JP3143578B2 - Driving method of display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a display device for controlling the amount of light transmitted or reflected from a light source.

[0002]

2. Description of the Related Art Optical modulation elements are used in various optical devices. For example, an optical modulation element of a display device. A liquid crystal display element will be described as the most familiar example. Conventionally, several methods have been proposed for performing gradation display using a liquid crystal element.

[0003] One is a method in which a twisted nematic liquid crystal (TN liquid crystal) is used to apply a voltage that changes according to gradation information to the TN liquid crystal, thereby modulating the transmittance of the entire pixel.

[0004] Second, one pixel is configured as an aggregate of a plurality of sub-pixels, and each sub-pixel is turned on / off by binary data, thereby modulating the area of the light-transmitting sub-pixel. It is a method.

[0005] This method is disclosed in, for example, Japanese Patent Application Laid-Open No. 56-88193.
And EP453033, EP361981
No. 6,009,036.

Third, by making the electric field strength or the inversion threshold value of the liquid crystal distributed in one pixel different, a part showing a bright state and a part showing a dark state coexist in one pixel. Is a method of modulating the area ratio of those portions.

[0007] This method is based on a "ferroelectric liquid crystal optical modulator (Ferroelectric Li) having a region where nucleation and inversion occur in a pixel" given to the inventor Kaneko et al.
liquid crystal optical module
lation devicewith regions
with in pixels to initia
te uncleation and inversi
on) ", US Pat. No. 4,796,98.
0, U.S. Pat. No. 4,712,877, U.S. Pat. No. 4,747,671, U.S. Pat. No. 4,763,994
No. and other specifications.

The fourth method is a method of modulating the length of a period during which one pixel is turned on to exhibit a bright state. This method was given to the inventor Kuribayashi et al. “Ferroelectric display panel and its gradation driving method (Ferroelectric display panel).
ay panel and driving method
d therefor to active gray
US Patent No. 4,70, entitled "scale).
No. 9,995. Another example of digital duty modulation is the inventor Nelson.
on) active row backlight
Column shutter LSD with one
Shutter Transition Parlow (Active
row backlight column shu
ter LCD with one shutter
No. 5,311,206, entitled "transition per row".

Here, the first method is called luminance modulation, the second method is called pixel division, the third method is called domain modulation, and the fourth method is called digital duty modulation.

[0010]

It is difficult to apply luminance modulation to an element using an optical modulation material having a characteristic in which transmittance changes sharply with applied voltage.

Further, since the response speed of TN liquid crystal is generally low in luminance modulation, it is not suitable for a system in which information changes at high speed.

Since pixel division is the same as arranging a large number of pixels with a small number of pixels, the spatial frequency is reduced and the resolution is liable to be reduced. Further, the area of the light-shielding portion increases and the aperture ratio decreases.

In the domain modulation, the structure of a pixel for giving a distribution to the electric field intensity or giving a distribution to the inversion threshold becomes complicated. Further, since the voltage margin for the halftone display is narrow, it is easily affected by the temperature.

In the digital duty modulation, since the ON / OFF time is modulated, and the unit time of the modulation is determined by the clock frequency and the gate switching time, it is difficult to perform highly accurate modulation. That is, the multi-tone display has a limit. In addition, since it is necessary to always convert analog data to analog / digital (A / D) to obtain digital gradation information, it is difficult to apply the method to a simple system.

The present invention has been made in view of the above technical problem, and has as its object to provide a display device having an element capable of performing optical modulation based on analog data.

Another object of the present invention is to provide a display device having an optical modulation element which can be applied to an optical material having a sharp applied voltage / transmittance characteristic.

Still another object of the present invention is to provide a display device having an optical modulator capable of achieving a high spatial frequency and high resolution.

Another object of the present invention is to provide a display device having an inexpensive optical modulation element capable of reproducing gradation information by analog duty modulation with a relatively simple system.

Still another object of the present invention is to provide an image display device capable of displaying good halftones.

[0020]

According to the present invention, there is provided an optical modulation element having a photoconductive layer and a layer of an optical modulating substance disposed between a pair of electrodes to which a voltage is applied, and gradation information is stored in the photoconductive layer. A method for driving an image display device, comprising: a signal light source that provides optical information including a light source; and a read light source that provides read light for reading image information to the layer of the optical modulation material. The readout light is applied to the layer and the readout light is scanned and applied to the layer of the optical modulation material, the lighting time of the readout light source is controlled, and the time during which the optical modulation material exhibits a predetermined optical state and the lighting time Is a method for driving a display device, wherein the overlap time is modulated according to gradation information.

(Operation) According to the present invention, the timing at which the voltage applied to the optical modulation substance exceeds the threshold value at which the optical state of the optical modulation substance transits changes analogously depending on the gradation information. I do. As a result, the length of the on-time of the optical modulator, that is, the time during which the optical shutter is open or the time during which the mirror is displaced in a predetermined direction, and the time during which the light source is turned on are modulated in an analog manner. Alternatively, the time integral value of the reflected light amount corresponds to the gradation information. Therefore, the number of gradations is not limited to a digital amount such as a clock frequency, and A / D conversion of gradation information is not required.

Moreover, even if a digital (binary) display element having a sharp applied voltage and transmittance characteristic is used, an effect that analog modulation can be realized, which has not been considered in the past, can be obtained.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention are shown in FIGS. 26 to 28 which will be described later. Before that, the basic configuration will be described.

First, a basic modulation method according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an example for realizing the modulation method of the present invention, wherein 1 is an optical shutter for controlling transmission of light as an optical modulation means, 2 is a light source for generating light,
DR1 is driving means for driving the optical shutter, DR2
Is a drive unit for turning on the light source, and CONT is a control unit for controlling power supply and operation timing to the two drive units.

FIG. 2 is a graph showing an example of the characteristics of the optical modulation element (substance) of the optical shutter 1. For example, when the applied voltage exceeds the threshold value _Vth when the pulse width is constant, the transmittance sharply increases. However, the transmittance is constant above the saturation value V _sat . If the optical modulator has a memory property, the optical state is kept constant even when the applied voltage is released.

FIG. 3 is a timing chart for explaining the basic operation of FIG. 1. In FIG. 3, reference numeral 10 denotes an optical transition of the optical shutter, reference numeral 20 denotes a light source lighting timing, and reference numeral 30 denotes an applied signal to the optical shutter. . The applied signal 30 is a signal in which the amplitude (peak value) V _op and the pulse width PW _op further change according to the gradation information.

