JP2002365611A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device by which satisfactory image quality can be always obtained even if use environment is changed by considering the property of a liquid crystal. SOLUTION: The liquid crystal display device for displaying color images by driving color irradiation light beams to a liquid crystal display panel while successively switching prescribed frequencies in every field is provided with a temperature detecting means for detecting the temperature of the surroundings of the liquid crystal display device and a switching frequency controlling means for controlling the switching driving frequency of the color irradiation light beams so as to be changed corresponding to the temperature of the surroundings of the liquid crystal display device detected by the temperature detecting means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field-sequential type liquid crystal display device for displaying a color image by switching image data of three colors and a backlight in synchronization with each field, and more particularly to a liquid crystal display device in which a use environment changes. The present invention relates to a liquid crystal display device capable of preventing image quality deterioration.

[0002]

2. Description of the Related Art FIG. 5 shows a structure of a liquid crystal display unit.
(A) is a front view, (b) is AA sectional drawing. Less than,
Description will be made with reference to the drawings.

Reference numeral 4 denotes a liquid crystal display for displaying a color image or the like. 6 is a liquid crystal display panel (LCD) in which liquid crystal is sealed between two glass plates provided with electrodes in the X and Y directions.
Then, by selecting each of the X and Y electrodes and applying a voltage, the light transmittance of the liquid crystal at the intersection is controlled. Reference numeral 7 denotes a light guide plate disposed at the rear of the liquid crystal display panel 6 for guiding light from the backlight 8 and diffusing the light therein to evenly illuminate the liquid crystal display panel 6. Reference numeral 8 denotes a backlight which is disposed on a side surface of the light guide plate 7 and illuminates the liquid crystal display panel 6 from the rear through the light guide plate 7. The red light emitting diode 8R, the green light emitting diode 8G, and the blue light emitting diode 8G of three colors are integrated. Light emitting unit. Reference numeral 9 denotes a reflector disposed on the back surface of the light guide plate 7 and reflecting light from the backlight 8 toward the liquid crystal display panel 6.

FIG. 6 is a block diagram showing a configuration of a driving circuit of a conventional liquid crystal display device. 7A and 7B are waveform diagrams of a backlight driving signal of a conventional liquid crystal display device, wherein FIG. 7A is a waveform diagram of a red LED driving signal, FIG.
(C) is a blue LED drive signal waveform diagram. Hereinafter, description will be made with reference to the drawings.

[0005] Reference numerals 21, 22, and 23 denote red, green, and blue video signal circuits in which television input signals and navigation input signals are decomposed into three color signals. Reference numeral 2 denotes a video signal switching circuit which includes a V-RAM written by an input signal, reads out the video signals of three colors written in the V-RAM at a predetermined frequency and timing for each field, and writes the read video signals into the liquid crystal display panel 6. It is. Reference numeral 3 denotes each light emitting diode 8 of the backlight 8 in synchronization with the switching of the three color video signals.
This is a backlight switching circuit that switches the lighting operation of R, 8G, and 8B.

In a field sequential (field sequential) type color liquid crystal display device, first, a V-RAM
When the red video signal for one screen (one field) written in the LCD is read out at time T0 intervals (for example, 60 Hz) and applied to the X and Y electrodes of the liquid crystal display panel 6, the red video signal is displayed on the liquid crystal display panel 6. An image corresponding to the signal is obtained. At this time, if only the red light emitting diode 8R of the backlight 8 is turned on for the time t0 by the red LED drive signal shown in FIG. 7A, the liquid crystal display panel 6 is illuminated by the red light uniformized by the light guide plate 7. The result is a red image.

Next, one screen (one field) of the red video signal written in the V-RAM is read out at time T0 intervals and applied to the X and Y electrodes of the liquid crystal display panel 6 (the timing is the red video signal). After T0 / 3), the liquid crystal display panel 6
An image corresponding to the green video signal is obtained above. At this time, if only the green light emitting diode 8G of the backlight 8 is turned on for the time t0 by the green LED driving signal shown in FIG. 7B, the liquid crystal display panel 6 is illuminated by the green light uniformed by the light guide plate 7. To obtain a green image.

