JPH09116836A - Video display - Google Patents

Abstract

(57) Abstract: A high-brightness video projector using a reflective liquid crystal light valve of light or charge writing type,
When the power of the projector main body is turned on, or when the video signal input in a system having at least two video signal input systems is switched, the sync signal is output on the screen in a transient state in which switching occurs. The purpose is to remove the video. SOLUTION: When the power is turned on or when the input signal is switched, the MUTE signal for a fixed time is sent to the MU.
It is generated from the TE signal generation circuit 15, and the drive control circuit 16
Enter The drive control circuit 16 controls the operation of the reset pulse generation circuit 2 for driving the light valve 1,
While the UTE signal is being generated, the driving is stopped and a constant DC voltage is applied to the light valve 1.

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 using a reflective liquid crystal light valve of a light or charge writing type.

[0002]

2. Description of the Related Art Here, an optical writing type light valve which is one of reflection type liquid crystal light valves of the light or charge writing type will be described. This is a device that plays a central role in the image projection system in which the intensity-modulated read light is reflected by the reflective layer in the light valve and projected, and has the advantage of being extremely bright compared to conventional transmissive liquid crystal projectors. There is.

The structure and operation of a conventional liquid crystal light valve will be briefly described here. FIG. 6 shows a structural diagram of the liquid crystal light valve 1. 50 is a glass substrate on the writing light side,
Reference numeral 51 is an ITO electrode on the writing light side, 52 is a photodiode having a pin structure formed of a-Si, and is a p-type 53, an insulating layer (i layer) 54, and an n-type 55 from the writing side.
Semiconductor layer. Reference numeral 56 denotes a reflective film for writing light of Al, and reference numeral 57 denotes an insulating layer having a matrix structure formed of carbon, which blocks Al conduction in the horizontal direction. Reference numeral 58 denotes a liquid crystal layer that controls gradation expression and uses a ferroelectric liquid crystal material. Further, 59 is an ITO electrode on the reading light side, and 60 is a glass substrate on the reading light side. 61 is writing light, while 62 is reading light,
Reference numeral 2 is a reset pulse generation circuit for generating a reset pulse applied between two ITO glasses for driving the light valve.

Next, the operation of the liquid crystal light valve 1 shown in FIG. 6 will be described. First, when no voltage is applied, the liquid crystal layer 58 reflects the reading light 6 reflected by the reflection layer 58.
2 is output while completely maintaining its polarization state, the polarization state gradually changes as the applied voltage increases, and the incident light completely transits when a voltage above a certain level is applied. It is oriented so that it is output at. The operation of the light valve 1 having the configuration shown in FIG.
Can be divided into a writing period for accumulating electric charges corresponding to the intensity and a reset period for extracting the electric charges.

In the writing period, assuming that the reading side is grounded, a negative voltage is applied to the writing side voltage. That is, the photodiode 52 is reverse-biased. First, when there is no writing light 61, most of the voltage applied between the electrodes is a-S
The voltage is applied to the i-diode 52 and no voltage is applied to the liquid crystal layer. That is, the read light 62
Is reflected and output as it is without changing its polarization state. As the intensity of the writing light 61 increases, a-S
A large number of electrons excited by light are generated near the interface between the p-type 53 layer of i52 and the i layer 54, and these electrons are pulled to a positive potential and move toward the liquid crystal layer 58.
As a result, opposite charges are accumulated at both ends of the liquid crystal layer,
As the intensity of the writing light 61 increases, the voltage applied to the liquid crystal layer 58 gradually increases, and the polarization state of the reflected reading light 62 is changed and output.

On the other hand, in the reset period, a positive voltage is applied to the write side electrode as seen from the read side. That is, the photodiode 52 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 write 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 58. Therefore, the output light on the reading side within the reset period is output while maintaining the polarization state when it is incident.

Here, the matrix-shaped insulating layer 57 made of carbon prevents the electric charge accumulated during the writing period from escaping laterally through the Al reflection layer 56, and is separated by the insulating layer 56. Each one formed forms a pixel.