The light source is turned on (ON) at time t ₁ and at time t ₃
The light is emitted during a period t until the light is turned off (OFF). This period t is a predetermined time so that halftones can be recognized.
When a signal modulated according to this timing is applied at time tt _on , the optical shutter is in the dark state (Mi) when the time integral of the applied voltage applied to the optical modulator exceeds a threshold value.
n) to the bright state (Max).

The rising timing t ₂ of this transition also depends on the amplitude V _op and the pulse width PW _op . Since the amplitude V _op is modulated by the gradation information, the timing t ₂
Eventually changes within the range of the time width TM according to the gradation information. tt _off is the application timing of the signal for turning _off the optical shutter, and the time integral of the amount of light transmitted through the optical shutter 1 is the overlap time of the lighting time and the time when the optical shutter is in the ON state. Will change accordingly. Therefore, if the pulse width PW _op is fixed and the amount of the amplitude V _op is changed in an analog manner, the time integral of the transmitted light amount can be easily modulated.

All conventional digital duty modulations are
The pulse width PW _op and the amplitude V _op of the applied signal 30 are kept constant, and the application timing tt _ON of the applied signal 30 is digitally changed according to the clock.

On the other hand, the present invention is novel in that the signal 30 is treated as an analog quantity, thereby enabling analog duty modulation.

FIG. 4 shows an example of a circuit for generating the analog signal 30.
The signal having the modulated amplitude and the predetermined pulse width required for driving the optical shutter can be obtained by amplifying the signal by the amplifier 1 and sampling by the switch including the transistor Tr2.

Next, another basic modulation method of the present invention will be described with reference to FIG.

The difference from the system shown in FIG. 1 is that the optical modulating means is the light reflecting means 1A. A liquid crystal element or a mirror element is used as the light reflecting means.
In the case of a liquid crystal element, one of a pair of substrates enclosing liquid crystal is used as a transparent body and the other is used as a reflector, and light absorption or light reflection is selectively performed according to the alignment state of the liquid crystal. In the case of a mirror element, the angle of the reflection surface of the mirror is controlled by displacing the mirror, and whether the reflection surface is directed in a predetermined direction or in another direction is selected.

Then, the overlap time of the lighting time of the light source and the ON time of the reflection means is analog-modulated according to the gradation data.

Here, the ON time of the reflecting means is a time during which the liquid crystal element is in a light reflecting state or a time during which the reflecting surface of the mirror element is oriented in a predetermined direction.

(Drive Circuit) A drive circuit used in the present invention will be described.

FIG. 6 is a diagram showing a drive circuit of the optical modulation means used in the present invention. Here, the optical modulation means is C
Shown by _LC .

Assuming that the value of the resistor R _PC changes according to the gradation information, first, a sufficient voltage exceeding the threshold value of the optical modulation means _CLC is applied. At this time, if the value of R _PC is high, C
_The time when the voltage applied to the _LC exceeds the threshold is delayed. Meanwhile, the time that the voltage value of R _PC is applied to the low if C _LC exceeds the threshold faster. So, at these times,
By adjusting the lighting timing and the lighting time of the light source, analog duty modulation of the transmitted light or the reflected light becomes possible.

FIG. 7 is a diagram showing another drive circuit. FIG.
Differs in that connected in parallel to the optical modulation means C _LC resistor R _PC, with capacitive C _PC. In this case, a drive voltage Vd sufficient to exceed the threshold is applied for a predetermined time and _CLC
Is turned on, discharge development based on the time constant of the RC circuit is used. Time the voltage applied to C _LC is lower than the threshold and the value of the resistance R _PC is if slow discharge high slower.

On the other hand, the higher the value of R _PC discharge faster, the time at which the voltage applied to C _LC is lower than the threshold faster. If this time is set within the lighting time of the light source, the light transmission or reflection time is subjected to analog duty modulation due to the difference in timing.

FIG. 8 shows another example of a driving circuit. The value indicated by the variable voltage Vv is the gradation information. The difference from FIG. 7 is that the time constants of the RC circuits R _PC and C _PC are fixed.
_The timing at which the voltage applied to the _LC falls below the threshold is determined by the voltage Vv that is the gradation information. Accordingly, analog duty modulation can be performed by adjusting the timing with the lighting time in the same manner as in FIG.

(Light Source) The light source used in the present invention will be described. The light emitted from this light source is selected from natural sunlight, white light, monochromatic light such as red (R), green (G), blue (B), and combinations thereof, as necessary.
Therefore, examples of the light source used in the present invention include a laser light source, a fluorescent lamp, a xenon lamp, a halogen lamp, a light emitting diode, and an electroluminescent element. ON / OFF of these lightings is controlled by the light source driving means according to the driving timing of the optical modulation means.
In particular, it is desired that the lighting time of the readout light source be not more than the reciprocal (1/60 second) of the flicker frequency (for example, 60 Hz) at which humans can recognize flicker. In the case of color display, it is desirable to turn on the R, G, and B light sources at different timings, and to perform optical modulation of R, G, and B in a time-division manner.

(Optical Modulation Element) Examples of the light modulation means used in the present invention include a light shutter (light valve) for modulating light transmittance and a reflection element as light reflection means for modulating light reflectance. .

The optical shutter used in the present invention may be any shutter that can exhibit two states with different transmittances. A preferred example is one using liquid crystal as the optical modulation material.

As the optical modulation element using liquid crystal, it is desirable to dispose liquid crystal between a pair of electrodes, and to change the alignment state of liquid crystal molecules according to an applied electric field. Then, the light transmittance is controlled through the polarizing element according to the optical characteristics of the molecular orientation. Therefore, in the liquid crystal element, the transmittance, the reflectance,
The transmission state and the reflection state are caused by a combination with a polarizing element.

Specifically, it is preferable to use a liquid crystal cell in which liquid crystal is sealed between a pair of substrates. A transparent electrode and an alignment film are provided on at least one inner surface of the pair of substrates as needed.

As the substrate, translucent glass, plastic, quartz or the like is used. As the transparent electrode, a metal oxide conductor such as tin oxide, indium oxide, and ITO is preferably used.

