JPH0437412B2 - - 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 liquid crystal, 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 consideration is required.

One driving method that does not apply this DC component to pixels for a long time is "SID'85Digest" (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 that the invention attempts to solve] However, in the latter driving method, a direct current component may be applied to the pixels for a long time, and the transparent electrodes for driving may be reduced and become dark, or the liquid crystal may become dark. There was a problem that it caused deterioration. On the other hand, with the former driving method, there is no problem of deterioration, but if the time T required to rewrite one screen is the time required to write one pixel, then T = 4 × t × N (N is the scanning line There were problems such as the rewriting time T was long and the number of scanning lines could not be increased very much, and it was not suitable for displaying moving images.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for driving a matrix-type liquid crystal optical device that can shorten the rewriting time and that does not darken the transparent electrode or deteriorate the liquid crystal even if the device is driven for a long time.

[Means for Solving the Problems] The present invention provides 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, and a plurality of screens using a plurality of scanning electrodes and a plurality of control electrodes. , and the pixel has 2n (n=1,
After initializing by applying an initialization pulse group consisting of 2,... initialization pulses, the first pulse group is applied to achieve the desired optical response state, and thereafter the second pulse group is applied to achieve the desired optical response state.
The optical response state of the pixel is maintained by an AC stabilizing effect by a group of pulses,
In the initialization pulse group and the first pulse group, there are negative polarity pulses with symmetrical waveforms with respect to all positive polarity pulses, and in the second pulse group, there are positive polarity pulses and pulses with waveforms symmetrical to this pulse. The above object is achieved by forming pulses of negative polarity to occur alternately.

[Example] In FIG. 1, a plurality of pixels are formed by interposing a ferroelectric liquid crystal having an AC stabilizing effect between scanning electrodes L ₁ to L _N and control electrodes R ₁ to R _x opposing thereto. ing. Scanning electrode from selection circuit SE
A plurality of initialization signals RS ₁ and RS ₂ (Fig. 2) for sequentially initializing L ₁ to L _N in a time-sharing manner and a selection signal S (Fig. 2) for selecting in a time-sharing manner are shown in Fig. 3. The non-selection signal NS (FIG. 2) is generated when the initialization signal and selection signal are not supplied. The initialization signal RS ₁ consists of a voltage (-V _R ±H), and RS ₂
is a voltage (V _R ±H), the selection signal S is a voltage ±V, and the non-selection signal NS is a voltage ±H.

On the other hand, from the drive control circuit DR, a response signal D or a reverse response signal RD shown in FIG. 2 is generated 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 is supplied, and control is performed. It is supplied to electrode groups R ₁ to R _X . That is, a response signal D is supplied to a pixel for which a response state (for example, a light transmission state) is desired, and a reverse response signal is supplied to a control electrode of a pixel for which a reverse response state (for example, a light blocking state) is desired.
It supplies RD. Response signal D is voltage 0
The reverse response signal RD is a high frequency voltage ± corresponding to the frequency at which the liquid crystal exhibits an AC stabilizing effect.
Consists of 2H.

By supplying the above signals, the initialization pulse P ₁ or P ₂ is applied to the pixel desired to respond by supplying the initialization signals RS ₁ and RS ₂ , and once the pixel is in a saturated response state, , an initialization pulse P ₃ or P ₄ is applied to initialize it to a saturated reverse response state,
After that, the selection signal S and the response signal D select the first
A pulse group _P5 is applied. In the pulse group _P5 , the high frequency AC pulse component is 0, so there is no AC stabilizing effect, and the pulses of voltages -V and ±V write into the saturated reverse response state and then into the saturated response state. Thereafter, the high-frequency AC pulses of the second pulse group P ₇ or P ₈ are applied by supplying the non-selection signal NS, and the response state is maintained stably by the AC stabilization effect.

On the other hand, a pixel for which a reverse response state is desired is initialized to a saturated reverse response state by applying an initialization pulse P ₁ or P ₂ , and then initialized to a saturated reverse response state by applying an initialization pulse P ₃ or P ₄ . Then, the first pulse group _P6 is applied by the selection signal S and the reverse response signal RD. Pulse group P ₆ 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 due to the AC stabilization effect of ±2H, it does not enter a saturated response state, but instead returns to the initialized saturated state. The reverse response state is maintained. and,
After the application of pulse group P ₆ , the second pulse group P ₇ or
When P ₈ is applied, the saturated reverse response state is maintained due to the AC stabilization effect.