FIG. 7 shows a structural example of a conventional system using the light valve 1. 1 is a liquid crystal light valve, 2 is a reset pulse generation circuit for driving the light valve 1, 3
Denotes a writing video light generator, and a CRT is generally used. Reference numeral 4 is a writing lens which plays a role of forming an image from the CRT on the light valve 1, and 5 is a beam splitter, which reflects the P wave and transmits the S wave due to the difference in the polarization state of the light. Reference numeral 6 denotes a light source for reading light, which is generally a xenon lamp or a metal halide lamp. Reference numeral 7 denotes a projection lens that forms a video signal on the screen 8.

Next, the operation of the above system will be described. The optical signal 70 of the image generated by the CRT 3 accumulates charges corresponding to the spatial intensity distribution in the light valve 1, and determines the polarization state of the reflected read light 73. Light 71 having an arbitrary polarization state is emitted from the light source 6, and the beam splitter 5 outputs the P wave 7 as described above.
2 is reflected and the S wave 75 is transmitted. That is, the only light that is read into the light valve 1 and is incident as the light 72 is the P wave reflected by the beam splitter 5. Here, considering the operation of the light valve 1 in combination, when the light intensity of the writing light 70 is high, a negative voltage is strongly applied to the liquid crystal layer 58 with respect to the reading side, and the liquid crystal layer 58 is reflected. Since the read light 73 changes from the P wave state when it is incident to the S wave, the image 74 transmitted through the beam splitter 5 and projected on the screen 8 through the projection lens 7 becomes bright. Conversely, writing light 7
0 is weak, and reading light is reflected as almost P wave.
3 is reflected again by the beam splitter 5, so that the image 74 on the screen becomes dark.

For the same reason, the image in the reset period is also read out and is output with almost no change in the polarization state of the light, so that the image on the screen becomes dark. if,
If the reset pulse becomes unstable due to the frequency difference between the video signal and the sync signal, or the ratio of the reset period and the write period is changed for some reason, the image projected on the screen is a black band-shaped image. There is an unpredictable part, a conversely it becomes a pure white state, or it becomes a beat-like disturbance, which is an unpredictable and inconvenient thing.

Reference numeral 9 is a video signal processing circuit, and 10
Is a synchronization signal processing circuit. As a general method of use, the output of the vertical synchronizing signal from the synchronizing signal processing circuit 10 is input to the reset pulse generating circuit 2 and synchronized with the video signal signal. On the other hand, the output of the video signal processing circuit 9 is CR.
Input to T3. Here, a commonly used reset pulse shape 76 is shown in FIG. The figure is based on the reading light side. The voltage during the writing period is -3.
The voltage is 5V and the voltage during the reset period is + 15V, which is a perfect square wave. Further, the time ratio between the writing period and the reset period is 60: 1, and the reset pulse is usually
It is not observed on the screen because it is within the blanking period of the video signal.

Here, a system capable of receiving a plurality of video signals from some external signal generator, specifically, the external input terminal A11 and the external input terminal B12.
Think about if you have. In such a system, two external signals are switched by the relay circuit 13, but when the signals are switched, the synchronization signal becomes unstable, and it takes some time for the synchronization frequency after switching to settle. Therefore, since the reset pulse also becomes unstable immediately after this switching, an inconvenient image that is not in the normal state as described above is output. The same can be said about this immediately after the power is turned on.

Next, consider the case where there is no externally input signal, or the case where there is a video signal but no sync signal. In this case, various cases are conceivable depending on the configured circuit, but in general, the light valve 1 is not driven. Therefore, even if an on-screen display or the like indicating a non-input state is performed as the system, the result is that the image is not projected on the screen.

[0014]

However, in the above-mentioned conventional configuration, the reset pulse becomes unstable in a transient state when switching to the next signal immediately after the input source of the video signal is switched or immediately after the power is turned on. However, there is a problem that an inconvenient image different from the normal state is output. Further, when there is no signal, the driving is stopped and nothing is output.