As the alignment film, a polymer film subjected to a uniaxial alignment treatment such as rubbing or an inorganic film formed by oblique evaporation is preferable.

As the liquid crystal, a nematic liquid crystal exhibiting a nematic phase when operating as a cell and a smectic liquid crystal exhibiting a smectic phase when operating as a cell are preferably used.

As a reflection element used in the present invention, a reflection surface of a metal film is moved by an electrostatic force by an applied voltage,
DM that modulates the direction of reflected light by changing the angle of the reflecting surface
D (Digital Micromirror Dev)
and a liquid crystal element that reflects light when the liquid crystal is aligned in a transmission state with one surface of the liquid crystal cell as a reflector and the other surface as a transmission member.

FIG. 9 is a graph showing the applied voltage transmittance characteristics of the optical modulation element (substance) used in the present invention. D
In the case of MD, it can be regarded as a graph showing the applied voltage dependence of the amount of reflected light reflected in a predetermined direction.

(A) shows a state transition with a positive threshold voltage as a boundary value, (b) shows a state with positive and negative thresholds and further has hysteresis, and (c).
Indicates that positive and negative threshold values are generated by hysteresis.
In (d), the voltage 0 is the threshold. This figure 9
Shows ideal characteristics for simplifying the description, and actually has a slight slope between the threshold value and the saturation value as shown in FIG.

Consider matching with the drive circuit. 9 (a) and 9 (b) are preferably combined with the parallel circuits shown in FIGS. 7 and 8, and FIGS. 9 (c) and 9 (d) are combined with the series circuit shown in FIG. Good.

Examples 1 to 5 described below are reference examples for easy understanding of the present invention.

(Example 1) FIG. 10 is a schematic diagram for explaining a method of driving an optical modulation element. 101 is a liquid crystal element in which a chiral smectic liquid crystal is arranged between a transparent substrate having a pair of electrodes, 103 is a gradation information generation circuit for generating gradation information, 104 is a light source, and 105 is a viewer. The driver circuit is a circuit including the capacitor C _pc and the transistor 102. When a resistance between a source and a drain (or an emitter and a collector) changes according to a potential of a gate or a base of the transistor, a voltage applied to a liquid crystal is reduced. The timing exceeding the inversion threshold of the liquid crystal changes. Vext is a voltage applying means for applying a voltage for resetting the liquid crystal element and a driving voltage. Cflc indicates the capacity of the liquid crystal.

The gradation information generating circuit 103 includes a light emitting diode PED and four variable resistors VRB, VRG, VRR, VR.
W and four transistors TB, TG,
TR, TW and power supply VCC. The diode PED and the transistor 102 constitute a photocoupler.

The electric signal as gradation information of each color given as a variable resistance value is converted into light information by the light emitting diode PDG.

The light source 104 includes light emitting diodes EDR, EDG, and EDB for generating light of three colors RGB. BR
Is a variable resistor for white balance provided as needed.

FIG. 11 is a timing chart of the driving of FIG. 10, where 103T indicates the output timing of optical information, Vflc indicates the voltage applied to the liquid crystal, Tran indicates the transmittance of the liquid crystal element, and 104 indicates the light source. The lighting timing is shown, and 105T indicates the transmitted light amount recognized by the observer.

First, a reset pulse is applied by the voltage applying means Vext at the same time that white light for reset is applied. Thus, the liquid crystal is once oriented to a dark state.

Next, at the same time that light corresponding to the gradation information of R is output, the light emitting diode EDR of R lights up, and Ve
xt applies a voltage of the opposite polarity to the electrode of the liquid crystal element. Since the R light amount is extremely small during this period, the effective voltage applied to the liquid crystal does not exceed the threshold value _Vth , so that the liquid crystal element does not transmit the R light.

Thereafter, white light is again supplied and V
ext increases, and the liquid crystal is inverted to a light transmitting state. However, at this time, since the light source is not turned on, the observer sees the dark state continuously.

Next, Vext becomes a negative voltage, but since the effective voltage applied to the liquid crystal does not exceed the threshold, the liquid crystal element remains in the bright state. However, the light source is not turned on during this period.

Thus, the display period of R ends.

The next is a G display period in which the same driving as the R display period is performed. Here, since the light amount of the G information is larger than the case of R, the voltage applied to the liquid crystal exceeds the threshold value at time trv. Then, the liquid crystal element transmits the G light until the time t _off when the lighting of the light source ends, so that the observer recognizes the intermediate level G light.

Similarly, the next is a B display period in which the same driving as that of the R and G display periods is performed. Here, since the light amount of the B information is larger than the case of G, the voltage applied to the liquid crystal exceeds the threshold value at time trv2. Then, since the liquid crystal element transmits the B light until time t _off 2 when the lighting of the light source ends, the observer recognizes the intermediate level B light closest to the maximum bright state.

As described above, in this embodiment, the timing at which Vflc exceeds the threshold is changed according to the gradation information. Then, when the gradation information corresponding to the minimum level transmission state is input, the transmission period (on period) of the liquid crystal element and the lighting period of the light source do not overlap with each other when the light source is on. , Set the light-off time.

Thus, in this embodiment, a desired intermediate state can be obtained from the range from the minimum brightness level to the maximum brightness level. In addition, since the voltage applied to the liquid crystal is symmetrical, the DC component applied to the liquid crystal becomes substantially zero, and the deterioration of the liquid crystal element can be suppressed.

(Example 2) FIG. 12 is a schematic diagram for explaining a method of driving an optical modulation element. Reference numeral 201 denotes a reflective liquid crystal element in which liquid crystal is arranged between substrates having a pair of electrodes;
4 is a light source driving circuit for driving the light source, C _pc is a capacitance element, R
_pc is a resistance element, and Vd is a drive voltage source. This system is a circuit in which the resistance value changes when gradation information is input to the resistance element _Rpc .

The characteristics of the liquid crystal used are as shown in FIG.

FIG. 13 is a timing chart of the driving of FIG. 12, where Vsl indicates the application timing of the power supply Vd,
1c indicates the voltage applied to the liquid crystal, Tran indicates the reflectance of the liquid crystal element, 204T indicates the lighting timing of the light source, and 205T indicates the amount of transmitted light recognized by the observer. 1 is a low value of R _pc , m is a middle value of R _pc , n is R
_This indicates a case where the value of _pc is high, and each corresponds to analog gradation information.

