JPH0438333B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a matrix type liquid crystal optical device.

[Prior Art] Recently, ferroelectric liquid crystals have been attracting attention instead of TN liquid crystals, and optical devices using them are being developed.

The optical modes of ferroelectric liquid crystals include birefringent optical mode and guest-host optical mode. When driving these, unlike conventional TN-type liquid crystals, the optical response state (brightness and darkness) is controlled by the direction of electric field application, so the driving method used for TN-type liquid crystals cannot be used, and special driving methods are required. It requires a method.

Furthermore, considering the lifespan of the optical device, it is undesirable for a DC component to be applied to the pixels for a long period of time, and a driving method that takes this point into account is required.

One of the driving methods that does not apply this DC component to pixels for a long time is "SID'85 Digest" (1985).
There are driving methods (P.131-P.134).

Further, JP-A-60-176097 discloses a driving method that uses a ferroelectric liquid crystal having an AC stabilizing effect to realize bistability of the optical response state with a driving electric signal.

[Problems to be Solved by the Invention] However, in the latter driving method, a DC component may be applied to the pixel for a long time, which may reduce the transparent electrode for driving and cause it to darken, or cause deterioration of the liquid crystal. There was a problem with causing it. On the other hand, with the former driving method, there is no problem with deterioration, but the time T required to rewrite one screen is the time T required to write one pixel.
Then, T=4×t×N (N is the number of scanning lines/screen), which caused problems such as the rewriting time T was long and the number of scanning lines could not be increased much, and it was not suitable for displaying moving images.

The present invention is capable of shortening the rewriting time and also prevents blackening of the transparent electrode and deterioration of the liquid crystal even when driven for a long time.

[Means for Solving the Problems] The present invention forms a matrix-type liquid crystal optical device using pixels using liquid crystal that changes the orientation state of molecules depending on the direction of application of an electric field and has an AC stabilizing effect. After applying a group of initialization pulses to the pixel to optically initialize the pixel, a first group of pulses is applied to bring the pixel into a desired optical response state, and then a second group of pulses is applied to bring the pixel into a desired optical response state. The initialization pulse group and the first pulse group each have a negative polarity pulse with a symmetrical waveform with respect to all positive polarity pulses, and the second pulse group The above object is achieved by the group having a frequency exhibiting an AC stabilizing effect, and in which pulses of positive polarity and pulses of negative polarity whose waveforms are symmetrical are generated alternately.

Furthermore, by supplying initialization signals to multiple scanning electrodes at the same time to perform initialization, and then writing the initialized pixels to a desired optical response state, it is possible to shorten the rewriting time and increase the gradation level. By adjusting the amplitude of the high frequency component of the write pulse included in the data signal according to the data signal, halftones can also be obtained.

[Example] In FIG. 1, a ferroelectric liquid crystal is interposed between scanning electrodes L ₁ to L _N and opposing control electrodes R ₁ to R _X to form a plurality of pixels at the intersections of each electrode. . The selection circuit SE sequentially selects scan electrodes L ₁ to L _N.
Initialization signal RS ₁ that is initialized in a time-division manner (Figure 2)
Then, the selection signal S ₁ (Fig. 2) for time-sharing selection is generated at the timing shown in Fig. 3, and when this initialization signal and selection signal are not supplied, the non-selection signal NS ₁ (second
Figure) occurs. The initialization signal RS ₁ has a voltage V _R ±
The selection signal S ₁ consists of a _voltage ±V, and the non-selection signal NS ₁ consists of a voltage ±H.

On the other hand, the drive control circuit DR generates a response signal D ₁ or a reverse response signal RD ₁ as a data signal in accordance with the desired optical response state of the pixel in the scanning electrode to which the selection signal S ₁ is supplied. and is supplied to the control electrodes R ₁ to R _X . In other words, a response signal D ₁ is supplied to the control electrode for which a responsive state (for example, a light transmitting state) is desired, and a reverse response signal RD ₁ is supplied to a control electrode for which a reverse responsive state (for example, a light blocking state) is desired. It is something. The reverse response signal RD ₁ includes a high frequency component corresponding to the frequency at which the liquid crystal exhibits an AC stabilizing effect.