[0015]

In order to solve this problem, the present invention can write an image spatially distributed by light or directly an electric charge, and modulate the read light so as to respond to the information. A reflection type liquid crystal light valve is provided, and the drive signal for driving the reflection type liquid crystal light valve is temporarily stopped during a transient state when the power is turned on or when the video signal input to the system is switched. It welcomes an inconvenient image projected on the screen.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a reflection type capable of writing an image spatially distributed by light or directly by an electric charge and modulating a read light so as to respond to the information. A liquid crystal light valve is provided, and the drive signal for driving the reflective liquid crystal light valve is temporarily stopped in a transient state when the power is turned on or when the video signal input to the system is switched. Therefore, when the synchronization signal input to the reset pulse generation circuit is in an unstable state or no input state, it has an effect of suppressing an inconvenient image projected on the screen.

The invention according to claim 2 of the present invention is a reflection type liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge and modulating read light so as to respond to the information. A video signal processing circuit that generates spatially distributed video information that is an input to the light valve, and a drive signal for driving the light valve is applied between the first and second electrodes of the light valve. And a MUT that generates a MUTE signal when the power source is turned on or when the video signal input to the video signal processing circuit is switched.
E signal generating circuit and M from the MUTE signal generating circuit
And a drive control circuit for controlling the drive signal of the light valve by a UTE signal, when the synchronization signal input to the reset pulse generation circuit is in an unstable state or no input state. This has the effect of suppressing an inconvenient image projected on the screen.

The invention according to claim 3 of the present invention is the image display device according to claim 2, wherein the light valve drive circuit receives a control signal from the drive control circuit and applies an arbitrary constant voltage to the light valve. It is characterized by
When the synchronization signal input to the reset pulse generation circuit is in an unstable state or no input state, it has an effect of suppressing an inconvenient image projected on the screen.

According to a fourth aspect of the present invention, there is provided a reflection type liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge and modulating read light so as to respond to the information. A video display device, characterized in that, when a vertical synchronizing signal for driving the reflection type light valve becomes undetectable, the light valve is switched to be driven by a synchronizing signal of internal oscillation. When the sync signal input to the pulse generation circuit is in an unstable state or no input state,
It has an effect of suppressing an inconvenient image projected on the screen.

According to a fifth aspect of the present invention, there is provided a reflective liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge and modulating read light so as to respond to the information. A video signal processing circuit for generating spatially distributed video information which is an input to the light valve, a sync signal processing circuit for processing a sync signal of the video information, and a drive signal for driving the light valve A light valve drive circuit for applying between the first and second electrodes of the light valve, a synchronization signal non-input determination circuit for determining the presence or absence of a synchronization signal input to the synchronization signal processing circuit, and an internal synchronization signal oscillation. Circuit, and a switching functioning to switch the synchronization signal to the synchronization signal from the internal synchronization signal oscillation circuit according to the determination signal from the synchronization signal non-input determination circuit. An image display device being characterized in that a road, when the synchronizing signal input to the reset pulse generator circuit is in an unstable state or no input,
It has an effect of suppressing an inconvenient image projected on the screen.

According to a sixth aspect of the present invention, there is provided a reflection type liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge and modulating read light so as to respond to the information. When the vertical synchronization signal for driving the reflection type liquid crystal light valve becomes undetectable and the reflection type light valve is switched to be driven by the synchronization signal of internal oscillation, the reflection type light valve is driven. An image display device characterized in that it is temporarily stopped in a transient state, and is inconveniently projected on the screen when the synchronization signal input to the reset pulse generation circuit is in an unstable state or no input state. It has an effect of suppressing a large image.

According to a seventh aspect of the present invention, there is provided a reflection type liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge and modulating read light so as to respond to the information. A video signal processing circuit for generating spatially distributed video information which is an input to the reflection type liquid crystal light valve, a sync signal processing circuit for processing a sync signal of the video information, and for driving the light valve A light valve drive circuit for applying the drive signal of 1. between the first and second electrodes of the light valve, a synchronization signal non-input determination circuit for determining the presence or absence of a synchronization signal input to the synchronization signal processing circuit, and an internal It functions to switch the synchronization signal to the synchronization signal from the internal synchronization signal oscillation circuit according to the determination signal from the synchronization signal oscillation circuit and the synchronization signal non-input determination circuit. A switching circuit and a MUTE signal generating circuit for generating a MUTE signal according to the judgment signal from the synchronization signal non-input judging circuit; and a drive control circuit for controlling the drive signal of the light valve by the output from the MUTE signal generating circuit. It is a video display device characterized in that it can suppress an inconvenient image projected on the screen when the synchronization signal input to the reset pulse generation circuit is in an unstable state or no input state. Have an effect.