First, when Vd is applied to the liquid crystal element at the time t _on , the voltage Vlc applied to the liquid crystal becomes the voltage V1 which sufficiently exceeds the threshold. At the same time, the liquid crystal element has a maximum reflectance.

At time t _off , the voltage Vd is released, so that the voltage Vlc applied to the liquid crystal gradually decreases in accordance with the resistance value _Rpc , and falls below the threshold at a certain timing. Since this timing depends on the gradation information, in the case of 1, the time t
In _X1, the case of m at time t _X2, reflectance Tran is minimized at time t _X3 For n. Here, since the light source is set to start lighting at time t _X1 and turn off at time t _X3 , the reflected light amount corresponding to l, m, and n is as shown in 205T.

As described above, in this example, the timing at which Vlc falls below the threshold is changed according to the gradation information. Then, when the gradation information corresponding to the minimum level of the reflection state is input, the reflection period (on period) of the liquid crystal element and the light emission period of the light source do not overlap each other when the light source is lit. , The lighting time of the light source is set.

Thus, in this example, the minimum brightness level 1
, The desired intermediate reflection state can be obtained from the range of the maximum brightness level m.

(Example 3) FIG. 14 is a schematic diagram for explaining a method of driving an optical modulation element. 301 is a reflective liquid crystal element in which liquid crystal is arranged between substrates having a pair of electrodes;
4 is a light source driving circuit for driving the light source, C _pc is a capacitance element, R
_pc is a resistance element, Vv is a drive voltage source, and Vs ₀ is a switch for turning on / off the supply of a voltage signal from the drive voltage source Vv. In this system, a supply voltage signal from a drive voltage source is analog gradation information.

The characteristics of the liquid crystal used are as shown in FIG.

FIG. 15 is a timing chart of the driving of FIG. 14, where Vs ₀ indicates the application timing of the gradation signal,
1c indicates the voltage applied to the liquid crystal, Tran indicates the reflectance of the liquid crystal element, 304T indicates the lighting timing of the light source, and 305T indicates the amount of transmitted light recognized by the observer. Reference numeral 1 denotes a case where the voltage value V1 of the gradation signal is low, m denotes a case where the voltage value Vm of the gradation signal is at an intermediate level, and n denotes a case where the voltage value Vn of the gradation signal is high.

First, when Vv is applied to the liquid crystal element at time t _on , the voltage Vlc applied to the liquid crystal becomes voltages V1, Vm, and Vn that sufficiently exceed the threshold. At the same time, the liquid crystal element has a maximum reflectance.

At time t _off , the voltage Vv is released, so that the voltage Vlc applied to the liquid crystal gradually decreases in accordance with the voltage Vv, and falls below the threshold at a certain timing. Since this timing depends on the gradation information, in the case of 1, at time t _X1 ,
In the case of m, the reflectivity Tran of the liquid crystal element transitions to the minimum state at time t _X2 , and in the case of n at time t _X3 .
Here, since the light source is set to start lighting at time t _X1 and turn off at time t _X3 , the reflected light amount corresponding to l, m, and n is as shown in 305T.

As described above, in this example, the timing at which Vlc falls below the threshold is changed according to the gradation information. Then, when the gradation information corresponding to the minimum level of the reflection state is input, the reflection period (on period) of the liquid crystal element and the light emission period of the light source do not overlap each other when the light source is lit. , The lighting time of the light source is set.

Thus, in this example, the minimum brightness level 1
, The desired intermediate reflection state can be obtained from the range of the maximum brightness level m.

(Example 4) FIG. 16 is a schematic diagram for explaining a method of driving an optical modulation element. 401 is a reflective liquid crystal element in which an antiferroelectric chiral smectic liquid crystal is arranged between substrates having a pair of electrodes, 404 is a light source driving circuit for driving a light source, C _pc is a capacitor, R _pc is a resistor, V
v is a drive voltage source Vs ₀ is a switch for turning on / off the supply of the voltage signal from the drive voltage source Vv. In this system, a supply voltage signal from a drive voltage source is analog gradation information. 405 indicates an observer.

The characteristics of the chiral smectic liquid crystal used are as shown in FIG.

FIG. 17 is a timing chart of the driving of FIG. 16, where Vs ₀ indicates the application timing of the gradation signal,
aflc is the voltage applied to the liquid crystal, Tran is the reflectance of the liquid crystal element, 404T is the lighting timing of the light source,
T indicates the transmitted light amount recognized by the observer. Numeral 1 indicates a case where the voltage value of the gradation signal is low, m indicates a case where the voltage value of the gradation signal is at an intermediate level, and n indicates a case where the voltage value of the gradation signal is high.

[0087] First, at time t _on Vv becomes Given to the liquid crystal element voltages V1, Vm voltage Vaflc applied to the liquid crystal exceeds sufficiently the threshold, and Vn. At the same time, the liquid crystal element has a maximum reflectance.

At time t _off , the voltage Vv is released, so that the voltage Vaflc applied to the liquid crystal gradually decreases in accordance with the voltage Vv, and falls below the threshold at a certain timing. Since this timing depends on the gradation information, in the case of 1, the time t _X1
In the case of m, the reflectance Tran of the liquid crystal element transitions to the minimum at time t _X2 , and in the case of n at time t _X3 . Here, since the light source is set to start lighting at time t _X1 and turn off at time t _X3 , the amount of reflected light corresponding to l, m, and n becomes as shown at 405T.

This example is different from the examples shown in FIGS. 14 and 15 in that a voltage Vv whose polarity is inverted from that of the previous period Prd1 is applied in the period Prd2 because the antiferroelectric liquid crystal is used. is there. Since the antiferroelectric liquid crystal is used, the threshold value becomes two of Vth1 and Vth2 due to the hysteresis. Even if the polarity of the voltage Vv is inverted, the alignment state of the liquid crystal is the same as shown in Tran. A chiral smectic liquid crystal has a high transition speed (switching speed) between two molecular alignment states, and is therefore most suitable as a liquid crystal used in the present invention.

As described above, in this example, the timing at which Vaflc falls below the threshold is changed according to the gradation information.
Then, when the gradation information corresponding to the minimum level of the reflection state is input, the reflection period (on period) of the liquid crystal element and the light emission period of the light source do not overlap each other when the light source is lit. , The lighting time of the light source is set.

