JPH03114025A - Driving method for matrix type ferroelectric liquid crystal panel - Google Patents

Abstract

PURPOSE:To shorten the write time of one screen by inverting the polarity of a reset signal voltage and selecting signal voltage at every frame, and applying a reset signal to an N + 1-th line at the time when a selecting signal is applied to an N-th line. CONSTITUTION:The pulse polarity of the latter half of a reset signal and the pulse polarity of the first half of a selecting signal are the same, a picture element is reset by both these pulses, and write is executed by a pulse of the latter half of the selecting signal. In a first frame, all picture elements in which an information signal of a selection period Ts is on, and a picture element in which an information signal of a reset period Tr is off, and also, the informa tion signal of the selection period Ts is off are written. In a second frame, the polarity of the reset signal and the selecting signal is reversed, and all picture elements in which the information signal of the selection period Ts is off, and a picture element in which the information signal of the reset period Tr is on, and also, the information signal of the selection period Ts is on are written. In such a way, the time required for rewriting of one screen can be shortened.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for driving a matrix type liquid crystal panel using ferroelectric liquid crystal, and in particular to a method for driving a matrix type liquid crystal panel that has a large screen and high speed display. Regarding drive method.

[Conventional technology]

In recent years, matrix-type liquid crystal panels have become larger and denser, but in order to achieve even higher density, matrix-type liquid crystal panels that utilize the memory properties, high-speed response, and wide viewing angle characteristics of ferroelectric liquid crystals are being developed. Panels are being studied. However, the operating principle of this ferroelectric liquid crystal panel is different from the voltage effective value drive of normal nematic liquid crystals, and is determined by the positive and negative polarity of the pulse, its voltage, and the Norculus width. It cannot be operated with the drive method of , and recently,
A number of methods for driving ferroelectric liquid crystal panels have been proposed.

As a driving method for a matrix type ferroelectric liquid crystal panel, there is a driving method (referred to as Conventional Example 1) which is a slightly modified conventional voltage averaging method, as disclosed in Japanese Patent Laid-Open No. 61-94026.

This driving method will be explained using a diagram illustrating a scanning signal and an information signal. The driving method of Conventional Example 1 writes all pixels for the first time using two frames, with only % writing in the on state in odd frames and only white writing in the off state in even frames. Since 4 pulses are required, the writing time becomes longer, it takes time to rewrite one screen, and the non-selection period from one writing to the next writing becomes twice as long (this makes the display contrast too low). It wasn't good.

To solve these problems, as an example of a driving method, JP-A-62-20
Publication No. 4233 is mentioned. This driving method (referred to as Conventional Example 2) will be explained using FIGS. 7 to 9. Figure 9 shows
91 is a configuration diagram of a matrix type ferroelectric liquid crystal panel;
9 is a scanning electrode group, and 92 is an information electrode group. As shown in Conventional Example 2 in FIG. 7, the scanning waveform of this driving method consists of a reset signal, a selection signal, and a non-selection signal, and the voltage of the reset signal is thicker than the voltage of the selection signal.

FIG. 8 is a time series waveform diagram of the 8-division drive of conventional example 2. S4 are the scanning waveforms of the 3rd and 4th lines, respectively.
Dl is the information waveform of the 1st column moon, G31 and 041! -1 is the driving waveform applied to the pixels G61 and G41, respectively.

In this driving method, by applying a reset signal voltage higher than the selection signal voltage during the reset period Tr, it is always reset to white regardless of the information signal, and then, during the selection period Ts, it is either inverted to black or held white. This allows all pixels to be committed in just one frame. Further, at the same time during the time Ts when the selection signal is applied to the scan electrode S3, the scan electrode S
Since the reset signal is applied to 4, the number of pulses required to write one line is essentially 2 pulses, and the writing time of 172 required by the driving method of Conventional Example 1 is now sufficient.

[Problem to be solved by the invention]

In Conventional Example 1 with a simple drive circuit, it takes time to rewrite one screen, and in the driving method of Conventional Example 2 described above, the reset signal voltage must be made higher than the selection signal voltage.
These ICs for driving liquid crystals could not be used because the driving power supply became complicated and the number of voltage levels exceeded the number of voltage levels of ICs commercially available for driving liquid crystals.

The purpose of the present invention is to shorten the time required to rewrite one screen in a ferroelectric liquid crystal driving method, and further,
It is an object of the present invention to provide a driving method that can be configured using a relatively simple driving circuit with a small number of voltage levels and even a commercially available liquid crystal driving IC.

