JPH06236166A - Method for driving liquid crystal display device - Google Patents

Abstract

PURPOSE:To correct the hysterisis characteristic of a liquid crystal display device and to reproduce an excellent video occurring no flicker by applying a DC voltage always or for a fixed period in addition to a pixel part applied voltage for driving a liquid crystal. CONSTITUTION:First of all, the maximum residual polarization values of respective positive and negative are obtained, and the difference of the absolute values is obtained also, and the applied voltage so that the maximum residual polarization values of positive/negative poles become the same value is set from the result. For obtaining the corrected maximum residual polarization values Pr<+>', Pr<->' of positive/negative poles, the DC voltage is applied to the usual signal of a signal electrode line newly. In such a case, by providing a certain DC component with positive polarity in the usual signal of the signal electrode line, the potential difference provided with the DC component with positive polarity becomes a liquid crystal applied voltage in addition to the potential difference with a usual scanning electrode line. Further, the DC component applied newly is the DC voltage equivalent to DELTAE, and the voltage value is decided by the conditions of ferroelectric material, etc. The liquid crystal is driven by using the signal of the signal electrode line provided with the DC component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of a liquid crystal display device used in a liquid crystal display device in which a liquid crystal containing a ferroelectric film is arranged in a cell having many pixels.

[0002]

2. Description of the Related Art In a liquid crystal display device in which a ferroelectric film is arranged in a cell, the relationship between an electric field E applied to the ferroelectric film and a polarization P generated by the electric field E is roughly shown in FIG. Thus, the polarization P is not proportional to the electric field E and exhibits a hysteresis (history) characteristic. In the figure, Pr is remanent polarization and E
c is called the coercive electric field.

Therefore, when the bias (voltage application) from the outside is cut off, although there is a voltage drop due to capacitance division,
Basically, the remanent polarization level becomes a voltage applied to the liquid crystal, and when the remanent polarization level is different, the remanent polarization level is different even if a constant voltage is applied to the device next time.

Therefore, the following driving method has been conventionally proposed. In the schematic panel structure shown in FIG. 8, paying attention to the Xn line of the scan electrode, the liquid crystal potential is “0” due to the scan electrode and the signal electrode in the selection period.
A voltage waveform that causes (polarization P = 0) or a voltage waveform that causes the liquid crystal potential to become “1” (polarization P = 1) is applied to erase the data held by the liquid crystal (reset Operation), and then, an operation of applying a voltage waveform corresponding to new data between the electrodes (writing operation).

Further, when the selection period shifts to the next line, Xn
When the line is in the non-selection period, a voltage waveform of the same polarity as the voltage written in the liquid crystal or a 0 level voltage waveform is always applied (voltage holding operation). As a result, the spontaneous polarization level written in the writing operation is maintained.

FIG. 9 shows an example of waveforms of the driving method shown above. First, in the reset period, a positive polarity pulse signal (+ Vrst: reset signal) is applied to the scan electrode lines to be reset (hereinafter referred to as scan lines), and the scan electrode lines not to be reset (hereinafter referred to as non-scan lines). ), A negative pulse signal (-Vrst: reset inhibit signal) having a polarity opposite to that of the reset signal is applied.

On the other hand, a signal (-Vrst) having the same potential as the reset inhibit signal is applied to the signal electrode line during the reset period. As a result, a voltage of 2Vrst is applied to the pixel portion connected to the scanning line, and the pixel portion connected to the non-scanning line has no potential change.
The previously written information will be retained. In addition,
The pixel portion shown in FIG. 8 is roughly composed of a liquid crystal layer and a ferroelectric layer.

When the capacitance of the liquid crystal layer is C _LC and the capacitance of the ferroelectric layer is C _F , it is applied to the pixel portion during scanning.
Of Vrst, the voltage V _F applied to the ferroelectric layer is divided into the expression (1). V _F = 2Vrst · C _LC / (C _LC + C _F ) ... (1) [C _LC / (C _LC + C _F ): This is hereinafter referred to as a constant A] This value is spontaneous in the ferroelectric layer. It is a voltage value sufficient to saturate the polarization.

After the reset is completed, the data writing period starts. During this period, the data write pulse signal is written to the scan line and the data write inhibit pulse signal (Vstp) is written to the non-scan line. Further, in the signal electrode line, the data write pulse signal is written to the electrode for writing the ON information, and the data write inhibit pulse signal is written to the electrode for writing the OFF information. In FIG. 9, the data write pulse signal has a 0 potential, but it may be a pulse signal having an arbitrary potential. Further, since the liquid crystal needs to be driven by an alternating current, a reverse polarity potential is applied to the next field.