The invention according to claim 8 of the present invention is the image display device light valve according to claim 7, wherein the drive circuit receives a control signal from the drive control circuit and applies an arbitrary constant voltage to the light valve. It is characterized by
When the synchronization signal input to the reset pulse generation circuit is in an unstable state or no input state, it has an effect of suppressing an inconvenient image projected on the screen.

According to a ninth aspect of the present invention, there is provided a reflection type liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge and modulating read light so as to respond to the information. A video display device, characterized in that the drive of the light valve is stopped when a vertical synchronizing signal for driving the reflection type liquid crystal light valve becomes undetectable. When the sync signal to be generated is in an unstable state or no input state, it is possible to suppress an inconvenient image projected on the screen.

According to a tenth aspect of the present invention, there is provided a reflective liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge and modulating read light so as to respond to the information. A video signal processing circuit for generating spatially distributed video information which is an input to the reflection type liquid crystal light valve, a synchronization signal processing circuit for processing a synchronization signal of the video information, and the reflection type liquid crystal light valve. A light valve drive circuit for applying a drive signal for driving between the first and second electrodes of the reflection type liquid crystal light valve, and no sync signal for determining the presence or absence of a sync signal input to the sync signal processing circuit An input determination circuit,
A video display device, comprising: a drive control circuit that controls a drive signal of the reflective liquid crystal light valve according to a determination signal from the synchronization signal non-input determination circuit,
When the synchronization signal input to the reset pulse generation circuit is in an unstable state or no input state, it has an effect of suppressing an inconvenient image projected on the screen.

The invention according to claim 11 of the present invention is the image display device according to claim 10, wherein the light valve drive circuit receives a control signal from the drive control circuit and applies an arbitrary constant voltage to the light valve. When the sync signal input to the reset pulse generation circuit is in an unstable state or no input state, it is possible to suppress an inconvenient image projected on the screen. Have.

Embodiments of the present invention will be described below with reference to FIGS.
This will be described with reference to FIGS. 3 and 4. In the figure, 1 is a liquid crystal light valve, 2 is a reset pulse generating circuit for driving the light valve 1, 3 is a writing image light generating device,
In the present invention, a CRT is used. 4 is CRT3
The writing lens 5 which plays a role of forming an image on the light valve 1 on the light valve 1 is a beam splitter and reflects a P wave and transmits an S wave due to a difference in polarization state of light. Reference numeral 6 is a light source for reading light, and a xenon lamp is used in the present invention. Reference numeral 7 denotes a projection lens that forms a video signal on the screen 8. Further, the configuration of the block that processes the video signal and the synchronizing signal is as follows. Reference numeral 11 is an external input terminal A, 12 is an external input terminal B, and 13 is a relay circuit for switching the video signals input to both external input terminals. The operation of the system of the present invention and the structure of the device are as described in the section of the related art, and are common to the four embodiments.

(Embodiment 1) First, FIG. 1 shows a first embodiment. Components other than the above will be specifically described. A microcomputer 14 is an external input terminal A11 according to a control signal such as a remote control signal.
Is output or a signal for determining whether to select the external input terminal B12 is output. Reference numeral 15 denotes a MUTE signal generation circuit, which outputs a MUTE signal for a fixed time when a video switching signal is output from the microcomputer 14. Note that, in general, this MUTE signal generation circuit 15
Is often incorporated as one function in the microcomputer 14. Also, immediately after the power is turned on, the MUTE signal for a certain period of time is output.

Reference numeral 16 denotes a drive control circuit, which controls the vertical synchronizing signal output to the reset pulse generating circuit 2 for driving the light valve 1. This drive control circuit 16 is a MUTE
While the signal is being output from the MUTE signal generating circuit 15, the reset pulse generating circuit 2 is in a state of stopping its operation. In this case, the reset pulse generation circuit 2
The output from the to the light valve 1 does not necessarily have to be 0V, and a constant voltage value may be set according to the design concept of the system, but in any case, the image on the screen is not affected by the writing light. I do not receive it. As described in the section of the related art, the voltage value of the reset pulse is dark when the positive voltage is applied and the image on the screen becomes dark when the positive electrode is applied. When a voltage is applied, the image projected reversely becomes bright.