By supplying the above signals, the initialization pulse group P ₁ or P ₂ is first applied to the pixel desired to be in the response state by supplying the initialization signal RS ₁ , and once the pixel enters the saturated response state, the pixel is saturated. It is initialized to a reverse response state, and then the first pulse group _P3 is applied by the selection signal _S1 and the response signal _D1 . Pulse group P ₃
Since the high-frequency AC pulse component is 0, there is no AC stabilizing effect, and the saturated reverse response state is maintained by the voltage -V, and then the saturated response state is written by the write pulse of the voltage +V. Thereafter, the second pulse group _P5 is activated by supplying the non-selection signal _NS1 .
Alternatively, a high frequency AC pulse of _P6 is applied, and the response state is maintained stably due to the AC smoothing effect.

On the other hand, for a pixel for which an inverse response is desired, pulse group P ₁
Alternatively, by applying P ₂ , the saturated response state is initialized to a saturated reverse response state, and then the first pulse group P ₄ is applied by the selection signal S ₁ and the reverse response signal RD ₁ . Pulse group P ₄ is a low-frequency AC pulse with a voltage of ±V superimposed with a high-voltage, high-frequency AC pulse with a voltage of ±2H, and is an initialized saturated reverse state that is not in a saturated response state due to the AC stabilization effect of ±2H. The response state is maintained. Then, after the application of the pulse group P ₄ , the second pulse group P ₅ or P ₆ is applied, and the saturated reverse response state is maintained due to the AC stabilization effect.

FIG. 4 shows examples of voltage waveforms applied to pixels for which these responses and reverse responses are desired.

In this way, the initialization pulse groups P ₁ , P ₂ and the first
The pulses in the pulse groups P ₃ and P ₄ are respectively,
For all positive polarity pulses, there is a negative polarity pulse with a symmetrical waveform, and in the second pulse group P ₅ and P ₆ , a positive polarity pulse and a negative polarity pulse whose waveform is symmetrical to this pulse are present. Since the voltages occur alternately, the DC voltage is not biasedly applied to the pixels, which prevents blackening of the transparent electrodes, deterioration of the liquid crystal, etc.

Further, by introducing the initialization signal, the next line can be initialized at the same time as the selection signal is supplied, so that the screen rewriting time can be shortened. In this example, the rewriting time T is T=2×t×N, which is 1/2 of the conventional time.

Furthermore, a second pulse group is applied when not selected.
Since P ₅ and P ₆ do not contain low frequency pulse components,
It has a strong ability to maintain the optical response state and can achieve high contrast.

Note that the frequency and pulse height V of the pulses in the first pulse group _P3 are appropriately determined in relation to the magnitude of spontaneous polarization of the ferroelectric liquid crystal and the thickness of the liquid crystal cell so as to obtain a saturated reverse response state and a saturated response state. Ru.

The frequency of the high-frequency AC pulses in the second pulse groups P ₅ and P ₆ is preferably at least twice the frequency of the pulses in the first pulse group P ₃ (preferably 4 times or more, an integral multiple), and the pulse height H is It is appropriately determined in relation to the magnitude of dielectric anisotropy of the ferroelectric liquid crystal so that the optical response state is stably maintained.

Furthermore, the initialization response voltage V _R of the initialization pulse group P ₁ or P ₂ is determined so that even if ±H high-frequency AC pulses are superimposed, a sufficient response or an inverse response is obtained.

Next, an example of realizing halftones will be explained. FIG. 5 shows an example in which halftones can be realized by applying the example of FIG. 2. In FIG. 5, the initialization signal RS ₁ and selection signal S ₁ are the same as in FIG. 2, and control the voltage ±h of the control signal C supplied to the control electrodes R ₁ to _R It was designed to do so.