Subsequently, the red video signal for one screen (one field) written in the V-RAM is read out at intervals of time T0 and applied to the X and Y electrodes of the liquid crystal display panel 6 (the timing is the green video signal). After T0 / 3), an image corresponding to the blue video signal is obtained on the liquid crystal display panel 6. At this time,
When only the blue light emitting diode 8B of the backlight 8 is turned on for the time t0 by the blue LED drive signal shown in FIG. 7C, the liquid crystal display panel 6 is illuminated by the blue light uniformed by the light guide plate 7 and becomes blue. An image is obtained.

In this manner, the image writing to the liquid crystal display panel 6 by the three color video signals and the backlight 3
When the lighting of the color light emitting diodes 8R, 8G, 8B is switched in synchronization with an appropriate frequency (for example, 60 Hz), a three-color image sequentially displayed for each field is mixed to obtain a color image. Note that the color balance of the three colors is adjusted by the height of the applied pulse.

[0010]

The field sequential type color liquid crystal display device has advantages such as higher resolution and lower cost than a color liquid crystal display device using a color filter corresponding to the pixel of the liquid crystal display panel. is there. However, the liquid crystal has a characteristic that the response is delayed at a low temperature, and when the switching frequency of the three-color video signal and the three-color backlight is constant, a clear color image can be displayed at a high temperature, but at a low temperature. There is a problem that the contrast of the image is reduced. In addition, there is a problem that the illuminance around the liquid crystal display device is reduced, and that the image flickers when the user looks away from the screen.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device which can always obtain good image quality even when the use environment changes in consideration of the properties of liquid crystal.

[0012]

According to the present invention, there is provided a liquid crystal display device for displaying a color image by sequentially switching and driving a color irradiation light at a predetermined frequency for each field on a liquid crystal display panel. A temperature detecting means for detecting a temperature around the liquid crystal display device, and a control for changing a switching drive frequency of the color irradiation light in accordance with a temperature around the liquid crystal display device detected by the temperature detecting means. Switching frequency control means for controlling the switching frequency.

Further, in a liquid crystal display device for displaying a color image by sequentially switching and driving a color irradiation light to a liquid crystal display panel at a predetermined frequency for each field, an illuminance detecting means for detecting illuminance around the liquid crystal display device And switching frequency control means for controlling to change the switching drive frequency of the color irradiation light in accordance with the illuminance around the liquid crystal display device detected by the illuminance detection means. is there.

A driving state detecting means for detecting a driving state of a vehicle in a liquid crystal display device for displaying a color image by sequentially driving a color irradiation light to a liquid crystal display panel at a predetermined frequency for each field, and Switching frequency control means for controlling to change the switching drive frequency of the color irradiation light in accordance with the running state of the vehicle detected by the running state detecting means is provided.

[0015]

FIG. 1 is a block diagram showing a configuration of a driving circuit of a liquid crystal display according to a first embodiment of the present invention. FIG. 2 is an explanatory diagram of a backlight drive signal waveform of the liquid crystal display device according to the first embodiment of the present invention.
7A is a diagram showing the relationship between the ambient temperature of the liquid crystal display panel and the optimum switching frequency, FIG. 7B is a time chart of the backlight drive signal at a high temperature, and FIG. 7C is a time chart of the backlight drive signal at a low temperature. Hereinafter, description will be made with reference to the drawings. Note that the configuration of the liquid crystal display unit 4 is the same as the configuration of the liquid crystal display unit 4 in FIG.

