JPH07199214A - Display device - Google Patents

Abstract

PURPOSE:To obtain a display device capable of performing large-capacity display without uneven display by using an optical address type AC-driven light valve performing display by sequential scanning with a laser beam. CONSTITUTION:In this optical address type AC-driven light valve 20; an optical modulating layer 3 made of liquid crystal is formed between one substrate being a transparent substrate 1b on which a transference electrode 2b, a photoconductive layer 6 and a light shielding layer 5 are successively laminated and another substrate being a transparent substrate 1a on which a transference electrode 2a is filmed, and the display is performed by sequentially scanning the photoconductive layer 6 with the laser beam while impressing AC voltage between two transference electrodes 2a and 2b from the outside. The light valve is provided with a sensor 7 detecting scanning timing and a control means 13 controlling the parameter of the polarity, the phase and the frequency of external impressed voltage based on an output signal from the sensor 7 and controls the external impressed voltage based on the output signal from the sensor 7, whereby the display with stable picture density is realized by simple constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly to a photo-address type liquid crystal light valve display device.

[0002]

2. Description of the Related Art A liquid crystal light valve, which is a kind of spatial light modulation type light valve, is known as a display method, a driving method, and an addressing method capable of supporting a large area, a large capacity, and a video rate.

The display device disclosed in Japanese Patent Application Laid-Open No. 4-261520 is a liquid crystal light valve which is a combination of a ferroelectric liquid crystal and a photoconductive layer made of amorphous silicon. For this device, any of a combination of a CRT as a scanning light source and a semiconductor laser and a two-dimensional optical scanning device can be used. However, in order to reduce the weight of the device, a combination of a semiconductor laser and a two-dimensional scanning device is used. In the case of adopting, the writing time depends on the responsiveness of the liquid crystal, so that there is a drawback that it takes too much time to rewrite one frame when displaying a large capacity. That is, since switching between bistable states is used in the ferroelectric liquid crystal, the cumulative response effect cannot be used as in the STN-LCD using the nematic liquid crystal or the active matrix TN-LCD, and each scan line is not used. You have to write the book surely. For example, even if writing one scanning line takes only 50 microseconds, writing 1000 lines results in 50 milliseconds.

On the other hand, the display device disclosed in JP-A-4-159514 is a liquid crystal light valve comprising a combination of a polymer / liquid crystal composite film and a photoconductive layer. However, this device has a semiconductor laser as a scanning light source and two
When using a combination with a three-dimensional optical scanning device,
There is a drawback that display unevenness is likely to occur. Hereinafter, the cause of the display unevenness will be described in detail.

An example of the element structure of this liquid crystal light valve is shown in FIG. FIG. 3 is a sectional view of the liquid crystal light valve.
As shown in the figure, the element 52 includes a polarizing plate 41, a transparent substrate 42, a transparent electrode 43, an alignment film 44, a sealing material 46, a liquid crystal (polymer / liquid crystal composite film) 47, and an alignment film 4 in this order from the observation side.
4, a dielectric mirror 48, a light shielding layer 49, a photoconductive layer 50, a transparent electrode 43, and a transparent substrate 42. The configuration of the entire display device including this element is shown in FIG. The display device includes an addressing light source device 51 and a liquid crystal light valve 5.
2, projection lens 53, aperture 54, mirror 55, condenser lens 56, projection light source 57, screen 60
Etc.

The operation of the liquid crystal light valve 52 when a CRT is used as the addressing light source 51 will be described below. In this case, the addressing light source 51
As shown in FIG. 5, a CRT 58 and an image forming lens 59 for forming an image on the CRT 58 on the liquid crystal light valve 52.
It is composed of

The high-luminance image appearing on the display surface of the CRT 58 is imaged by the imaging lens 59 on the photoconductive layer 50 of the liquid crystal light bab 52. At that time, the impedance of the photoconductive layer 50 corresponding to the image portion decreases and becomes smaller than the impedance of the liquid crystal 47.
Most of the voltage applied during 3 is the liquid crystal 47 in the image portion.
Will be applied to. As a result, the light from the projection light source 57 passes through the liquid crystal 47 in the image portion and passes through the screen 6
An image is formed on 0 as a bright portion. On the other hand, since the impedance of the photoconductive layer 50 in the non-image portion is larger than that of the liquid crystal 47, most of the voltage applied between the two transparent electrodes 43 is applied to the photoconductive layer 50 in the non-image portion. become. Therefore, in the non-image portion, the light from the projection light source 57 does not pass through the liquid crystal 47, and a bright portion cannot be formed on the screen.

