JP2652886B2 - Driving method of liquid crystal device - Google Patents

Abstract

A liquid crystal apparatus includes: a ferroelectric liquid crystal device comprising an electrode matrix including a plurality of scanning lines and a plurality of data lines intersecting with the scanning lines, and a ferroelectric liquid crystal disposed between the scanning lines and data lines, and drive means for sequentially applying a scanning signal to the scanning lines for selecting a particular scanning line, and for applying data signals for the pixels on the selected scanning line to the data lines; wherein each of the data signals has a plurality of pulses including a pulse in a controlled phase and a pulse in an auxiliary phase, and the scanning signal for the selected scanning line has a compensation pulse for compensating the pulse in the auxiliary phase of a data signal for a pixel on the selected scanning line.

Description

The present invention relates to a method for driving a liquid crystal device using a chiral smectic liquid crystal substance.

[Prior Art] In recent years, as an improved type of a conventional TN type liquid crystal device, the use of a liquid crystal device having bistability has been disclosed in both Clark and Lagerwall by Japanese Patent Laid-Open No.
-107216 and U.S. Pat. No. 4,367,924. Generally, a ferroelectric liquid crystal having a chiral smectic C phase (SmC *) or an H phase (SmH *) is used as the bistable liquid crystal. This liquid crystal has a bistable state composed of first and second optically stable states with respect to an electric field. Therefore, unlike the optical modulation element used in the above-mentioned TN type liquid crystal, for example, one electric field vector In contrast, the liquid crystal is oriented in the first optically stable state, and the liquid crystal is oriented in the second optically stable state for the other electric field vector. In addition, the liquid crystal element has a property of rapidly taking one of the above two stable states in response to an applied electric field and maintaining the state when no electric field is applied. By utilizing such properties, a substantial improvement can be obtained for many of the problems of the conventional TN-type device described above.

In addition, many driving methods for driving such a bistable ferroelectric liquid crystal element in a matrix have been proposed. FIG. 4 shows the waveforms of the driving signals in one example. S ₁ ′ to S ₄ ′ are scanning signals corresponding to the scanning signal lines s _{1 to} s ₄ in the case of the display pattern as shown in FIG.
I ₁ ′ and S ₂ ′ are information signals corresponding to the information signal lines i ₁ and i ₂ , and (I ₁ ′ −S ₃ ′) and (I ₂ ′ −S ₂ ′) are waveforms.
The composite waveforms of I ₁ ′ and S ₃ ′ and I ₂ ′ and S ₂ ′ are shown as time-series waveforms. This driving waveform is a driving method of a type in which all pixels on a selected scanning line are written once to “black”, and then “black” is held or “white” is written according to information. Are devised so as to reduce "flicker" during matrix driving.

[Problems to be solved by the invention] However, the above-mentioned conventional example has the following problems.

(1) Although the response speed of the liquid crystal itself is faster than that of the conventional nematic liquid crystal, the frame frequency in the case of matrix driving is slow.

(2) The allowable range of the voltage value or pulse width of the drive pulse that can be matrix-driven, that is, the drive margin is small.

Therefore, as an improved type for the problem (1), as shown in FIG. 5, a driving method for increasing the frame frequency by providing an overlap in the scanning line selection period has been proposed. In the figure, S ₁ ″ to S ₄ ″ and I ₁ ″, I ₂ ″ are the fourth
2 shows a scanning signal and an information signal in the same case as in the drawing. In this driving method, the frame frequency can be increased 1.5 times as compared with the driving method shown in FIG. However, the drive margin described in the problem (2) tends to further decrease, and it is difficult to achieve both a high frame frequency and a sufficient drive margin.

An object of the present invention is to provide a method for driving a liquid crystal device using a chiral smectic liquid crystal, which achieves both higher frame frequency and secures a driving margin, in view of the problems of the related art.

