JP3214939B2 - Driving method of liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a liquid crystal display device used in a liquid crystal display device in which a liquid crystal including a ferroelectric film is disposed in a cell having a large number of pixels.

[0002]

2. Description of the Related Art In a liquid crystal display device in which a ferroelectric film is disposed 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. As described above, the polarization P is not proportional to the electric field E and exhibits a hysteresis (history) characteristic. In the figure, Pr is the remanent polarization, E
c is called the coercive electric field.

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

[0004] For this reason, the following driving method has been conventionally proposed. In the panel structure schematic diagram shown in FIG. 8, paying attention to the Xn line of the scanning electrode, during the selection period, the liquid crystal potential is set to “0” by the scanning electrode and the signal electrode.
(Polarization P = 0) or a voltage waveform such that the liquid crystal potential is “1” (polarization P = 1) is applied, and the data held by the liquid crystal is erased (reset). Operation), and thereafter, an operation of applying a voltage waveform corresponding to new data between the electrodes is performed (write operation).

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

FIG. 9 shows an example of a waveform of the driving method described above. First, in a reset period, a pulse signal of a positive polarity (+ Vrst: reset signal) is applied to a scan electrode line to be reset (hereinafter, referred to as a scan line), and a scan electrode line which is not reset (hereinafter, referred to as a non-scan line). ), A negative polarity 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 2 Vrst 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 section shown in FIG. 8 is generally constituted by a liquid crystal layer and a ferroelectric layer.

Assuming that the capacitance of the liquid crystal layer is C _LC and the capacitance of the ferroelectric layer is C _F , 2
Of Vrst, the voltage V _F applied to the ferroelectric layer is divided and becomes as shown in Equation (1). V _F = 2V rst · 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 the spontaneous value of the ferroelectric layer. This is a voltage value sufficient to saturate the polarization.

After completion of the reset, the operation shifts to a data writing period. During this period, a data write pulse signal is written to the scan lines, and a data write inhibit pulse signal (Vstp) is written to the non-scan lines. In the signal electrode line, a data write pulse signal is written to an electrode for writing ON information, and a data write inhibit pulse signal is written to an electrode for writing OFF information. Note that in FIG. 9, the data write pulse signal is set to 0 potential, but this may be a pulse signal of an arbitrary potential. Further, since the liquid crystal needs to be driven by an alternating current, a potential of the opposite polarity is applied to the next field.

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

[0011]

Here, the hysteresis characteristic is caused by ionic impurities and the like contained in the ferroelectric film, and the positive and negative absolute values of the remanent polarization often differ.
There is a case where the symmetry of the hysteresis characteristic is not satisfied. Originally, the liquid crystal had to be driven by an alternating current. In the above-described case, even if the same electric field was applied, the positive and negative spontaneous polarizations were different from each other, which caused a problem such as flicker.

The present invention has been made in view of such circumstances, and aims at correcting the hysteresis characteristics of a liquid crystal display device, and can drive a liquid crystal display device capable of reproducing a high-quality image free from flicker. It provides a method.

[0013]

In order to solve such a problem, in the present invention, by applying a new DC voltage in addition to the conventional liquid crystal application voltage, the same positive and negative absolute values of the remanent polarization can be obtained. Value. Further, in the residual saturation polarization of the hysteresis characteristic originally possessed by the liquid crystal, the smaller one of the absolute values of the positive and negative polarities is set as the maximum residual polarization during data writing, and the positive and negative absolute values of the residual polarization during data writing are set to the same value. I do. Furthermore, by combining the above two driving methods, the positive and negative absolute values of the remanent polarization are more accurately made equal.

That is, according to the first aspect of the present invention, a liquid crystal including a ferroelectric film is arranged in a cell having a large number of pixels,
In a method for driving a liquid crystal display device, in which a voltage for data erasing is applied to a pixel portion and then a voltage for data writing is applied to the pixel portion, a hysteresis characteristic of a liquid crystal in a cell is reduced. When applying at least the data erasing voltage to the pixel unit so that the positive and negative absolute values of the remanent polarization in each pixel unit when the voltage is applied to the pixel unit are the same, the DC voltage is applied to the pixel unit applied voltage. component
A driving method for a liquid crystal display device, wherein the offset voltage is applied to a pixel portion.