The present invention employs a configuration in which a large number of optical modulating elements are two-dimensionally arranged for the optical modulating means, that is, the optical shutter and the light reflecting means in each of the above-described examples.

Specifically, it is a panel in which many pixels are arranged in a matrix or a DMD in which many micromirrors are arranged in a matrix.

Next, a driving method of the image display device according to the present invention will be described.

(Reference Example) FIG. 18 is a sectional view of an optical modulation element for an image display device according to a reference example of the present invention.

FIG. 19 is a diagram showing the molecular orientation of the chiral smectic liquid crystal used in the device.

FIG. 20 is a diagram showing the electro-optical characteristics of the liquid crystal molecules.

FIG. 21 is a timing chart showing the operation.

The device shown in FIG. 18 is a so-called reflection type liquid crystal panel, in which a transparent electrode 512 is formed on a transparent substrate 511, a photoconductive layer 513 as a photosensitive layer is provided thereon, and a reflection layer is provided thereon. A dielectric multilayer film 514 is provided as a layer. On the other transparent substrate 516, the transparent electrode 5
15 are provided. A chiral smectic liquid crystal 517 as an optical modulator is disposed between these two substrates. 522 is a polarizing element. Although not shown, an alignment film for aligning liquid crystal molecules is provided at a liquid crystal interface between the electrode 515 and the reflective layer 514. Vext is a voltage applying means for applying a voltage to the electrodes 512 and 515;
21 is a reset light, 518 is a write light containing gradation information, and 519 is read light for reading out modulated gradation information, that is, an image.

The equivalent circuit of this element is the same as that of FIG.

FIG. 19A shows a state where the liquid crystal molecules MOL are in the first alignment state, and FIG. 19B shows a state where the liquid crystal molecules MOL are in the second alignment state. When a voltage + Vu is applied to the liquid crystal in the first alignment state A, the liquid crystal transitions to the second alignment state. Thereafter, the liquid crystal remains in state B even when the voltage is set to 0, that is, when there is no electric field. Next, when a voltage -Vu is applied, the liquid crystal transits to state A and maintains state A even when the electric field is released. Such a transition is called liquid crystal inversion or switching.

Since these states A and B are optically different states, when appropriately combined with a polarizing element, one state is a state where the light transmittance is maximum and the other state is a state where the light transmittance is minimum. be able to. Here, Vu is set assuming that the saturation value of the applied voltage is substantially the same as the inversion threshold value of the liquid crystal.

The operation of this device will be described. To illustrate the nature of the operation, the capacitance C _pc equal volume capacity Cflc and the photoconductive layer of the liquid crystal layer, the resistance component of the liquid crystal layer is infinite, the impedance of the reflective layer to 0. 5 in FIG.
21T is the reset light applied to the photoconductive layer 513;
Reference numeral 18T indicates the irradiation timing of the writing light, which is applied to the photoconductive layer 513 and whose intensity changes according to the gradation information. Ve
xt indicates an AC voltage applied between the transparent electrodes 512 and 515 at both ends of the element, and Vflc indicates an effective voltage applied to both ends of the liquid crystal layer 517. + Vu and -Vu are voltages at which the liquid crystal is inverted from the first to the second or from the second to the first alignment state as shown in FIG. Tran indicates the orientation state of FLC, and here, it is composed of a polarizer analyzer so that the first orientation state is a dark state having a minimum transmittance and the second orientation state is a bright state having a maximum transmittance. It is assumed that the positional relationship between the polarizing elements has been set. 504T is the liquid crystal layer 51
Numeral 505T of the read irradiation light irradiating the light 7 is extracted light reflected and extracted by the reflection layer via the liquid crystal, the polarizer, and the analyzer.

First, a reset period is from t50 to t51. Potential -V ₁ is applied as Vext, the reset light is irradiated to the photoconductive layer. By reset light,
Photocarriers (electron-hole pairs) are generated in the photoconductive layer, and the electron-holes are separated by the electric field applied to the photoconductive layer, travel in the opposite direction, and face each other with the liquid crystal layer 517 therebetween. Become. Vflc approaches the potential -V ₁ by this behavior. In the equivalent circuit of FIG. 6, the resistance component in the photoconductive layer is reduced due to the photoconductive effect, self-discharge occurs, and the potential applied to the photoconductive layer by the divided voltage is reduced.
flc may be considered as approaches to -V _1. When the reset light has a sufficient light intensity, regardless of the previous state, V flc by the time of t ₅₁ is reset to -V _1, also the liquid crystal is first orientation state (dark) is ensured. t
Off the reset light at _51, the Vext to + V _2. At this time, the potential of Vflc is changed to V ₃ by the capacitance division of 1: 1.
= −V ₁ + (V ₂ − (− V ₁ )) / 2.
If irradiated with writing light as in the first cycle, V flc until t ₅₂ remains V _3, the liquid crystal which is still the first orientation state (dark) because it is V ₃ <Vu. t ₅₂ after the time period by inverting the polarity of Vext, again do the same thing from t ₅₀ to t _52. Thereby, Vflc becomes 0 when integrated within one cycle, that is, the DC component becomes 0, and the stable FLC
The AC symmetry of the driving waveform required for driving is guaranteed. Vflc between from t ₅₂ t ₅₃ is past the Vu + V ₁
And the liquid crystal is in the second alignment state (bright).

In the second cycle, the writing light is irradiated. The write light is not as strong as the reset light, so the time constant is slower, but Vflc approaches Vext. If the writing light intensity is high to some extent, t ₅₁ to t ₅₂
At time T = t _X1 , Vflc exceeds Vu, and at this time, the liquid crystal is inverted from the first alignment state to the second alignment state (bright). When the write light is further intensified as in the third cycle, t _X1 approaches t ₅₁ , and the second
It turns into an alignment state. T _{53 in} both the second and third cycles
Since during t ₅₄ illuminates the same writing light and when irradiated between t ₅₂ from t ₅₁ from, V flc to t _X2 is below -Vu, liquid is returned to the first orientation state (dark). 1st, 2nd
In each of the third periods, the AC symmetry of Vflc is ensured, and the liquid crystal is in the first alignment state and the second alignment state for 50% of the time in each period. As the writing light intensity increases, the phase of the FLC in the second alignment state shifts forward. Against these liquid crystal operation, the observer when irradiated with reading light in a period of t ₅₂ from t ₅₁ in each cycle, to observe the overlapping light by the time the second orientation state of the irradiation time and FLC of the readout light (bright) Will be. Although light cannot be extracted in the first cycle, as the writing light intensity increases, the overlapping time increases as in the second and third cycles, and the number of extracted light fluxes also increases. If each cycle is a time equal to or shorter than the flicker frequency of the human eye (for example, 1/60 second), it will be observed by the observer's eyes as a change in light intensity.