If the reset pulse becomes unstable due to the frequency difference between the video signal and the synchronizing signal or the ratio between the reset period and the write period is changed for some reason, the image projected on the screen is projected. Is an unpredictable inconvenience, for example, a part without a black band-like image appears, or conversely it becomes a pure white state, or it becomes a beat-shaped disturbance. Therefore, by using the configuration shown in FIG. 1, the video signal is switched,
When the sync signal becomes unstable like immediately after the power is turned on, a MUTE signal is generated and a uniform signal that is unrelated to the writing light is displayed on the screen. Is never output.

In order to perform full color expression using the system shown in the first embodiment, three liquid crystal light valves, a writing image light generator, a writing lens, a beam splitter and a projection lens are provided for each of the three primary colors of RGB. Further, it is necessary to prepare a system for dividing the light from the light source into RGB three primary colors by a dichroic mirror. Needless to say, the same effect can be obtained by the present invention even in a system for full color display. Described below is an application example for full color display.

For full-color display, the light valve 1
Three reset pulse generating circuits 2 for driving R, G, and B are also prepared for RGB. As described above, the output from the reset pulse generating circuit 2 operated by the drive control circuit 16, that is, the voltage applied to the light valve 1 does not necessarily have to be 0 V, and may be any voltage according to the design concept of the system. It is sufficient to output the voltage. In the case of the present invention, halftone is displayed when the applied voltage is 0V. An example is shown in FIG.
When RGB is biased to the same potential, as shown in 30, 31, and 32 in FIG.
On the contrary, this can also be white-displayed by negatively biasing RGB as 33, 34, and 35, respectively. Further, in RGB of FIG. 2, 36, 37, and 38, respectively.
As shown in (3), by making only the voltage applied to the blue light valve negative and making the other green and red positive voltages, it is possible to obtain a blue back display that is common in ordinary TV sets. However, the wavy line in the figure indicates a normal reset pulse.

(Second Embodiment) Next, a second embodiment shown in FIG. 3 will be described. Reference numeral 21 denotes a synchronization signal non-input determination circuit, which outputs a LOW signal in a normal state, but when the synchronization signal is not input, or when it is determined that there is no input due to deformation or compression of the synchronization signal, HI signal
It outputs a GH state signal. Reference numeral 22 denotes an internal synchronization signal oscillator circuit. The output from the synchronization signal non-input determination circuit 21 switches the switching circuit 23, and when it is determined that there is no synchronization signal, an internal oscillation synchronization signal is sent to the reset pulse generation circuit 2. Supplied.

When it is judged that there is no input of the synchronizing signal or there is no synchronizing signal due to deformation or compression of the synchronizing signal, C
It is general that the internal synchronizing signal is supplied to the deflection circuit for driving the RT3. At this time, if the synchronizing signal is not input by the on-screen signal, the driving frequency of the light valve 1 is increased. Must also be synchronized with the internal oscillator sync signal. Therefore, by adopting the configuration shown in FIG. 3, even when it is determined that the sync signal is in the non-input state, the signal such as the on-screen signal is not inconvenient as described in the first embodiment. A normal image can be projected.

In order to perform full color expression using the system shown in the second embodiment, three liquid crystal light valves, a writing image light generator, a writing lens, a beam splitter and a projection lens are provided for each of the three primary colors of RGB. It is necessary to further prepare a system in which the light from the light source is divided into RGB three primary colors by a dichroic mirror, but it goes without saying that the same effect can be obtained by the present invention even in a system for full color display.

However, in the case of the embodiment shown in FIG. 3, when the reset pulse is switched to the internal oscillation frequency, it is supplied to the reset pulse generating circuit 2 in the same manner as when the external input signal is switched in the first embodiment. The sync signal becomes unstable for a while and an inconvenient image is output.

There is also a case where there is no on-screen display or the like and it is not always necessary to display an image in a non-synchronized signal state. That is, in such a case, the light valve 1
Will be driven insignificantly, which is also disadvantageous in terms of life.

Countermeasures for the above two problems will be described in the third and fourth embodiments of the present invention.