According to a second aspect of the present invention, a liquid crystal including a ferroelectric film is arranged in a cell having a large number of pixels, a voltage for erasing data is applied to a pixel portion, and then a voltage for data writing is applied. In a driving method of a liquid crystal display device in which a voltage is applied to a pixel portion, the reversal polarization of each pixel portion when a voltage for writing data is applied to the pixel portion is compared with the hysteresis characteristic of the liquid crystal in the cell. The absolute value of the positive and negative polarities in the maximum remanent polarization of the hysteresis characteristic of the liquid crystal in the cell is set as the maximum remanent polarization value so that the absolute value of
Positive and negative reset signals of the same amplitude
And No., a method of driving a liquid crystal display device, characterized in that applied to the pixel portion as a voltage for data erasing.

Further, according to the invention of claim 3 of the present application, a liquid crystal including a ferroelectric film is arranged in a cell having a large number of pixels, a voltage for erasing data is applied to a pixel portion, and then a data writing operation is performed. In a driving method of a liquid crystal display device in which a voltage is applied to a pixel portion, the reversal polarization of each pixel portion when a voltage for writing data is applied to the pixel portion is compared with the hysteresis characteristic of the liquid crystal in the cell. The absolute value of the maximum remanent polarization of the hysteresis characteristic of the liquid crystal in the cell is set to the smaller absolute value of the positive and negative polarities so that the absolute value of the liquid crystal in the cell becomes the same value, and the same amplitude according to the maximum remanent polarization value is set. Reset signal and negative reset signal
And a signal as a data erasing voltage to the pixel portion, and the hysteresis characteristic of the liquid crystal in the cell, with respect to the hysteresis characteristic of the liquid crystal in the cell, the positive and negative remanent polarization in each pixel portion when the data writing voltage is applied to the pixel portion. When applying at least a data erasing voltage to the pixel portion so that the absolute value becomes the same value, in addition to the pixel portion applied voltage, a DC component offset voltage is applied to the pixel portion. This is a method for driving a liquid crystal display device.

[0017]

According to the first aspect of the present invention, when at least a data erasing voltage is applied to the pixel portion, an offset voltage of a DC component is applied to the pixel portion in addition to the pixel portion applied voltage. With respect to the hysteresis characteristic of the liquid crystal in the cell, the positive and negative absolute values of the remanent polarization in each pixel when the voltage for writing data is applied to the pixel are the same.

According to the second aspect of the present invention, the smaller of the absolute values of the positive and negative polarities in the maximum remanent polarization of the hysteresis characteristic of the liquid crystal in the cell is set as the maximum remanent polarization value. The same amplitude positive polarity
The set signal and the reset signal of the negative polarity are applied to the pixel portion as a voltage for data erasing, whereby the voltage for data writing is applied to the pixel portion with respect to the hysteresis characteristic of the liquid crystal in the cell. The positive and negative absolute values of the remanent polarization in each pixel portion are the same.

According to the third aspect of the present invention, the smaller of the absolute values of the positive and negative polarities in the maximum remanent polarization of the hysteresis characteristic of the liquid crystal in the cell is set as the maximum remanent polarization value. Positive polarity of the same amplitude according to
The reset signal and the reset signal of the negative polarity are applied to the pixel portion as a data erasing voltage, and when at least the data erasing voltage is applied to the pixel portion, a DC voltage is applied in addition to the pixel portion applied voltage. The offset voltage of the component is applied to the pixel portion, whereby the positive and negative absolute values of the remanent polarization in each pixel portion when a voltage for writing data is applied to the pixel portion with respect to the hysteresis characteristic of the liquid crystal in the cell. It has the same value.

As described above, by driving the liquid crystal 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 polarizations are the same. Therefore, in the data write operation to each liquid crystal element by the AC drive, the absolute value of the written data becomes the same value in positive and negative,
No adverse effects such as flicker occur.

[0021]

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

Embodiment 1 FIG. 1 is an explanatory diagram showing signal waveforms of each line signal and a voltage applied to a ferroelectric layer in the driving method of Embodiment 1, and FIG. FIG. 4 is an explanatory diagram showing improved hysteresis characteristics in a dielectric layer.

In carrying out the liquid crystal driving method of the present embodiment, first, the maximum remanent polarization value for each of the positive and negative polarities is determined, and the difference between the absolute values is also determined. Set the appropriate applied voltage.

Let the maximum remanent polarization values of the positive and negative electrodes before correction be 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.