[0105] Also, rather than between _{t 51 ~t 52, t 53 ~t} 54
If the reading light is irradiated during the period, as the writing light intensity is increased, the overlapping time is reduced, and the number of extracted light beams is reduced. That is, negative-positive conversion can be performed between the writing light and the extracted light. Since the writing light has a secondary planar spread, an in-plane potential distribution can be created by the writing light intensity, and a so-called optical writing type spatial light modulator capable of two-dimensional optical writing and reading can be constructed. it can. Using this, a monochrome film viewer can be configured.

FIG. 22 is a system configuration diagram of a full-color film viewer as an image display device using the optical writing type spatial light modulator according to the present invention.

For the light source on the writing side, light-emitting diodes (LEDs) of three colors of R, G and B are prepared for each color.

Reference numeral 530R denotes an R writing light source LED, 5
30G is a G light source LED, 530B is a B light source LED, 535 is a reset light source, 53 is a three-color mixing prism having an R reflection surface and a B reflection surface. 536 is a light modulation element, 532 and 534 are lenses, 5
33 is a film and 537 is a prism. 539R is an LED for reading light of R, 539G is an LED for reading light of G, 539B is an LED for reading light of B, 5
Reference numeral 38 denotes a three-color mixing prism having an R reflection surface and a B reflection surface.

FIG. 23 is a timing chart showing the operation.

Each of the above-mentioned periods is defined as 1 / (flicker frequency ×
3) = Set to about 5 ms or less, and set the writing light source to RGB1
The lights are turned on sequentially in cycles. RGB LEDs are also prepared for the light source on the reading side, and the same color as the writing side is sequentially turned on. The film 533 has video information, and here, gradation information having a transmittance of 0% for R, 50% for G, and 100% for B is included.

During the three cycles, the eyes are added and mixed, so that they are seen in full color.

As described above, the film 533 can be used for either a positive film or a negative film simply by switching the lighting liming of the reading light source.

If a transmissive liquid crystal TV with a color filter is arranged in place of the film 533, and a brighter halogen lamp + color rotating filter is used as a reading light source,
It can be a video projector.

In the case of monochromatic writing, the monochrome OH
In the case where the amount of light to be written in a specific pixel area does not change, such as when forming P, the reset light is not always necessary.

In the case where the reset light is used, it is sufficient that the intensity is higher than a certain level. Therefore, there is no problem even if writing is superimposed during the reset period.

Referring to FIGS. 24 and 25, another example of the optical writing type film viewer will be described.

The optical system configuration of the image display device is shown in FIG.
2 is the same as that shown in FIG.
8, the description is omitted.

FIG. 24 is a timing chart showing a method of driving an image display device using the optical modulation device according to this embodiment.

[0119] The basic operation is the same as the embodiment shown in FIG. 21, is different from the write beam during a period of t ₆₁ ~t ₆₂ and t ₆₄ ~t ₆₅ of each period as shown in 518T Irradiation only and leave it off for the rest of the time. The light irradiated during the period t _{64 to} t ₆₅ is the voltage A applied to the liquid crystal.
This is for ensuring C symmetry. And t ₆₂ ~
The period t ₆₃ to irradiate a uniform bias light (550
If T) write light including gradation information is zero as in the first period, the voltage applied to the liquid crystal is constant during the t ₆₁ ~t ₆₂ at -V _6. If then the bias light is irradiated to the t ₆₂ time the voltage applied to the liquid crystal by reducing the resistance of the photoconductive layer becomes larger in the positive direction. Here, when the writing light has the minimum value, the value of R _pc or C _pc and the timing of time t ₃ are set so as not to exceed the threshold value (+ Vu) of the liquid crystal even at time t _63. To match.

Therefore, in the first cycle, the write light is minimum, ie, 0, and the read light is also minimum, ie, 0 (50).
5T).

The period from t _{63 to} t _{0 in the} next cycle is an inversion operation. Therefore, during this period, there is no irradiation for reading out, and no image information is reproduced.

[0122] Since the second periodic writing light is an intermediate level, t ₆₁ ~t reduces the resistance of the photoconductive layer during the _62, a high voltage in the positive direction according than -V ₆ in the liquid crystal.

[0123] When the bias light in a period t ₆₂ ~t ₆₃ is illuminated, in the second period different from the first period, since the initial value of the voltage applied to the liquid crystal at time t ₆₂ is higher than -V _6, reading light Vflc in the middle of the time t _x1 of the periods being irradiated (t ₆₁ -t ₆₃₎ exceeds the threshold + Vu. Therefore T _x1
During the period from t to t ₆₃ , the liquid crystal is in the second alignment state (bright) (T
ran). Then, a period (t _x1 -t ₆₃ ) during which the reading light can be extracted is modulated according to the writing light amount.
t ₆₃ and later is the inversion operation.

In the third period, the writing light is at a maximum.
(518T). Therefore, the period during which the bias light is irradiated
(T₆₂~ T₆₃) First time t₆₂The voltage V applied to the liquid crystal
flc exceeds the threshold value + Vu. Therefore, the reading light
The entire period of irradiation (t₆₂-T ₆₃), The liquid crystal is in the second alignment
State (bright). So it can be taken out of the device
The time integration of the read light amount becomes maximum.

As described above, the time during which the reading light is extracted is determined according to the amount of the writing light.
If the writing light quantity changes in an analog manner, the read time also changes in an analog manner.

The period t _{63 to} t ₆₀ is an inversion operation. In this period, the polarity of the applied voltage Vext is inverted, and the same amount of write light bias light is applied again. This allows
Since the time integral per one cycle of the effective voltage applied to the liquid crystal is 0, deterioration of the liquid crystal can be suppressed.

In this example, the amount of the bias light is appropriately determined in consideration of the time constant of the photoconductive layer and the length of the period t ₆ -t ₆₃ . The light source of the bias light may be the same as or different from the light source of the reset light. Preferably, both the light source of the bias light and the light source of the reset light have dimming means, respectively, so that the light amount can be set independently.

In this example, one cycle is 1/30.
Second, good halftone without being seen flicker When you set up t ₆₀ ~t ₆₃ to about 1 second of 60 minutes can be displayed.

FIG. 25 is a timing chart showing a driving method of an image display device using an optical modulation element according to still another example.

The basic operation is the same as the example shown in FIG. The difference is that instead of irradiating bias light,
The voltage Vext applied to the element is changed with time (t ₇₂ −t
₇₃ ) It is in operation.

During a period t ₇₀ -t ₇₁ , reset light is irradiated (721T). At this time, Vext is 0.

[0132] While the Vext at time t ₇₁ to the liquid crystal threshold voltage + Vu, the writing light to the photoconductive layer minimum (0)
Therefore, the voltage Vflc applied to the liquid crystal becomes + Vuu. If the capacity of the photoconductive layer is the same as the capacity of the liquid crystal, + Vuu is の of + Vu.

At time t ₇₂ , the write light is set to 0,
The voltage Vext applied to the element is gradually increased from + Vu to + Vem.
Up with time. In response, the voltage Vflc applied to the liquid crystal also increases with Vext.

Here, if + Vem is set to twice the value of + Vu, Vflc exceeds threshold value + Vu at time t.
It becomes ₇₃ . Having thus the period t ₇₂ -t ₇₃ in the read light is on (704t), a liquid crystal for the liquid crystal alignment state is not a transition is not a alignment state exhibiting a maximum transmittance.

The inverting operation is performed during the remaining period from t ₇₃ to t ₇₀ . During this operation, there is no irradiation of the reading light, so that no image reproduction is performed.

The second cycle shows a case where irradiation of the intermediate level writing light (718T) is performed. Liquid crystal at time t ₇₀ is in the non-light-transmissive state by the reverse operation.
With Vext = 0, Vflc approaches voltage level 0.

[0137] At time t _71, Vext is the threshold + Vu
And the readout light starts to be turned on (704T). Ve
Although xfl increases Vflc, the threshold voltage + Vu
Does not reach.

[0138] At the time t _72, Vext begins to rise. Accordingly, Vflc also rises, so that Vflc exceeds threshold value + Vu at time t _x1 . Thus, the liquid crystal transitions to the alignment state exhibiting the maximum transmittance. Therefore, at this time _t72 , the lit readout light is reflected by the reflection layer through the liquid crystal layer, so that the image can be recognized. Then, the reflection time t _x1 -t _{73 of the} read light is modulated according to the write light amount. t ₇₃ and later is the inversion operation.

The third cycle shows the case where the light amount of the writing light is maximum. operation in the period of t ₇₀ -t ₇₁ is the same for each cycle.

[0140] By writing amount of light applied at time t _71, the time t ₇₂ V flc exceeds the threshold + Vu. Therefore, during the lighting period t ₇₂ -t _{73 of the} reading light, the liquid crystal transitions to the alignment state exhibiting the maximum transmittance. Therefore, the time during which the reading light is reflected by the element is maximum (705).
T).

As described above, since the time for which the reading light is reflected is determined according to the amount of the writing light, if the writing light amount changes in an analog manner, the reflection time also changes in an analogous manner.

The period t _{73 to} t ₇₀ is an inversion operation. In this period, the polarity of the applied voltage Vext is inverted, and the same amount of writing light bias light is applied again. This allows
Since the time integral per one cycle of the effective voltage applied to the liquid crystal is 0, deterioration of the liquid crystal can be suppressed.

In the present embodiment, the time change rate of Vext is appropriately determined in consideration of the time constant of the photoconductive layer, the length of the period t ₇₁ -t _{73 and} the like.

[0144] In the present embodiment, it can be displayed 1/30 second one cycle, a good halftone not observed flicker Setting up t ₆₀ ~t ₆₃ to about 1 second 60 minutes.

[0145]

Next, a first embodiment of the present invention will be described. FIG.
In the reference example described with reference to 2, the two-dimensional image having the gradation information of the film or the like is written in the photoconductive layer of the liquid crystal element as the optical modulation element by one-time writing light irradiation. By vertically and horizontally scanning a two-dimensional image, a two-dimensional image is written in a liquid crystal element in time series. And
In order to read out the gradation information, the reading light is similarly scanned at an appropriate timing.

FIG. 26 is a view for explaining the scanning method. Reference numeral 801 denotes a reflection type liquid crystal element having a chiral smectic liquid crystal and a photoconductive layer, as shown in FIG. The writing light 802 scans from the top to the bottom of the figure in a non-interlaced manner in the same manner as in normal CRT drawing. That is, the operation of irradiating the photoconductive layer of the element with light by the writing light is performed in time series. On the other hand, the reading light 803
Is applied to the liquid crystal portion corresponding to the position of the photoconductive layer in which the information is written, and this is also considered as a predetermined period in order to reproduce the gradation information. Therefore, the operation of irradiating the element with the reading light is also performed in time series. The scanning timing of the writing light 802 and the reading light 803 is such that the scanning of the reading light is performed after the scanning of the writing light is performed.

FIG. 29 is a timing chart for explaining the operation of the embodiment more specifically. In the example of FIG. 21, three periods are illustrated, but in FIG. 29, only one period is illustrated.

A reset light 821 is similar to the reset light 521 in FIG.

818T1, 820-1, Tran1, 5
04T1 indicates the operation of the first pixel to which the writing light 802 is first written in a non-interlace manner.

Reference numeral 818T1 denotes the timing of the writing light applied to the first pixel. At time t ₈₁₁ the writing light 80
When 2 is irradiated, an electron-hole pair having a charge amount ΔQ is generated in proportion to the writing light intensity, and a potential change of ΔV = ΔQ / C occurs. When a stronger writing light intensity is given, Vflc exceeds Vu earlier, and the FLC undergoes an orientation change, turning from dark to bright. That is, the writing light intensity-FLC phase conversion is performed.

In FIG. 29, the case where the writing light is applied with the maximum intensity to extract the maximum light amount, the case where the writing light is applied with the offset light intensity of a certain value for displaying black, and the intermediate light amount between the two. For three cases where writing light was given at the maximum intensity between the two to take out,
Illustrated.

