JPH07122707B2 - Driving method of optical modulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical modulation element for a display device, and more particularly to an optical modulation element that performs halftone display using an inversion region partially formed in a pixel. The present invention relates to a driving method of an element.

[Prior Art] A liquid crystal display device using a twisted nematic (TN) liquid crystal is known that uses a display panel of a passive matrix drive system and an active matrix drive system.

In an active matrix drive type liquid crystal television panel, thin film transistors (TFTs) are arranged in a matrix for each pixel, and a gate-on pulse is applied to the TFT to establish a conduction state between the source and drain. At this time, a video image signal is applied from the source. Then, the TN liquid crystal is stored in the capacitor, and the TN liquid crystal is driven in response to the stored image signal, and at the same time, the voltage of the video signal is modulated to perform gray scale display.

Such a gradation display method is called luminance gradation,
The halftone display in this case controls the light transmittance of the entire pixel.

[Technical problem to be solved by the invention] However, in such an active matrix drive type television panel using a TN liquid crystal, since the light transmittance completely depends on the applied electric field, a halftone state occurs when the applied electric field changes. Will also fluctuate.

Moreover, since the viewing angle is narrow, the appearance of the halftone state changes depending on the viewing position.

Alternatively, in a passive matrix drive type display panel that can be manufactured at low manufacturing cost, an effective electric field is applied to one selection point while scanning one screen (one frame) as the number of scanning lines (N) increases. The time (duty ratio) is reduced at a rate of 1 / N, which causes crosstalk. Moreover, in addition to having a technical problem to be solved in that a high-contrast image is not obtained, it becomes difficult to control the gradation of each pixel by voltage modulation when the duty ratio becomes low. In particular, it was not optimal for a liquid crystal television panel.

[Means for Solving the Problems] An object of the present invention is to solve the above-mentioned problems, and more specifically, it is suitable for easily producing a display panel having high-density pixels over a wide area and for displaying gray scales. Another object of the present invention is to provide a method for driving an optical modulator.

That is, according to the present invention, a large number of first transmission lines are arranged with a predetermined gap and a conductive film having a resistance higher than that of the first transmission line is provided in each of the gaps of the first transmission line, and a second transmission line. A second substrate in which a plurality of lines are arranged in a predetermined gap so as to intersect the first transmission line, and a conductive film having a resistance higher than that of the second transmission line is provided in the gap between the second transmission lines; A method of driving an optical modulation element having a large number of pixels, the optical modulation material being disposed between a first substrate and a second substrate, wherein one of three first transmission lines is provided with grayscale information. The reference voltage is applied to two lines on both sides of the one first transmission line, and at the same time, one of the three second transmission lines is supplied with a voltage corresponding to the gradation information. By applying a reference voltage to the two lines on both sides of the transmission line, A pixel defined by the three first transmission lines and the three second transmission lines is formed by maximizing the applied electric field strength at the intersection of the first and second transmission lines to which a voltage according to A method of driving an optical modulation element, which comprises a driving step of causing a potential difference gradient between opposing portions of the conductive film to determine an optical state of the pixel, and performing the driving step dot-sequentially for each pixel. It is provided.

[Operation] According to the present invention, the maximum applied electric field strength is applied to the intersection of the first transmission line and the second transmission line, and the conductivity forming the pixel defined by the first transmission line and the second transmission line is set. By generating a potential difference gradient between the facing portions of the film, it is possible to control the middle of the inversion region of the optical modulation substance and perform gradation display using the potential difference gradient. Thereby, the growth of the reversal region is made uniform in the vertical and horizontal directions, and a high-density and high-quality image can be displayed by the potential difference gradient method.

EXAMPLES Examples of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of the optical modulator used in the present invention. In FIG. 1, reference numeral 1 is one substrate and 2 is a display conductive film laminated on the substrate 1. Reference numeral 3 denotes a transmission electrode made of a low resistance metal film, which is laminated on the display conductive film 2 in parallel at equal intervals. Another substrate 4 is opposed to the substrate 1, a counter conductive film 5 is laminated on the counter substrate 4, and another transfer electrode 6 is formed on the counter conductive film 5. It is made of the same material as, and is arranged in parallel stripes at equal intervals. A pixel area A is formed at the intersection of the two transfer electrodes. The optical modulation substance is sandwiched between the display conductive film 2 and the counter conductive film 5.

