JPH0437409B2 - - 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] Ferroelectric liquid crystals have recently been attracting attention in place 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, it is not preferable that a DC component is applied to the pixels for a long time, and a driving method that takes this point into account is required. One driving method that does not apply this DC component to pixels for a long time is "SID 85Digest" (1985) (P.135-P.134).
There are several driving methods. 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 direct current component may be applied to the pixel for a long time, which may reduce the transparent electrode and cause it to darken, or cause deterioration of the liquid crystal. I had the problem of waking up. 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 to a pixel, then T = 4 x t x N (N is the number of scanning lines). / screen), the rewriting time T was long, the number of scanning lines could not be increased much, and the problem was that it was not suitable for displaying moving images.

The present invention does not cause blackening of the transparent electrode or deterioration of the liquid crystal even when driven for a long time, shortens the rewriting time, and furthermore allows the number of scanning lines to be increased within the same rewriting time. .

[Means for Solving the Problems] The present invention forms a plurality of pixels using a liquid crystal having an AC stabilizing effect, sequentially supplies an initialization signal and a subsequent selection signal to the scanning electrodes, and The data signal is supplied in synchronization with the supply of the selection signal, and the data signal contains a frequency component corresponding to the frequency at which the liquid crystal exhibits an AC stabilizing effect, and the pixels are first initialized by an initialization pulse. After the initialization, the pixel is brought into a desired optical response state by a write pulse, and thereafter the optical response state of the pixel is maintained by an AC pulse, and the average voltage value of the write pulse is equal to that of the initialization pulse. The average voltage value and absolute value are equal and the polarity is different, and the AC pulse has a frequency that exhibits an AC stabilizing effect, and the negative polarity pulse is present in contrast to the positive polarity pulse. , has achieved the above objectives.

[Example] In FIG. 1, scanning electrodes L ₁ to L ₇ and control electrodes
A plurality of pixels are formed by interposing a ferroelectric liquid crystal having an AC stabilizing effect between R ₁ and _{R 5} .
The selection circuit SE sends an initialization signal RS ₁ (Fig. 2) that sequentially initializes the scanning electrodes L ₁ to _{L 7} in a time-sharing manner;
The selection signal S ₁ (Fig. 2), which is selected in a time-division manner, is
Generated at the timing shown in the figure, and when this initialization signal and selection signal are not supplied, the non-selection signal NS ₁ (Figure 2)
occurs. The initialization signal RS ₁ consists of a voltage V,
The selection signal S ₁ consists of a voltage (-V±2H), and the non-selection signal NS ₁ consists of a voltage ±3H.

On the other hand, the drive control circuit DR outputs 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 on the scanning electrode to which the selection signal S ₁ is supplied. Generating and controlling electrodes
Supplied to R ₁ to R ₅ . That is, a response signal D 1 is supplied to the control electrode of a pixel for which a response state (for example, a light transmission state) is desired, and a reverse response signal D ₁ is supplied to the control electrode of a pixel for which a reverse response state (for example, a light blocking state) is desired. It supplies RD ₁ .

Both the response signal D ₁ and the reverse response signal RD ₁ include frequency components corresponding to the frequency at which the liquid crystal exhibits an AC stabilizing effect.

By supplying the above signals, the initialization pulse P ₁ or P ₂ is first applied to the pixel for which the response state is desired by supplying the initialization signal RS ₁ , and the pixel is once initialized to the saturated inverse response state. After that, a write pulse P ₃ is applied according to the selection signal S ₁ and the response signal D ₁ to enter a saturated response state. Initialization pulse P ₁ or
P ₂ is a DC pulse of voltage -V superimposed with a high frequency AC pulse of voltage ±H, and write pulse P ₃ is a DC pulse of voltage V superimposed with a high frequency AC pulse of voltage ±H. . Therefore, each pulse has a DC component, but since the write pulse P ₃ is applied after the initialization pulse P ₁ or P ₂ , the average voltage level applied to the pixel is reduced to 0.
It can be done. In other words, since the initialization pulses P ₁ and P ₂ and the write pulse P ₃ have the same absolute value of the average voltage value but different polarities,
The DC component is canceled out and becomes 0.

Pulses P ₁ , P ₂ , and P ₃ are superimposed with ±H high-frequency AC pulses, but because the voltage is low, the AC stabilizing effect is small, and they are in a saturated response state and a saturated reverse response state at +V and -V, respectively. is switched to. After applying the pulse _P3 , an AC pulse _P5 or _P6 having a frequency that exhibits an AC stabilizing effect is applied by the non-selection signal _NS1 .
The optical response state is stabilized by the AC stabilizing effect.

In both of the AC pulses P ₅ and P ₆ , pulses of positive polarity and pulses of negative polarity whose waveforms are symmetrical are generated alternately, so that a biased DC component is not applied to the pixel.

On the other hand, for pixels for which a reverse response is desired, an initialization pulse is applied.
After being initialized to the saturated reverse response state by applying P ₁ or P ₂ , the selection signal S ₁ and the reverse response signal RD ₁
A write pulse _P4 is applied by. pulse
P ₄ is a DC pulse of voltage V superimposed with a high voltage, high frequency AC pulse of voltage ±3H, and due to the AC stabilization effect of ±3H, a saturated response state does not occur, and a saturated reverse response state is maintained. . Also in this case, the average voltage value of the initialization pulse P ₁ or P ₂ and the average voltage value of the write pulse P ₄ have the same absolute value but different polarities, so that the DC components are canceled out. Furthermore, after applying the above pulse _P4 ,
When AC pulse P ₅ or P ₆ is applied, the reverse response state is stabilized by the AC stabilizing effect. FIG. 4 shows examples of waveforms applied to pixels for which these responses and reverse responses are desired.