[Failure to solve the problem]

In order to achieve the above object, a scanning waveform according to the present invention includes a reset signal, a selection signal, and a non-selection signal,
The reset signal voltage and the selection signal voltage may be the same voltage, and the polarity of each signal is inverted every frame.

Also, when the selection signal is applied to the Nth line,
By applying a reset signal to the +1st line, most pixels are essentially written with 2 pulses.
The writing time for one screen can be shortened.

[Effect]

In the present invention, unlike Conventional Example 2, when the reset signal voltage and the selection signal voltage are the same, in the first frame, some pixels are insufficiently written due to information and noise signals when the reset signal is applied. However, in the second frame, by applying the reset signal and selection signal with reversed polarity,
Even pixels with insufficient writing can be completely written.

Moreover, since most pixels can be written in only one frame, it is actually driven by two pulses, and the writing time can be reduced compared to the driving method using four pulses in Conventional Example 1.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

The liquid crystal used in this example was a mixture of ester-based ferroelectric liquid crystals, and the alignment was performed by a rubbing method, and the distance between the substrates was about 2 μm.

FIG. 9 is a configuration diagram of a matrix type ferroelectric liquid crystal panel used in the conventional example and the present invention. 91 is a scanning electrode group, 92 is an information electrode group, and 1 to 10 μm between them.
A large amount of ferroelectric liquid crystal is sandwiched between them. Here, for simplicity, when displaying in binary, the pixels indicated by diagonal lines are turned on (black) and the other pixels are turned off (white).

Figures 1, 3, and 5 are waveform diagrams of drive signals according to the present invention, and Figures 2, 4, and 6 are diagrams showing the number of scanning electrodes (8 scanning electrodes) (1/8 duty cycle) using them. ) is an example of a time series waveform diagram of a 1/4 bias ratio. In each case, S6 is the scanning waveform applied to the scanning electrode in the third row, S4 is the scanning waveform applied to the scanning electrode in the fourth row, S5 is the scanning waveform applied to the scanning electrode in the fifth row, and Dl is the scanning waveform applied to the scanning electrode in the first row. This is an information waveform applied to the information electrodes of the eye. G31 is in the on state with the waveform applied to the pixel G31, and G41 is in the off state with the waveform applied to the pixel G41.

(Embodiment 1) FIG. 1 is a signal example in which the polarities of the reset signal and the selection signal are reversed between odd frames and even frames. Since the polarity of the second half pulse of the reset signal and the first half pulse of the selection signal are the same, the pixel is essentially reset by these two pulses, and four writing operations are performed by the second half pulse of the selection signal. The reset signal voltage and selection signal voltage were set to be the same voltage. FIG. 2 is a time-series waveform diagram of the signal shown in FIG. During the time Ts when the selection signal is applied to S3, the reset signal is applied to S4 at the same time,
Similarly, the reset signal is applied to 85 during the time when the selection signal is applied to 84.

Here, the operating voltage of the ferroelectric liquid crystal will be explained. Figure 10 shows a ferroelectric liquid crystal panel with a cell thickness of 2 μm.
Width: 60 μsec, 80 μSeC, 120 μsec
This figure illustrates the values of the operating voltage vth and the operating voltage ythx pulse width when the display is reversed from black to white when a single pulse of c is applied and the pulse voltage is gradually increased. It can be seen that the operating voltage decreases as the pulse width becomes wider, and on the other hand, the value of operating voltage x pulse width does not change much, but it increases as the pulse width becomes wider.

Therefore, Vth at pulse 1@Ts2 is 2V0(:
The following description assumes that Vth (4V0) is satisfied.

In the reset period Tr of the first frame in FIG. 2, it is uncertain whether the information electrode signal is on or off, and the pulse in the latter half of the reset period when it is off is 4 pulses like G31.
■o, and the pulse of Tsl in the first half of the selection period is also added, so the reset pulse is 6VO or 8■. Since it far exceeds yth, it must be reset to white, which is the off state. Next, the negative selection pulse applied to the pixel during the selection period Ts2 is 4VO when it is on, depending on the applied information signal, and since it exceeds Vth, it is written in black. However, when it is off, the write pulse is 2Vo, and since it is less than yth, writing is not possible and the reset white state is maintained.

Next, when the information signal in the reset period Tr is on, the reset pulse is 2Vo, as in G41, and when the information signal is off, the pulse voltage of the first half period TSI of the selection pulse is also 2V, and is added. and 4■. However, as explained above, since the pulse width is widened, the value of the panel operating voltage x pulse width is also increased, so it is impossible to completely reset. +1 when the information signal is off, the pulse 'IEE of the selection period Ts2 is 4V
.