FIG. 7 shows the operation of the liquid crystal light valve 52 using the CRT 58, focusing on one pixel. In FIG. 7, a time series 71 of electron beam irradiation in the CRT 58, a light emission time series 72 of phosphors in the CRT 58 forming a pixel of interest, a drive voltage 73 of the liquid crystal light valve 52,
Time series 74 of voltage applied to liquid crystal 47, liquid crystal 47
7 shows a time series 75 of the transmittance of the. In this figure, the electron beam irradiation cycle is 20 milliseconds, and the phosphor afterglow time is 100 milliseconds.
Assume millisecond, external drive voltage is 50 Hertz.

When the time t is T ₁ <t <T ₂ , the pixel of interest forms a non-image portion. Therefore, the CRT
58, a time series 71 of electron beam irradiation in 58, a light emission time series 72 of phosphors in the CRT 58 forming a pixel of interest, a time series 74 of voltage applied to the liquid crystal 47 portion, and a time series 75 of liquid crystal 47 transmittance. Also shows zero. After that, when the time T ₂ <t <T ₃ at which the target pixel forms an image portion is reached, the electron beam is periodically irradiated to the target pixel. Although the irradiation of the electron beam is discrete, the afterglow time of the phosphor used in the CRT 58 is sufficiently longer than the irradiation period of the electron beam, so that the phosphor emits light continuously and the liquid crystal 47 part Since the effective value of the time series 74 of the applied voltage always exceeds the threshold voltage for operating the liquid crystal 47, the pixel of interest is at time T ₂ <
It operates stably during t <T ₃ . That is, the liquid crystal 47
As shown in the time series 75 of the transmittance of, the density of the pixel of interest does not change during the time T ₂ <t <T ₃ .

Next, the operation of the liquid crystal light valve 52 when a semiconductor laser is used as the light source 51 for addressing will be described. In this case, as shown in FIG. 6, the addressing light source 51 includes a semiconductor laser 63, a main scanning optical element 64, an imaging lens 59, and a sub-scanning optical element 6.
It is composed of 5.

The principle of operation is the same as when the CRT 58 is used as a light source for addressing. That is, the light from the semiconductor laser 63 is imaged on the photoconductive layer 50 of the liquid crystal light valve 52 by the scanning optical elements 64 and 65 and the imaging lens 59. At that time, the impedance of the photoconductive layer 50 in the semiconductor laser light irradiation portion corresponding to the image portion is lowered and becomes smaller than the impedance of the liquid crystal 47, so that most of the voltage applied between the two transparent electrodes 43 is the image. The liquid crystal 47 is applied in part. As a result, the light from the projection light source 57 passes through the liquid crystal 47 in the image portion and forms an image on the screen 60 as a bright portion. On the other hand, since the impedance of the photoconductive layer 50 in the non-image portion is larger than that of the liquid crystal 47, the two transparent electrodes 4
Most of the voltage applied during 3 will be applied to the photoconductive layer 50 in the non-image portion. Therefore, in the non-image portion, the light from the projection light source 57 does not pass through the liquid crystal 47,
No bright areas can be formed on the screen.

FIG. 8 illustrates the operation of the liquid crystal light valve 52 using the semiconductor laser 63, focusing on one pixel. FIG. 8 shows a semiconductor laser light exposure time series 81,
The driving voltage 82 of the liquid crystal light valve 52, the time series 83 of the voltage applied to the liquid crystal 47 portion, and the time series 84 of the transmittance of the liquid crystal 47 are shown. In this figure, the exposure time series 81 of the semiconductor laser light and the drive voltage 82 are not synchronized, the electron beam irradiation period is 20 milliseconds, and the external drive voltage is 5
It is slightly off from 0 Hertz.

When the time t is T ₁ <t <T ₂ , the target pixel forms a non-image portion. Therefore, the exposure time series 81 of the semiconductor laser light, the time series 83 of the voltage applied to the liquid crystal 47 portion, and the time series 84 of the liquid crystal 47 transmittance all show zero. After that, when the time T ₂ <t <T ₃ at which the target pixel forms an image portion is reached, the semiconductor laser light is periodically irradiated to the target pixel. Since the irradiation of the semiconductor laser light is discrete as compared with the phosphor of the CRT, the effective value of the time series 83 of the voltage applied to the liquid crystal 47 portion always exceeds the threshold voltage for operating the liquid crystal 47. However, the density of the target pixel changes with time. In the case of FIG. 8, at time T ₂ <t <T ₃ , the driving voltage 82 rises to the plus side at the time of the first irradiation of the semiconductor laser light, so the voltage 83 applied to the liquid crystal 47 portion exceeds the threshold voltage. However, at the next irradiation of the semiconductor laser beam, the drive voltage 82 coincides with the instant when the plus voltage is switched to the minus voltage, so that the voltage 83 applied to the liquid crystal 47 portion does not exceed the threshold voltage. Therefore, the brightness of the pixel of interest projected on the screen changes with time during the time T ₂ <t <T ₃ at which the image portion is formed. As described above, when the exposure time series 81 of the semiconductor laser light and the drive voltage 82 are not synchronized, the temporal change of the density of the pixel of interest becomes particularly large. Even if the synchronism is established, the temporal change of the density is large even when the position where the polarity of the AC drive voltage 82 changes is located at almost the same position in the image display area.

The problem of uneven display density when using a combination of a semiconductor laser and a two-dimensional optical scanning device as such a scanning light source is limited to the liquid crystal light valve using the polymer / liquid crystal composite film. However, it similarly occurs in other AC driven liquid crystal light valves.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in order to eliminate or improve the above-mentioned drawbacks of the prior art, and an object thereof is an optical address type which sequentially displays laser light for display. With the AC drive light valve of
It is an object of the present invention to provide a display device capable of displaying a large capacity without display unevenness.

[0016]

As shown in FIG. 1, a display device of the present invention that achieves the above-mentioned object is arranged in order from the observation side.
When operating the optical writing type liquid crystal light valve 20 in which the transparent substrate 1a, the transparent electrode 2a, the liquid crystal 3, the dielectric layer 4, the light shielding layer 5, the photoconductive layer 6, the transparent electrode 2b and the transparent substrate 1b are sequentially laminated. The drive power supply 12 which is an AC power supply applied between the transparent electrodes 2a and 2b can be controlled by the output of the drive power supply control circuit 13 according to the output of the optical sensor 7 which detects the start of scanning. is there.

A detailed description will be given below with reference to the drawings. As the transparent substrates 1a and 1b described above, inorganic transparent solids such as non-alkali glass, organic transparent solids such as PES, PET, and polyethylene are used. As the transparent electrodes 2a and 2b, inorganic transparent electrodes such as indium oxide and indium tin oxide, and organic transparent electrodes such as ion-doped polyacetylene are used. The liquid crystal 3 is, for example, a nematic, smectic, or cholesteric liquid crystal material that has been orientated, or nematic, smectic,
A so-called polymer dispersed liquid crystal in which a liquid crystal showing each phase such as cholesteric is dispersed in a resin is used. Dielectric layer 4
For this, a dielectric mirror or the like in which silicon and silicon oxide are laminated in a multilayer film is used. As the light-shielding layer 5, cadmium tellurium, a resin in which a pigment is dispersed, or the like is used. As the photoconductive layer 6, an inorganic chalcogenide such as selenium, selenium tellurium, or selenium arsenide, cadmium sulfide, amorphous silicon, or the like is used.

In the photo-addressable liquid crystal light valve 20 as described above, the conductivity of the photo-conductive layer 6 is increased in the exposed photo-conductor portion, and most of the external drive voltage from the drive power source 12 is applied to the liquid crystal 3. When applied, the liquid crystal in that area becomes transparent. On the other hand, the photoconductive layer 6 in the unexposed area
In, the conductivity of the photoconductive layer 6 remains low, and there is almost no driving voltage applied to the liquid crystal 3. Therefore, the liquid crystal 3 in that portion remains opaque. In the present invention, an image is displayed by scanning and exposing the liquid crystal light valve 20 with laser light.

A typical configuration of the scanning optical system is shown in FIG. The light emitted from the semiconductor laser 11 strikes the polygon mirror 8 through a collimator lens (not shown in the figure),
Scanning is performed in the main scanning direction. The optical path of the laser light emitted from the polygon mirror 8 is bent by the reflecting mirror 9,
The galvano mirror (or polygon mirror) 10 scans in the sub-scanning direction, and the two-dimensional scanning is performed together with the scanning by the polygon mirror 8. This beam is further imaged on the photoconductive layer 6 of the photo-addressable liquid crystal light valve 20 through a two-dimensional f-θ lens (not shown in the figure).

The relationship between the intensity of the scanning light, the voltage of the driving power source 12 and the voltage applied to the liquid crystal is shown in FIG. Semiconductor laser 1
The output light 21 of No. 1 is scanned by the polygon mirror 8 and the galvano mirror 10 and is incident on the optical sensor 7. At that time, a pulse is output to the optical sensor output 22, and the modulation of the output light of the semiconductor laser 11 by the display information is started. The modulation of the output light of the semiconductor laser 11 by the trigger of the optical sensor output 22 as described above displays one screen.
It is repeated every frame period. Optical sensor output 22
Is input to the drive power supply control circuit 13 in FIG. 1 and the output thereof controls the phase, frequency, etc. of the drive power supply 12 for each frame. That is, in the case of the example shown in FIG. 2, an operation of reversing the polarity of the drive voltage 24 applied between the electrodes 2a and 2b of the liquid crystal light valve 20 outside the image region is performed every frame period. As a result, the voltage 24 applied to the target pixel is alternately inverted for each frame period at the time t of T ₂ <t <T ₃ , and the exposure timing 23
It becomes possible to suppress the change in the effective value of the voltage 25 applied to the liquid crystal 3 due to the timing shift of the drive voltage 24 and the change in the effective value of the voltage applied to the liquid crystal 3 with time. It becomes possible. Therefore, it is possible to minimize the temporal change 26 in the density of the pixels in the image portion.

Here, the control method using the scanning start signal 22 from the optical sensor 7 of the driving voltage 24 has been described only by switching the polarity, but the present invention is not limited to this control method, and the phase or frequency is not limited. Even if is changed randomly for each frame, the display unevenness is averaged and becomes inconspicuous.

That is, in the display device of the present invention, a transparent electrode, a photoconductive layer, and a light-shielding layer are sequentially stacked on a transparent substrate, and the transparent substrate is provided between the substrate and the other substrate on which the transparent electrode is formed. A sensor for detecting scanning timing in an optical address type light valve that forms a light modulation layer and sequentially scans laser light on the photoconductive layer while applying an AC voltage from the outside between two transparent electrodes to display. And a control means for controlling the parameter of the externally applied voltage based on the output signal of the sensor.

In this case, the control means may invert the polarity of the externally applied voltage based on the output of the sensor or may change the phase of the externally applied voltage.
The frequency of the externally applied voltage may be changed.

[0024]

In the present invention, since the sensor for detecting the scanning timing and the control means for controlling the parameter of the externally applied voltage based on the output signal of this sensor are provided, the external device based on the output signal of the sensor is used. By controlling the applied voltage, display with stable image density is possible with a simple configuration. Further, by attaching a control means for controlling the parameter of the externally applied voltage, it is possible to display an image with a uniform density on a lightweight display device.

[0025]

EXAMPLES Examples of the display device of the present invention will be described below. A first embodiment of the present invention will be described with reference to FIG. A transparent electrode 2b made of indium oxide is formed by sputtering on a transparent substrate 1b made of Corning 7059 glass (trade name) of 50 mm x 50 mm x 1.1 mm, and is made of hydrogenated amorphous silicon by plasma CVD. Photoconductive layer 6 is 5 μm
And a dielectric layer 4 having an alternating laminated structure of hydrogenated amorphous silicon and hydrogenated amorphous silicon nitride is formed on the light-shielding layer 5 made of cadmium tellurium. Got In addition, a transparent electrode 2 made of indium tin oxide is formed on the transparent substrate 1a made of 7059 glass of the same size by sputtering.
A film was formed on a to obtain a second substrate. A polymer-dispersed liquid crystal 3 was formed between the substrates with glass surfaces facing outward through glass spacers (not shown in the figure), and an optically addressed liquid crystal light valve 20 was obtained. With respect to this liquid crystal light valve 20, a 20-sided polygon mirror 8 having a diameter of 40 mm is set to 60,000 revolutions / minute, a galvano mirror 10 is set to 50 hertz, and a wavelength 69
Beam from semiconductor laser 11 of 2 nanometers 3
An image is formed on the photoconductive layer 6 with a diameter of 0 micron. Imaging is 2
It is performed from the side of the hydrogenated amorphous silicon 6 through a three-dimensional f-θ lens (not shown in the figure). The image appearing on the polymer dispersed liquid crystal 3 is projected on the screen 60 from the side opposite to the hydrogenated amorphous silicon 6 through the projection optical system. As shown in FIG. 4, the projection optical system includes a projection lens 53, an aperture 54, a mirror 55, and a condenser lens 5.
6, a projection light source 57, a screen 60, and the like. While scanning and exposing the light of the semiconductor laser 11, a rectangular wave having an amplitude of 20 V and a frequency of 50 Hz is applied between the pair of transparent electrodes 1a and 1b of the liquid crystal light valve 20 to generate 640 × 4.
When 00 pixels were displayed, it was confirmed by visual observation that light and shade appeared in the image projected on the screen 60. This light and shade appeared on a part of the display screen, and moved in the screen at intervals of several tens of seconds. The moving speed is the transparent electrodes 1a, 1
Although it was changed by finely adjusting the frequency of the voltage applied between points b, it was difficult to set the frequency completely removed.

