JPH0438332B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of 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 the ferroelectric liquid phase include a birefringent optical mode and a 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 orbital method used in TN-type liquid crystals cannot be used, and special This requires a driving method.

Furthermore, considering the lifespan of the liquid crystal, it is not preferable that a DC component be applied to the pixels for a long period of time, and a driving method that takes this point into consideration 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 either driving method, stable halftones cannot be obtained, and in driving methods such as the latter driving method in which a DC component is applied to the pixels for a long time, There were also problems in that the transparent drive electrodes were reduced and turned dark, and the liquid crystals deteriorated.

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

[Means for Solving the Problems] The present invention forms complex pixels using a liquid crystal having an AC stabilizing effect, first applies an initialization pulse to the pixels to optically initialize the pixels, and then applies a high-frequency component to the pixels. A writing pulse containing the AC stabilizing effect is applied to obtain a desired optical response state, and thereafter a second pulse group having a frequency exhibiting an AC stabilizing effect is applied to maintain the optical response state, and the optical response state is maintained according to the gradation. The above objective is achieved by adjusting the amplitude of the high frequency component of the write pulse to obtain desired optical response conditions including halftones.

[Example] In FIG. 1, a ferroelectric liquid crystal having an AC stabilizing effect is interposed between the control electrodes R ₁ to _{R 5} facing the scanning electrodes L ₁ to _{L 2} , and a plurality of pixels are formed at the intersection of each electrode. is formed. Selection circuit SE
A selection signal S ₁ (FIG. 2) for sequentially and time-divisionally selecting scanning electrodes L ₁ to L ₇ is generated, and when this selection signal is not supplied, a non-selection signal NS ₁ is generated. 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 outputs a control signal C ₁ consisting of the voltage 0 shown in FIG. 2 and the voltage ±h corresponding to the desired halftone.
is supplied to control electrodes R ₁ to R ₅ as data signals. The control signal _C1 includes a high frequency component that causes the liquid crystal to exhibit an AC stabilizing effect.

By supplying the above signals, the first pulse group _P1 is first applied to the pixel as shown in the third diagram.
In the pulse group _P1 , an initialization pulse of voltage -V is first applied to initialize the state to a saturated reverse response state, and then a write pulse in which a high-frequency AC pulse of ±h is superimposed on the DC voltage V is applied. Halftones are realized according to the height of the high-frequency alternating current pulse. That is, when the pulse height h is 0, a saturated response state occurs due to the DC voltage V, and as h increases, an unsaturated response state (half tone) is obtained due to the AC stabilization effect.

After applying the pulse group _P1 , a second pulse group, high-frequency alternating current pulse _P2 , is applied in response to the non-selection signal _NS1 , and the halftone is maintained.

Here, in the first pulse group _P1 , the average voltage value of the initialization pulse is equal in absolute value to the average voltage value of the write pulse, but has a different polarity.
The pulse group _P2 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, so that blackening of the transparent electrode and liquid crystal This eliminates the possibility of deterioration, etc.

In addition, stable halftones can be achieved by initializing to a saturated inverse response state before applying a write pulse. In other words, if only an unsaturated response pulse is applied to produce a halftone, the same unsaturated response pulse will produce different halftones due to the influence of the previous response state, making it impossible to obtain a stable halftone.

Note that the pulse width and pulse height V of the initialization pulse are appropriately determined in relation to the magnitude of spontaneous polarization of the ferroelectric liquid phase and the cell thickness so as to obtain a saturated reverse response state and a saturated response state. Furthermore, the pulse width of the high-frequency AC pulse is preferably 1/4 or less of the initialization pulse width, and the pulse height H is appropriately determined in relation to the magnitude of dielectric anisotropy of the ferroelectric liquid crystal so that the response state can be maintained stably. Ru.

Next, an example will be described in which a signal for initializing a pixel is supplied at a timing before a selection signal is supplied. In FIG. 4, the selection signal S ₂ consisting of voltage -V±H is sequentially supplied to the scanning electrodes L ₁ to _{L 7} of FIG. It supplies the signal RS. At the time of non-selection, a non-selection signal NS ₂ consisting of voltage ±H is supplied.

On the other hand, a control signal _C2 consisting of a voltage ±h corresponding to a desired halftone is supplied as a data signal to the control electrodes _R1 to _R5 . This control signal _C2 includes a high frequency component that causes the liquid crystal to exhibit an AC stabilizing effect.

As a result, as shown in FIG. 5, an initialization pulse _P3 is first applied to the pixel. Pulse P ₃ is a pulse obtained by superimposing a high frequency AC pulse ±(h-H) on a DC voltage -V. After initializing to a saturated reverse response state by applying this pulse P ₃ , applying a write pulse P ₄ to return to an intermediate state. After writing the tone, the second pulse group, high-frequency pulse _P5 , is applied to maintain the intermediate tone.

According to this example, since the initialization signal is used, pixels in the next scan electrode can be initialized when writing pixels in one scan electrode,
Since the supply time of each signal is 1/2 of the above example,
The number of digits that can be scanned in the same amount of time can be doubled. In other words, if the number of scanning digits is the same, the rewriting speed for one screen can be doubled.

Note that the above explanation responds depending 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.

In addition, the voltage ±h is used as a pulse to realize halftones.
The intermediate tone may be produced not only by the modulation of , but also by modulation of the application width (duty) of ±h.

By the way, the signals supplied to each electrode and the method of applying the signals are not limited to those described above, and various changes can be made.

[Effects of the Invention] According to the present invention, halftones can be realized by controlling the amplitude of the high frequency component of the write pulse.
A stable halftone can be achieved by once initializing the pixel before the write pulse for writing the halftone. In addition, the average voltage value of the initialization pulse applied to the pixel is equal in absolute value to the average voltage value of the write pulse, but the polarity is opposite, and in the second pulse group, the positive polarity pulse and the negative polarity pulse of the symmetrical waveform Since the pulses occur alternately, the transparent electrode does not darken or the liquid crystal deteriorates even after long-term driving. Furthermore, by introducing an initialization signal, it is possible to initialize the pixels in the next scan electrode when writing to the pixels in one scan electrode, which shortens the time required to rewrite the optical response state of the pixel. The number of digits that can be scanned can be increased.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing an example of a matrix type liquid crystal optical device, Figures 2 and 4 are diagrams showing voltage waveforms for realizing the present invention, and Figures 3 and 5 are diagrams showing voltage waveforms applied to pixels. FIG. _L1 to _L7 ...scanning electrodes, _R1 to _R5 ...control electrodes,
S ₁ , S ₂ ... selection signal, NS ₁ , NS ₂ ... non-selection signal, C ₁ , C ₂ ... data signal, RS ... initialization signal,
P ₁ ... first pulse group, P ₂ ... second pulse group,
P ₃ ...Initialization pulse, P ₄ ...Write pulse, P ₅
...Second pulse group.

Claims (1)

[Claims] 1. A liquid crystal that has an alternating current stabilizing effect by varying the orientation of molecules depending on the method of applying an electric field 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, a selection signal is sequentially supplied to each scanning electrode, a non-selection signal is supplied when the selection signal is not supplied, and the liquid crystal has an AC stabilizing effect on each control electrode. A data signal containing a high-frequency component corresponding to a frequency exhibiting is supplied in synchronization with the supply of the selection signal, and a first group of pulses is applied to the pixel based on the potential difference between the selection signal and the data signal to obtain the desired signal. In the optical response state, due to 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 stabilization effect, and the first pulse group initializes the pixel to a light transmitting state or a light blocking state. pulse followed by a write pulse that changes the pixel to a desired optical response state, the write pulse containing a high frequency component and whose average voltage value is equal in absolute value to the average voltage value of the initialization pulse. The second pulse group 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. A matrix type liquid crystal optical device characterized in that the amplitude of the high frequency component of the write pulse is adjusted by changing the amplitude of the high frequency component of the data signal according to the tone, thereby obtaining a desired optical response state including halftones. driving method. 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 exhibiting negative dielectric anisotropy in the frequency range of the alternating current pulse. 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 the selection signal are not supplied, and each control electrode is supplied with a non-selection signal. 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,
applying an initialization pulse to the pixel to optically initialize it; applying a write pulse with a pulse width equal to the initialization pulse to the pixel to achieve a desired optical response state, depending on the potential difference between the selection signal and the data signal; Due to the potential difference between the non-selection signal and the data signal,
An AC pulse is applied to the pixel to maintain the optical response state of the pixel by an AC stabilization effect, and the initialization pulse puts the pixel into a light transmitting state or a light blocking state, and the writing pulse is It is a pulse that changes to a desired optical response state, contains a high frequency component, and its average voltage value is equal in absolute value to the average voltage value of the initialization pulse, but has a different polarity.The AC pulse has an AC stabilizing effect. It has a frequency exhibiting , and pulses of positive polarity and pulses of negative polarity whose waveforms are symmetrical are generated alternately, and by changing the amplitude of the high frequency component of the data signal 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 the alternating current pulse.