Therefore, it is written in black. Therefore, in the first frame, all pixels for which the information signal of the selection period Ts is on and pixels for which the information signal of the reset period Tr is off and the information signal of the selection period Ts are off are written.

In the second frame, by reversing the polarity of the reset signal and the selection signal, all the pixels have the information signal of the selection period Ts off, and the information signal of the reset period Tr is on and the information signal of the selection period Ts is on. The pixels are scented.

Therefore, although it is not possible to write completely in one frame as in Conventional Example 2, the writing time can be reduced compared to the two-frame drive method in Conventional Example 1, and the non-selection period until the next selection period after writing can be reduced. Since the period is also shortened, the display contrast has also increased.

Normally, ferroelectric liquid crystal panels have afterimage development, so writing operations must be performed several times, but in Conventional Example 1, a panel that required 10 frames of writing could be used with the driving method of the present invention. As a result, writing was completed in 6 to 7 frames.

(Example 2) FIG. 3 is a signal example in which the drive waveform of Example 1 is provided with a pause period in which no voltage is applied. The reset period, selection period, and non-selection period are each divided into three, and the final period is a rest period. FIG. 4 is a time-series waveform diagram of the signal in FIG. 3, and is the same as FIG. 2 except that there is a pause period. In Fig. 2, the pulse width of the non-selection period applied to the pixel when the information signal repeats on-off-on-off is 2XTS2, but in Fig. 4 with the rest period added, , all have the pulse width of TS2, so the memory state during the non-selection period is stabilized and the display contrast is further improved. In this embodiment, the pause period is the selected period Ts.
However, it is obvious that the ratio of the pause period can be set arbitrarily.

(Example 3) Figure 5 shows waveforms of the signals shown in Figure 1 with the polarity reversed when applying the selection signal to the odd-numbered scanning lines and when applying the selection signal to the even-numbered scanning lines. This is an example. Figure 6 shows
6 is a time-series waveform diagram of the signal of FIG. 5. FIG. Although the reset signal and selection signal are inverted for each scanning line, the selection signal of S6 and the reset signal of 84, which are applied at the same time, have the same waveform, which further simplifies the drive circuit and makes it commercially available. It was possible to drive the LCD panel using a liquid crystal panel driving IC.

〔Effect of the invention〕

According to the present invention, the time required to rewrite one screen can be shortened, and the display quality can be further improved, while being configured with a relatively simple drive circuit with a small number of voltage levels.

[Brief explanation of drawings]

Figures 1, 3, and 5 are waveform diagrams of the drive signals used in the present invention, Figures 2, 4, and 6 are time series 1 drive waveform diagrams corresponding to the respective drive signals, and Fig. 7 is a waveform diagram of the drive signal of the conventional example, Fig. 8 is a time series drive waveform diagram of Fig. 7, and Fig. 9 is a waveform diagram of the drive signal of the conventional example.
The figure is a configuration diagram of a matrix type ferroelectric liquid crystal panel used in the conventional example and the present invention, and FIG. 10 is a graph showing the relationship between the driving voltage and the applied pulse width of the ferroelectric liquid crystal panel. 91... Scanning image group, 92... Information cable group, G61... Pixel 3rd row, 1st column, G41... Pixel 4th row, 1st column. eye. Figure 3 Figure 4 Figure 5 Figure 8 Figure 92 Figure 9

Claims (3)

[Claims] (1) Driving a matrix type ferroelectric liquid crystal panel in which ferroelectric liquid crystal is sandwiched between a first substrate on which a plurality of scanning electrodes are formed and a second substrate on which a plurality of information electrodes are formed. In the method, the scanning waveform applied for each scanning line includes a set of positive and negative reset signals that sets the initial state of the pixel formed between the two electrodes to either white or black;
a set of positive and negative selection signals for inverting the pixel to either black or white according to an information signal applied from an information electrode;
and a non-selection signal, and has a waveform in which the positive and negative polarities of the reset signal and selection signal are reversed every fixed frame, and in each scanning line, the selection signal of the scanning waveform is applied to the Nth line. 1. A method for driving a matrix type ferroelectric liquid crystal panel, characterized in that when the N+1th line is driven by applying a reset signal of the scanning waveform. (2) A method for driving a matrix type ferroelectric liquid crystal panel according to claim 1, characterized in that a pause signal for maintaining the display state is added to the reset signal, selection signal, and non-selection signal of the scanning waveform. . (3) The method for driving a matrix type ferroelectric liquid crystal panel according to claim 1 or 2, characterized in that the polarities of the reset signal and the selection signal of the scanning waveform are reversed for each scanning line.