In this way, the average voltage level applied to the pixels can be reduced to 0, and blackening of the transparent electrode, deterioration of the liquid crystal, etc. will not occur. Furthermore, by introducing the initialization signal, the next line can be initialized at the same time as the selection signal is supplied, reducing the time required to rewrite the screen.

By the way, the write pulses P ₃ and P ₄ in this example are not composed of a single voltage, but are composed of two voltages.
Although it is composed of different voltages, each of them is referred to as a write pulse, and the total application time of each is referred to as a pulse width. Similarly, the initialization pulses P ₁ and P ₂ are collectively referred to as an initialization pulse, and the total application time of each is referred to as a pulse width. This designation is the same in each of the following examples.

The frequency of the AC pulses P ₅ and P ₆ should preferably be an integral multiple of 4 times or more the frequency for time-division scanning of the scanning electrodes L ₁ to L ₇ , and the pulse height H should be set according to the dielectric anomaly of the ferroelectric liquid crystal. It is determined appropriately in relation to the magnitude of orientation. In other words, when a high frequency AC pulse of ±H is superimposed on a DC pulse of voltage -V or V,
When switched to a saturated reverse response state and a saturated response state, respectively, and a high frequency AC pulse of ±3H is superimposed, the pulse height H is determined so as not to change the optical response state.

FIG. 5 shows other examples of signal waveforms, which allow the same driving as in FIG. 2.

Fig. 6 shows yet another example of signal waveforms, which can perform the same driving as in Fig. 2, but especially when changing from a response state to a reverse response state, and from a reverse response state to a response state. This is effective for pixels that have asymmetric switching characteristics and are likely to be in a reverse response state and difficult to be in a response state. That is, a write pulse P ₁₅ containing only a DC component and not including a high-frequency AC pulse component is applied to a pixel for which a response state is desired by the selection signal S ₃ and the response signal D ₃ which is a data signal.
This makes it easier to obtain the response status.

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.

In addition, by applying a high-frequency AC pulse with a voltage intermediate between the response signal and the reverse response signal, or a signal that combines the response signal and the reverse response signal at a predetermined ratio to the control electrodes _R1 to _R5 , Halftones are obtained by setting the amplitude of the high-frequency AC pulse superimposed on the DC pulse V to an intermediate value between ±H and ±3H, or by applying a signal that combines ±H and ±3H in the desired ratio. It is also possible.

Furthermore, in the above embodiment, a matrix optical device as shown in FIG. 1 has been 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 use in other applications. In this case, high contrast can be achieved by setting the initialization state to a dark state (light-blocking state).

[Effects of the Invention] According to the present invention, the average voltage values of the initialization pulse and the write pulse applied to the pixel are equal in absolute value and opposite in polarity, and the alternating current pulse is different from that of the positive polarity pulse. Since pulses of negative polarity with symmetrical waveforms are generated alternately, the transparent electrode does not darken or the liquid crystal deteriorates even after long-term driving. Moreover, by introducing the initialization signal, the next line can be initialized at the same time as the selection signal is supplied, and the rewriting time can be shortened. In other words, the number of digits scanned within the same time can be increased.

In addition, since only the above-mentioned AC pulse is applied when not selected, a stable holding force can be obtained due to the AC stabilizing effect, and this has great effects such as high 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 voltage waveforms for realizing the present invention, and Fig. 3 is an explanatory diagram showing an _example of a matrix type liquid crystal optical device.
An explanatory diagram showing the signal supply timing to L ₇ , FIG. 4 is a waveform diagram showing an example of a pulse applied to a pixel, and FIGS. 5 and 6 each show other waveforms for realizing the present invention. FIG. _R1 to _R5 ...control electrode, _L1 to _L7 ...scanning electrode,
RS ₁ , RS ₂ , RS ₃ ... Initialization signal, S ₁ , S ₂ , S ₃ ...
...Selection signal, NS ₁ , NS ₂ , NS ₃ ...Non-selection signal,
D ₁ , D ₂ , D ₃ ...Data signal, RD ₁ , RD ₂ , RD ₃
...Data signal, _P1 , _P2 , _P7 ...Initialization pulse,
P ₈ , P ₁₃ , P ₁₄ ... Initialization pulse, P ₃ , P ₄ , P ₉ ...
...Write pulse, _P10 , _P15 , _P16 ...Write pulse, _P5 , _P6 , _P11 ...AC pulse, _P12 , _P17 , _P18
...AC pulse.

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, an initialization signal and a subsequent selection signal are sequentially supplied to each scanning electrode, and a non-selection signal is supplied when each initialization signal and selection signal are not supplied. , A data signal containing a frequency component corresponding to the frequency at which the liquid crystal exhibits an AC stabilizing effect is supplied to each control electrode in synchronization with the supply of the selection signal, and by 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 , a pulse that changes the pixel to a desired optical response state or a pulse that maintains the state initialized by the initialization pulse, and whose average voltage value is equal in absolute value to the average voltage value of the initialization pulse. The AC pulses have a frequency that exhibits an AC stabilizing effect, and are characterized in that pulses of positive polarity and pulses of negative polarity whose waveforms are symmetrical occur alternately. A method for driving a matrix type liquid crystal optical device. 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.