Reference numeral 11 denotes a temperature sensor which is disposed near the liquid crystal display section 4 and comprises a thermistor for measuring the temperature of the liquid crystal display panel 6 or the like. Reference numeral 12 denotes an illuminance sensor which is arranged near the liquid crystal display unit 4 and measures the illuminance in the room. Reference numeral 13 denotes a vehicle speed sensor for detecting a traveling distance and a traveling speed of the vehicle, and uses a signal from a speedometer of the vehicle. A microcomputer 1 instructs a video signal switching circuit 2 and a backlight switching circuit 3 to switch a video signal of each color and a backlight at an optimum frequency based on signals from a temperature sensor 11, an illuminance sensor 12, and a vehicle speed sensor 13. This is a control unit composed of:

Reference numerals 21, 22, and 23 denote red, green, and blue video signal circuits in which television input signals and navigation input signals are decomposed into three color signals. Reference numeral 2 denotes a video signal switching circuit which includes a V-RAM written by an input signal, reads out the video signals of three colors written in the V-RAM at a predetermined frequency and timing for each field, and writes the read video signals into the liquid crystal display panel 6. It is. Reference numeral 3 denotes each light emitting diode 8 of the backlight 8 in synchronization with the switching of the three color video signals.
This is a backlight switching circuit that switches the lighting operation of R, 8G, and 8B.

As a response characteristic of a liquid crystal when a voltage is applied from the outside, the response speed tends to decrease as the temperature decreases. At a low temperature, a video signal is applied between electrodes (X and Y electrodes) sandwiching the liquid crystal. Also, the response speed is slow and the image appears slowly. Therefore, when each color is switched for each field, the time during which an image is displayed is short, and the contrast is reduced.
FIG. 2A is a graph showing the relationship between the ambient temperature of the liquid crystal display panel and the optimum switching frequency. As a result of experimentally obtaining the optimum switching frequency, the lower the temperature of the liquid crystal display panel 6, the lower the response of the liquid crystal. It is necessary to lower the switching frequency to cope with the delay. Therefore, at high temperatures (above the reference temperature), the liquid crystal responds even if the switching frequency is increased.
At a low temperature, the switching frequency is set lower (according to the ambient temperature) than the reference frequency (60 Hz) in order to improve the contrast at a low temperature. In the liquid crystal display device of the present embodiment, switching between a video signal and a backlight is performed according to the temperature around the liquid crystal display panel 6 as shown in FIGS. It controls the frequency.

First, the temperature around the liquid crystal display panel 6 is detected by the temperature sensor 11. If the temperature is higher than a reference temperature (for example, 15 ° C.) (high temperature), the control unit 1 controls the video signal switching circuit 2 In addition, the video signal of each color and the drive signal of the light emitting diodes 8R, 8G, 8B of each color of the backlight 8 are transmitted to the backlight switching circuit 3 at time T0 intervals (for example,
60 Hz). That is, V-
The red video signal for one screen (one field) written in the RAM is read out at time T0 intervals and applied to the X and Y electrodes of the liquid crystal display panel 6. In synchronization with this, only the red light emitting diode 8R is turned on for the time t0 by the R drive signal shown in FIG. Similarly, the green video signal for one screen (one field) written in the V-RAM is transmitted in the time T0.
It is read out at intervals (the timing is after T0 / 3 of the red video signal) and applied to the X and Y electrodes of the liquid crystal display panel 6. In synchronization with this, only the green light emitting diode 8G is turned on for the time t0 by the G drive signal shown in FIG. 2B. V-RAM
The blue video signal for one screen (one field) written in the image is written at the time T0 interval (the timing is T0 / 3 of the green video signal).
After that, the data is read out and applied to the X and Y electrodes of the liquid crystal display panel 6. In synchronization with this, only the blue light emitting diode 8B is turned on for the time t0 by the B drive signal shown in FIG. 2B. In this manner, a color image is displayed by sequentially switching the video signal written to the liquid crystal display panel 6 and the light emitting diodes 8R, 8G, 8B of the respective colors of the backlight 8 provided on the light guide plate 7 at a frequency of 60 Hz. Can be.

