KR920007127B1 - Method for driving a liquid crystal optical apparatus - Google Patents

Abstract

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Description

Driving Method of Matrix Liquid Crystal Optical Device

1 is an explanatory diagram showing an example of a matrix liquid crystal optical device.

2 is an explanatory diagram showing an example of a voltage waveform for realizing the present invention.

3 is an explanatory diagram showing signal supply timings to scan electrodes L ₁ to L _N.

4 is a waveform diagram showing an example of a pulse applied to a pixel.

* Explanation of symbols for main parts of the drawings

R ₁ to R _X : control electrode L ₁ to L _N : scan electrode

RS ₁ to RS ₂ : Initialization signal S: Selection signal

NS: non-selection signal D: data signal

RD: Data signal P _{1 to} P ₄ : Initialization pulse

P _5, P _6: the first pulse group P ₇ ~P _8: the second pulse group

The present invention relates to a method of driving a matrix liquid crystal optical device.

In recent years, ferroelectric liquid crystal has attracted attention instead of the TN type liquid crystal, and development of an optical device using the same has been advanced.

As an optical mode of ferroelectric liquid crystal, there exist a birefringent optical mode and a guest host optical mode. When driving these, it is different from the conventional TN type liquid crystal, and in order to control the optical response state (contrast) by the application direction of an electric field, the driving method used for the TN type liquid crystal is not used, and a special driving method is required. It is.

In consideration of the lifetime of the liquid crystal, it is not preferable that the direct current component is applied to the pixel for a long time, and a driving method in consideration of the advantage is required. One driving method in which this DC component is not applied to the pixel for a long time is a driving method of "SID'85 Digest" (1985) (p. 131 to p. 134). Japanese Patent Laid-Open No. 60-176097 also discloses a driving method capable of realizing a bistable in an optical response state using a ferroelectric liquid crystal having an AC stabilizing effect as a driving electric signal.

However, in the latter driving method, the direct current component may be applied to the pixel for a long time, and there has been a problem that the transparent electrode for driving is reduced and blackened, or causes the liquid crystal to become sharp. On the other hand, in the previous driving method, there is no problem of drawing, but if the time T required for rewriting of one screen is t required for writing of one pixel, t = 4 x t x N (N is the number of scanning lines / screen). There is a problem that the rewriting time T is long and does not increase the number of scanning lines too much, or is not suitable for moving picture display.

An object of the present invention is to provide a method for driving a matrix type liquid crystal optical device in which the rewriting time can be shortened, and the transparent electrode does not blacken or the liquid crystal is instantiated even after long driving.

According to the present invention, a plurality of pixels are formed by a liquid crystal, a plurality of scan electrodes, and a plurality of control electrodes having an alternating current stabilization effect by varying the compounding state of the molecules depending on the direction in which the electric field is applied, and 2n (n = 1) in the pixel. After initializing by initializing the initializing pulse group formed by the initializing pulses (2, ...), the first pulse group is applied to the desired optical response state, and after that, the second pulse group is applied. By maintaining the optical response state of the pixel by the AC stabilization effect, the initializing pulse group and the first pulse group have symmetrical waveform negative polarity pulses with respect to all the positive polarity pulses, respectively. The above object is achieved by forming a positive pulse and a negative pulse having a symmetrical waveform.

In Fig. 1, a plurality of pixels are formed through a ferroelectric liquid crystal having an alternating current stabilizing effect between the scan electrodes L ₁ to L _N and the control electrodes R ₁ to R _X facing the same. In the selection circuit SE, a plurality of initialization signals RS ₁ and RS ₂ (FIG. 2) for sequentially time-divisionally initializing the scan electrodes L ₁ to LN, and a selection signal S (FIG. 2) for time-divisionally selecting the third circuit are shown in FIG. It occurs at the timing shown in FIG. And, when this initialization signal and the selection signal are not supplied, the non-selection signal NS (FIG. 2) is generated. The initialization signal RS ₁ is formed with a voltage (-V _R ± H), RS ₂ is formed with a voltage (V _R ± H), the selection signal S is formed with a voltage ± V, and the unselected signal NS is a voltage. Formed to ± H.

On the other hand, from the drive control circuit DR, in response to the desired optical response state of the pixel in the scan electrode supplied with the selection signal S, the response signal D or the reverse response signal RD in FIG. 2 is generated as a data signal and the control electrode R ₁ To R _X. That is, the response signal D is supplied to the pixel that desires the response state (for example, the light transmission state), and the reverse response signal RD is supplied to the control electrode of the pixel which desires the reverse response state (for example, the light blocking state). To supply. The response signal D is formed at a voltage of 0, and the reverse response signal RD is formed at a high frequency voltage of ± 2H 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 which desires the response state by the supply of the initialization signals RS ₁ and RS ₂ to become the saturation response state, and then the initialization pulse group P ₃ Or P ₄ is applied and initialized to the saturation reverse response state, and then the first pulse group P ₅ is applied by the selection signal S and the response signal D. In the pulse group P ₅ , since the high frequency AC pulse component is 0, there is no AC stabilizing effect, and the pulses of voltages -V and + V are written in the saturation response state to the saturation reverse response state. Thereafter, the high frequency AC pulses of the second pulse group P ₇ or P ₈ are applied by the supply of the non-selection signal NS, so that the unanswered state is stably maintained by the AC stabilization effect.