In the liquid crystal optical element configured as described above, the transmission electrode 3
By applying a potential gradient in the surface of the display conductive film 2 by the signal voltage applied to the counter electrode 6, a potential difference gradient is generated in the electric field between the counter electrode 6. At this time, the transmission electrode 3a and
When 3c is connected to a reference potential point V _E (for example, 0 volt) and a predetermined signal voltage V _a is applied to another transmission electrode 3b, as shown in FIG. 2 (a), between the transmission electrodes 3a and 3b, A potential gradient of V _a can be applied to the in-plane length directions L ₁ and L ₂ of the conductive film 2 between 3b and 3c. Similarly, with respect to the transfer electrode 6 provided on the counter substrate 4, a potential difference is applied to the electric field between the transfer electrode 6 and the transfer electrode 3 by applying a potential gradient in the plane of the counter conductive film 5 by the applied signal voltage. Create a gradient. At this time, when the transmission electrodes 6a and 6c are connected to a reference point V _E (for example, 0 volt) and _a signal voltage V _b having the same potential as V _a is applied to the transmission electrode 6b, it is shown in FIG. 2 (b). it is possible to impart a potential gradient of V _b to the electrical transmission electrode 6a and 6b or 6b and the length direction L ₁ and L ₂ in the plane of the conductive film 5 between 6c as. At this time, if both of the voltages V _a and V _{b have} a potential higher than half of the inversion threshold voltage V _th of the ferroelectric liquid crystal, the signal voltage applied to the ferroelectric liquid crystal becomes the second voltage. As shown in FIG. 7C, V _a and V _b are applied as potentials having different polarities, and the absolute value of the voltage is V _a + V _b , which is applied to the liquid crystal. At this time, V _a + V _b
When the potential of V is _{equal to} or higher than V _th , the conductive film 2 and the counter conductive film 5 are
The potential difference V _a ′ + V _b ′ of the inversion threshold voltage V _th or more is applied to the ferroelectric liquid crystal corresponding to the longitudinal directions M ₁ and M ₂ and m ₁ and m ₂ in the plane of _The regions corresponding to ₁ , M ₂ and m ₁ , m ₂ can be inverted from the bright state to the dark state, for example. Therefore, in the present invention, it is possible to express the gradation by applying the same voltage to V _a and V _b with _a value corresponding to the gradation for each pixel. At this time, the voltage values of the voltage signals V _a and V _b applied to the transmission electrode 3 and the counter electrode 6 may be modulated according to the gradation information, or their pulse widths may be modulated according to the gradation information. Alternatively, the gradation can be controlled by modulating the pulse number.

Further, prior to applying the gradation signal, after performing an erasing step for setting the pixel to either the bright state or the dark state, the inversion voltage for inverting the state is controlled according to the gradation, It is necessary to be applied to the ferroelectric liquid crystal.

Furthermore, preferred specific examples of the present invention will be described.

A transparent conductive film of SnO ₂ film having a thickness of about 200Å was formed on the glass substrate 1 in FIG. The sheet resistance of this SnO ₂ film is
It was 10 ⁵ Ω / mouth. Next, by vacuum-depositing Al with a thickness of 1000 Å on the SnO ₂ film and patterning again,
As shown in the figure, a plurality of transfer electrodes 3 were formed. In this embodiment,
The distance between the transmission electrodes 3 was 230 μm. The sheet resistance of this transmission electrode 3 is about 0.4 Ω / port, and its width is about 20 μ. On the other hand, with respect to the counter substrate 4, the counter conductive film 5 and the counter electrode 6 are formed using the same method and material as described above.
Both substrates are provided with exactly the same configuration, and the transmission electrode 3 of the substrate 1 and the counter electrode 6 of the counter substrate 4 are arranged so as to cross each other and face each other.

A polyvinyl alcohol layer having a thickness of about 500 Å was formed as a liquid crystal alignment film on each surface of the two substrates thus prepared, and subjected to rubbing treatment.

Next, adjust the gap between the two substrates to be about 1μ,
Ferroelectric liquid crystal (p-η-octyloxybenzoic acid-p '
-(2-methylbutyloxy) phenyl ester and p-
Liquid crystal composition containing η-nonyloxybenzoic acid-p ′-(2-methylbutyloxy) phenyl ester as a main component)
Was injected. The shape of the partial pixel A in which the transmission electrode 3 and the counter electrode 6 overlap was 230 μ × 230 μ, and the electrostatic capacity after the liquid crystal injection was about 3 PF. However, the width of the pixel _{A L 1/2 + L 2} /2
And Then, polarizing plates were arranged in crossed Nicols on both sides of the liquid crystal cell thus formed, and the optical characteristics were observed.

