light valve has an advantage that a very bright image can be projected as compared with an image display device using a conventional transmission type liquid crystal projector.

As a conventional light valve of the optical writing type, for example, there is one having a configuration described in JP-A-9-74533.

Hereinafter, the above-mentioned conventional liquid crystal light valve will be described with reference to FIG. 3 showing a cross-sectional view of the structure of the liquid crystal light valve. As shown in FIG. The glass substrate 3, the ITO electrode 4 on the writing light input side, and p
A photodiode 5 having a pin structure made of a-Si and including a semiconductor layer 51, a non-doped semiconductor layer 52, and an n-type semiconductor layer 53; a reflective film 6 for writing light 1 made of Al; and a ferroelectric liquid crystal material A liquid crystal layer 7 for controlling the gradation expression, an ITO electrode 8 on the readout light input / output side, and a glass substrate 9 on the readout light input / output side.
An insulating layer 10 of a matrix structure made of carbon is formed on the reflective film 6 of the writing light 1 made of Al so as to block lateral conduction. In addition, in order to drive the light valve, the two write light input side IT
A reset pulse generating circuit 11 for generating a reset pulse applied between the O electrode 4 and the ITO electrode 8 on the read light input / output side is connected between the ITO electrode 4 on the write light input side and the ITO electrode 8 on the read light input / output side. ing.

Next, the operation of the liquid crystal light valve shown in FIG. 3 will be described. First, when no voltage is applied to the liquid crystal layer 7, when the readout light 2 input from the glass substrate 9 on the readout light input / output side is reflected by the reflective film 6, the polarization state at the time of input is completely maintained. As the voltage applied to the liquid crystal layer 7 increases, the polarization state gradually changes, and when a certain voltage or more is applied, the incident light is output in a completely transitioned polarization state. Oriented.

The operation of the light valve having the configuration as shown in FIG. 3 can be considered in two parts: a writing period in which electric charges corresponding to the intensity of the writing light 1 are stored, and a reset period in which the electric charges are extracted.

In the writing period, assuming that the ITO electrode 8 on the read light input / output side is grounded, a negative voltage is applied to the ITO electrode 4 on the write light input side. That is, the photodiode 5 is reverse-biased. First, when there is no writing light 1, most of the voltage applied between the ITO electrode 4 on the writing light input side and the ITO electrode 8 on the reading light input / output side is applied to the photodiode 5, and the voltage is applied to the liquid crystal layer 7. Is not applied. That is, the incident read light 2 is reflected and output as it is without changing its polarization state. As the intensity of the writing light 1 increases, the photodiode 5
A large number of electrons excited by light are generated in the p-type semiconductor layer 51, and the electrons are pulled to a positive potential and move toward the liquid crystal layer 7. As a result, charges opposite to each other accumulate at both ends of the liquid crystal layer 7, and as the intensity of the writing light 1 increases, the voltage applied to the liquid crystal layer 7 gradually increases, and the polarization state of the reflected reading light 2 Is changed and output.

On the other hand, during the reset period, the ITO electrode 8 on the write light input side is viewed from the ITO electrode 8 on the read light input / output side.
A positive voltage is applied to the electrode 4. That is, the photodiode 5 is biased in the forward direction, and operates so as to pull out the charge stored during the writing period at a stretch. If a positive voltage is applied to the ITO electrode 4 on the write light input side in an attempt to completely remove the charge during this reset period, a voltage having a polarity different from that in the normal operation state is applied to the liquid crystal layer 7. . Therefore, the output light on the read side during the reset period is output while maintaining the polarization state at the time of incidence.

Here, the insulating layer 10 having a matrix structure made of carbon prevents charges accumulated during the writing period from escaping laterally through the reflective film 6 made of Al. Each one separated by 10 forms a pixel.