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

In this way, the pulses applied to the pixels include all positive polarity pulses in the initialization pulse group and the first pulse group consisting of the initialization pulse P ₁ or P ₂ and the initialization pulse P ₃ or P ₄ . There are negative polarity pulses with symmetrical waveforms, and in the second pulse group, positive polarity pulses and negative polarity pulses with symmetrical waveforms occur alternately, so the biased DC voltage Since no voltage is applied, blackening of the transparent electrode, deterioration of the liquid crystal, etc. will not occur. In addition, by introducing an initialization signal, the next line can be initialized at the same time as the selection signal is supplied.
Screen rewriting time can be shortened. For this example,
The rewriting time T is T=2×t×N, which is 1/2 of the conventional one. Furthermore, a second pulse group is applied when not selected.
Since P ₇ and P ₈ do not contain low frequency pulse components,
Strong retention of optical response state and high contrast can be obtained.

Note that the frequency and pulse height V of the first pulse group _P5 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.

Moreover, the frequency of the second pulse group P _{7 and} P ₈ is the same as that of the first pulse group P 7 , P 8 .
The pulse height H is preferably at least twice the frequency of the pulse group _P5 (preferably an integral multiple of four times or more), and the pulse height H is such that the optical response state is maintained stably due to the magnitude of the dielectric anisotropy of the ferroelectric liquid crystal. Appropriate decisions will be made to ensure that

Furthermore, the initialization response voltage V _R of the initialization pulses P ₁ , P ₂ , P _{3 ,} and P ₄ is set such that the pixel is sufficiently in a response state or a reverse response state even when ±H high-frequency AC pulses are superimposed. It is determined.

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.
An appropriate bias voltage may be applied as necessary.

Furthermore, the number of initialization signals is not limited to the above example, but can be 2n (n = 1, 2, ...), which can be initialized before supplying the selection signal, and which can be used for all positive initialization pulses. On the other hand, it is sufficient that the initialization pulse is applied to the pixel so that there is a negative polarity initialization pulse with a symmetrical waveform.

[Effects of the Invention] According to the present invention, pixels in the next scan electrode can be initialized when writing pixels in one scan electrode, so rewriting time can be shortened. Moreover,
In the initialization pulse group and the first pulse group, the pulses applied to the pixels include negative polarity pulses with symmetrical waveforms with respect to all positive polarity pulses,
In the second pulse group, positive polarity pulses and negative polarity pulses whose waveforms are symmetrical are generated alternately, so that a biased DC voltage is not applied to the pixels, and long-term driving is possible. The transparent electrode will not darken or the liquid crystal will deteriorate.

Furthermore, the initialization signal is 2n (n=1, 2,...)
By using a single circuit, complete initialization can be performed even when the initialization pulse is at a low voltage, so the drive margin can be increased.

In addition, since only the high-frequency AC pulse is applied when not selected, a stable holding force can be obtained due to the AC stabilizing effect, which has great effects such as improving contrast.

[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 an explanatory diagram showing an example of a pulse applied to a pixel. R ₁ ~ R _X ... Control electrode, L ₁ ~ L _N ... Scanning electrode,
RS _1, RS ₂ ...Initialization signal, S...Selection signal,
NS...Non-selection signal, D...Data signal, RD...
...Data signal, _P1 to _P4 ...Initialization pulse, _P5 ,
_P6 ...first pulse group, P7 _{, P8} ...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 method for driving a matrix type liquid crystal optical device, 2n (n=1, 2,...) initialization signals and subsequent selection signals are sequentially supplied to each scanning electrode,
When each initialization signal and selection signal are not supplied, a non-selection signal is supplied, and 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. is supplied in synchronization with the supply of the selection signal, and the supply time of each initialization signal is set equal to the supply time of the selection signal, and each initialization signal is An initialization pulse group consisting of a plurality of initialization pulses corresponding to the selection signal is applied to the pixel to optically initialize it, and a first pulse group is applied to the pixel based on the potential difference between the selection signal and the data signal. to achieve 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 negative initialization pulse with a symmetrical waveform for every positive initialization pulse, and the first pulse group is a write pulse or initial pulse that changes the pixel to the desired optical response state. The second pulse group includes pulses that maintain the state initialized by the initializing pulse group, and has a negative polarity pulse with a symmetrical waveform to all the positive polarity pulses. 1. A method for driving a matrix type liquid crystal optical device, characterized in that positive polarity pulses having a frequency exhibiting a stabilizing effect and negative polarity pulses having waveforms symmetrical thereto 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.