Means for Solving the Problems In order to achieve this object, according to the present invention, a scanning signal line of a liquid crystal element having a chiral smectic liquid crystal material sandwiched between a scanning signal line group and an information signal line group is sequentially selected and By supplying an information signal to the information signal line within the selection period, erasing pixels on the selected scanning signal line to a predetermined state in the erasing phase unit, and holding or inverting that state in the control phase unit In the method of driving a liquid crystal device that determines a display state of a pixel, the information signal includes a pulse of a control phase part whose polarity is determined according to display information, and a pulse width opposite to the pulse of the control phase part and shorter than that. A scanning phase selection signal for selecting a scanning signal line includes a pulse of an erasing phase section and a pulse of an erasing phase. A pulse of a control phase part having a polarity opposite to that of the phase part pulse and a pulse of an auxiliary phase part having a polarity opposite to that of the control phase part are provided. The characteristic feature is that a voltage having the same polarity is not continuous from the control phase section to the auxiliary phase section. The scan selection signal has a period that is simultaneously supplied to at least two or more scan signal lines.

Here, the “control phase section” is a phase portion that determines whether to maintain or reverse the state after erasing in the erasing phase section, and in the information signal,
The polarity of the control phase unit is determined according to the information to be displayed. The “auxiliary phase unit” is a period during which a pulse having a polarity opposite to that of the pulse of the control phase unit is applied so that the DC component is not continuously applied to the non-selected pixels for a long time. Since this pulse has a voltage value such that the composite voltage waveform does not exceed the threshold value unlike the pulse of the control phase section, it does not basically affect the display state (white or black) to be determined. .

[Operation] In this configuration, the pulse of the auxiliary phase portion of the information signal is necessary to reduce the flickering of the image, etc., but the composite voltage applied to the pixels to be kept in the erased state due to the pulse However, assuming that a voltage of the same polarity has a continuous waveform from the control phase portion to the auxiliary phase portion, the voltage of the auxiliary phase portion makes it easy for the pixel to be inverted involuntarily. As a result, the drive margin deteriorates. This tendency of deterioration becomes stronger as the frame frequency is increased. However, in the present invention, the scan selection signal includes a pulse of the auxiliary phase part having a polarity opposite to that of the pulse of the control phase part, whereby the combined voltage applied to the pixels to be maintained in the erased state is output from the control phase part. Since the voltage having the same polarity is not continuous over the auxiliary phase portion, the inversion of the pixel is suppressed,
The driving margin is greatly improved. Therefore, even if the frame frequency is increased by simultaneously supplying the scan selection signal to two or more scan signal lines, a sufficient drive margin is secured.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a waveform of a drive signal in a liquid crystal element according to an embodiment of the present invention. FIG. 1 (a) shows a selection signal waveform, and FIGS. 1 (b) and 1 (c) show “white” and “black” waveforms. 4 shows an information signal waveform corresponding to image information. In FIG. (B), the pulse width t _2, the phase control the phase of the voltage value V _5, the pulse width t _3, the phase of the voltage value -V ₄ are auxiliary phases. As described above, by forming the information signal into such a pulse configuration, defects in image quality such as "flicker" in non-selection are reduced. The selection signal waveform in FIG. 7A has a pulse width t ₁ and a voltage value V ₁
, The pulse width t ₂ , the control phase of the voltage value −V ₂ , and the auxiliary phase of the pulse width t ₃ and the voltage value V ₃ , that is, the phase for compensating the auxiliary phase of the information signal. Here, the voltage value V ₃ is in the range of _{0 <V 3 <V 1,} | V 3 | = | V 4 | a desirably. The provision of this compensation phase is a feature of the present invention, whereby the driving margin described above is significantly improved.

Further, it is preferable that the pixels on the scanning line selected in the erasing phase be simultaneously erased to a black state.

FIGS. 2A and 2B show time-series waveforms when a display as shown in FIG. 3 is performed by this driving example.