The maximum remanent polarization value Pr ⁺ ',
Pr ^- in order to obtain a ', in this embodiment, newly added to the DC voltage to the signal of the conventional signal electrode lines. I mean
Apply the offset voltage. In this case, with reference to the signal waveform of the signal electrode line shown in FIG. 1, the signal of the conventional signal electrode line is provided with a positive DC component, so that in addition to the potential difference from the conventional scan electrode line, The potential difference having a DC component of a positive polarity is the voltage applied to the liquid crystal. The newly applied DC component is a DC voltage corresponding to ΔE shown in FIG. 2, and the voltage value is determined by conditions such as a ferroelectric material.

The liquid crystal driving is performed 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 a scan electrode line to be reset (hereinafter, referred to as a scan line), and a scan electrode line that is not reset (hereinafter, referred to as a non-scan line) is applied. Is a negative pulse signal (−V
rst: reset disable signal). Then, -Vrst 'is applied to the signal electrode line at that time. Therefore, the voltages applied to the pixel portions connected to the scanning lines and the non-scanning lines are as follows. 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 V _{DC, which} is the voltage of the non-scanning line pixel portion, 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 process proceeds to a data writing period. During this period, 0 potential or a data write pulse signal is written to the scanning line, and Vstp is written to the non-scanning line. In the signal electrode line, 0 potential + V _DC is written as a signal for writing ON information, and Vstp + _VDC is written as a potential for writing OFF information. Furthermore, since the liquid crystal needs to be driven by AC, the next field
Apply a potential of the opposite polarity.

By the above operation, as shown in FIG. 2, the EP hysteresis characteristic draws a curve shifted downward in a pseudo manner, so that the absolute values of the maximum positive and negative remanent polarization become the same value. , Hysteresis characteristics with high symmetry can be obtained.

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

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

However, if the positive and negative remanent polarization values before correction are already significantly different, the DC component provided in the signal of the signal electrode line or the scanning electrode line also becomes large, and in some cases, the DC component may be affected by the DC component. For example, when a potential difference of | A · Vstp | or more is applied to the ferroelectric layer of the non-scanning line, the 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 not to always apply a DC component but to apply a DC component only during the reset period of the scanning line.

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

Although there is no significant difference in the driving method itself,
By providing a DC component only during the reset period, a potential difference does not occur in the ferroelectric layer in a non-scanning line, so that a data signal written during scanning can be held.

Embodiment 2 FIG. 4 is an explanatory diagram showing signal waveforms of each line signal and a voltage applied to a ferroelectric layer in the driving method of Embodiment 2, and FIG. FIG. 4 is an explanatory diagram showing improved hysteresis characteristics in a dielectric layer.

In carrying out the liquid crystal driving method of this embodiment, first, the maximum remanent polarization value for each of the positive and negative polarities is obtained, and the difference ΔPr between the absolute values is also obtained. Further, a difference ΔPr of the absolute value is subtracted from the maximum remanent polarization value having the higher absolute value, and a temporary maximum remanent polarization value is obtained.

That is, the maximum remanent polarization value of the positive electrode is P
r ⁺ and the maximum remanent polarization value of the negative electrode as Pr ⁻ , and | P
If that, the absolute value of the maximum remanent polarization values of the provisional positive electrode | | Pr ⁺ '| a, the absolute value of the maximum remanent polarization of the negative electrode ^{| - r + | |> Pr} Pr - | to the same value. ^{ΔPr = | Pr + | - |} Pr - | .............................. (4) | Pr + '| = | Pr - | = | Pr + | - ΔPr ............ (5)

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

Then, in order to change the conventional electric potential difference for determining the maximum remanent polarization value Pr ⁺ to the obtained electric potential difference value,
In this embodiment, the potential of the reset signal of the scanning electrode line is changed.

The liquid crystal drive is performed by using the scanning electrode lines having different reset signals from the conventional one. Referring to FIG. 4, first, during 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, the pixel portion connected to the scanning line has + Vrst '+ Vrs
This means that t has been applied. This potential difference is the potential difference that determines Pr ⁺ . Note that the writing period is the same as in the conventional case, and will not be described.

Referring to FIG. 4, the potential difference applied to the pixel portion during the reset period of the scanning line in the next field is 2
Vrst. The potential value Pr ^- is the potential difference determined.

By repeating the above operations, the absolute values of the positive and negative maximum remanent polarization values of the EP hysteresis characteristic become equal as shown in FIG.