In FIG. 5, the initialization pulse group _P7 is applied to the pixel by supplying the initialization signal _RS1 and the control signal C, and the pixel is initialized to a saturated response state and then to a saturated inverse response state, and then a selection signal is sent to the pixel. The first pulse group P ₈ is applied by supplying S ₁ . The first half of the pulse group _P8 is composed of pulses in which a high-frequency AC pulse is superimposed on the voltage -V, and the saturated reverse response state initialized by the pulse group acting on the reverse response state is maintained, but the voltage V in the second half is ± h high-frequency alternating current pulses are superimposed,
An unsaturated response state (halftone) can be realized by applying a write pulse that writes an unsaturated response state.

In other words, a saturated response state can be obtained with only a pulse of voltage V, but an unsaturated response state can be obtained by controlling the AC stabilizing effect using the amplitude of the high-frequency AC pulse superimposed thereon.

After that, the non-selection signal NS′ ₁ and the control signal C
The high frequency AC pulse which is the second pulse group is
P ₉ is applied and the above optical response state is maintained. Note that the non-selection signal _NS'1 is a signal whose phase is different from that of the non-selection signal NS in FIG. 2 in order to further stabilize the AC smoothing effect during non-selection.

By the way, before the pulse that produces the intermediate tone, the system is initialized to a saturated inverse response state, and this point has an important meaning. If a pulse is simply applied to produce halftones, the optical response state before pulse application will change the optical response state after pulse application, making it impossible to achieve stable halftones. However, in the example shown in Figure 5, Since it is initialized to a saturated reverse response state before rewriting, stable halftones can be produced despite the previous optical response state.

Next, a method will be described in which a plurality of scan electrodes (for example, M scan electrodes) are initialized simultaneously in blocks, and then the scan electrodes within the initialized block are sequentially selected and driven in a time-division manner.

6 and 7, first, an initialization signal RS ₂ (FIG. 6) consisting of a voltage ±V _R is applied to a plurality of scanning electrodes L ₁ to L _N in FIG. 1 (for example, L ₁ to _{L M} ), and a non-initialization signal NRS (FIG. 6) is supplied to the other scan electrodes. On the other hand, control electrode group R ₁
An initialization control signal C _R (FIG. 6) is supplied to R _X.

By supplying the above signals, the pixels in the M scanning electrodes to which the initialization signal RS ₂ is supplied enter the saturated response state by applying the initialization pulse group P ₁₀ , and then initialize to the saturated reverse response state. The high frequency alternating current pulse _P11 is applied to the other pixels, and the optical response state remains unchanged.

Subsequently, the initialized scanning electrodes are sequentially supplied with a signal S ₂ (FIG. 7) consisting of a voltage of ±V, and the scanning electrodes to which the selection signal is not supplied are supplied with a non-selection signal NS ₂ (of a voltage ±H). FIG. 7) is supplied.

On the other hand, _{a seventh response signal D 2 or} a reverse response signal RD ₂ is applied to the control electrodes R ₁ to _R Supplied as.

By supplying the above signals, the first pulse group _P12 is applied to the pixel desired to respond, and the voltage -V
The saturated reverse response state is maintained with a pulse of +V, and then the saturated response state is written with a write pulse of voltage +V. After that, the second pulse group, high frequency AC pulse P ₁₄ or P ₁₅ is applied, and the response state is maintained. Retained. On the other hand, a pixel for which a reverse response is desired is supplied with the first pulse group by the selection signal S ₂ and the reverse response signal RD ₂ .
P ₁₃ is applied. Pulse group P ₁₃ is a combination of a low-frequency AC pulse with a voltage of ±V and a high-voltage, high-frequency AC pulse with a voltage of ±2H, and the optical response state does not change due to the AC stabilization effect of ±2H and is in an initialized state. A saturated reverse response state is maintained.
After applying this pulse group P ₁₃ , pulse group P ₁₄ or
P ₁₅ maintains the saturated reverse response state.

When the M time-division scans are completed, initialization and time-division scan of the next M blocks are sequentially performed.