(Embodiment 3) FIG. 4 shows a third embodiment of the present invention. Synchronous signal non-input judgment circuit 2
1. The operations of the internal synchronization signal oscillation circuit 22 and the switching circuit 23 are the same as those in the second embodiment, and therefore will be omitted here.

As described above, in the embodiment shown in FIG. 3 alone, it is determined that the sync signal is not input, and when the internal oscillation frequency is switched to, the synchronization becomes unstable in the transient state. . Therefore, when the determination signal from the synchronization signal non-input determination circuit 21 changes, the no input MUTE
The signal generation circuit 24 generates a MUTE signal for a fixed time, and the drive control circuit 25 stops the operation of the reset pulse generation circuit 2 while the MUTE signal is generated. This series of operations is performed not only when the state in which the synchronization signal is present is determined to be absent, but also when the state determined to be absent is changed to the state determined to be present.

Normally, the non-input MUTE signal generation circuit 24 and the drive control circuit 25 are commonly used as the MUTE signal generation circuit 15 and the drive control circuit 16 in FIG. 1 showing the first embodiment. It is possible.

In order to perform full color expression using the system shown in the third embodiment, three liquid crystal light valves, a writing image light generating device, a writing lens, a beam splitter and a projection lens are provided for each of the RGB three primary colors. Further, it is necessary to prepare a system for dividing the light from the light source into RGB three primary colors by a dichroic mirror. Needless to say, the same effect can be obtained by the present invention even in a system for full color display. Described below is an application example for full color display.

For full-color display, the light valve 1
Three reset pulse generating circuits 2 for driving R, G, and B are also prepared for RGB. As described in the section of the first embodiment, the output from the reset pulse generating circuit 2 operated by the drive control circuit 25, that is, the voltage applied to the light valve 1 does not necessarily have to be 0 V, and the Any voltage may be output according to the design concept. As shown in Fig. 2, the applied voltage should be positive with respect to the read side to display black, or only the voltage applied to the blue light valve should be negative, and the other green and red should be positive. This makes it possible to provide a blue-back display that is common in ordinary TV sets.

(Embodiment 4) FIG. 5 shows a fourth embodiment of the present invention. As described above, when it is determined that the sync signal is not input, it may not be necessary to display an image with the internal oscillation sync signal. 21 is a sync signal non-input determination circuit, 26 is a drive control circuit,
When it is determined that the output of the sync signal non-input determination circuit 21 is no input, the drive control circuit 26 functions to stop the operation of the reset pulse generation circuit 2.

By doing so, the synchronization instability that occurs in the transient state when the synchronization signal is in the non-input state can be dealt with as in the third embodiment, and when the synchronization signal is not input. The light valve 1 is no longer continuously driven meaninglessly, which is also meaningful in terms of life.

As an application example of the present invention, when it is determined that the sync signal is not input, the light valve 1 is operated at the internal oscillation frequency for a while as shown in the third embodiment.
However, if the synchronization signal is not input even after a fixed time of about 10 minutes elapses, the driving may be stopped.

In order to perform full-color expression using the system shown in the third embodiment, three liquid crystal light valves, a writing image light generator, a writing lens, a beam splitter, and a projection lens are provided for each of the RGB three primary colors. Further, it is necessary to prepare a system for dividing the light from the light source into RGB three primary colors by a dichroic mirror. Needless to say, the same effect can be obtained by the present invention even in a system for full color display. Described below is an application example for full color display.

For full color display, the light valve 1
Three reset pulse generating circuits 2 for driving R, G, and B are also prepared for RGB. As described in the section of the first embodiment, the output from the reset pulse generation circuit 2 operated by the drive control circuit 26, that is, the voltage applied to the light valve 1 does not necessarily have to be 0 V, and the Any voltage may be output according to the design concept. As shown in Fig. 2, the applied voltage should be positive with respect to the read side to display black, or only the voltage applied to the blue light valve should be negative, and the other green and red should be positive. This makes it possible to provide a blue-back display that is common in ordinary TV sets.

Here, the effects of the present invention, which are commonly considered in the case of the first to fourth embodiments, will be described.