On the other hand, to the pixel in which the reverse response state is desired, after the saturation response state by the application of the initialization pulse P ₁ or P ₂ , it is initialized to the saturation reverse response state by the application of the initialization pulse P ₃ or P ₄ , and then the selection signal S And the first pulse group P ₆ is added by the reverse response signal RD. The pulse group P ₆ superimposes a low frequency AC pulse of voltage ± V and a high voltage high frequency AC pulse of voltage ± 2H, and does not become a saturation response state due to the AC stabilization effect of ± 2H, and the initialized saturation response state is maintained. Thus, after the application of the pulse group P ₆ , the second pulse group P ₇ or P ₈ is applied, and the saturation reverse response state is maintained by the AC stabilization effect. FIG. 4 shows examples of the voltage waveforms applied to the pixels in the response and the reverse response.

In this manner, the pulses applied to the pixels are negative in the symmetrical waveform with respect to all positive pulses in the initial pulse group and the first pulse group formed by the initialization pulses P ₁ or P ₂ and the initialization pulses P ₃ or P ₄ . Since there exists a pulse and in a 2nd pulse group, since a positive pulse and a negative pulse of a symmetrical waveform generate | occur | produce alternately, the biased DC voltage is not applied but the black side of a transparent electrode and the example of a liquid crystal are made. It does not cause back. In addition, since the introduction of the initialization signal allows the initialization of the next line at the same time as the supply of the selection signal, the screen rewriting time is shortened. In this example, the rewrite time T is 1/2 of the prior art as T = 2 × t × N. Again, since the second pulse groups P ₇ and P ₈ to be applied at the time of non-selection do not contain low frequency pulse components, the holding force of the optical response state is strong and high contrast is obtained.

In addition, the frequency and the pulse height V of the first pulse group P ₅ are appropriately determined so that the saturation reverse response state and the saturation response state can be obtained in relation to the magnitude of the spontaneous polarization of the ferroelectric liquid crystal and the liquid crystal cell thickness. In addition, the frequency of the second pulse groups P ₇ and P ₈ is preferably two times or more (preferably an integer multiple of four times or more) of the frequency of the first pulse group P ₈ , and the pulse height H is the dielectric anisotropy of the ferroelectric liquid crystal. It is appropriately determined that the optical response state remains stable in relation to the magnitude of. Again, the initialization response voltages V _R of the initialization pulse groups P ₁ , P ₂ , P _3, and P ₄ are determined such that the pixels are sufficiently in response or reverse response even when a high frequency AC pulse of ± H is superimposed.

In addition, in the above description, the response is referred to as the response by the voltage on the positive side and the response by the voltage on the negative side. However, since the response and the reverse response are a bundle, the reverse response and the voltage on the negative side are reversed. May be referred to as answering. By the way, the signal supplied to each electrode is not limited to the above, various kinds of changes are possible, and you may make it apply a bias voltage suitably as needed.

In addition, the number of initialization signals is not limited to the above example, but is initialized before supply of the selection signal with 2n (n = 1, 2,. The initialization pulse may be applied to the pixel so that the negative initialization pulse exists.

According to the invention. Since the pixel is initialized in the next scan electrode when the pixel is written in one scan electrode, the rewriting time can be shortened. Furthermore, in the pulses applied to the pixels, in the initialization pulse group and the first pulse group, there are negative pulses of symmetric waveform with respect to all the positive pulse pulses. Since negative pulses having symmetrical and wavy waveforms are alternately generated, the direct current voltage biased to the pixel is not applied, and the transparent electrode is not blacked or the liquid crystal is instantiated even when driven for a long time.

In addition, by setting the initialization signals to 2n (n = 1, 2, ...), even if the initialization pulse is low voltage, the initialization is completed, so that the driving margin can be increased.

In addition, at the time of non-selection, since only the high frequency AC pulse is applied, the stabilization holding force is obtained by the AC stabilizing effect, and the contrast can be improved.

Claims (2)

The liquid crystal optical device of the matrix type liquid crystal device comprising a liquid crystal having an alternating state of molecules depending on an application direction of an electric field and sandwiching a liquid crystal having an alternating current stabilizing effect between a plurality of scan electrodes and a plurality of control electrodes to form pixels at the intersections of the electrodes. In the driving method, 2n (n = 1, 2, ...) initialization signals and a selection signal subsequent thereto are supplied to each scan electrode in turn, and non-selection when each of the initialization signals and the selection signal is not supplied. The signal is supplied to each control electrode by supplying a data signal containing a high frequency component corresponding to a frequency at which the liquid crystal has an alternating current stabilizing effect or a data signal not including the high frequency component in registration with the supply of the selection signal, The supply time of each initialization signal is set equal to the supply time of the selection signal, and the potential difference between each initialization signal and data signal The initial pulse group formed by a plurality of initialization pulses corresponding to the vaporized signal is optically initialized by applying to the pixel, and the first optical pulse group is added to the pixel by the potential difference between the selection signal and the data signal. The second pulse group is applied to the pixel by the potential difference between the unselected signal and the data signal, and the optical response state of the pixel is maintained by the AC stabilizing effect. State or light-blocking state, and there is a negative initialization pulse of symmetrical waveform for all the positive initialization pulses, and the first pulse group is a write pulse or initialization for changing the pixel to a desired optical response state. The cathode of the symmetrical waveform for all positive polarity pulses, including pulses that remain initialized by the pulse group The second pulse group has a frequency exhibiting an alternating stabilizing effect, and a positive pulse and a negative pulse having a symmetrical waveform are alternately formed. Method of driving. The method according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal showing negative dielectric anisotropy in the frequency range of an alternating pulse in the second pulse group.