In this example, the initialization pulse group P ₁₀ and the first
In the second pulse group P ₁₂ , P ₁₃ , there is a negative polarity pulse with a symmetrical waveform to all the positive polarity pulses, and in the second pulse group P ₁₄ , P ₁₅ , there is a negative polarity pulse with a symmetrical waveform to all the positive polarity pulses. Since pulses and negative pulses whose waveforms are symmetrical are generated alternately, a biased DC voltage is not applied.

Also, the rewriting time T for one screen is T=(2×t×
N/M)+(2×t×N)=2×t(N+N/M)
By setting M large, rewriting time can be shortened.

Furthermore, as in the above example, it is also possible to obtain halftones by controlling the amplitude of the high frequency alternating current pulse superimposed on the low frequency pulse.

In the above explanation, the response depends on the voltage on the + side.
Although it has been referred to as a reverse response due to a voltage on the − side, since the response and reverse response are two sides of the same coin, it may also be referred to as a reverse response due to a voltage on the + side and a response due to a voltage on the − side.

By the way, the signals supplied to each electrode are not limited to the above, and various changes are possible.
A bias voltage may be applied as necessary.

Furthermore, in the above embodiment, a matrix optical device as shown in FIG. 1 was described, but the invention is not limited to this.
Needless to say, the present invention can also be applied to driving a liquid crystal shutter array for an optical printer in which an optical shutter array arranged in a line is divided into a plurality of blocks and wired in a matrix. in this case,
High contrast can be obtained by setting the reverse response state to a dark (light-blocking) state.

[Effects of the Invention] According to the present invention, by using an initialization signal, pixels in the next scan electrode can be initialized when writing pixels in one scan electrode, and the time for rewriting pixels can be shortened. , the pulses applied to the pixels include a negative polarity pulse for every positive polarity pulse, or positive polarity pulses and negative polarity pulses whose waveforms are symmetrical to each other alternately. Therefore, a biased DC voltage is not applied, and even if the device is driven for a long time, it does not cause blackening of the transparent electrode or deterioration of the liquid crystal. Further, by controlling the amplitude of the high frequency component included in the write pulse, a stable optical response state including halftones can be obtained.

Furthermore, rewriting time can be shortened by writing a desired optical response state after simultaneously initializing pixels in a plurality of scan electrodes.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of a matrix type liquid crystal optical device, Fig. 2 is an explanatory diagram showing an example of a voltage waveform for realizing the present invention, and Fig. 3 is an explanatory diagram showing an example of a voltage waveform for realizing the present invention _.
~L An explanatory diagram showing the signal supply timing to _N ,
FIG. 4 is a waveform diagram showing an example of a pulse applied to a pixel, and FIGS. 5, 6, and 7 are explanatory diagrams showing other waveform examples for realizing the present invention, respectively. R ₁ ~ R _X ... Control electrode, L ₁ ~ L _N ... Scanning electrode,
RS ₁ , RS ₂ ... Initialization signal, S ₁ , S ₂ ... Selection signal, NS ₁ , NS' ₁ , NS ₂ ... Non-selection signal, D ₁ , D ₂
...Data signal, RD ₁ , RD ₂ ...Data signal, C
...Data signal, C _R ...Initialization control signal, P ₁ ,
P ₂ , P ₇ , P ₁₀ ... Initialization pulse group, P ₃ , P ₄ , P ₈ ,
P ₁₂ , P ₁₃ ...first pulse group, P ₅ , P ₆ , P ₉ , P ₁₄ ,
P ₁₅ ...Second pulse group.