Although the embodiments of the present invention are all directed to the optical writing type light valve by the light from the CRT 3, the charges are indirectly excited in this way and a voltage is applied to the liquid crystal layer 58. The present invention is effective not only in such a case but also in the case of directly modulating the light incident on the liquid crystal layer 58 by the electric charge.

For example, when considering a device having a structure in which a liquid crystal and a CCD or TFT are directly sandwiched instead of the a-Si diode layer 52, a video signal is digitally processed and the CCD or TFT is directly processed for each pixel. Written by the element. The charge written according to the video signal applies a desired voltage to the liquid crystal layer and modulates the read light as in the previous embodiments, but these charges must be extracted by some reset signal. It's clear.

Further, in the embodiment of the present invention, the signal for driving the light valve is treated as the reset pulse for extracting the electric charge, but the following light valve may be considered. As shown in FIG.

Numeral 80 is a glass substrate on the writing side, 81 is an ITO electrode on the writing side, and 82 is a photoconductive layer. Usually, a-Si is used. Reference numeral 83 denotes a dielectric band reflection layer that reflects the read light. Further, reference numeral 84 is a liquid crystal layer, and twisted nematic liquid crystal is used for the light valve having such a structure. Reference numeral 85 is an ITO electrode on the reading side, and 86 is a glass substrate on the reading side.

The operation of the light valve is basically the same as that described in the section of the prior art, but the photoconductive layer 8 is used.
It is easy to understand that 2 is that the resistance changes due to the charge generated by light. The generated charges are not forcibly extracted as in the above-described examples, but mainly in the photoconductive layer 8.
It is gradually discharged with a CR time constant of 2. In addition, since the device has little lateral conductivity, it is also characteristic that an insulating layer such as a black matrix is not inserted.

Here, 87 is a drive circuit for driving the light valve shown in FIG. 9, but the drive voltage is not an AC voltage for protecting the liquid crystal layer 84, but for extracting charges as in a reset pulse. Is applied. However, like the light valve 1 shown in FIG. 8, no image is output on the screen because no voltage is applied to the liquid crystal layer unless a drive voltage is applied. In this example, the drive signal has the same voltage on the plus side and the minus side and the time ratio is 50.
It is a rectangular wave 88 which is%. This drive signal does not necessarily have to be synchronized with the synchronizing signal of the video signal, and the frequency is also optional from several times the vertical synchronizing signal to several kHz.
It is the same that an inconvenient image is output because the CRT is out of synchronization when the image signal is switched.

Therefore, it is understood that the present invention is also effective for the light valve having the structure as shown in FIG.

[0057]

According to the present invention, with respect to an image display device using a reflection type liquid crystal light valve of a light or charge writing type, it is determined that the image signal input to the image display device is switched or there is no synchronizing signal. It is possible to suppress an inconvenient image that is output on the screen when the synchronization is unstable, such as when, and its practical effect is great.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a voltage when the light valve drive is stopped in the embodiment of the present invention.

FIG. 3 is a system configuration diagram showing an embodiment of the present invention.

FIG. 4 is a system configuration diagram showing an embodiment of the present invention.

FIG. 5 is a system configuration diagram showing an embodiment of the present invention.

FIG. 6 is a structural diagram of a light valve.

FIG. 7 is a block diagram of a conventional system

FIG. 8 is a diagram showing the shape of a reset pulse.

FIG. 9 is a structural diagram showing another example of a light valve.

[Explanation of symbols]

 1 Liquid Crystal Light Valve 2 Reset Pulse Generation Circuit 3 Writing Video Light Generator (CRT) 4 Writing Lens 5 Beam Splitter 6 Light Source 7 Projection Lens 8 Screen 9 Video Signal Processing Circuit 10 Synchronous Signal Processing Circuit 11 External Input Terminal A 12 External Input Terminal B 13 Relay circuit 14 Microcomputer 15 MUTE signal generation circuit 16 Drive control circuit

Claims (11)