By the above operation, the data can be correctly rewritten in the selected period, and the voltage of the same polarity as the voltage written in the liquid crystal is always applied in the non-selected period, so that the written liquid crystal is applied. The potential fluctuation was suppressed.

[0011]

The hysteresis characteristic is often caused by the ionic impurities contained in the ferroelectric film and the like, and the absolute value of the remanent polarization is different,
In some cases, the symmetry of the hysteresis characteristic is not satisfied. Since the liquid crystal is originally required to be driven by an alternating current, in the above-described case, even if the same electric field is applied, the positive and negative spontaneous polarizations are different, which causes a problem such as flicker.

The present invention has been made in view of the above circumstances, and drives a liquid crystal display device capable of correcting the hysteresis characteristic of the liquid crystal display device and reproducing a high quality image without flicker. It provides a method.

[0013]

In order to solve such a problem, in the present invention, a new direct current voltage is applied in addition to the conventional liquid crystal applied voltage so that the absolute values of the remanent polarization are the same. Value. Also, in the residual saturation polarization of the hysteresis characteristic that liquid crystal originally has, the smaller absolute value of positive and negative polarities is set as the maximum residual polarization during data writing, and the positive and negative absolute values of residual polarization during data writing are set to the same value. To do. Furthermore, the two driving methods are combined so that the positive and negative absolute values of the remanent polarization are more accurately equalized.

That is, according to the invention of claim 1 of the present application, in a driving method of a liquid crystal display device in which a liquid crystal containing a ferroelectric film is arranged in a cell having a large number of pixels, the hysteresis characteristic of the liquid crystal in the cell is , A liquid crystal display characterized in that, in addition to the voltage applied to the pixel portion for driving the liquid crystal, a direct current voltage is applied all the time or within a certain period of time so that the absolute values of the remnant polarization during writing become the same value. This is a method of driving the device.

Further, according to the invention of claim 2 of the present application, in a driving method of a liquid crystal display device in which a liquid crystal containing a ferroelectric film is arranged in a cell having a large number of pixels, the hysteresis characteristic of the liquid crystal in the cell is , In the saturated remanent polarization of the hysteresis characteristic, the smaller absolute value of positive and negative polarities is set as the maximum remanent polarization during data writing so that the positive and negative absolute values of remanent polarization during writing become the same. A method of driving a liquid crystal display device, characterized in that a voltage applied to a pixel portion is determined and data is written.

Further, in the invention of claim 3 of the present application, in a driving method of a liquid crystal display device in which a liquid crystal containing a ferroelectric film is arranged in a cell having a large number of pixels, the hysteresis characteristic of the liquid crystal in the cell is , In the saturated remanent polarization of the hysteresis characteristic, the smaller absolute value of positive and negative polarities is set as the maximum remanent polarization during data writing so that the positive and negative absolute values of remanent polarization during writing become the same. While determining the pixel section applied voltage, in addition to the pixel section applied voltage for driving the liquid crystal, a DC voltage is always applied,
Alternatively, it is a method of driving a liquid crystal display device, which is characterized in that it is applied within a certain fixed period.

[0017]

According to the first aspect of the invention, in addition to the voltage applied to the pixel portion for driving the liquid crystal, a direct current voltage is applied at all times or within a certain period of time, whereby the hysteresis characteristic of the liquid crystal in the cell is improved. On the other hand, the positive and negative absolute values of the remanent polarization at the time of writing become the same value.

According to the second aspect of the present invention, in the saturated remanent polarization of the hysteresis characteristic, the smaller absolute value of positive and negative polarities is set as the maximum remanent polarization at the time of data writing, and the voltage applied to the pixel portion for driving the liquid crystal is set. Is determined and data writing is performed, whereby the absolute value of the remanent polarization at the time of writing becomes the same value as the hysteresis characteristic of the liquid crystal in the cell.

Further, according to the third aspect of the invention, in the saturated remanent polarization of the hysteresis characteristic, the smaller absolute value of positive and negative polarities is set as the maximum remanent polarization at the time of data writing, and the voltage applied to the pixel portion for driving the liquid crystal is set. In addition to the voltage applied to the pixel portion for driving the liquid crystal, a direct current voltage is applied at all times or within a certain period of time, whereby the hysteresis characteristic of the liquid crystal in the cell is increased during writing. The positive and negative absolute values of the remanent polarization have the same value.

