JPH0458220A - Driving method of ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To uniformly set molecular fluctuation in picture elements independently of the classification and contents of a non-select signal, namely, an information signal by equalizing quantities of transmitted light of non-selected picture elements in a certain period of the non-select signal, namely, the information signal. CONSTITUTION:A driving circuit consists of an FLC cell 1, segment side driving circuit 3, latch circuit 5, segment side shift register 7, common side driving circuit 9, common side shift register 11, controller 13, driving power supply circuit 15, picture information input part 17, etc. In this driving circuit, the information signal generated based on picture information inputted from a picture information input part 17 by the controller 13 is supplied to the segment side shift register 7 and the common side shift register 11. The FLC cell 1 is driven by driving circuits 3 and 9 to display a picture or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a technique for suppressing screen flickering and improving display quality in a display element using ferroelectric liquid crystal.

[Prior art] Regarding display elements using ferroelectric liquid crystal, Japanese Patent Application Laid-open No. 61-
As shown in No. 94023, etc., a liquid crystal cell is constructed by facing two glass substrates that have been subjected to alignment treatment and have transparent electrodes formed on their inner surfaces while maintaining a cell gap of about 1 to 3 microns. , one in which ferroelectric liquid crystal is injected is known.

The characteristics of the above display element using ferroelectric liquid crystal are that the ferroelectric liquid crystal has spontaneous polarization, so the coupling force between an external electric field and the spontaneous polarization can be used for switching, and the long axis direction of the ferroelectric liquid crystal molecules is the polarization of the spontaneous polarization. Since there is a one-to-one correspondence with the direction, switching can be performed depending on the polarity of the external electric field. In addition, since ferroelectric liquid crystals generally use chiral smectic liquid crystals (SmC*, SmH*), the long axes of liquid crystal molecules exhibit a twisted orientation in the bulk state. 6N, A. CLARK et al., MCLC, 1983, Vol. 1
94, pp. 213-234.

The structure of an actual ferroelectric liquid crystal cell used a simple matrix substrate as shown in FIG. This board is shown in Figure 5 (
As shown in a), ITO stripe electrodes 32.2 are formed on the opposing inner surfaces of the glass substrate 31 at predetermined intervals.
A ferroelectric liquid crystal is injected into a liquid crystal cell having a structure in which an insulating film 33 of iO2) and a polyimide alignment film 34 are sequentially deposited. The ITO stripe electrode has a shape as shown in FIG. 5(b), for example. Note that 35 is a sealing member.

Driving methods conventionally used to display gradation using such a substrate include a voltage modulation method (modulating the pulse height value) and a frequency modulation method (modulating the pulse width). However, in such a method, when a pixel is not selected, there is a large difference in the amount of light transmitted through the non-selected pixel depending on the type of information signal waveform applied to the pixel (this is the write information signal waveform of another pixel).

FIG. 6 shows the difference in information signal waveforms when the voltage modulation method is used. Here, IH" indicates one selection time. In this figure, It
, Is, and 12, and these signals also serve as gradation information in this order.

Incidentally, FIG. 7 shows an example of typical voltage modulated scanning signal waveforms and information signal waveforms.

Furthermore, among these, the difference in optical response of, for example, 11.12 is shown in FIG. 4(a) as an experimental example.

Such a difference in optical response causes flickering on the entire screen in large screens and high-definition cells, significantly reducing display quality.

[Problems to be Solved by the Invention] As described above, the conventional method has the disadvantage that the average transmission amount of non-selected signals varies greatly depending on the information content (type of information signal), resulting in deterioration of display quality. there were. Moreover, this phenomenon was particularly remarkable in the voltage modulation method and the pulse width method.

The purpose of the present invention is to solve the problems in the conventional example described above.
The purpose of this invention is to prevent screen flickering regardless of the type and content of information signals, thereby improving the display quality of a display element using ferroelectric liquid crystal.

[i! [Means and effects for solving the problem] According to the present invention, an information signal waveform is composed of a voltage signal portion including information content and a voltage signal portion not including information content, and the signal portion including information content and the information content are separated. The time low average value of the sum of the amounts of transmitted light of non-selected signal pixels in the signal portion that does not include is controlled to a constant value regardless of the information content.

This makes it possible to equalize the amount of transmitted light when not selected (light amount variation D due to molecular fluctuations of black and white pixels), thereby improving display quality. This method is particularly effective in a method of displaying gradations by forming a threshold distribution within a pixel and changing the selection voltage or pulse width.

[Embodiment 1] Hereinafter, the present invention will be described in detail with reference to the drawings. Table 1 shows liquid crystal A used in this example.

The electrode substrate for the display element was a polished glass substrate on which ITO with a sheet resistance of about 40 Ω was formed by sputtering. Furthermore, LQ-1802 (polyimide alignment film) made by Hitachi Chemical Co., Ltd. was baked on the above electrode substrate, and a nylon flocked cloth (hair tip of about 0.3 m) was placed on top of it.
A rubbing treatment was performed in step m). The rubbing treatment was carried out in the same direction up and down. Further, liquid crystal A was injected into the cell in an ISO state, and was allowed to cool and align at night. The cell thickness is approximately 1.4 μm.

The measurement temperature was about 30°C.

Note that FIG. 3 shows the drive circuit used in this example.

The drive circuit shown in the figure uses the above-mentioned electrode substrate.

FLC cell 1, segment side drive circuit 3, latch circuit 5
, segment side shift register 7, common side drive circuit 9, common side shift register 11, controller 13,
It is comprised of a driving power supply circuit 15, an image information input section 17, and the like. In such a drive circuit, information signals generated by the controller 13 based on image information input from the image information input section 17 are supplied to the segment side shift register 7 and the common side shift register 11, respectively. The FLC cells are driven by the respective drive circuits 3 and 9 as described later, and images and the like are displayed.