Claims (1)

[Claims] 1. A liquid crystal that changes the orientation of molecules depending on the direction of application of an electric field and has an AC stabilizing effect is interposed between a plurality of scanning electrodes and a plurality of control electrodes, and pixels are formed at the intersections of each electrode. In the driving method of a matrix type liquid crystal optical device, an initialization signal and a subsequent selection signal are sequentially supplied to each scanning electrode, and when the initialization signal and the selection signal are not supplied, a non-selection signal is supplied, A data signal containing a high frequency component corresponding to the frequency at which the liquid crystal exhibits an AC stabilizing effect or a data signal not containing this high frequency component is supplied to each control electrode in synchronization with the supply of the selection signal, and the initialization signal and data signal are supplied to each control electrode in synchronization with the supply of the selection signal. Due to the potential difference between
A group of initialization pulses is applied to the pixel to optically initialize it, and a first group of pulses is applied to the pixel to set it to a desired optical response state depending on the potential difference between the selection signal and the data signal, and a non-selection signal and Due to the potential difference with the data signal,
A second pulse group is applied to the pixel to maintain the optical response state of the pixel by an AC stabilizing effect, and the initialization pulse group is to put the pixel into a light transmitting state or a light blocking state. , and there is a negative polarity pulse with a symmetrical waveform for every positive polarity pulse, and the first pulse group is a write pulse or initialization pulse group that changes the pixel to a desired optical response state. Therefore, there is a negative polarity pulse that includes a pulse that maintains the initialized state and has a symmetrical waveform with respect to all positive polarity pulses, and the second pulse group exhibits an AC stabilizing effect. 1. A method for driving a matrix type liquid crystal optical device, characterized in that pulses of positive polarity having a high frequency and pulses of negative polarity having a waveform symmetrical therewith are alternately generated. 2. The method of driving a matrix type liquid crystal optical device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal that exhibits negative dielectric anisotropy in the frequency range of AC pulses in the second pulse group. 3. A matrix type liquid crystal in which a liquid crystal that has an alternating current stabilizing effect by varying the orientation of molecules depending on the direction of electric field application is interposed between a plurality of scanning electrodes and a plurality of control electrodes, and pixels are formed at the intersections of each electrode. In a method for driving an optical device, an initialization signal and a subsequent selection signal are sequentially supplied to each scanning electrode, a non-selection signal is supplied when the initialization signal and selection signal are not supplied, and each control electrode is supplied with: A data signal containing a high frequency component corresponding to the frequency at which the liquid crystal exhibits an AC stabilizing effect is supplied in synchronization with the supply of the selection signal, and due to the potential difference between the initialization signal and the data signal,
A group of initialization pulses is applied to the pixel to optically initialize it, and a first group of pulses is applied to the pixel to set it to a desired optical response state depending on the potential difference between the selection signal and the data signal, and a non-selection signal and Due to the potential difference with the data signal,
A second pulse group is applied to the pixel to maintain the optical response state of the pixel by an AC stabilizing effect, and the initialization pulse group is to put the pixel into a light transmitting state or a light blocking state. , and there is a pulse of negative polarity with a symmetrical waveform with respect to all the pulses of positive polarity, and the first pulse group is a write pulse or pulse that includes a high frequency component and changes the pixel to a desired optical response state The second pulse group includes a pulse that maintains the state initialized by the initialization pulse group, and has a negative polarity pulse with a symmetrical waveform to all positive polarity pulses, and the second pulse group is It has a frequency that exhibits an AC stabilizing effect, and pulses of positive polarity and pulses of negative polarity whose waveforms are symmetrical are generated alternately, and the amplitude of the high frequency component of the data signal is changed according to the gradation. A method for driving a matrix type liquid crystal optical device, which comprises adjusting the amplitude of a high frequency component of a write pulse to obtain a desired optical response state including halftones. 4. The method of driving a matrix-type liquid crystal optical device according to claim 3, wherein the liquid crystal is a ferroelectric liquid crystal exhibiting negative dielectric anisotropy in the frequency range of AC pulses in the second pulse group. 