In the figure, S _{1 to} S ₄ are scanning signal lines s ₁ to s _{1 in} FIG.
scanning signal waveform s _4, I ₁ and I ₂ are the information signal lines i ₁ and i ₂ of the information signal waveform of FIG. 3, and (I ₁ -S ₃₎ and (I ₂ -S ₂₎ the information signal waveform I ₁ and a synthetic waveform and the information signal waveform I ₂ and composite waveform of the scanning signal waveform S ₂ scan signal waveform S _3. In particular, the sequence shown in FIG. 2A is preferable because the frame frequency can be set low.

When driven at 1/400 duty at room temperature in accordance with the driving example shown in FIG. 1, compared with the driving method shown in FIG.
The frame frequency has increased about 1.3 times, and the driving margin has increased by about 10%. Further, as compared with the conventional driving method shown in FIG. 5, the driving margin is increased by about 50%.

[Effects of the Invention] As described above, according to the present invention, the scan selection signal includes a pulse of the auxiliary phase unit having a polarity opposite to that of the pulse of the control phase unit. Since the resultant voltage has a waveform in which voltages of the same polarity are not continuous from the control phase unit to the auxiliary phase unit, the driving margin can be greatly improved. Therefore, even if the frame frequency is increased by simultaneously supplying the scanning selection signal to two or more scanning signal lines, a sufficient driving margin can be secured and the driving characteristics can be significantly improved.

[Brief description of the drawings]

1A to 1C are waveform diagrams showing waveforms of drive signals in a liquid crystal element according to an embodiment of the present invention, and FIGS. 2A and 2B are as shown in FIG. FIG. 3 is a timing chart showing a time-series waveform of a driving signal according to various driving examples, FIG. 3 is a schematic diagram illustrating a display pattern by a liquid crystal element, and FIG. 4 and FIG. 6 is a timing chart showing a waveform.

Claims (8)

(57) [Claims] 1. A scanning signal line of a liquid crystal element having a chiral smectic liquid crystal material interposed between the scanning signal line group and the information signal line group is sequentially selected, and an information signal is supplied to the information signal line within a selection period. Then, a pixel on the selected scanning signal line is erased to a predetermined state by an erasing phase unit, and the state is held or inverted by a control phase unit, and a driving method of the liquid crystal device that determines a display state of the pixel In the information signal, a pulse of the control phase part whose polarity is determined according to display information, and a pulse of the control phase part having a polarity opposite to that of the pulse of the control phase part and having a shorter pulse width. And a pulse of an auxiliary phase unit supplied subsequently to the scan signal line, wherein the scan selection signal for selecting the scan signal line comprises a pulse of the erase phase unit and a pulse of the opposite polarity to the pulse of the erase phase unit. A pulse of the control phase section and a pulse of the auxiliary phase section having a polarity opposite to that of the pulse of the control phase section. A method for driving a liquid crystal device, wherein a voltage having the same polarity is not continuous over an auxiliary phase section. 2. The driving method according to claim 1, wherein the scanning selection signal has a period in which the scanning selection signal is simultaneously supplied to at least two or more scanning signal lines. 3. The scanning selection signal is simultaneously supplied to two scanning signal lines during the period, and one of the scanning signal lines is supplied with the pulse of the erasing phase unit and the other is supplied with the auxiliary signal. 3. The driving method according to claim 2, wherein the pulses of the phase section are supplied simultaneously. 4. The information signal is supplied prior to the supply of a pulse of the control phase part, and the information signal is supplied to another auxiliary phase part having a polarity opposite to that of the control phase part and having a shorter pulse width. The driving method according to claim 1, further comprising a pulse. 5. The driving method according to claim 4, wherein a falling edge of a pulse of said another auxiliary phase part coincides with a falling edge of a pulse of said erasing phase part combined with said pulse. 6. The driving method according to claim 1, wherein the voltage value of the pulse of the auxiliary phase portion of the scan selection signal is smaller than the voltage value of the pulse of the erasing phase portion. 7. The driving method according to claim 1, wherein a voltage value of a pulse of the auxiliary phase portion of the scan selection signal is equal to a voltage value of the auxiliary phase portion of the information signal. 8. The driving method according to claim 1, wherein the display state of the pixel in the erased state is black.