FIG. 1(A) shows the drive waveform used in the present invention. The pixels on the scanning line to which the scanning selection signal is applied are reset all at once at phase T1. In phase T2, a voltage with an amplitude corresponding to the gradation display (voltage set between 0 and 1±V, 1,
1±v, 1: maximum amplitude voltage)v2 is applied to the information line. The pixels on the scanning line to which this voltage V2 is applied produce optical transmittance according to the gradation information. In phase T3, a voltage −V2 with the same amplitude and opposite polarity to the applied voltage in phase T2 is applied.
is applied. The periods of phases T2 and I3 are equal to each other.

Phase T4 is an effective phase for preventing flickering, and the voltage applied during this phase T4 has a maximum amplitude voltage of 1±V11-1±V, and a bipolar pulse with an amplitude of 1 is applied to the information line. is applied to

It diagram (B) shows a timing chart when the drive waveform shown in Figure 1 (A) is used.
, the information signal applied to the information line corresponds to a voltage signal portion containing information content, and the voltage signal applied to the information line at phase T4 corresponds to a voltage signal portion not containing information content. .

'$1 Figure (C) shows the information signal waveform of the present invention.

In the figure, the time indicated as IH' is one line scanning time. In this IH' time, the part indicated as "A" indicates the information content, and the part indicated as "B" indicates "
This part is combined with the part "A" and contributes to making the amount of transmitted light between IH' constant regardless of the part "A".

To explain the operation, the waveform 11' in Fig. 1(C) shows "A".
The voltage value at the portion ``is larger than the voltage value at the A' portion of I2 and Is.

(In other words, consider a case where such an information signal is applied as a non-selection signal.) If a voltage signal is applied only to the "A" part, for example, the fluctuation when a black pixel is not selected is I+ > Is >I2, and the magnitude of the fluctuation varies depending on which non-selection signal is applied to the pixel, resulting in deterioration of display quality. However, in the present invention, the "B" part is replaced by "A".
” by setting I+, 1
It is possible to make the fluctuations of all the pixels to which 2' and Is' are equal.

As a specific experimental example, 11Iz', Is'
The waveforms when the voltage is applied are shown in FIGS. 4(b) and 4(c). It is clear from these figures that in the cases of Figures 4(b) and (c), the fluctuation of the non-selected pixel is less dependent on the non-selected signal than in the case of (a), and the ferroelectric liquid crystal cell The display quality has been significantly improved.

In addition, the width of each pulse in FIG. 1(C) is 40 μs, the voltage value is each (therefore, IH'-160 μs), and the arrangement of "B" section in FIG. 1(C) is similar to "A" section. However, the actual arrangement of the "B" section is before and after the "A" section, regardless of the presence or absence of temporal adhesion. It suffices if the setting is set so that it becomes "significantly".

However, the period needs to be within a period that is visually perceived as one by humans. In other words, too IH
If ' is made too long, the signals will be separated by the human eye, and the meaning of equalizing fluctuations when not selected will be lost.

[Embodiment 2] As another embodiment, FIG. 2 shows an example of improvement of another non-selection signal (information signal). It can be seen that in this case as well, the amount of transmitted light within IH' can be kept constant regardless of the information content.

[Effects of the Invention] As explained above, according to the present invention, the non-selection signal (
By equalizing the amount of transmitted light of unselected pixels within a fixed period of the information signal, uniform molecular fluctuation within the pixel can be set regardless of the type and content of the unselected signal (information signal).

This suppresses flickering and the like on the screen of a ferroelectric liquid crystal (FLC) display element, making it possible to significantly improve display quality.

[Brief explanation of drawings]

FIG. 1(A) is a waveform diagram according to an embodiment of the present invention, FIG. 1(B) is a timing chart diagram thereof, and FIG.
C) is a waveform diagram showing an example of a non-selection signal used in a method according to an embodiment of the present invention; FIG. 2 is a waveform diagram showing an example of a signal used in a method according to another embodiment of the present invention; FIG. 3 is a block diagram showing a drive circuit used in the method according to the present invention, and FIG. 4 is a waveform diagram showing signal waveforms of the conventional example and the method of the present invention. FIG. J5 is a cross-sectional view and a plan view showing a conventional cell structure, FIG. 6 is a waveform diagram showing an example of a conventional non-selection signal, and FIG. 7 is a waveform diagram showing a conventional drive signal. A: Information content display section, B: Transmitted light amount adjustment section, IH': 1 line scanning time, 1: FLC cell, 3 segment side drive circuit, 5 near: 9 = latch circuit, segment side shift register, common side drive Circuit, :Common side shift register, :Controller, :Drive power supply, :Image information input section.

Claims (3)

[Claims] (1) When matrix-driving a ferroelectric liquid crystal element in which a ferroelectric liquid crystal is arranged between two electrode substrates arranged facing each other, the information signal waveform applied to the ferroelectric liquid crystal element is A temporal average of the sum of the amplitude of the voltage signal part containing information content and the amplitude of the voltage signal part not containing information signal, which is composed of a voltage signal part containing information content and a voltage signal part not including information content. A method for driving a ferroelectric liquid crystal, characterized in that the value is equal to the maximum amplitude of a voltage signal portion containing information content. (2) Claim 1, characterized in that the voltage signal part containing information content and the voltage signal part not including information signal are each composed of an alternating current signal whose temporal average value is 0.
2. Method for driving a ferroelectric liquid crystal described in Section 1. (3) The method for driving a ferroelectric liquid crystal according to claim 1 or 2, wherein the non-selected pixels are black pixels.