5. A matrix type liquid crystal in which a liquid crystal that has an AC stabilizing effect by varying the orientation of molecules depending on the direction of electric field application is interposed between a plurality of scanning electrodes and a plurality of control electrodes, and pixels are formed at the intersections of each electrode. In a method for driving an optical device, an initialization signal is simultaneously supplied to a plurality of scan electrodes, and then a selection signal is sequentially supplied to each scan electrode to which this initialization signal has been supplied, and when the initialization signal and selection signal are not supplied, a non-initialization signal is supplied. A selection signal is supplied, an initialization control signal is supplied to each control electrode in synchronization with the supply of the initialization signal, and a high frequency component corresponding to the frequency at which the liquid crystal exhibits an AC stabilizing effect is synchronized with the supply of the selection signal. or a data signal that does not include this high frequency component, and optically initializes the pixel by applying an initialization pulse group to the pixel based on the potential difference between the initialization signal and the initialization control signal, and generates the selection signal. A first group of pulses is applied to the pixel to achieve the desired optical response state by the potential difference between the non-selection signal and the data signal, and by the potential difference between the non-selection signal and the data signal,
A second pulse group is applied to the pixel to maintain the optical response state of the pixel by an AC stabilizing effect, and the initialization pulse group is to put the pixel into a light transmitting state or a light blocking state. , and there is a negative polarity pulse with a symmetrical waveform for every positive polarity pulse, and the first pulse group is a write pulse or initialization pulse group that changes the pixel to a desired optical response state. Therefore, there is a negative polarity pulse that includes a pulse that maintains the initialized state and has a symmetrical waveform with respect to all positive polarity pulses, and the second pulse group exhibits an AC stabilizing effect. 1. A method for driving a matrix type liquid crystal optical device, characterized in that pulses of positive polarity and pulses of negative polarity having a waveform symmetrical therewith are alternately generated. 6. The method of driving a matrix type liquid crystal optical device according to claim 5, wherein the liquid crystal is a ferroelectric liquid crystal exhibiting negative dielectric anisotropy in the frequency range of AC pulses in the second pulse group. 7. A matrix type liquid crystal in which a liquid crystal that has an AC stabilizing effect by changing the orientation of molecules depending on the direction of electric field application is interposed between a plurality of scanning electrodes and a plurality of control electrodes, and pixels are formed at the intersections of each electrode. In a method for driving an optical device, an initialization signal is simultaneously supplied to a plurality of scan electrodes, and then a selection signal is sequentially supplied to each scan electrode to which this initialization signal has been supplied, and when the initialization signal and selection signal are not supplied, a non-initialization signal is supplied. A selection signal is supplied, an initialization control signal is supplied to each control electrode in synchronization with the supply of the initialization signal, and a high frequency component corresponding to the frequency at which the liquid crystal exhibits an AC stabilizing effect is synchronized with the supply of the selection signal. A group of initialization pulses is applied to the pixel to optically initialize it by a potential difference between the initialization signal and the initialization control signal, and a voltage difference between the selection signal and the data signal is applied to the pixel. , applying a first group of pulses to the pixel to bring it into the desired optical response state, and by the potential difference between the non-selection signal and the data signal,
A second pulse group is applied to the pixel to maintain the optical response state of the pixel by an AC stabilizing effect, and the initialization pulse group is to put the pixel into a light transmitting state or a light blocking state. , and there is a pulse of negative polarity with a symmetrical waveform with respect to all the pulses of positive polarity, and the first pulse group is a write pulse or pulse that includes a high frequency component and changes the pixel to a desired optical response state The second pulse group includes a pulse that maintains the state initialized by the initialization pulse group, and has a negative polarity pulse with a symmetrical waveform to all positive polarity pulses, and the second pulse group is It has a frequency that exhibits an AC stabilizing effect, and pulses of positive polarity and pulses of negative polarity whose waveforms are symmetrical are generated alternately, and the amplitude of the high frequency component of the data signal is changed according to the gradation. A method for driving a matrix type liquid crystal optical device, which comprises adjusting the amplitude of a high frequency component of a write pulse to obtain a desired optical response state including halftones. 8. The method of driving a matrix type liquid crystal optical device according to claim 7, wherein the liquid crystal is a ferroelectric liquid crystal that exhibits negative dielectric anisotropy in the frequency range of the AC pulses in the second pulse group.