[Claims] 1. A reflective liquid crystal light valve capable of writing an image spatially distributed by light or directly by electric charges and modulating read light so as to respond to the information, and drives the reflective liquid crystal light valve. An image display device characterized in that the drive signal to be turned on is temporarily stopped during a transient state when the power is turned on or when the image signal input to the system is switched. 2. A reflective liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge and modulating read light so as to respond to the information, and a space serving as an input to the light valve. A video signal processing circuit for generating video information that is distributed in a uniform manner, a light valve drive circuit for applying a drive signal for driving the light valve between the first and second electrodes of the light valve, and a power source is turned on. Or when the video signal input to the video signal processing circuit is switched.
A MUTE signal generating circuit for generating a signal, and the MUT
An image display device, comprising: a drive control circuit for controlling a drive signal of the light valve according to a MUTE signal from an E signal generation circuit. 3. The image display device according to claim 2, wherein the light valve drive circuit receives a control signal from the drive control circuit and applies an arbitrary constant voltage to the light valve. 4. A reflective liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge and modulating read light according to the information, and driving the reflective light valve. An image display device characterized by switching the light valve to be driven by a synchronizing signal of internal oscillation when a vertical synchronizing signal for detecting is not detected. 5. A reflective liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge, and modulating read light so as to respond to the information, and a space serving as an input to the light valve. Image signal processing circuit for generating image information distributed in a uniform manner, a synchronization signal processing circuit for processing a synchronization signal of the image information, and a drive signal for driving the light valve, the first and second drive signals for the light valve. A light valve drive circuit applied between the electrodes of the sync signal, a sync signal non-input judgment circuit for judging the presence or absence of a sync signal input to the sync signal processing circuit, an internal sync signal oscillation circuit, and the sync signal non-input judgment circuit And a switching circuit that functions to switch the synchronization signal to the synchronization signal from the internal synchronization signal oscillation circuit according to the determination signal from Image display device. 6. A reflective liquid crystal light valve capable of writing a spatially distributed image by light or directly by an electric charge and modulating read light so as to respond to the information, and drives the reflective liquid crystal light valve. When the vertical light sync signal for switching is not detected and the reflective light valve is switched to be driven by the synchronous signal of the internal oscillation, the drive of the reflective light valve is temporarily stopped in the transient state. Video display device characterized by. 7. A reflection type liquid crystal light valve capable of writing a spatially distributed image by light or a direct charge and modulating read light according to the information, and an input to the reflection type liquid crystal light valve. A video signal processing circuit for generating spatially distributed video information,
A sync signal processing circuit for processing a sync signal of the image information; a light valve drive circuit for applying a drive signal for driving the light valve between the first and second electrodes of the light valve; and the sync signal. A synchronization signal non-input determination circuit for determining the presence or absence of a synchronization signal input to the processing circuit, an internal synchronization signal oscillation circuit, and a synchronization signal from the internal synchronization signal oscillation circuit according to the determination signal from the synchronization signal non-input determination circuit. Switching circuit for switching to the synchronization signal, a MUTE signal generating circuit for generating a MUTE signal in response to the determination signal from the synchronization signal non-input determination circuit, and an output from the MUTE signal generation circuit for driving the light valve drive signal. An image display device comprising a drive control circuit for controlling. 8. The image display device according to claim 7, wherein the light valve drive circuit receives a control signal from the drive control circuit and applies an arbitrary constant voltage to the light valve. 9. A reflective liquid crystal light valve capable of writing a spatially distributed image by light or directly by an electric charge and modulating read light according to the information, and driving the reflective liquid crystal light valve. An image display device, characterized in that the drive of the light valve is stopped when the vertical synchronizing signal for the operation cannot be detected. 10. A reflective liquid crystal light valve capable of writing an image spatially distributed by light or directly by an electric charge and modulating read light so as to respond to the information, and an input to the reflective liquid crystal light valve. A video signal processing circuit for generating spatially distributed video information,
A sync signal processing circuit for processing a sync signal of the video information, and a light valve drive for applying a drive signal for driving the reflection type liquid crystal light valve between the first and second electrodes of the reflection type liquid crystal light valve. Circuit, a sync signal non-input judging circuit for judging the presence / absence of a sync signal input to the sync signal processing circuit, and a drive signal for the reflection type liquid crystal light valve by a judgment signal from the sync signal non-input judging circuit And a drive control circuit for operating the image display device. 11. The image display device according to claim 10, wherein the light valve drive circuit receives a control signal from the drive control circuit and applies an arbitrary constant voltage to the light valve.