When writing light is given at the maximum intensity, FL
The time at which C changes to the second alignment state (bright) is t _X111 , and the time at which FLC changes to the second alignment state (bright) when a minimum write light is given at a certain offset light intensity is t _X113.
In this case, the change in the alignment state of the FLC is as shown in Tran1.

Reference numeral 504T1 denotes the timing of the readout light applied to the first pixel. When the first pixel is irradiated with the readout light during the period from _tX111 to _tX113, the observer observes the light for the overlap time of the irradiation time of the readout light and the second alignment state (bright) of the FLC. If writing and reading to and from the first pixel are repeated at a time equal to or lower than the flicker frequency, the light will be observed as a change in the light intensity of the first pixel to the observer's eyes.

Similarly, 818Tn, 820n, Tran
n and 504Tn indicate the operation of the n-th pixel at the position substantially at the center of the screen where the writing light 802 is written in a non-interlaced manner.

The 818TN, 820N, Tran
N and 504TN indicate the operation of the N-th pixel to which the writing light 802 is written last in a non-interlace manner.

The operation of each pixel is the same as that of the first pixel, except that
The pixel is written at time t _81n and the N-th pixel is written at time t _81N .

FIG. 27 is a diagram showing the configuration of the image display system of this embodiment. Reference numeral 810 denotes a CR as a writing light source.
T, 811 is an imaging lens, 812 is a reset light source, 81
3 is a mirror, 814 is a polarization beam splitter, 815
Denotes a movable mirror, 816 denotes a filter for cutting infrared light or ultraviolet light, 817 denotes a reading light source, 818 denotes an illumination lens, and 819 denotes an image reproduction screen.

After irradiation with the reset light, the writing light 8
02 is performed. Since a voltage is applied to the element 801, the effective voltage applied to the liquid crystal changes with time according to the amount of light due to light absorption in the photoconductive layer. The time during which the light can be reflected changes according to the gradation information. The reading light 803 is scanned in accordance with this timing.
Scanning is performed by movement of the movable mirror 815. That is, when the movable mirror 815 moves in the direction of the arrow AA, the element 80
The readout light 803 applied to 1 also moves in the direction of the arrow AA. Thus, the band-shaped readout light is vertically scanned.
Since the horizontal scanning time of the reading light 803 is set to 1/60 second or less, halftone can be recognized. The scanning between the movable mirror 815 and the CRT 810 is synchronized by a control circuit (not shown).

The second embodiment is an example in which the first embodiment described above is changed to support full color. As shown in FIG. 28, three write means and three liquid crystal elements are provided for each of R, G, and B.
00R, 800G, and 800B.

By synchronizing the writing light scanning timing for the three colors, full-color display can be performed by additive color mixing. Since this display device is suitable for displaying full-color moving images, it is suitable as a large-screen television. In this embodiment, the writing is described in the non-interlaced manner using the spot light similar to the CRT. However, it is needless to say that the writing may be performed in a line sequential manner such as a line LED.

[0161]

According to the present invention, good gradation display can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram of a basic driving device of an optical modulation element according to the present invention.

FIG. 2 is a diagram showing the dependence of the transmittance of an optical modulation substance used in the present invention on the applied voltage (pulse width).

FIG. 3 is a timing chart for explaining another example of the basic driving method of the optical modulation element of the present invention.

FIG. 4 is a diagram showing an example of a circuit for generating gradation information used in the present invention.

FIG. 5 is a diagram of another driving device of the optical modulation element of the present invention.

FIG. 6 is a diagram illustrating an example of a drive circuit of an optical modulation element used in the present invention.

FIG. 7 is a diagram showing another example of a drive circuit of the optical modulation element used in the present invention.

FIG. 8 is a diagram showing still another example of the drive circuit of the optical modulation element used in the present invention.

FIG. 9 is a diagram showing the applied voltage dependence of the transmittance of the optical modulator used in the present invention.

FIG. 10 is a diagram showing an optical modulation element.

FIG. 11 is a diagram showing a drive timing chart of the optical modulation element.

FIG. 12 is a diagram showing an optical modulation element.

FIG. 13 is a diagram showing a drive timing chart of the optical modulation element.

FIG. 14 is a diagram showing an optical modulation element.

FIG. 15 is a diagram showing a drive timing chart of the optical modulation element.

FIG. 16 is a diagram showing an optical modulation element.

FIG. 17 is a diagram showing a drive timing chart of the optical modulation element.

FIG. 18 is a sectional view of an optical modulation element for an image display device used in the present invention.

19 is a diagram showing the molecular orientation of a chiral smectic liquid crystal used in the device of FIG.

20 is a diagram showing the electro-optical characteristics of the liquid crystal molecules of FIG.

FIG. 21 is a timing chart showing the operation of the device of FIG.

FIG. 22 is a diagram illustrating an image display device used in a reference example of the present invention.

FIG. 23 is an operation timing chart of the image display device according to the reference example of the present invention.

FIG. 24 is an operation timing chart of the image display device according to the reference example of the present invention.

FIG. 25 is an operation timing chart of the image display device according to the reference example of the present invention.

FIG. 26 is a diagram for explaining scanning of writing light and reading light according to the embodiment of the present invention.

FIG. 27 is a diagram showing an example of a display device according to the present invention.

FIG. 28 is a diagram showing another example of the display device according to the present invention.

FIG. 29 is an operation timing chart of the display device according to the embodiment of the present invention.

Claims (2)

(57) [Claims] 1. An optical modulation element in which a photoconductive layer and a layer of an optical modulation material are arranged between a pair of electrodes to which a voltage is applied, and a signal light source that supplies optical information including gradation information to the photoconductive layer. A read light source for providing read light for reading image information to the layer of the optical modulation material, wherein the optical information is provided to the photoconductive layer by scanning the optical information and the read light is scanned. The light modulation time is given to the layer of the optical modulation material, and the lighting time of the readout light source is controlled, and the overlap time between the time when the optical modulation material exhibits a predetermined optical state and the lighting time is determined according to the gradation information. A method for driving a display device, comprising: 2. The method of driving a display device according to claim 1, wherein after one horizontal scan of the optical information, scanning of the corresponding portion is performed by the readout light.