FIG. 3 is a cross-sectional view taken along the line aa ′ in FIG. 1, and is a diagram schematically showing a method of applying an electric signal, in which the conductive film 2 for display is formed on the substrate 1, and The transfer electrode 3 is arranged on the counter electrode 4, the counter conductive film 5 is formed on the counter substrate 4, and the counter electrode 6 is arranged on the counter conductive film 5 so as to intersect with the transfer electrode 3. The liquid crystal 31 is included. The counter electrode 6 is connected to the first drive circuit 32, and the transmission electrode 3 is connected to the second drive circuit 33.
FIG. 4 shows the signal (a) generated by the drive circuit 32 of FIG.
5 shows the waveform of the signal (b) generated in the drive circuit 33 of FIG.

Now, as the signal (a), the counter electrodes 6a, 6b, 6c, etc. are given −12
V, 200μsec pulse, transmission electrode 3,3 as signal (b)
When an erasing step for applying an 8V, 200 μsec pulse to a, 3b 3c in advance (referred to as an erasing pulse) is provided, the liquid crystal is switched to the first stable state and, for example, pixel A
The whole is in a bright state (the cross polarizing plate is arranged in this way). The liquid crystal inversion threshold used here is ± 15 to ± 16V for convenience of explanation. From this state, FIG.
Signal various pulses as shown in (e) (b)
Is applied to the counter electrode 6b. At this time, the counter electrodes 6a and 6c adjacent to the applied counter electrode 6b are connected to the reference potential point V
Connected to _E (eg 0 Volts). In addition, the transmitting electrode 3b is synchronized with various pulses of FIG. 4 applied to the counter electrode 6b.
Various pulses shown in FIGS. 5 (a) to 5 (e) are applied as the signal (b). Also at this time, the transfer electrodes 3a and 3c adjacent to the applied transfer electrode 3b have the reference potential point V
Connected to _E (eg 0 Volts). The optical state of the pixel A in such a state is shown in FIG.

Corresponds to the -2V as V _b potential corresponding the pulse voltage applied to the 4 (a), FIG. 5 as a voltage applied to the electrical transmission electrode 3b opposed to correspond with the potential of the V _b (a) The potential of V _a is +2 V, and similarly, −5 V corresponding to FIG.
At + 5V, which corresponds to FIG. 7B, no change occurs from the bright state 61 because the inversion threshold voltage of the liquid crystal is not exceeded. However, at −8 V corresponding to FIG. 4 (c) and +8 V corresponding to FIG. 5 (c), the liquid crystal near the intersection point where the transmission electrode 3b and the counter electrode 6b are orthogonal to each other is in the dark state 62. Is switched to.

Further, when the applied voltage is set to −14V shown in FIG. 4 (d) and + 14V corresponding to FIG. 5 (d), the area of the dark state 62 becomes wider as shown in FIG. 6 (c). , The applied voltage is -20V shown in Fig. 4 (e) and + 20V corresponding to Fig. 5 (e).
Then, as shown in FIG. 6D, the entire screen A is switched to the dark state 62. In this way, by applying a voltage corresponding to the gradation signal to the transmission electrode and the counter electrode as the same voltage, it is possible to form an image having gradation.

In the gradation display method for a ferroelectric liquid crystal element according to the present invention, a voltage corresponding to a gradation signal is applied to the transmission electrode and its counter electrode, and switching is started from an intersection point where the respective electrodes are orthogonal to each other. Therefore, the change of the liquid crystal switching region in one pixel is seen as a change of the liquid crystal from light to dark in a regular quadrilateral shape from the intersection of the electrodes, as shown in FIGS. 6 (a) to 6 (d). . Such a change in the orientation of the liquid crystal has the same effect as the gradation display method by halftone dot printing which is generally used for photographic display of newspapers, etc. when displaying an image with gradation. Is. Therefore, for example, as in the conventional driving method shown in FIG. 7, a conductive film made of, for example, an ITO film is formed in stripes as the counter electrode 6 on the counter substrate 4 (not shown) with respect to the substrate 1,
An arbitrary constant voltage is applied as a scanning voltage to the counter electrode 6, and a voltage corresponding to the grayscale signal is applied to the opposing transfer electrode 3b as shown in FIGS. 4 (a) to 4 (e) or 5 (a).
When gray scale display is performed by applying the voltage shown in (e), the change state of the liquid crystal region for switching from bright to dark by driving these is shown in FIGS. 8 (a) to (d). Thus, it can be seen that the dark state 82 changes in the rectangular orientation from the vicinity of the transmission electrode 3b. When an image display having gradation is formed by changing the alignment of these liquid crystals, the alignment state in one pixel is rectangular along the transfer electrode.
When viewed as the entire image, the image has many frequency components in the longitudinal direction of the liquid crystal alignment within one pixel, that is, in the L direction in FIG. Therefore, for example, when performing liquid crystal display in which high density and high image quality are desired, the conventional driving method is not optimal, and the present invention is different from these conventional driving methods in high-speed writing in gradation display. The image quality can be improved, and high density and high image quality can be supported similarly to the effect of improving the image quality by halftone printing.

The liquid crystal 31 of this embodiment shown in FIG. 3 is a ferroelectric liquid crystal, more preferably a chiral smectic liquid crystal in a bistable state.

In addition to aluminum (Al), metals such as gold, silver, copper, and chromium can be used for the transfer electrode 3 and the counter electrode 6, and the sheet resistance thereof is preferably 10 ² Ω /
Be below mouth. Furthermore, the conductive film 2 to which a potential gradient is applied
As the counter conductive film 5, a transparent conductive film having a sheet resistance of 10 KΩ / port to 1 MΩ / port can be used.

FIG. 9 is a configuration diagram specifically showing an example of a gray scale display driving method according to the present invention. In the figure, 91 is a liquid crystal display panel using an optical modulator, 92 is an information side driving circuit, and 93 is a scanning side. Drive circuits, I ₁ , I ₂ , I ₃ , ... I _N are information lines, and S ₁ , S ₂ , S ₃ , ... S _N are scanning lines. Further, 94 is the information side drive circuit 92 in which information lines I ₁ , I
₂ , I ₃ , ... I _N is an information side decoding circuit for sequentially selecting signal lines, and 95 is a scanning side driving circuit 93 in which scanning lines S ₁ , S
_{This is} a scanning-side decoding circuit that sequentially selects the signal lines of ₂ , S ₃ , ... _SN . The terminal A is an information input, the terminal B is a control input for controlling the information side decoding circuit 94, and the information side decoding circuit 94 generates a decoding function by the rising of a pulse, and the terminal C controls the scanning side decoding circuit 95. With the control input, the scanning side decoding circuit 95 has a decoding function due to, for example, the rising edge of the pulse.

The signal line when the information side drive circuit 92 and the scanning side drive circuit 93 are not selected from the decoding circuits 94 and 95 is always kept at the reference potential point V _E (for example, 0 volt).

Here, when the information signal is taken in through the terminal A of FIG. 9 and is displayed on the display panel 91, the same voltage is input to both the information side and the scanning side of the information signal A, so as shown in FIG. , Information signals 1, 2, 3, ... N corresponding to one scanning time
Corresponds to the information side signal lines I ₁ , I ₂ , I ₃ , ... I _N. The pulse of the control input B input to the information side decoding circuit 94 is input in synchronization with the change of each information signal, and therefore, the information side decoding circuit 94 due to the rising of the control input pulse V.
As a decoding function of, the information line of I ₁ of the information side drive circuit 92 is selected at the rising edge of the B pulse in the case of the information signal 1, and the information content of the information signal ₁ is output to the information line I ₁ . Similarly, the information signal 2 is output to I ₂ , and the information signal 3 is
Is output to the I _3, and the information signal N I _N, 1 scan line of information signals 1, 2, 3, ... N is information-side decoder circuit information side signal line I ₁ corresponding with 94, I _2, I _3, it is output to the ... I _N.

In contrast to the information side driving, in the scanning side driving, the control input C input to the scanning side decoding circuit 95 performs the decoding function once for one scanning time, whereby the control input is the scanning line S. Only one scanning line is selected from ₁ , S ₂ , S ₃ , ... _SN , and the information signal C is displayed on the display panel 1 in real time.

FIG. 11 is a diagram showing a display state of the display panel 1 by the above-described driving method. As the scanning line, the scanning line S ₂ is selected by the scanning side decoding circuit 95 in FIG. 9, and the other scanning lines are at the reference potential. It is connected to V _E (eg 0 volt) and the information line is
The information side signal lines I ₁ , I ₂ , I ₃ , ... I _N are sequentially selected at the timing of the pulse B in FIG. 10, and the unselected information side signal lines are connected to the reference potential point V _E (for example, 0 volt). Connected. As for the information signal, a signal voltage corresponding to the gradation signal is sequentially input to both the information side and the scanning side. At the intersection of I ₂ and S ₂ , the information side has “a” and the scanning side has the same value “a ′”. Is output,
"B" to the information side in the intersection of the I ₃ and S _2, "b '" of the same value on the scanning side is outputted, "c" to the information side in the intersection of the I ₄ and S _2, the scanning side The same value "c '" is output as the information signal voltage. Areas a, b, c in which the sum of the information signal voltages output to the information side and the scanning side exceeds the threshold voltage V _{th of the} liquid crystal (the voltage on the information side and the scanning side is V _th / 2 or more) Has been inverted. The information signals written in one pixel by these liquid crystal driving methods are
An information voltage corresponding to a gradation signal was applied to both scanning sides, and a gradation display image could be formed on the liquid crystal display panel by a dot sequential operation.

The driving method of the above embodiment can be applied to color gradation display and color binary display by using a color filter in addition to black and white gradation display. Further, simple binary display is also possible. For example, a flip-flop type shift register is used as a drive circuit in the case of binary display, and in the case of gradation display, as shown in FIG. Analog memory used.

As described above, according to the present invention, the information signal corresponding to the gradation signal is input to the information side and the scanning side, and the dot-sequential driving is performed to enable the gradation display using the potential gradient.

As for the optical modulator, the ferroelectric liquid crystal, in particular, the ferroelectric liquid crystal having at least two stable states has been described as the most preferable example, but the present invention is not limited thereto and other optical modulators. It can be applied to twist nematic liquid crystal, guest-host liquid crystal, etc. as a modulator.

[Effects of the Invention] As described above, according to the present invention, an information signal corresponding to a gradation signal is simultaneously input to the information-side electrode and the operation-side electrode, and information is displayed in real time on the liquid crystal display panel by dot-sequential driving. By writing, it is possible to remarkably improve the image quality in gradation display and provide a method for driving an optical modulator capable of obtaining high-density display over a wide area.

[Brief description of drawings]

1 and 7 are perspective views of the basic structure of an optical modulator for implementing the driving method of the present invention, FIG. 2 its potential gradient diagram, FIG. 3, FIG. 9 and FIG. 12 are wiring diagrams. , Fig. 4, Fig. 5
FIGS. 10 and 10 are voltage waveform diagrams, FIGS. 6, 8 and 11 are pixel state diagrams, and FIGS. 13 and 14 are schematic alignment diagrams of ferroelectric liquid crystals. 1: substrate, 2: conductive film, 3: transfer electrode, 4: counter substrate, 5: counter conductive film, 6: counter electrode, 91: display panel, 92, 93: drive circuit, 9
4: Control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 61-201217 (JP, A) JP 52-20851 (JP, A) JP 52-122098 (JP, A)

Claims (1)

[Claims] 1. A first substrate, wherein a large number of first transmission lines are arranged with a predetermined gap, and a conductive film having a resistance higher than that of the first transmission line is provided in the respective gaps of the first transmission line, and a second transmission line. A plurality of second substrates each having a predetermined gap so as to intersect the first transmission line, and a conductive film having a resistance higher than that of the second transmission line is provided in each gap of the second transmission lines; A method of driving an optical modulation element having a large number of pixels, comprising: an optical modulation substance disposed between a first substrate and a second substrate, wherein gradation information is provided to one of the three first transmission lines. A corresponding voltage is applied to two lines on both sides of the one first transmission line, and at the same time, one of the three second transmission lines is supplied with a voltage corresponding to the gradation information. By applying the reference voltage to the two lines on both sides of the two transmission lines, The pixel defined by the three first transmission lines and the three second transmission lines is formed by maximizing the applied electric field strength at the intersection of the first and second transmission lines to which the same voltage is applied. A method of driving an optical modulation element, comprising a driving step of causing a potential difference gradient between opposing portions of the conductive film to determine an optical state of the pixel, and performing the driving step dot-sequentially for each pixel.