As described above, by driving the liquid crystal by using the liquid crystal driving method according to any one of claims 1, 2 and 3, the asymmetry of the hysteresis characteristic is corrected,
The absolute values of the positive and negative remanent polarization become the same value. Therefore, in the data writing operation to each liquid crystal element by the AC drive, the absolute value of the written data becomes the same value as positive and negative,
The adverse effects such as flicker will not occur.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to Embodiments 1 to 3 shown in the drawings. The present invention is not limited to this.

Example 1 FIG. 1 is an explanatory diagram showing the signal waveforms of each line signal and the voltage applied to the ferroelectric layer in the driving method of Example 1, and FIG. 2 is the strong waveform when the driving method of Example 1 is used. It is explanatory drawing which shows the improved hysteresis characteristic in a dielectric material layer.

In carrying out the liquid crystal driving method of this embodiment, first, the maximum remanent polarization values of positive and negative are obtained, and the difference between their absolute values is also obtained. From the result, the maximum remanent polarization values of positive and negative are made equal. Set the applied voltage.

The maximum remanent polarization values of the positive and negative electrodes before correction are respectively P
r ^+, Pr ^-, each P the maximum remanent polarization of the positive and negative poles of the modified
and, in this embodiment ^{- r + 'Pr' | Pr} + |> | Pr - | assuming.

Maximum remanent polarization value P of positive and negative electrodes after correction
r ⁺ ', Pr ^-' in order to obtain, in this embodiment, newly added to the DC voltage to the signal of the conventional signal electrode lines.
In this case, referring to the signal waveform of the signal electrode line shown in FIG. 1, by providing a positive DC component in the signal of the conventional signal electrode line, in addition to the potential difference from the conventional scan electrode line, The potential difference having a positive DC component becomes the liquid crystal applied voltage. The newly applied DC component is a DC voltage corresponding to ΔE shown in FIG. 2, and the voltage value is determined by the conditions such as the ferroelectric material.

The liquid crystal is driven by using the signal of the signal electrode line having the DC component. Referring to FIG. 1, first,
In the reset period, a positive polarity pulse signal (+ Vrst: reset signal) is applied to the scan electrode lines to be reset (hereinafter, referred to as scan lines) so that the scan electrode lines not to be reset (hereinafter, referred to as non-scan lines) are added. Is a negative pulse signal (-V) having a polarity opposite to that of the reset signal.
rst: Apply reset inhibit signal. Then, -Vrst 'is applied to the signal electrode line at that time. Therefore, the voltage applied to the pixel portion connected to the scanning line and the non-scanning line is expressed by the following equation. Scan line pixel portion voltage _{V S = Vrst + Vrst '(} Vrst'<Vrst) ......... (2) non-scan line pixel portion voltage V _NS = Vrst -Vrst '(= referred to as V _DC) ............... (3 )

Since the non-scanning line pixel portion voltage V _DC can be regarded as an extremely small value for reversing the polarization in the ferroelectric layer, the previously written information is retained.

After the reset is completed, the data writing period starts. During this period, 0 potential or a data write pulse signal is written in the scanning line and Vstp is written in the non-scanning line. Further, in the signal electrode line, 0 potential + V _DC is written in the signal for writing the ON information, and Vstp + V _DC is written in the potential for writing the OFF information. Furthermore, since the liquid crystal needs to be driven by alternating current, in the next field,
A potential of opposite polarity is applied.

By the above operation, the E-P hysteresis characteristic draws a curve that is artificially shifted downward as shown in FIG. 2, so that the absolute values of the maximum positive and negative remanent polarization become the same value. A highly symmetrical hysteresis characteristic can be obtained.

[0030] In the present ^{embodiment, | Pr + |> | Pr} - |
However, of course, in the case of | Pr ⁺ |> | Pr ⁻ |, it is only necessary to reverse the polarity of the DC voltage corresponding to ΔE.

Further, in this embodiment, only the signal on the signal electrode line is provided with the DC component, but the signal on the scan electrode line may be provided with the DC component, or the signal electrode line and the scan electrode line may be provided. Each signal may have a DC component. In short, if the potential difference due to the mutual line has a direct current component for making the absolute value of the positive and negative maximum remanent polarization values equal, the same effect as above can be obtained.
The symmetry of the hysteresis characteristic is improved.

However, when the positive and negative remanent polarization values before correction are already largely different, the DC component included in the signal of the signal electrode line or the scan electrode line also becomes large. For example, a potential difference of | A · Vstp | or more may be applied to the ferroelectric layer of the non-scanning line, and polarization in the ferroelectric layer may be inverted. That is, it is assumed that the written data signal cannot be held during scanning.

In such a case, it is desirable to apply the DC component only during the reset period of the scanning line instead of applying the DC component all the time.

FIG. 3 is an explanatory diagram showing the signal waveform of each line and the signal waveform of the voltage applied to the ferroelectric layer in the driving method using the signal of the scan electrode line having a DC component only during the reset period of the scan line. Note that here also | Pr ⁺ |>
| Pr ^- | to be assumed.

There is no big difference in the driving method itself,
By providing a DC component only in the reset period, a potential difference does not occur in the ferroelectric layer in the non-scanning line, so that it is possible to retain the data signal written during scanning.

Example 2 FIG. 4 is an explanatory diagram showing the signal waveforms of each line signal and the voltage applied to the ferroelectric layer in the driving method of Example 2, and FIG. 5 shows the strong waveforms when driving by the driving method of Example 2. It is explanatory drawing which shows the improved hysteresis characteristic in a dielectric material layer.

In carrying out the liquid crystal driving method of the present embodiment, first, the maximum remanent polarization value of each positive and negative is obtained, and the difference ΔPr between the absolute values thereof is also obtained. Furthermore, the difference ΔPr between the absolute values is calculated by subtracting the absolute value difference ΔPr from the maximum absolute residual polarization value having the higher absolute value.

That is, the maximum remanent polarization value of the positive electrode is P
Let r ^{+ be} the maximum remanent polarization value of the negative electrode Pr ⁻ ,
When r ⁺ |> | Pr ⁻ |, the absolute value | Pr ⁺ '| of the temporary maximum remanent polarization value of the positive electrode is set to the same value as the absolute value | Pr ⁻ | of the maximum remanent polarization value of the negative electrode. ^{ΔPr = | Pr + | - |} Pr - | .............................. (4) | Pr + '| = | Pr - | = | Pr + | - ΔPr ............ (5)

The potential difference between the signal on the signal electrode line and the signal on the scan electrode line, that is, the voltage value corresponding to ΔE shown in FIG. 5, is obtained to obtain this provisional maximum remanent polarization value | Pr ⁺ '|. This voltage value is determined by the conditions such as the ferroelectric material.

Then, in order to change the potential difference which has conventionally determined the maximum remanent polarization value Pr ⁺ to the obtained potential difference value,
In this embodiment, the potential of the reset signal of the scan electrode line is changed.

Liquid crystal driving is performed using the conventional scan electrode lines having different reset signals. Referring to FIG. 4, first, in the reset period, + Vrst is applied to the scan line.
', -Vrst is applied to the non-scanning line, and -Vrst is applied to the signal electrode line at that time. Therefore, in the pixel portion connected to the scan line, + Vrst '+ Vrs
t is being applied. This potential difference is the potential difference that determines Pr ⁺ . Note that the writing period is the same as the conventional one, and thus the description thereof is omitted.

The potential difference applied to the pixel portion during the reset period of the scanning line of the next field is 2 as shown in FIG.
It becomes Vrst. This potential difference value is the potential difference that determines Pr ⁻ .

By repeating the above operation, the E-P hysteresis characteristics have equal absolute values of the positive and negative maximum remanent polarization values, as shown in FIG.

[0044] In the present ^{embodiment, | Pr + |> | Pr} - |
Has been described, of course ^{| Pr + | <| Pr -} | in the case of the formula (4), (5) ^{each, ΔPr = | Pr - | -} | Pr + | ........................ ^{...... (4 ') | Pr -} ' | = | Pr + | = | Pr - | - ΔPr ............ becomes (5 '). Therefore, the potential difference due to each line that determines the remanent polarization is only changed to the negative potential difference.

Further, in FIG. 4, only the signal of the scanning electrode line is changed as the potential level which determines the residual polarization, but only the signal of the signal electrode line may be changed, or the signal of the signal electrode line and the scanning electrode line may be changed. Each of the signals may be changed. In short, if the potential difference due to the mutual line is set to obtain the potential difference that determines the temporary remanent polarization value for making the absolute values of the positive and negative maximum remanent polarization values equal, the same effect as described above can be obtained.

Example 3 FIG. 6 is an explanatory diagram showing signal waveforms of each line signal and a voltage applied to the ferroelectric layer in the driving method of Example 3.

The signal applied from the signal electrode line is the signal having the DC component shown in the first embodiment, and the signal applied from the scan electrode line is the positive scan line signal shown in the second embodiment. This is a signal obtained by changing the reset signal.
These signal waveforms are waveforms that make the absolute values of the positive and negative maximum remanent polarization values the same during the reset period during scanning. Liquid crystal driving is performed using these signals. The main operation procedure is the same as in the first and second embodiments, and will not be described.

In this example, it is also assumed that the absolute value of the maximum remanent polarization value of the positive polarity is larger than the absolute value of the maximum remanent polarization value of the negative polarity. Even if it is larger, the same effect can be obtained by adding the same correction as in the first and second embodiments.

Even if the driving method according to the first or second embodiment is used and the correction of the hysteresis characteristic is not satisfactory, the present embodiment in which these two driving methods are combined is an effective means.

[0050]

According to the present invention, it is possible to correct the hysteresis characteristic of the liquid crystal display device, and it is possible to reproduce a high quality image without causing flicker.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a signal waveform of each line signal and a voltage applied to a ferroelectric layer in a driving method according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an improved hysteresis characteristic in the ferroelectric layer when driven by the driving method of Example 1 of the present invention.

FIG. 3 is a signal waveform of each line and a signal of a voltage applied to a ferroelectric layer when a signal of a scan electrode line having a DC component is used only in a reset period of the scan line in the driving method according to the first embodiment of the present invention. It is explanatory drawing which shows a waveform.

FIG. 4 is an explanatory diagram showing signal waveforms of each line signal and a voltage applied to a ferroelectric layer in a driving method according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing an improved hysteresis characteristic in the ferroelectric layer when driven by the driving method according to the second embodiment of the present invention.

FIG. 6 is an explanatory diagram showing signal waveforms of each line signal and a voltage applied to a ferroelectric layer in a driving method according to a third embodiment of the present invention.

FIG. 7 is an explanatory diagram showing ideal hysteresis characteristics in a ferroelectric layer generated when driving a liquid crystal.

FIG. 8 is a schematic view of a panel structure in the display device.

FIG. 9 is an explanatory diagram showing signal waveforms of each line signal and a voltage applied to a ferroelectric layer in a conventional driving method.

[Explanation of symbols]

Pr ⁺ unmodified positive maximum remanent polarization Pr ^- unmodified negative maximum remanent polarization Pr ⁺ 'fix the maximum remanent polarization of positive polarity after Pr ^-' negative maximum residual polarization value of the corrected + Vrst reset signal -Vrst reset inhibit signal V _S scan line pixel portion voltage V _NS non-scan line pixel portion voltage Vstp data write inhibit pulse signal

Claims (3)

[Claims] 1. A method for driving a liquid crystal display device in which a liquid crystal containing a ferroelectric film is arranged in a cell having a large number of pixels, wherein the residual polarization at the time of writing is positive or negative with respect to the hysteresis characteristic of the liquid crystal in the cell. A method for driving a liquid crystal display device, characterized in that, in addition to a voltage applied to a pixel portion for driving a liquid crystal, a direct current voltage is applied at all times or within a certain period so that the absolute values become the same value. 2. A driving method of a liquid crystal display device in which a liquid crystal containing a ferroelectric film is arranged in a cell having a large number of pixels, wherein the residual polarization at the time of writing is positive or negative with respect to the hysteresis characteristic of the liquid crystal in the cell. In the saturated remanent polarization of the hysteresis characteristic, the smaller absolute value of positive and negative polarities is set as the maximum remanent polarization during data writing so that the absolute values are the same, and the voltage applied to the pixel section for liquid crystal drive is determined. A method for driving a liquid crystal display device, which comprises: 3. A driving method of a liquid crystal display device in which a liquid crystal containing a ferroelectric film is arranged in a cell having a large number of pixels, wherein the residual polarization at the time of writing is positive or negative with respect to the hysteresis characteristic of the liquid crystal in the cell. In the saturated remanent polarization of the hysteresis characteristic, the smaller absolute value of positive and negative polarities is set as the maximum remanent polarization during data writing so that the absolute value becomes the same value, and the voltage applied to the pixel portion for liquid crystal driving is determined, A method of driving a liquid crystal display device, characterized in that, in addition to the voltage applied to the pixel portion for driving the liquid crystal, a DC voltage is applied constantly or within a certain period.