[0044] In the present ^{embodiment, | Pr + |> | Pr} - |
Of course, when | Pr ⁺ | <| Pr ⁻ |, equations (4) and (5) respectively represent ΔPr = | Pr ⁻ | − | Pr ⁺ |... ^{...... (4 ') | Pr -} ' | = | Pr + | = | Pr - | - ΔPr ............ becomes (5 '). Therefore, the potential difference between the lines that determine the remanent polarization merely changes to a negative potential difference.

Further, in FIG. 4, the potential level for determining the remanent polarization is changed only for the signal of the scanning electrode line. However, only the signal of the signal electrode line may be changed. May be changed. In short, the same effect as described above can be obtained if the potential difference between the mutual lines is such that a potential difference that determines a tentative remanent polarization value for making the absolute value of the positive and negative maximum remanent polarization values the same is obtained.

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

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 scanning electrode line is the signal of the positive scanning 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 maximum positive and negative residual polarization values the same during the reset period during scanning. The liquid crystal drive is performed using these signals. The main operation procedure is the same as that of the first and second embodiments, and thus the description is omitted.

In this embodiment, it is 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 in the case where the value is larger, the same effect can be obtained by making the same modification as in the first and second embodiments.

If the correction of the hysteresis characteristic is not satisfactory even if the driving method according to the first or second embodiment is used, the present embodiment combining these two driving methods 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 to reproduce a high quality image free from flicker and the like.

[Brief description of the drawings]

FIG. 1 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 first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing improved hysteresis characteristics in a ferroelectric layer when driven by the driving method according to the first embodiment of the present invention.

FIG. 3 shows 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 during a reset period of the scan line in the driving method according to the first embodiment of the present invention. FIG. 4 is an explanatory diagram showing a waveform.

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

FIG. 5 is an explanatory diagram showing improved hysteresis characteristics in a 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 the driving method according to the 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 diagram 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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G09G 3/36 G02F 1/133 545 G09G 3/20 611 G09G 3/20 642

Claims (3)

(57) [Claims] A liquid crystal including a ferroelectric film is arranged in a cell having a large number of pixels, a voltage for erasing data is applied to a pixel portion, and a voltage for writing data is applied to the pixel portion. In the driving method of the liquid crystal display device, the positive and negative absolute values of the remanent polarization in each pixel portion when a voltage for data writing is applied to the pixel portion are made equal to the hysteresis characteristic of the liquid crystal in the cell. And a method of driving a liquid crystal display device, wherein when applying at least a data erasing voltage to a pixel portion, an offset voltage of a DC component is applied to the pixel portion in addition to the voltage applied to the pixel portion. 2. A method in which a liquid crystal including a ferroelectric film is disposed in a cell having a large number of pixels, a voltage for erasing data is applied to the pixel portion, and a voltage for writing data is applied to the pixel portion. In the driving method of the liquid crystal display device, the positive and negative absolute values of the remanent polarization in each pixel portion when a voltage for data writing is applied to the pixel portion are made equal to the hysteresis characteristic of the liquid crystal in the cell. , The smaller of the absolute value of the positive and negative polarities in the maximum remanent polarization of the hysteresis characteristic of the liquid crystal in the cell is set as the maximum remanent polarization value, and the positive amplitude of the same amplitude according to this maximum remanent polarization value
A method for driving a liquid crystal display device, wherein a reset signal and a reset signal of negative polarity are applied to a pixel portion as a data erasing voltage. 3. A method in which a liquid crystal including a ferroelectric film is arranged in a cell having a large number of pixels, a voltage for erasing data is applied to the pixel portion, and a voltage for writing data is applied to the pixel portion. In the driving method of the liquid crystal display device, the positive and negative absolute values of the remanent polarization in each pixel portion when a voltage for data writing is applied to the pixel portion are made equal to the hysteresis characteristic of the liquid crystal in the cell. , The smaller of the absolute value of the positive and negative polarities in the maximum remanent polarization of the hysteresis characteristic of the liquid crystal in the cell is set as the maximum remanent polarization value, and the positive amplitude of the same amplitude according to this maximum remanent polarization value
A reset signal and a reset signal of negative polarity are applied to the pixel unit as a voltage for data erasing, and each pixel when a voltage for data writing is applied to the pixel unit with respect to the hysteresis characteristic of the liquid crystal in the cell. When applying at least a voltage for data erasure to the pixel unit so that the absolute values of the positive and negative remanent polarizations in the unit become the same, an offset voltage of a DC component is applied to the pixel unit in addition to the voltage applied to the pixel unit. A method for driving a liquid crystal display device, comprising: