JP2001159753A - Liquid crystal panel drive method, liquid crystal device and electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal panel drive method capable of performing a suitable gradation display even at a low temp. by performing temperature compensation to a drive signal, a liquid crystal device and an electronic equipment using the liquid crystal device. SOLUTION: In the liquid crystal device 1, when the gradation display of a pulse width modulation system is performed, a table control circuit 41 of a temperature compensation circuit 40 controls whether the gradation data 600 are generated by using either pulse width data for a regular temperature or for a low temperature stored in a gradation table 60 based on the temperature detection result by a temperature detector 70. At a low temperature, since a threshold value voltage is different when a gradation level is minimum and maximum and when it is a halftone, so as to compensate it, the pulse width of an image signal when the gradation level is minimum and maximum is brought near to the pulse width of the image signal when it is the halftone.

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 panel, a liquid crystal device, and electronic equipment. More specifically, the present invention relates to a temperature compensation technique for driving a liquid crystal panel.

[0002]

2. Description of the Related Art Among liquid crystal devices used for a matrix type display device, for example, a simple matrix type liquid crystal device has a liquid crystal panel 1 as shown in a block diagram of FIG.
0 and a drive circuit for driving the liquid crystal panel 10 (signal electrode drive circuit 20 and scan electrode drive circuit 30)
And control signals 200, 3 to these drive circuits 20, 30.
A liquid crystal drive control circuit 50 that outputs 00 (clock signal) and outputs predetermined signals (image signal 21 and scanning signal 31) from the drive circuits 20 and 30 to the liquid crystal panel 10 is configured.

As schematically shown in FIGS. 2 and 3, an upper polarizing plate 11 and a retardation film 1
2. Striped Y electrodes Y1, Y2, Y3
Are formed on the upper substrate 13, the liquid crystal layer 15, and the lower substrate 18, the lower polarizing plate 14, and the light diffusing plate 19, on which the stripe-shaped X electrodes X1, X2, X3. They are arranged in order. X electrodes X1, X2, X3 ...
And the Y electrodes Y1, Y2, Y3,... Extend in directions intersecting each other, and as shown in FIG. 4, the pixels P11, P12, P13.
Are formed in a matrix.

In such a liquid crystal panel 10, an X electrode X
1, X2, X3... And Y electrodes Y1, Y2, Y3.
Controlling the alignment state of the liquid crystal in each pixel (each liquid crystal cell) by the drive signal applied to... Changes the optical characteristics of each pixel P11, P12, P13. , P13... Can be used to display various images.

In such a liquid crystal device, each pixel P1
The method of time-sharing driving of P1, P12, P13,... Will be briefly described with reference to FIGS.

FIGS. 5A and 5B respectively show a Y electrode Y
1, Y2, Y3... (Scanning signal 3
1) and a waveform diagram of a drive signal (image signal 21) applied to X electrodes X1, X2, X3,... FIGS. 5A and 5B show waveforms corresponding to two frame periods, and a voltage corresponding to the difference between the scanning signal 31 and the image signal 21 is substantially applied to the liquid crystal layer. Applied as a signal.

In FIG. 5A, in the first frame period F, the voltage V5 of the scanning signal is at the non-selection voltage level, and the voltage V1 is at the selection voltage level. When the voltage V6 is applied to the X electrodes X1, X2, X3,... In the selection period H, the ON voltage is applied to the liquid crystal layer 15, and the voltage V4 is applied to the X electrodes X1, X2, X3,. Then, an OFF voltage is applied to the liquid crystal layer 15. In accordance with such a voltage change, the polarization of the light incident on the liquid crystal layer 15 is controlled, and an image is displayed on the liquid crystal panel 10.

In this liquid crystal device, when performing a gray scale display by a pulse width modulation method, as shown in FIG. 19, a gray scale for holding pulse width data defining a pulse width corresponding to a gray scale level is provided. A table 60 is provided. Accordingly, the liquid crystal drive control circuit 50 causes the signal electrode drive circuit 20 to output predetermined gradation data 600 corresponding to the display data from the gradation table 60 according to the display data 500. As a result, the liquid crystal panel 1 is
For the 0 signal electrode, for example, image signals as shown in FIGS. 7A to 7E are output corresponding to each gradation level.

FIGS. 7A to 7E show scanning signals 31. FIG.
(The H level shown indicates the selection voltage level V1) and the image signals 21 corresponding to five gray levels among the waveforms of the respective image signals 21 when displaying 16 gray levels, for example.
The pulse width for maintaining the ON voltage is different depending on each gradation level. Therefore, the difference voltage between the voltages applied to the liquid crystal layer 15, that is, the effective voltage value differs depending on the gray level. Therefore, based on the relationship between the effective voltage value to the liquid crystal layer of each pixel and the luminance (transmittance or reflectance) of each pixel shown in FIG.
As a result of changing the voltage applied to the liquid crystal of P13..., As shown in FIG.
13 can be controlled according to the gradation level. FIG. 21 schematically illustrates each gradation level and luminance (brightness / darkness), and the liquid crystal panel 10 is assumed to be in a normally white mode.

[0010]

However, when the liquid crystal device is used also as a display device of a mobile phone, the liquid crystal device may be used not only at room temperature but also outdoors in a winter period. When a conventional liquid crystal device is used in an environment, the correspondence between the gradation level and the brightness may be disturbed as shown in FIG. For example, a part of the intermediate gradation may be brighter than the lightness of the highest gradation level. The inventors of the present invention have studied the cause of such a problem, and as a result, it has been found that the correspondence between the gradation level and the brightness is disturbed for the following reason.

First, when an image signal 21 having a waveform shown in FIGS. 7A to 7E is continuously applied, a change in voltage actually applied to the liquid crystal is analyzed by Fourier transform or the like. When the gradation level is the lowest gradation (the waveform shown in FIG. 7A) or the highest gradation (the waveform shown in FIG. 7E), while the high frequency component of the signal actually applied to the liquid crystal is small, At the time of gradation (the waveforms shown in FIGS. 7B, 7C, and 7D), a considerable high-frequency component is included in the drive signal applied to the liquid crystal. That is, the relationship between the gradation level and the magnitude of the high-frequency component included in the drive signal applied to the liquid crystal corresponding to each gradation level is approximately
This is represented as shown by a solid line L9 in FIG. Therefore, based on FIG. 10, when the gradation level is low (the waveform shown in FIG. 7 (A)) or high (the waveform shown in FIG. 7 (E)), the liquid crystal has a low frequency component because the high frequency component is small. Driven by a low signal, the intermediate gradation (FIGS. 7 (B), (C),
In the case of the waveform (D), since the high frequency component is large, it can be considered that the liquid crystal is driven by a high frequency signal.

On the other hand, the liquid crystal has the frequency dependency shown in FIG. That is, the liquid crystal has a high dielectric anisotropy Δε when the frequency is low, and the dielectric anisotropy Δε sharply decreases when the frequency is high. In addition, the dielectric anisotropy Δε of the liquid crystal changes depending on the temperature, and the frequency at which the dielectric anisotropy Δε sharply decreases when the frequency increases is on the high frequency side when the temperature is high. Becomes lower, the frequency shifts to the lower frequency side.

Here, the threshold voltage Vth for driving the liquid crystal is proportional to the value obtained by the following equation (1) (k / Δε) 1/2 (1). The threshold voltage Vth is
If the voltage applied to the liquid crystal is equal to or higher than this voltage, it is a voltage at which the optical properties begin to change. In the above equation (1), Δε is related to the dielectric anisotropy, and k is related to the elastic modulus of the liquid crystal. Value. This formula is introduced in detail in “Principles and Applications of Liquid Crystals” published by the Industrial Research Institute, Equation 36 (2.15), written by Shoichi Matsumoto and Ryo Tsunoda.

According to equation (1), the threshold voltage Vth
Is obviously dependent on the dielectric anisotropy Δε, and the temperature-frequency characteristics of the dielectric anisotropy Δε described with reference to FIG. Is suggested to vary. Therefore, as shown in FIG. 12, the relationship between the temperature and the threshold voltage Vth for each drive frequency can be considered to be equal on the normal temperature side and the high temperature side regardless of the frequency. At low temperatures, the solid line L5 in FIG.
As shown by 1, if the frequency is low, the threshold voltage Vth
Does not rise sharply, but when the frequency is high, the threshold voltage V
th rapidly increases.

Therefore, in the conventional liquid crystal device, when the image is displayed at exactly the intermediate gradation, the solid line L53 in FIG.
When the liquid crystal is driven under the characteristics represented by, and the display is performed at the highest and lowest gradations, the liquid crystal is driven under the characteristics represented by the solid line L51 in FIG. When displaying, it can be considered that the liquid crystal is driven under the characteristics represented by the solid line L52 in FIG.

Therefore, as shown in FIG. 20A, the relationship between the effective voltage value (pulse width) corresponding to the gradation level and the luminance (transmittance or reflectance) in a normal temperature environment is exactly intermediate. The liquid crystal is driven under the characteristics represented by the solid line L63 in FIG. 20A when displaying with gray scale, and is displayed with the solid line L61 in FIG. 20A when displaying with the highest and lowest gray scale. When the liquid crystal is driven under the characteristic shown in FIG. 20 and the image is displayed at the intermediate gradation between the intermediate gradation and the maximum or minimum gradation, the liquid crystal is displayed under the characteristic represented by the solid line L62 in FIG. Is driven.

On the other hand, FIG. 20 shows the relationship between the effective voltage value applied to the liquid crystal and the luminance in a low temperature environment.
As is clear from FIG. 20B, when a signal of an effective voltage value (pulse width) set on the assumption that the use environment is at room temperature is applied to the liquid crystal, when a display is performed at exactly the middle gradation, FIG. The liquid crystal is driven under the characteristics represented by the solid line L73, and when displaying at the highest and lowest gradations, the liquid crystal is driven under the characteristics represented by the solid line L71 in FIG. When an image is displayed at an intermediate gradation between the above-described intermediate gradation and the highest or low gradation, the liquid crystal is driven under the characteristics represented by the solid line L72 in FIG. There is a problem that the luminance is higher than the luminance of the highest gradation, though it should be displayed in the middle gradation.

In view of the above problems, an object of the present invention is to
An object of the present invention is to provide a liquid crystal panel driving method, a liquid crystal device, and an electronic device using the liquid crystal device, which can perform appropriate gradation display even at a low temperature by performing temperature compensation on a driving signal.

[0019]

In order to solve the above-mentioned problems, according to the present invention, a drive signal subjected to pulse width modulation corresponding to a gradation level is applied to a liquid crystal panel having a liquid crystal between a pair of electrodes. A method of driving a liquid crystal panel that performs gradation display by detecting the temperature of the liquid crystal panel or the temperature of the environment in which the liquid crystal panel is disposed, and based on the detection result of the temperature, at normal temperature and at low temperature. And changing the relationship between the gradation level and the pulse width of the drive signal.

In the present invention, the normal temperature is from + 15 ° C. to +2
It means 5 ° C.

In order to implement such a driving method, according to the present invention, a driving signal subjected to pulse width modulation corresponding to a gradation level is applied to a liquid crystal panel having a liquid crystal between a pair of electrodes. A temperature detecting means for detecting a temperature of the liquid crystal panel or a temperature of an environment in which the liquid crystal panel is arranged, and a temperature detecting means for detecting a temperature of the liquid crystal panel at normal temperature. And a temperature compensating means for changing the relationship between the gradation level and the pulse width of the drive signal between low and low temperatures.

In the liquid crystal device, when the display is continued at the same gradation level, when the gradation level is the lowest gradation or the highest gradation, while the high frequency component of the signal actually applied to the liquid crystal is small, At the time of tuning, a signal applied to the liquid crystal has a considerable high frequency component. That is,
The frequency of the signal for driving the liquid crystal is different between the case of the lowest gradation or the highest gradation and the case of the intermediate gradation. In addition, as for the liquid crystal, the frequency characteristic of the dielectric anisotropy Δε changes depending on the temperature. As a result, the threshold voltage changes depending on the driving frequency at a low temperature. However, according to the present invention, the temperature of the liquid crystal panel is detected, and based on the detection result, on the low temperature side where the difference in the threshold voltage increases depending on the driving frequency,
By approximating the pulse widths of the highest and lowest gradation levels to the pulse widths of the intermediate gradations, the liquid crystal is applied to the liquid crystal even when displaying the highest and lowest gradation levels in the same manner as when displaying the intermediate gradations. The high frequency component is superimposed on the signal to be obtained. Therefore, even when displaying at the highest and lowest gradation levels in a low-temperature environment, driving is performed under the same conditions as for the intermediate gradations. There is no significant difference in threshold voltage between the case of displaying and the case of displaying. Therefore, even at low temperatures, an image can be displayed with appropriate brightness without disturbing the order of the gradation levels.

In the present invention, as a relationship between the gradation level and the pulse width of the drive signal, for example, the temperature compensating means may compare the drive signal at low temperature with the drive signal at room temperature. A signal in which the difference in pulse width between gradation levels is reduced on one of the high gradation side and the low gradation side of the gradation level. Here, the temperature compensating means compares the drive signal used at low temperature with the drive signal at normal temperature and sets the pulse width between the gray levels on both the high gray level side and the low gray level side of the gray level. May be narrowed.

Further, in the present invention, it is preferable that a liquid crystal material having a luminance change with respect to an effective voltage value of the drive signal which is equal to or greater than a normal temperature at a low temperature than that at a normal temperature is used as the liquid crystal. With this configuration,
Even when the difference in pulse width between the gradation levels is narrowed on the low temperature side as compared with the normal temperature side to prevent the occurrence of disturbance in the brightness corresponding to the gradation level on the low temperature side, the sharpness of the liquid crystal is high, In addition, it is possible to sufficiently secure the luminance difference between the gradation levels. Therefore, high-quality display can always be performed even when the environmental temperature changes.

In the present invention, the temperature compensating means may be configured such that the temperature compensating means determines the gradation level and the pulse width of the drive signal at normal temperature and at low temperature based on a temperature detection result by the temperature detecting means. It is preferable to include a correction data storage unit for storing data for changing the relationship.

The liquid crystal device configured as described above can be used as a display device for various kinds of electronic equipment. However, since it can perform appropriate gradation display even in a low temperature environment, it can be used outdoors even in winter. The electronic device is suitable for use as a display device such as a mobile phone.

[0027]

Embodiments of the present invention will be described with reference to the drawings. In the embodiment of the present invention, an example in which the present invention is applied to a simple matrix liquid crystal device will be described. In addition, since the basic configuration of the liquid crystal device to which the present invention is applied is the same as that of the conventional liquid crystal device, in the following description, common portions are denoted by the same reference numerals, and Description will be made with reference to the same drawings.

Embodiment 1 (Overall Configuration) FIG. 1 is a block diagram showing a schematic configuration of a liquid crystal device according to Embodiment 1 of the present invention. 2 and 3 are a plan view and a cross-sectional view, respectively, of the liquid crystal panel 10 used in the liquid crystal device. FIG. 4 shows this liquid crystal panel 1.
It is an equivalent circuit diagram of 0. FIG. 5 is a waveform diagram of a drive signal used in this liquid crystal device.

As shown in FIG. 1, a simple matrix type liquid crystal device 1 of the present embodiment includes a liquid crystal panel 10 and a driving circuit (signal electrode driving circuit 2) for driving the liquid crystal panel 10.
0 and the scan electrode driving circuit 30) and control signals 200 and 300 (clock signals) to these driving circuits 20 and 30.
And a liquid crystal drive control circuit 50 for outputting predetermined drive signals (image signal 21 and scanning signal 31) from the drive circuits 20 and 30 to the liquid crystal panel 10.

As will be described in detail later, the liquid crystal device 1 of the present embodiment
Then, gradation display is performed by the pulse width modulation method. For this purpose, a gradation table 60 for storing gradation data defining a pulse width corresponding to the gradation level is provided. Accordingly, the liquid crystal drive control circuit 50 causes the signal electrode drive circuit 20 to output the gradation data 600 indicating the predetermined pulse width corresponding to the display data from the gradation table 60 according to the display data 500. As a result, an image signal 21 having a pulse width corresponding to each gradation level is output from the signal electrode drive circuit 20 to the signal electrode of the liquid crystal panel 10.

Further, in the liquid crystal device 1 of the present embodiment, a temperature detector 70 (temperature detecting means) for directly detecting the temperature of the liquid crystal panel 10 or detecting the temperature of the environment in which the liquid crystal panel 10 is disposed, which will be described in detail later. And a temperature compensating circuit for correcting the relationship between the gradation level and the pulse width of the drive signal for use at normal temperature and for use at low temperature based on the result of temperature detection by the temperature detector 70. 40 (temperature compensation means).

In this embodiment, the temperature compensation circuit 40 is composed of a gradation table 60 (correction data storage means) and a table control circuit 41. The gradation table 60 includes, as gradation data, a pattern of pulse width data for normal temperature that defines the relationship between the gradation level and the pulse width of the image signal 21 under normal temperature environment, and a pattern under normal temperature environment. At least a pattern of low-temperature pulse width data that defines the relationship between the gradation level and the pulse width of the drive signal is stored, and the table control circuit 41 specifies the gradation data based on the temperature detection result of the temperature detector 70. A signal 400 is output to specify which pulse width data pattern corresponding to the temperature stored in the gradation table 60 is to be used.

As the temperature detector 70, various sensors can be externally attached. In this embodiment, a thermistor utilizing the fact that the resistance of a bulk semiconductor (silicon substrate) changes with temperature is used. . Drive circuits 20, 30 and a liquid crystal drive control circuit 50 are also formed on the silicon substrate. Further, since the temperature compensation circuit 40 can be formed on the same silicon substrate, these circuits and the like can be made into one chip.

(Structure of Liquid Crystal Panel 10) In the liquid crystal panel 10 used in such a liquid crystal device 1, as shown in FIGS. 2 and 3, a stripe-shaped Y electrode Y1 made of a transparent conductive film such as ITO is formed on the inner surface. , Y2, Y3... Are formed, and the lower substrate 18 on which the stripe-shaped X electrodes X1, X2, X3. For example, a liquid crystal layer 15 of a super twisted nematic (STN) mode is sandwiched. An upper polarizing plate 11 and a retardation film 12 are arranged outside one of the substrates, and a lower polarizing plate 14 and a light diffusing plate 19 are arranged outside the other substrate. Further, the pair of substrates 13 and 18 are bonded with a sealant, and the liquid crystal layer 15 is sealed in the gap. Here, both the upper substrate 13 and the lower substrate 18
It consists of a transparent substrate such as glass. Also, X electrodes X1, X
, X3 ... and Y electrodes Y1, Y2, Y3 ...
Extend in directions crossing each other. One of the X electrode and the Y electrode is a scanning electrode to which a scanning voltage is applied, and the other is a signal electrode to which an image signal is applied.

When the liquid crystal panel 10 is of a reflection type,
A reflection plate is disposed on the lowermost side, or X formed on the inner surface of the lower substrate 18 instead of removing the lower polarizing plate 14 and the light diffusing plate 19.
The electrodes X1, X2, X3,... Are reflection electrodes. Also,
When the liquid crystal panel 10 is used in a transmission type, the diffusion plate 19 is used.
The lighting device may be arranged under the lighting device.

In the liquid crystal device 1 configured as described above,
As shown in FIG. 4, the liquid crystal panel 10 has electrodes X1 and X
, Y1, Y2, Y3,... Form pixels P11, P12, P13,. Therefore, in the liquid crystal panel 10, the X electrodes X1, X2, X3,.
.. (The respective liquid crystal cells) are controlled by the driving signals applied to 1, Y2, Y3,.
Since the optical characteristics of P12, P13,... Change, various images can be displayed using the difference in the optical characteristics of the pixels 11, P12, P13,.

(Explanation of Time Division Drive) FIGS. 5A and 5B
, The normally white mode liquid crystal panel 10
An example of a drive signal for driving the drive will be described. FIG. 5 (A),
(B) shows Y electrodes (scanning electrodes) Y1, Y2, and Y, respectively.
3 and a waveform diagram of an image signal 21 applied to X electrodes (signal electrodes) X1, X2, X3,... 5A and 5B show waveforms corresponding to two frame periods, and a voltage corresponding to the difference between the scanning signal 31 and the image signal 21 is substantially applied to the liquid crystal. Is applied. In this waveform diagram, the Y electrodes Y1, Y2, Y3,... Are sequentially selected in each selection period, and a selection voltage level V1 or V6 is applied.

In FIG. 5A, in the first frame period F, the voltage V5 of the scanning signal 31 is at the non-selection voltage level, and the voltage V1 is at the selection voltage level. When the ON voltage V6 is applied to the X electrodes X1, X2, X3,... In the selection period H, the liquid crystal layer 15 is turned on,
When the OFF voltage V4 is applied to the X electrodes X1, X2, X3,..., The liquid crystal layer 15 is turned off. In accordance with such a voltage change, the polarization of the light incident on the liquid crystal layer 15 is controlled, and an image is displayed on the liquid crystal panel 10.

In the next frame, the polarity of the voltage waveform applied to the liquid crystal layer is inverted, so that the selection voltage level of the scanning signal becomes V6 and the non-selection level becomes V2. When the ON voltage V1 is applied,
An OFF voltage V3 is applied when turning OFF.

(Construction for Tone Display) FIG. 6 is an explanatory diagram schematically showing the brightness of the liquid crystal device for gradation display in a normally white mode liquid crystal device to which the present invention is applied. . FIGS. 7A to 7E each show one selection period (1H) of an image signal when displaying at a predetermined gradation level in a normally white mode liquid crystal device.
It is a wave form diagram in the inside.

In the liquid crystal device 1 configured as described above, FIG.
As shown in (1), an effective voltage is applied to the liquid crystal layer of each pixel so as to perform gradation display by the pulse width modulation method and to make the luminance (lightness of transmittance or reflectance) of each pixel correspond to the gradation level. Control. For this reason, in this embodiment, in FIG. 1, the liquid crystal drive control circuit 50 causes the signal electrode drive circuit 20 to output predetermined gradation data 600 from the gradation table 60 based on the display data 500. Therefore, the image signal 21 output from the signal electrode drive circuit 20 to the signal electrode of the liquid crystal panel 10 corresponds to each gradation level, and at room temperature,
For example, image signals as shown in FIGS. 7A to 7E are output.

FIGS. 7A to 7E respectively show the waveforms of the image signal 21 corresponding to five gradation levels out of the display of, for example, 16 gradations. The pulse width for maintaining the voltage V6 is different. Therefore, since the effective voltage value of the difference voltage applied to the liquid crystal layer 15 differs depending on the gradation level, as shown in FIG. 6, the brightness of each pixel P11, P12, P13. Can be controlled.

The scanning voltage 3 illustrated in FIGS.
1 and the waveforms of the image signal 21 are shown as (A) to (E) from the top in the order of the gradation level from the low gradation side to the high gradation side. 21 O
N voltage pulse width (scanning voltage 31 is selected voltage level V
1 during the selection period (the time width of the ON voltage V6 of the image signal 21) is narrowed. Therefore, the effective voltage value of the voltage applied to the liquid crystal becomes lower as going from the low gradation to the high gradation. As described above, in the present embodiment, the liquid crystal panel 10 is set in the normally white mode, so that the effective voltage on the high gradation (high luminance) side is low. The relationship between the grayscale level and the effective voltage is reversed, with the high grayscale side having a high effective voltage and the low grayscale side having a low effective voltage.

(Configuration for Temperature Compensation) FIGS.
Each of (E), in the same manner as FIGS. 7 (A) to (E), in the liquid crystal device to which the present invention is applied, one selection period of an image signal when displaying at a predetermined gradation level in a low temperature environment ( 1
It is a waveform diagram in H). FIG. 9 is a graph showing the relationship between the ambient temperature and the pulse width of the image signal when displaying each gradation level in the liquid crystal device to which the present invention is applied.

Referring again to FIG. 1, in the liquid crystal device 1 according to the present embodiment, the table control circuit 41 determines the pulse corresponding to any temperature stored in the gradation table 60 based on the temperature detection result of the temperature detector 70. Whether to use the width data pattern is designated, and an image signal 21 having a waveform (pulse width) pattern corresponding to the designated result is output from the signal electrode drive circuit 20 to the signal electrode of the liquid crystal panel 10.

That is, when the current temperature is equal to or higher than 0 ° C. (normal temperature side) in the temperature detection result of the temperature detector 70, the table control circuit 41 outputs the gradation data designation signal 400, and FIG. A pattern of pulse width data (gradation data) for normal temperature that generates the image signal 21 having the waveforms shown in FIGS. Therefore, the liquid crystal drive control circuit 50 sets the display data 50
When the grayscale data 600 corresponding to 0 is output from the grayscale table 60 to the signal electrode drive circuit 20, the grayscale data 600 is generated based on the normal temperature pulse width data pattern. Key data. Therefore, the signal electrode drive circuit 20 outputs the image signal 21 having the normal temperature waveform as shown in FIGS. 7A to 7E to the liquid crystal panel 10 based on the normal temperature gradation data 600.

On the other hand, the table control circuit 41
The current temperature is 0 in the temperature detection result of the temperature detector 70.
When the temperature is lower than 0 ° C. (low temperature side), a switching signal switching signal 400 is output to the gradation table 60, and FIG.
The low-temperature pulse width data for generating the image signal 21 having the waveform shown in FIG. Therefore, the liquid crystal drive control circuit 50 stores the gradation data 600 corresponding to the display data 500 in the gradation table 60.
When this is output to the signal electrode drive circuit 20, the gray-scale data 600 outputs low-temperature gray-scale data as shown in FIG. Therefore, the signal electrode drive circuit 20 outputs the image signal 21 having a low-temperature waveform as shown by a solid line in FIGS. 8A to 8E to the liquid crystal panel 10 based on the low-temperature gradation data 600. I do. The dotted lines in the figure are from FIG.
3E shows a waveform of the image signal 21 at the time of normal temperature shown in FIG.

The waveforms of the image signals shown in FIGS. 8A to 8E respectively correspond to five gradation levels in the case of displaying 16 gradations in a low-temperature environment. The corresponding gradation level is shown in FIG.
To (E). That is, the image signal 21 shown in FIG. 7A is used when displaying at the lowest gradation level at normal temperature, but the image signal 21 shown in FIG. Is used. When displaying the highest gradation level at normal temperature, the image signal 21 shown in FIG. 7E is used. When displaying the highest gradation level on the low temperature side, the image signal 21 shown in FIG. Is used. Further, the waveform at the time of displaying the intermediate gradation level is also shown in FIG.
The waveforms shown in (B) to (D) correspond to the waveforms shown in FIGS.

The low-temperature waveform thus set is also shown in FIG.
As shown in (A) to (E), when the gradation level is different, the pulse width for maintaining the ON voltage V6 is different. The waveforms of the image signal 21 shown in FIGS.
Compared with the waveform of the normal-temperature image signal 21 shown in (A) and (B), the potential of the image signal 21 changes from OFF level V4 to O level.
The transition timing to the N level V6 is slightly delayed, and the pulse width for maintaining the ON voltage V6 is slightly shorter than normal temperature. On the other hand, the waveform of the image signal 21 shown in FIGS. 8D and 8E is compared with the waveform of the image signal 21 for normal temperature shown in FIGS. The timing at which the potential changes from the OFF level V4 to the ON level V6 is slightly earlier, and the pulse width for maintaining the ON voltage V6 is slightly longer than normal temperature. The waveform of the image signal 21 shown in FIG. 8C is substantially the same as the waveform of the normal-temperature image signal 21 shown in FIG.

Therefore, as shown in FIG. 9 showing the relationship between the operating environment temperature and the pulse width of the image signal, in the present embodiment, the image signal 21 used on the low temperature side is the image signal 2 used at room temperature.
Compared with 1, the difference in pulse width between the gradation levels on both the high gradation side and the low gradation side of the gradation level is smaller. Here, since the effective voltage value of the drive signal applied to the liquid crystal is defined by the pulse width, the voltage difference between each gradation level of the effective voltage value of the drive signal applied to the liquid crystal is normal temperature on the low temperature side. It is smaller on both the high gradation side and the low gradation side of the gradation level as compared with the time.

(Relationship Between Liquid Crystal Characteristics and Driving Frequency) FIG.
0 appears when the liquid crystal device 1 displays a display of each gradation level and analyzes a potential change of a drive signal (difference voltage between the scanning voltage 31 and the image signal 21) applied to the liquid crystal by Fourier transform or the like. 5 is a graph showing the magnitude of the high-frequency component of the drive signal. By performing Fourier transformation and expanding it into a Fourier series, the waveform of the driving signal can be decomposed into a sine wave, and the magnitude of the high frequency component can be obtained therefrom. FIG. 11 is a graph showing the frequency characteristics of the dielectric anisotropy of the liquid crystal at each temperature. The driving frequency and the driving frequency obtained by the cycle of the voltage change (change of the voltage polarity) of the drive signal applied to the liquid crystal of each pixel are shown. 3 shows the relationship between the ambient temperature and the dielectric anisotropy Δε. FIG. 12 shows the liquid crystal device 1
5 is a graph showing the relationship between the temperature at the driving frequency level of the liquid crystal and the threshold voltage Vth of the liquid crystal,
13 is a graph shown for explaining a change in threshold value Vth with respect to temperature for each driving frequency level of the liquid crystal based on the result of FIG. 11.

In the liquid crystal device 1, FIGS.
When the image signal having the waveform shown in FIG. 3 is continuously applied, the voltage change of the drive signal actually applied to the liquid crystal is analyzed by Fourier transform or the like. 7 (A)) or the highest gradation (the waveform shown in FIG. 7 (E)).
5, while the high frequency component of the drive signal actually applied is small, while in the case of the intermediate gradation (the waveforms shown in FIGS. 7B, 7C and 7D), the drive signal applied to the liquid crystal is considerably large. It turned out that a high frequency component was mounted. That is, the relationship between the grayscale level and the magnitude of the high-frequency component included in the drive signal applied to the liquid crystal corresponding to each grayscale level is approximately represented by a solid line L9 in FIG. Therefore,
Based on the relationship of FIG. 10, when the gradation level is low (see FIG.
When the waveform is as shown in FIG. 7A, or when the waveform is high (the waveform as shown in FIG. 7E), the liquid crystal layer 15 is driven by a signal with a low frequency because the high-frequency component is small. ,
In the case of (C) and (D)), it can be considered that the liquid crystal is driven by a signal with a high frequency since there are many high frequency components.

However, in this embodiment, on the low temperature side, FIG.
As shown in (A) to (E), the potential change timing is shifted so that the pulse widths of the highest and lowest gradation levels are approximated to the pulse widths of the intermediate gradations. Since a new signal is generated, the driving signal applied to the liquid crystal is set so that a high-frequency component is included even when displaying at the highest and lowest gradation levels. Therefore, at the time of low temperature, when displaying the highest and lowest grayscale levels, as shown by the dashed line L10 in FIG. Therefore, it can be considered that the liquid crystal is driven by a signal having a high frequency.

On the other hand, the liquid crystal has the frequency characteristics shown in FIG. FIG. 11 is a graph showing frequency characteristics of the dielectric anisotropy Δε of the liquid crystal at each temperature. Here, the solid line L1 to the solid line L6 respectively have a temperature of −20 ° C. and −10 ° C.
The frequency characteristics at 0 ° C., 0 ° C., + 25 ° C., + 50 ° C., and + 70 ° C. are shown. Note that the frequency referred to here is
The driving frequency is an average obtained by the period of the voltage transition (change in voltage polarity) of the applied voltage (the difference voltage between the scanning voltage 31 and the image signal 21) to the liquid crystal layer of each pixel.

As shown in FIG. 11, the liquid crystal has a tendency that the dielectric anisotropy Δε is high when the frequency is low, and the dielectric anisotropy Δε is sharply reduced when the frequency is high. In addition, the dielectric anisotropy Δε of the liquid crystal varies depending on the temperature,
In addition, the frequency region (boundary region) where the dielectric anisotropy Δε of the liquid crystal sharply decreases is on the high frequency side when the temperature is high, and shifts to the low frequency side when the temperature is low.
Therefore, when the frequency is low, the dielectric anisotropy Δε of the liquid crystal tends to be high on the low temperature side, and when the frequency is high, the dielectric anisotropy Δε of the liquid crystal tends to be high on the high temperature side. For example, at room temperature (for example, + 25 ° C.), the dielectric anisotropy Δε is about 10
It shows a substantially flat frequency characteristic up to 0 kHz. On the other hand, at a temperature of −20 ° C. (low temperature), it can be seen that the dielectric anisotropy Δε starts to drop sharply at about 1 kHz.
That is, when the temperature decreases, the frequency band of the drive signal is applied to the transition region of dielectric constant anisotropy Δε (the region where Δε changes rapidly), and Δε of the liquid crystal decreases rapidly. As a result, the threshold voltage Vth decreases. It drops sharply.

Since the threshold voltage Vth for driving the liquid crystal is proportional to the value obtained by the above equation (1), the threshold voltage Vth of the dielectric anisotropy Δε described with reference to FIG. In the frequency characteristics, the threshold voltage Vth fluctuates according to the temperature and the frequency. Therefore, as shown in FIG. 12, the relationship between the temperature and the threshold voltage Vth can be considered to be equal on the normal temperature side and the high temperature side regardless of the frequency. On the other hand, at low temperatures, as shown by the solid line L51 in FIG. 12, if the frequency is low, the threshold voltage Vth does not rise sharply. To solid line L
As indicated by 53, the threshold voltage Vth sharply increases. Therefore, at low temperatures, the threshold voltage Vth varies according to the frequency level of the drive signal, so that the highest gray scale, the lowest gray scale, and the intermediate gray scale have almost the same frequency components as much as possible. It is preferable to drive in this manner.

In consideration of such characteristics of the liquid crystal, in the present embodiment, as described with reference to FIGS. 7 and 8, in a normal temperature environment, display is performed at the lowest and highest gradation levels. There is a difference in the frequency of the drive signal applied to the liquid crystal between the case where the display is performed at the intermediate gradation and the case where the drive signal is applied to the liquid crystal when the display is performed at the lowest and highest gradation levels in a low temperature environment. By substantially increasing the frequency of the signal, the frequency of the driving signal applied to the liquid crystal when displaying at an intermediate gray level is made closer to the frequency.

That is, at 25 ° C. at normal temperature, when displaying at the lowest and highest gradation levels,
In FIG. 11, the liquid crystal is driven at the frequency indicated by the area A1 with respect to the solid line L4. On the other hand, when the image is displayed at the intermediate gradation, the high frequency component increases as described above.
In 1, the liquid crystal is substantially driven at the frequency indicated by the region B1 with respect to the solid line L4. On the other hand, at a low temperature of −20 ° C., when displaying at the lowest and highest gradation levels, a new voltage change of the drive signal is generated as shown in FIGS. 8A and 8E. Image signal 2
1 is shifted, the high frequency component is increased as shown by the dotted line L10 in FIG.
In FIG. 1, the liquid crystal is substantially driven at the frequency indicated by the area A2 with respect to the solid line L1, and when the display is performed at the intermediate gradation, the voltage transition timing of the image signal 21 is set to the normal temperature as described with reference to FIG. Since the time is set to be equal to that at the time of normal temperature, it becomes equal to that at the time of normal temperature, and the solid line L1 in FIG.
, The liquid crystal is substantially driven at the frequency indicated by the region B2. Therefore, there is no large difference in the dielectric anisotropy Δε of the liquid crystal between the case where the display is performed at the lowest and highest gradation levels and the case where the display is performed at the intermediate gradation, in both the normal temperature and low temperature environments. . Therefore, according to the present embodiment, the threshold voltage Vth of the liquid crystal is changed between the case where the display is performed at the lowest and highest gradation levels and the case where the display is performed at the intermediate gradation under any environment of normal temperature and low temperature. It can be driven under the condition that there is no large difference.

(Indication under normal temperature conditions) FIG.
(B) is an explanatory diagram showing the relationship between the effective voltage and the luminance corresponding to each gradation level at normal temperature and the relationship between the effective voltage and the luminance corresponding to each gradation level at low temperature in the liquid crystal device to which the present invention is applied. It is explanatory drawing which shows a relationship. 13A and 13B, L61, L61, and L63 show the relationship between the effective voltage and the luminance when driven by a signal containing a large number of high-frequency components (or a high-frequency drive signal). L71 is when the frequency level is low,
L63 and L63 are L62 and L63 when the frequency level is high.
Numeral 72 indicates a case where the frequency level is intermediate.

In this embodiment, when gradation display is performed at normal temperature with waveforms as shown in FIGS. 7A to 7E, the gradation level is lowest (see FIG. At the time of the waveform shown in FIG. 7A) or the maximum (the waveform shown in FIG. 7E), the high frequency component of the drive signal actually applied to the liquid crystal layer 15 is small, while the intermediate gradation (shown in FIG. Waveform)
In this case, a considerable high-frequency component is present in the signal applied to the liquid crystal. However, as shown in FIG. 12, in a normal temperature environment, the fluctuation of the threshold value Vth of the liquid crystal is almost the same even if the frequency of the drive signal is different.

Therefore, as shown in FIG. 12, on the high ambient temperature side, the threshold voltage Vth of the liquid crystal is almost equal even if there is a difference in the frequency of the signal applied to the liquid crystal.
At room temperature, if a signal of the effective voltage value (pulse width) corresponding to the gradation level (the signal shown in FIGS. 7A to 7E) is applied to the liquid crystal, the liquid crystal is displayed at an intermediate gradation. When the liquid crystal is driven under the characteristics of the drive signal having a high frequency level represented by the solid line L63 in FIG.
When the liquid crystal is driven under the characteristics of the drive signal having a low frequency level represented by the solid line L61 in FIG. 13A and the display is performed with other intermediate gradations, the solid line L62 in FIG.
The liquid crystal is driven under the characteristic of a medium frequency level represented by the following equation.

As a result, the luminance changes in the order of the effective voltage values when gradation display is performed with the waveforms shown in FIGS. 7A to 7E. Therefore, an appropriate gradation display as shown in FIG. 6 can be performed.

(Display under Low Temperature Conditions) On the other hand, under low temperature conditions, gradation display is performed with waveforms as shown in FIGS. Of these waveforms, FIGS.
The magnitude of the high-frequency component of the drive signal applied to the liquid crystal when performing the intermediate gradation using the waveform shown in FIG. 10D is shown by the solid line L9 (at room temperature) and the dotted line L10 in FIG.
As is clear from (at low temperatures), this is almost the same as the case where gradation display is performed with the waveforms shown in FIGS. On the other hand, with respect to the waveforms shown in FIGS. 8A and 8E corresponding to the lowest or highest gradation level, when the intermediate gradation is performed by shifting the change timing of the pulse width of the image signal 21. Since the driving signal has a high frequency component as shown by L10 in FIG. 10 due to the approximation of the waveform shape shown in FIG. 10, the liquid crystal has a high frequency component compared to the waveforms shown in FIGS. Will be applied.

Therefore, in FIG. 12, if there is a difference in the frequency of the drive signal applied to the liquid crystal, a large difference is likely to occur in the threshold voltage of the liquid crystal on the low temperature side. The timing of the voltage change of the pulse width is set so that the waveform shape at the time of displaying the lowest level or the highest level is close to the waveform shape at the time of performing the intermediate gray scale. The liquid crystal is driven by a signal including a certain degree or more. Therefore, in a low-temperature environment, when the image is displayed at exactly the middle gradation, FIG.
When the liquid crystal is substantially driven under the characteristics in the case where the frequency level represented by the solid line L53 is high as shown in FIG. 2 and the display is performed at other intermediate gradations, the frequency level represented by the solid line L52 in FIG. The liquid crystal is substantially driven based on the characteristic of the case of the degree, but the characteristic when the frequency level represented by the solid line L52 in FIG. It can be considered that the liquid crystal is substantially driven under the condition. Therefore, even at low temperatures, there is no large difference in the threshold voltage Vth between when displaying at the highest and lowest grayscale levels and when displaying at the intermediate grayscale.

In a low-temperature environment, the relationship between the effective voltage applied to the liquid crystal and the luminance changes to the characteristic shown in FIG. However, even in this case,
When the image is displayed at exactly the middle gradation, FIG.
When the liquid crystal is substantially driven under the characteristic of the case where the frequency level represented by the solid line L73 is high, and the display is performed at other intermediate gradations, the frequency level represented by the solid line L72 in FIG. When the liquid crystal is substantially driven under the characteristics of the case where the frequency is medium and the display is performed at the highest and lowest gradations, the frequency represented by the solid line L72 in FIG. The liquid crystal is substantially driven under the characteristics described above.
That is, the characteristics when the frequency is extremely low (FIG. 13)
The liquid crystal is not driven under the condition (characteristic indicated by the solid line L71 in (B)). Therefore, when displaying at the highest and lowest gradations, the luminance is defined along the same characteristics (the characteristics indicated by the solid line L72) as in the case of the intermediate gradations in FIG. 13B. As shown in FIG. 6, it is possible to display an image with appropriate brightness without disturbing the order of the gradation levels.

[Second Embodiment] FIG. 14 is a block diagram showing a schematic configuration of a liquid crystal device according to a second embodiment of the present invention. In addition, Embodiments 2, 3, 4, 5 described below.
In each case, the basic configuration and the driving conditions for the liquid crystal are the same as those in the first embodiment. Therefore, only the characteristic portions of each embodiment will be described, and the description of the common portions will be omitted.

As shown in FIG. 14, the liquid crystal device 1 of the present embodiment
Also, the liquid crystal panel 10, a driving circuit (the signal electrode driving circuit 20 and the scanning electrode driving circuit 30) for driving the liquid crystal panel 10, and control signals 200 and 300 (clock signals) are supplied to these driving circuits 20 and 30. And a liquid crystal drive control circuit 50 for outputting predetermined drive signals (image signal 21 and scanning signal 31) from the drive circuits 20 and 30 to the liquid crystal panel 10.

The liquid crystal device 1 of the present embodiment also performs gradation display by the pulse width modulation method. For this reason, in the liquid crystal device 1 of the present embodiment, the gradation table 60 storing pulse width data (gradation data) for defining the pulse width corresponding to the gradation level is provided.
Is provided. Therefore, the liquid crystal drive control circuit 50
Based on the display data 500, the gradation data 600 indicating a predetermined pulse width is outputted from the gradation table 60 to the signal electrode driving circuit 2.
Output to 0. As a result, an image signal 21 having a pulse width corresponding to each gradation level is output from the signal electrode drive circuit 20 to the signal electrode of the liquid crystal panel 10.

Further, in the liquid crystal device 1 of the present embodiment, a temperature detector 70 (temperature detecting means) for directly detecting the temperature of the liquid crystal panel 10 or the temperature of the environment in which the liquid crystal panel 10 is disposed, and the temperature detector 70 A temperature compensating circuit 40 is configured to correct the relationship between the gradation level and the pulse width of the drive signal between the normal temperature side and the low temperature side based on the temperature detection result by 70.

In this embodiment, the temperature compensating circuit 40 comprises a gradation data storage section 42 (correction data storage means) formed in the liquid crystal drive control circuit 50 and a table control circuit 41. In the gradation data storage unit 42,
The pattern of the pulse width data for normal temperature that defines the relationship between the gradation level and the pulse width of the drive signal at normal temperature as the gradation data, and the relationship between the gradation level and the pulse width of the drive signal at low temperature Is stored at least in the pattern of the pulse width data for low temperature.

Accordingly, the table control circuit 41 outputs the gradation data designation signal 4 based on the temperature detection result of the temperature detector 70.
00 is output to the liquid crystal drive control circuit 50, the liquid crystal drive control circuit 50 outputs the grayscale data storage unit 4 based on the grayscale data designation signal 400 output from the table control circuit 41.
Of the pulse width data pattern for normal temperature and the pulse width data pattern for low temperature stored in step 2, a predetermined pulse width data pattern is output to the gradation table 60 as gradation data 401, The data stored in 60 is rewritten. Therefore, the gradation table 6
0 indicates that when the gradation data 600 corresponding to the display data 500 is output to the signal electrode drive circuit 20, the pattern of the pulse width data corresponding to the environmental temperature is set regardless of whether the current temperature is normal temperature or low temperature. The stored gradation data 600 is output in accordance with the display data 500. Therefore, the signal electrode drive circuit 20 outputs the image signals 21 shown in FIGS. 7A to 7E to the liquid crystal panel 10 at normal temperature, and FIGS. 8A to 8E at low temperature. Is output.

[Embodiment 3] FIG. 15 is a block diagram showing a schematic configuration of a liquid crystal device according to Embodiment 3 of the present invention.

As shown in FIG. 15, the liquid crystal device 1 of the present embodiment
Also, the liquid crystal panel 10, a driving circuit (the signal electrode driving circuit 20 and the scanning electrode driving circuit 30) for driving the liquid crystal panel 10, and control signals 200 and 300 (clock signals) are supplied to these driving circuits 20 and 30. And a liquid crystal drive control circuit 50 for outputting predetermined drive signals (image signal 21 and scanning signal 31) from the drive circuits 20 and 30 to the liquid crystal panel 10.

The liquid crystal device 1 of the present embodiment also performs gradation display by the pulse width modulation method. Therefore, in the liquid crystal device 1 of the present embodiment, a gradation table 60 for generating gradation data corresponding to a gradation level based on the display data 500 is formed in the signal electrode drive circuit 20. Therefore, the liquid crystal drive control circuit 50 transmits the display data 500 to the signal electrode drive circuit 2
0 is output to the gradation table 60, the gradation table 60
Generates gradation data in the signal electrode drive circuit 20.
As a result, an image signal 21 having a pulse width corresponding to each gradation level is output from the signal electrode drive circuit 20 to the signal electrode of the liquid crystal panel 10.

Further, in the liquid crystal device 1 of the present embodiment, a temperature detector 70 (temperature detecting means) for directly detecting the temperature of the liquid crystal panel 10 or the temperature of the environment in which the liquid crystal panel 10 is disposed, and the temperature detector 70 A temperature compensating circuit 40 is configured to correct the relationship between the gradation level and the pulse width of the drive signal between the normal temperature side and the low temperature side based on the temperature detection result by 70.

In this embodiment, the temperature compensating circuit 40 comprises a gradation data storage section 42 (correction data storage means) formed in the liquid crystal drive control circuit 50, and a table control circuit 41. In the gradation data storage unit 42,
The pattern of the pulse width data for normal temperature that defines the relationship between the gradation level and the pulse width of the drive signal at normal temperature as the gradation data, and the relationship between the gradation level and the pulse width of the drive signal at low temperature Is stored at least in the pattern of the pulse width data for low temperature.

Therefore, the table control circuit 41 outputs the gradation data designation signal 4 based on the temperature detection result of the temperature detector 70.
00 is output to the liquid crystal drive control circuit 50, the liquid crystal drive control circuit 50 outputs the grayscale data storage unit 4 based on the grayscale data designation signal 400 output from the table control circuit 41.
In the tone table 60, predetermined pulse width data is used as tone data 401 in accordance with the tone data designation signal 400, out of the normal temperature pulse width data pattern and the low temperature pulse width data pattern stored in the second table. And the data stored in the gradation table 60 is rewritten.
Therefore, when the gradation data corresponding to the display data 500 is generated in the signal electrode drive circuit 20, the pulse width corresponding to the ambient temperature is obtained regardless of whether the current temperature is room temperature or low temperature. The data pattern is stored, and appropriate gradation data 60 is stored in accordance with the display data 500.
Outputs 0. Therefore, the signal electrode drive circuit 20 operates as shown in FIGS.
The image signal 21 shown in (E) is output, and the image signal 21 shown in FIGS.

[Fourth Embodiment] FIG. 16 is a block diagram showing a schematic configuration of a liquid crystal device according to a fourth embodiment of the present invention.

As shown in FIG. 16, the liquid crystal device 1 of the present embodiment
Also, the liquid crystal panel 10, a driving circuit (the signal electrode driving circuit 20 and the scanning electrode driving circuit 30) for driving the liquid crystal panel 10, and control signals 200 and 300 (clock signals) are supplied to these driving circuits 20 and 30. And a liquid crystal drive control circuit 50 for outputting predetermined drive signals (image signal 21 and scanning signal 31) from the drive circuits 20 and 30 to the liquid crystal panel 10.

The liquid crystal device 1 of this embodiment also performs gradation display by the pulse width modulation method. For this reason, a gradation table 60 for storing pulse width data defining a pulse width corresponding to a gradation level is provided. However, in the present embodiment, the gradation table 60 is formed as a part of the liquid crystal drive control circuit 50. Therefore, the liquid crystal drive control circuit 5
0 outputs appropriate gradation data 600 to the signal electrode drive circuit 20 based on display data and gradation data (pulse width data) stored in the gradation table 60 in this circuit.

In the liquid crystal device 1 of the present embodiment, the temperature detector 70 (temperature detecting means) for directly detecting the temperature of the liquid crystal panel 10 or the temperature of the environment in which the liquid crystal panel 10 is disposed, and the temperature detector 70 A temperature compensating circuit 40 is configured to correct the relationship between the gradation level and the pulse width of the drive signal between the normal temperature side and the low temperature side based on the temperature detection result by 70.

In this embodiment, the temperature compensating circuit 40 includes a gradation table 60 formed in the liquid crystal drive control circuit 50.
(Correction data storage means) and table control circuit 41
It is composed of The gradation table 60 includes, as gradation data, a pattern of pulse width data for normal temperature that defines the relationship between the gradation level and the pulse width of the image signal 21 at normal temperature, and the gradation level at low temperature. Image signal 21
And a low-temperature pulse width data pattern that defines the relationship with the pulse width.

Therefore, the table control circuit 41 outputs the gradation data designation signal 4 based on the temperature detection result of the temperature detector 70.
00 is output to the liquid crystal drive control circuit 50, the liquid crystal drive control circuit 50 outputs the grayscale data of the normal temperature pulse width data pattern and the low temperature pulse width data pattern stored in the grayscale table 60. The gradation data 600 is output using predetermined pulse width data as gradation data in accordance with the designation signal 400. Therefore, the signal electrode drive circuit 20 outputs the image signals 21 shown in FIGS. 7A to 7E to the liquid crystal panel 10 at normal temperature, and FIGS. 8A to 8E at low temperature. Is output.

[Fifth Embodiment] In the first embodiment, the relationship between the effective voltage value applied to the liquid crystal and the luminance changes from the characteristic shown in FIG. In the present embodiment, the relationship between the effective voltage value applied to the liquid crystal and the luminance when the temperature of the liquid crystal changes from room temperature to a low temperature is described based on the characteristic shown in FIG. The liquid crystal which changes to the characteristic shown in B) is used.

FIGS. 17A and 17B show the relationship between the effective voltage and the luminance (transmittance or reflectance) corresponding to each gradation level at normal temperature in the liquid crystal device according to the fifth embodiment of the present invention. And an explanatory diagram showing a relationship between an effective voltage and luminance corresponding to each gradation level at a low temperature. FIGS. 17A and 17B show the relationship between the effective voltage and the luminance when driven by a signal containing a large number of high frequency components (or a high frequency drive signal), L61, L61, and L63.
L61 and L71 are L6 when the frequency level is low, and L63 and L63 are L6 when the frequency level is high.
2, L72 indicates the case where the frequency level is intermediate.

The liquid crystal having the characteristics shown in this embodiment is shown in FIG.
As is clear from comparison between (A) and (B), the luminance change with respect to the effective voltage value of the drive signal has a higher steepness at a low temperature side than at a normal temperature. That is, FIG.
In (B), the ratio V10 / V90 of the effective voltage value V10 for realizing the luminance 10% to the effective voltage value V90 for realizing the luminance 90% is smaller on the lower temperature side than the normal temperature. That is, the characteristic curve of the effective voltage-luminance at low temperature is steeper than the characteristic curve at normal temperature.

For this reason, as described in the first embodiment, in order to prevent the occurrence of disturbance in brightness corresponding to the gradation level on the low-temperature side, the temperature is lower on the low-temperature side than on the normal-temperature side. Even if the difference in the pulse width between the gray levels is narrowed and the difference in the effective voltage value between each gray level is smaller on the low temperature side than on the normal temperature side, the effective voltage with respect to the change width of the gray level is low at the low temperature. Since the change width is small, the change in luminance corresponding to each change in gradation level can be made equal to that at room temperature. Therefore, according to the present embodiment, there is an advantage that the display quality does not change even if the environmental temperature changes.

It is to be noted that the liquid crystal displays a high-quality gradation display regardless of the ambient temperature even when the luminance change with respect to the effective voltage value of the drive signal has the same steepness on the low temperature side as compared with the normal temperature. Can be.

[Other Embodiments] Although the above embodiment has been described with reference to the STN panel, the present invention is not limited to this, and can be applied to various liquid crystal modes such as TN.

Further, in the description of the above embodiment, multiplex driving was used as a driving waveform as shown in FIG. 5 so as to easily explain the features of the present invention.
The present invention is not limited to this, and a plurality of X electrodes X1, X
The present invention can be applied to a liquid crystal device adopting multi-line driving (MLS or MLA) in which 2, X3... Are simultaneously selected.

In the above embodiment, in a low-temperature environment, the pulse width is corrected on both the high gradation side and the low gradation side of the gradation level, but the pulse width is corrected on the high gradation side and the low gradation side of the gradation level. The pulse width may be corrected in only one of them.

The pulse width pattern is not two stages of low temperature and normal temperature, but a pulse width data pattern of two or more stages is prepared according to the temperature change, and is finely adapted to the environmental temperature change. The pulse width may be corrected.

It is needless to say that not only the adjustment of the pulse width corresponding to the ambient temperature but also the correction of the ON voltage and the OFF voltage is performed according to the temperature change, so that the effective voltage to the liquid crystal may be adjusted. No.

The pulse width in FIGS. 7 and 8 is OFF.
Although the trailing edge driving method is such that the ON voltage is located after the voltage, the leading edge driving method may be that the ON voltage is first and the OFF voltage is later.

Note that the present invention may be applied to a normally black mode liquid crystal panel instead of a normally white mode liquid crystal panel. In this case, when the effective voltage is increased by increasing the pulse width, the high gradation side is obtained, and when the effective voltage is reduced by reducing the pulse width, the low gradation side is obtained. The relationship is reversed.

[Specific Example of Electronic Apparatus] FIG.
(B) and (C) are external views of electronic equipment using the liquid crystal device 1 to which the present invention is applied.

FIG. 18A is an external view of a mobile phone. In this figure, reference numeral 1000 denotes a mobile phone main body, and reference numeral 1001 denotes an image display device using the liquid crystal device 1 to which the present invention is applied.

FIG. 18B is an external view of a wristwatch-type electronic device. In this figure, reference numeral 1100 denotes a watch main body, and reference numeral 1101 denotes an image display device using the liquid crystal device 1 to which the present invention is applied.

FIG. 18C is an external view of a portable information processing device such as a word processor or a personal computer. In this figure, reference numeral 1200 denotes an information processing device, 1202 denotes an input unit such as a keyboard, 1206 denotes an image display device using the liquid crystal device 1 to which the present invention is applied, and 1204 denotes an information processing device main body.

Since all of these electronic devices are equipped with the liquid crystal device 1 to which the present invention is applied as a display device, a clear display is performed from a low operating temperature of about -25 ° C. to a high temperature of about + 70 ° C. be able to.

[0101]

As described above, according to the present invention, when display is continued at the same gradation level in a liquid crystal device,
When the gradation level is the lowest gradation or the highest gradation, while the high frequency component of the signal actually applied to the liquid crystal is small,
In the case of the intermediate gradation, the signal applied to the liquid crystal has a considerably high frequency component, and the frequency characteristic of the dielectric anisotropy Δε of the liquid crystal has temperature dependence. Considering that the threshold voltage changes,
On the low temperature side where the difference in threshold voltage becomes large depending on the driving frequency, the relationship between the gradation level and the pulse width is corrected. Therefore, even at low temperatures, an image can be displayed with appropriate brightness without disturbing the order of the gradation levels.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a liquid crystal device according to Embodiment 1 of the present invention.

FIG. 2 is a plan view of a liquid crystal panel used in the liquid crystal device shown in FIG.

FIG. 3 is a cross-sectional view of the liquid crystal panel shown in FIG.

4 is an equivalent circuit diagram of the liquid crystal panel shown in FIG.

5A and 5B are waveform diagrams of two driving signals (image signal and scanning signal) for driving the liquid crystal panel shown in FIG. 4, respectively.

FIG. 6 is an explanatory diagram showing a state where gradation display is performed in a liquid crystal device to which the present invention is applied.

FIGS. 7A to 7E are waveform diagrams of an image signal during one selection period when displaying a predetermined gradation level in a liquid crystal device.

FIGS. 8A to 8E are waveform charts of a liquid crystal device to which the present invention is applied, during a selection period of an image signal when a predetermined gradation level is displayed in a low-temperature environment. .

FIG. 9 is a graph showing a relationship between an ambient temperature and a pulse width (effective voltage value) of an image signal when displaying each gradation level in a liquid crystal device to which the present invention is applied.

FIG. 10 is a graph showing the magnitude of a high-frequency component appearing in a change in the potential of a signal applied to the liquid crystal when displaying at each gradation level in the liquid crystal device.

FIG. 11 is a graph showing frequency characteristics of dielectric anisotropy of liquid crystal at each temperature.

FIG. 12 is a graph showing the relationship between the temperature at each frequency level and the threshold voltage of the liquid crystal in the liquid crystal device.

FIGS. 13A and 13B are explanatory diagrams showing a relationship between an effective voltage of each gradation level at normal temperature and luminance in a liquid crystal device to which the present invention is applied, and an effective voltage of each gradation level at low temperature, respectively. FIG. 4 is an explanatory diagram showing a relationship between the brightness and the brightness.

FIG. 14 is a block diagram illustrating a schematic configuration of a liquid crystal device according to Embodiment 2 of the present invention.

FIG. 15 is a block diagram illustrating a schematic configuration of a liquid crystal device according to Embodiment 3 of the present invention.

FIG. 16 is a block diagram illustrating a schematic configuration of a liquid crystal device according to Embodiment 4 of the present invention.

FIGS. 17A and 17B are explanatory diagrams showing a relationship between an effective voltage of each gradation level at normal temperature and luminance in a liquid crystal device according to Embodiment 5 of the present invention, and each gradation at low temperature, respectively. FIG. 4 is an explanatory diagram showing a relationship between a level effective voltage and luminance.

FIGS. 18A, 18B, and 18C are explanatory views of an electronic device equipped with a liquid crystal device to which the present invention is applied.

FIG. 19 is a block diagram illustrating a schematic configuration of a conventional liquid crystal device.

FIGS. 20A and 20B are explanatory diagrams showing the relationship between the effective voltage and luminance at each gradation level at normal temperature and the effective voltage and luminance at each gradation level at low temperature in a conventional liquid crystal device, respectively. It is explanatory drawing which shows the relationship.

FIGS. 21A and 21B are explanatory diagrams showing a state in which gradation display is performed at room temperature and a state in which gradation display is performed in a low-temperature environment in a conventional liquid crystal device, respectively. It is.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 liquid crystal device 10 liquid crystal panel 11 upper polarizing plate 12 retardation film 13 upper substrate 14 lower polarizing plate 15 liquid crystal layer 16 sealant 18 lower substrate 20 signal electrode drive circuit 21 image signal 30 scan electrode drive circuit 31 scan signal 40 temperature compensation circuit (Temperature Compensation Unit) 41 Table Control Circuit 42 Gradation Data Storage Unit 50 Liquid Crystal Drive Control Circuit 60 Gradation Table 70 Temperature Detector (Temperature Detection Unit) 200, 300 Control Signal 400 Gradation Data Designation Signal 401 Gradation Data 500 Display Data 600 Gradation data X1, X2, X3... X electrode Y1, Y2, Y3.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H093 NA51 NB26 NC46 NC57 ND02 ND44 5C006 AA15 AC02 AF13 BB12 BC20 BF14 BF38 FA19 FA56 5C080 AA10 BB05 DD03 DD20 EE29 FF09 JJ02 JJ04 JJ05

Claims (10)

[Claims] 1. A method for driving a liquid crystal panel that performs gradation display by applying a drive signal that has been subjected to pulse width modulation corresponding to a gradation level to a liquid crystal panel including a liquid crystal between a pair of electrodes, The temperature of the liquid crystal panel or the temperature of the environment in which the liquid crystal panel is disposed is detected, and based on the detection result of the temperature, the relationship between the gradation level and the pulse width of the drive signal at normal temperature and low temperature is detected. A method for driving a liquid crystal panel, wherein the relationship is changed. 2. The driving signal according to claim 1, wherein the driving signal used at a low temperature is compared with the driving signal used at a normal temperature.
A method of driving a liquid crystal panel, wherein a difference in pulse width between gray levels is narrowed on one of a high gray level side and a low gray level side of a gray level. 3. The driving signal according to claim 1, wherein the driving signal used at a low temperature is compared with the driving signal used at a normal temperature.
A method for driving a liquid crystal panel, characterized in that a difference in pulse width between gradation levels is reduced on both the high gradation side and the low gradation side of the gradation level. 4. The method according to claim 1, wherein
A method of driving a liquid crystal panel, wherein a liquid crystal material having a luminance change with respect to an effective voltage value of the drive signal at a low temperature compared with a normal temperature is equal to or greater than that at a normal temperature is used as the liquid crystal. 5. A liquid crystal device that performs gradation display by applying a drive signal that has been subjected to pulse width modulation corresponding to a gradation level to a liquid crystal panel including a liquid crystal between a pair of electrodes. Temperature detection means for detecting the temperature or the temperature of the environment in which the liquid crystal panel is arranged; and based on the temperature detection result by the temperature detection means, the pulse of the gradation level and the drive signal at normal temperature and low temperature. A liquid crystal device comprising: a temperature compensator for changing a relationship with a width. 6. The temperature compensation unit according to claim 5, wherein the drive signal used at a low temperature has a higher gray scale level and a lower gray scale side as compared with the drive signal used at a normal temperature. A difference in pulse width between gradation levels on one side of the liquid crystal device. 7. The temperature compensation device according to claim 5, wherein the drive signal used at a low temperature is higher than the drive signal used at a normal temperature on both the high gradation side and the low gradation side. 3. The liquid crystal device according to claim 1, wherein a difference in pulse width between gradation levels is reduced. 8. The method according to claim 5, wherein
The liquid crystal device according to claim 1, wherein the liquid crystal has a luminance change with respect to an effective voltage value of the drive signal which is equal to or more steep at a low temperature than at a normal temperature. 9. The method according to claim 5, wherein
The temperature compensating means stores data for changing a relationship between the gradation level and the pulse width of the drive signal between normal temperature and low temperature based on a temperature detection result by the temperature detecting means. A liquid crystal device comprising a correction data storage means for storing. 10. An electronic apparatus comprising the liquid crystal device defined in claim 5 as a display device.