FIG. 4 is a system configuration diagram of a conventional image display apparatus using the liquid crystal light valve shown in FIG. 3 described above. The liquid crystal light valve 12 is driven by the liquid crystal light valve 12 shown in FIG. Reset pulse generation circuit 11
Is connected to the liquid crystal light valve 12, and a video signal generator C to which a video signal 13 is input is input to a write light input side of the liquid crystal light valve 12.
The optical signal 15 of the image from the RT 14 is written and the lens 16 is written.
The beam splitter 19 is formed by irradiating a beam splitter 19 with readout light 18 emitted from a light source 17 composed of a xenon lamp or a metal halide lamp.
9, the reflected S wave 20 is reflected by the beam splitter 19 and reflected by the liquid crystal light valve 12.
The readout light 21 input to the input / output side and reflected by the liquid crystal light valve 12 passes through the beam splitter 19 and forms an image signal on a screen 23 via a projection lens 22. Further, of the readout light 18 applied to the beam splitter 19, a P-wave 24, which is a transmitted wave, passes through the beam splitter 19.

Next, the operation of the above-described conventional video display system will be described. The video signal 13 input to the CRT 14 is output as a video optical signal 15 from the CRT 14, irradiates the writing light input side of the liquid crystal light valve 12, and charges the liquid crystal light valve according to its spatial intensity distribution. The polarization state of the readout light 21 stored in the liquid crystal light valve 12 and reflected by the liquid crystal light valve 12 is determined. Light source 17
The beam splitter 19 reflects the S-wave 20 and transmits the P-wave 24 as described above.

That is, the only light that enters the liquid crystal light valve 12 as read light is the S wave 20 reflected by the beam splitter 19. Here, considering the operation of the liquid crystal light valve 12 described above, when the light intensity of the image light signal 15 which is the writing light to the liquid crystal light valve 12 is strong, the liquid crystal layer 7 of the liquid crystal light valve 12 (FIG. ), A negative voltage is strongly applied with reference to the readout light input / output side, and the reflected readout light 21 changes from the state of the S wave 20 at the time of incidence to the P wave. An image 25 transmitted through and projected on a screen 23 through a projection lens 22
Becomes bright. The intensity of the reflected reading light 21 is modulated by the light intensity of the image light signal 15 which is the writing light to the liquid crystal light valve 12.

Conversely, the optical signal 15 of the image which is the writing light
Is weak, the reflected read-out light 21 is reflected as it is when the S-wave 20 is incident, and is reflected again by the beam splitter 19, so that the image 25 on the screen 23 is dark.

That is, the reading light 21 reflected by the light intensity of the image light signal 15 which is the writing light to the liquid crystal light valve 12 is intensity-modulated.

In the above-described conventional video display system, a constant voltage is applied to the liquid crystal light valve 12 as a reset pulse during both the writing period and the reset period.

[0017]

In the above-mentioned conventional image display device of a projection display, an optical system (writing optical system) between a writing light generating device such as a CRT and a light valve is used. Scattered light is generated due to irregular reflection of light on the surface or in other optical system components.

Due to the unnecessary light such as the scattered light, for example, even if there is a black image in a part of a bright image, the unnecessary light is written on the light valve, whereby the part of the black image is slightly modulated. As a result, there is a problem that the contrast of a black image portion is significantly reduced on a screen.

An object of the present invention is to provide a projection-type image display device capable of suppressing a decrease in image contrast due to unnecessary light such as scattered light generated in a writing optical system or the like and displaying a bright image. .

[0020]

In order to solve the above-mentioned problems, an image display device according to the present invention comprises an image light generating device for generating writing light, and an irradiation intensity of the writing light from the image light generating device. A modulation element that intensity-modulates reflected light of the read light that is separately irradiated, a drive control device that controls light writing to the modulation element, and a screen that projects the reflected light, and a modulation element for the write light. An image display device that changes the threshold value of modulation, suppresses a decrease in contrast due to unnecessary light such as scattered light in a writing optical system, and can express good contrast even when displaying a bright image. Can be provided.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to an image light generating device for generating a writing light, and a reading light separately irradiated according to an irradiation intensity of the writing light from the image light generating device. A modulation element that modulates the intensity of the reflected light, a drive control device that controls light writing to the modulation element, and a screen that projects the reflected light. This is a video display device that changes the value, and has an effect that the influence of unnecessary light of the writing optical system can be substantially eliminated by controlling the threshold value of the modulation of the modulation element with respect to the writing light.

According to a second aspect of the present invention, the drive control device controls the drive voltage of the modulation element at the time of optical writing to change the modulation threshold of the modulation element with respect to the write light. The image display device according to claim 1, wherein a threshold value of modulation of the modulation element with respect to the writing light is controlled by changing a driving voltage of the modulation element,
This has the effect that the influence of unnecessary light from the writing optical system can be substantially eliminated.

According to a third aspect of the present invention, in the second aspect, the drive control device is controlled with a value corresponding to an average value of video signal levels of at least one field or more to determine a drive voltage of the modulation element. The video display device described above determines a threshold value for modulation of a modulation element according to an average value of a video signal level, and has an effect that an optimum threshold value can always be controlled.

According to a fourth aspect of the present invention, there is provided the image display device according to the first or second or third aspect, wherein the modulation element is a liquid crystal light valve, and the modulation element is a liquid crystal light valve. This has an effect that the voltage applied to the liquid crystal layer changes according to the intensity of the writing light, and the polarization state of the reflected reading light changes.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment) FIG. 1 is a system configuration diagram of a video display device using a liquid crystal light valve according to an embodiment of the present invention. FIG. 4 is a diagram showing a system configuration diagram of a conventional video display device.
The same components as those described above are denoted by the same reference numerals. A reset pulse generating circuit 11 for driving the liquid crystal light valve 12 is connected to the liquid crystal light valve 12 shown in FIG. On the input side, a video light signal 15 from a CRT 14 which is a video light generator
Is imaged through a writing lens 16, and a reading light 18 emitted from a light source 17 composed of a xenon lamp or a metal halide lamp is irradiated on a beam splitter 19.
The reflected S wave 20 is reflected by the beam splitter 19 and input to the input / output side of the liquid crystal light valve 12, and the readout light 21 reflected by the liquid crystal light valve 12 passes through the beam splitter 19 and passes through the projection lens 22. To form an image signal on the screen 23. Also, of the readout light 18 applied to the beam splitter 19, the transmitted wave P
The wave 24 passes through the beam splitter 19. FIG. 4 shows a system configuration diagram of a conventional video display device.
Is the same as FIG. 1 showing the configuration of the present embodiment differs from FIG. 4 showing a conventional example in that a video signal 27 from a video signal processing device 26 is input to both a CRT 14 as a video light generation device and an integration circuit 28, The point is that the output from the integration circuit 28 is input to the drive control device 29 that drives the reset pulse generation circuit 11.

The basic operation of the image display apparatus system according to the present embodiment, which is different from that of the conventional example, is as described in the operation of the conventional image display apparatus system.

Here, the reset pulse generated by the reset pulse generation circuit 11 for driving the liquid crystal light valve 12 will be described with reference to the drawings.

FIG. 2 is a voltage waveform diagram for explaining a reset pulse, that is, a change in a pulse voltage applied to the writing electrode with respect to the reading electrode of the liquid crystal light valve 12.

FIG. 2A is a voltage waveform diagram of the reset pulse of the conventional video display device, and the potential during the writing period 30 is constant. The timing of the reset period 31 is within the vertical flyback period.

FIG. 2B is a voltage waveform diagram of the reset pulse of the video display device according to the present embodiment.

In FIG. 1 showing the present embodiment, the output of the integrating circuit 28 is converted into a voltage proportional to the average value of the video signal by integrating a signal of about one frame of the video signal. The drive control device 29 determines the voltage of the reset pulse writing period 30 in FIG. 2 and drives the reset pulse generation circuit 11. Therefore, as shown in FIG. 2, the voltage in the reset pulse writing period 30, that is, the voltage applied to the liquid crystal layer of the liquid crystal light valve 12 during the writing period 30 changes, and the modulation threshold for the writing light changes.

Here, the CRT 14 which is an image light generating device
When there is much output light from the optical disk, unnecessary light such as scattered light in the writing optical system is generated as in the conventional case. However, the drive control device 29 controls the liquid crystal light valve 12 to change the threshold value of the modulation for the writing light so as to be hardly affected by the unnecessary light.

Accordingly, the screen 23 of substantially unnecessary light is used.
The influence on the contrast of the above image can be eliminated.

The output of the integrating circuit 28 in FIG. 1 is configured to integrate a signal of about one frame of the video signal, and the drive control device 29 determines the voltage of the reset pulse writing period based on the voltage. The reset pulse generation circuit 11 is driven. Therefore, as shown in FIG. 2, the voltage in the reset pulse writing period 30 changes every frame. The voltage in the reset pulse writing period 30 is substantially linked to the average value of the video signal, so that even when the video signal fluctuates, the voltage of the reset pulse is always controlled optimally, and a good contrast expression of the projected video is obtained. Can be kept.

In order to perform full-color expression using such a system, the liquid crystal light valve 12, the CRT 14, which is an image light generator, the writing lens 16, the beam splitter 19, and the projection lens 22, are each composed of three primary colors of RGB. By preparing a system that divides the light from the light source 17 into three primary colors of RGB using a dichroic mirror, the same effect as that of the present embodiment can be obtained in a system that performs full-color display.

In the present embodiment, the case where the liquid crystal light valve 12 is used as a modulation element for modulating the intensity of the read light by the write light has been described.
The modulation element is not limited to the liquid crystal light valve, and needless to say, an element having a function of modulating input light (writing light) can provide the same effect as that of the present embodiment. .

[0037]

As described above, according to the image display apparatus of the present invention, it is possible to suppress a decrease in contrast of an image due to unnecessary light such as scattered light generated in a writing optical system or the like, and to provide a good image even when a bright image is projected. The effect is great, such as the ability to express contrast images.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a video display device according to an embodiment of the present invention.

FIG. 2 is a voltage waveform diagram of a reset pulse.

FIG. 3 is a sectional configuration diagram of a liquid crystal light valve.

FIG. 4 is a system configuration diagram of a conventional video display device.

[Explanation of symbols]

 Reference Signs List 1 writing light 2, 18 reading light 3 glass substrate on writing light input side 4 ITO electrode on writing light input side 5 photodiode 6 reflective film 7 liquid crystal layer 8 ITO electrode on reading light input / output side 9 glass on reading light input / output side Substrate 10 Insulating layer of matrix structure 11 Reset pulse generating circuit 12 Liquid crystal light valve 13, 27 Video signal 14 CRT 15 Optical signal of video 16 Writing lens 17 Light source 19 Beam splitter 20 S wave 21 Reflected reading light 22 Projection lens 23 Screen 24 P-wave 25 Video 26 Video signal processor 28 Integrator 29 Drive controller 30 Write period 31 Reset period 51 p-type semiconductor layer 52 undoped semiconductor layer 53 n-type semiconductor layer

Claims (4)

[Claims] 1. An image light generating device for generating writing light, a modulation element for intensity-modulating reflected light of read light separately irradiated by an irradiation intensity of writing light from the image light generating device, and the modulation element An image display device, comprising: a drive control device that controls light writing to the device; and a screen that projects the reflected light, wherein the threshold value of modulation of a modulation element for the writing light is changed. 2. The video display device according to claim 1, wherein the drive control device controls the drive voltage of the modulation element at the time of optical writing to change the threshold value of the modulation of the modulation element with respect to the writing light. 3. The video display device according to claim 2, wherein the drive control device is controlled with a value corresponding to an average value of video signal levels of at least one field to determine a drive voltage of the modulation element. 4. The image display device according to claim 1, wherein the modulation element is a liquid crystal light valve.