An optical sensor 7 for detecting the start of scanning as shown in FIG. 1 and a driving power supply control circuit 13 for inverting the polarity of the driving power supply 12 are attached to this apparatus, and a scanning start signal from the optical sensor 7 is supplied to the driving power supply. When it was taken into the control circuit 13 and the polarity of the drive voltage was changed for each frame, the shade of the image could not be visually confirmed.

Next, as a second embodiment, in the same configuration as the first embodiment, every time a scanning start signal from the optical sensor 7 is input to the drive power supply control circuit 13, it is applied to the polymer dispersed liquid crystal 3. The alternating current was made to change randomly between 1 and 50 kilohertz. First, a rectangular wave having an amplitude of 20 V and a frequency of 25 kHz is applied between the transparent electrodes 1a and 1b, and the same display as in the first embodiment is performed.
It was confirmed by visual observation that fine shades appeared on the entire surface of the image projected on.

When the scanning start signal of this apparatus is fetched into the driving power supply control circuit 13 and the frequency of the driving voltage is changed in a random number for each frame within the range of 10, 20, 30, 40 and 50 kHz, the image The light and shade could not be visually confirmed.

The display device of the present invention has been described above based on its principle configuration and examples, but the present invention is not limited to these and various modifications are possible.

[0030]

As is apparent from the above description, according to the display device of the present invention, the sensor for detecting the scanning timing and the control for controlling the parameter of the externally applied voltage based on the output signal of the sensor. Since the externally applied voltage is controlled based on the output signal of the sensor, it is possible to display with stable image density with a simple configuration. Further, by attaching a control means for controlling the parameter of the externally applied voltage, it is possible to display an image with a uniform density on a lightweight display device. The method of inverting the polarity and the method of changing the phase have a feature that the drive circuit can be simplified. The method of changing the frequency is convenient when using a special driving method such as two-frequency driving.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining a principle configuration and an embodiment of the present invention.

FIG. 2 is a time chart showing the relationship between the intensity of scanning light, the driving power supply voltage, and the voltage applied to the liquid crystal.

FIG. 3 is a sectional view of a liquid crystal light valve.

FIG. 4 is a sectional view of a conventional liquid crystal light valve display device.

FIG. 5 is a diagram showing a configuration of an addressing light source using a CRT.

FIG. 6 is a diagram showing a configuration of an addressing light source using a semiconductor laser.

FIG. 7 is a time chart diagram showing an operation of a liquid crystal light valve display device using a conventional CRT as a light source.

FIG. 8 is a time chart showing the operation of a liquid crystal light valve display device using a conventional semiconductor laser as a light source.

[Explanation of symbols]

1a, 1b ... Transparent substrate, 2a, 2b ... Transparent electrode, 3 ... Liquid crystal, 4 ... Dielectric layer, 5 ... Light shielding layer, 6 ... Photoconductive layer, 7 ... Photosensor, 8 ... Polygon mirror, 9 ... Reflecting mirror, 10 ... Galvano mirror, 11 ... Semiconductor laser, 12 ... Drive power supply, 13 ... Drive power supply control circuit, 20 ... Optical writing type liquid crystal light valve, 21 ... Semiconductor laser output light, 22 ... Optical sensor output, 23 ... Photoconductive layer exposure,
24 ... Driving voltage, 25 ... Voltage applied to liquid crystal of target pixel portion, 26 ... Liquid crystal transmittance of target pixel portion, 53 ... Projection lens, 54 ... Aperture, 55 ... Mirror, 56 ... Condenser lens, 57 ... Light source for projection, 60 ... Screen

Claims (4)

[Claims] 1. A light modulation layer is formed between one substrate in which a transparent electrode, a photoconductive layer, and a light shielding layer are sequentially laminated on a transparent substrate and the other substrate in which a transparent electrode is formed on the transparent substrate, A sensor for detecting scanning timing and an output signal of the sensor in a photo-addressable light valve that sequentially scans a laser beam on a photoconductive layer while applying an AC voltage from the outside between two transparent electrodes. And a control means for controlling the parameter of the externally applied voltage based on the above. 2. The display device according to claim 1, wherein the control means inverts the polarity of an externally applied voltage based on the output of the sensor. 3. The display device according to claim 1, wherein the control means changes the phase of the externally applied voltage based on the output of the sensor. 4. The display device according to claim 1, wherein the control unit changes the frequency of the externally applied voltage based on the output of the sensor.