Next, the temperature sensor 11 is connected to the liquid crystal display panel 6.
Temperature around (for example, less than 15 ° C, low temperature)
When the control section 1 detects that, the video signal switching circuit 2 and the backlight switching circuit 3 transmit the video signal of each color and the driving signals of the light emitting diodes 8R, 8G, 8B of each color of the backlight 8 to FIG. As described above, the switching cycle is instructed to switch at intervals of T1 (for example, 50 Hz) longer than at the time of high temperature. That is, the red video signal for one screen (one field) written in the V-RAM is read out at time T1 intervals and applied to the X and Y electrodes of the liquid crystal display panel 6. In synchronization with this, only the red light emitting diode 8R is turned on for the time t1 by the R drive signal shown in FIG. 2C. Similarly, the green video signal for one screen (one field) written in the V-RAM is read out at the time T1 interval (the timing is after T1 / 3 of the red video signal), and X of the liquid crystal display panel 6 is read out. , Y electrodes. In synchronization with this, only the green light emitting diode 8G is turned on for the time t1 by the G drive signal shown in FIG. Further, a blue video signal for one screen (one field) written in the V-RAM is read at time T1 intervals (timing is after T1 / 3 of the green video signal) and applied to the X and Y electrodes of the liquid crystal display panel 6. Apply. Figure 2
Only the blue light emitting diode 8B is turned on for the time t1 by the B drive signal shown in (c). In this way, the video signal to be written to the liquid crystal display panel 6 and the light emitting diodes 8R, 8G, 8B of the respective colors of the backlight 8 provided on the light guide plate 7 are sequentially switched in synchronization with a frequency of 50 Hz, whereby good contrast is obtained even in a low temperature environment. A color image can be displayed.

In the liquid crystal display device of the present embodiment, the case where the switching frequency is changed stepwise according to the temperature around the device has been described, but the switching frequency is continuously changed according to the ambient temperature. May be. When the ambient temperature is higher than the reference temperature, the switching frequency is kept constant at the reference frequency. However, the switching frequency may be controlled to increase as the temperature increases.

As described above, in this embodiment, the contrast is reduced by controlling the switching frequency of the video signal and the backlight drive signal that are switched synchronously in response to the response delay of the liquid crystal display panel at low temperatures. Can be prevented.

FIG. 3 is an explanatory diagram of a backlight drive signal waveform of the liquid crystal display device according to the second embodiment of the present invention.
(A) is a diagram showing the relationship between the peripheral illuminance of the liquid crystal display panel and the optimum switching frequency, (b) is a time chart of the backlight drive signal at high illuminance, and (c) is a time chart of the backlight drive signal at low illuminance. is there. Hereinafter, description will be made with reference to the drawings. The configuration of the driving circuit of the liquid crystal display device is the same as that of the first embodiment, and the configuration of the liquid crystal display unit 4 is the same as the configuration of the liquid crystal display unit 4 of FIG. I do.

When an image is displayed by switching the liquid crystal display panel at the same frequency, flickering occurs when the peripheral illuminance is reduced. FIG. 3A is a diagram showing the relationship between the illuminance around the liquid crystal display panel and the optimum switching frequency. As a result of experimentally finding the optimum switching frequency, the lower the illuminance around the liquid crystal display panel is, the more the human illuminance decreases. The eye tends to flicker and the switching frequency must be increased. Therefore, at high illuminance (above the reference illuminance), the switching frequency is kept constant at the reference frequency (for example, 60 Hz which is the field frequency of the television), and at low illuminance, the switching frequency is set higher than the reference frequency (60 Hz) in order to improve flicker. Increase (depending on ambient illumination). The liquid crystal display device according to the present embodiment takes into account the characteristics of the human eye in this way and takes into account the video signal and the backlight as shown in FIGS. 3B and 3C according to the illuminance around the liquid crystal display panel. It controls the switching frequency.

First, the illuminance around the liquid crystal display panel 6 is detected by the illuminance sensor 12, and when the illuminance is equal to or higher than a reference illuminance (for example, illuminance corresponding to daytime) (high illuminance),
The control unit 1 supplies the video signal switching circuit 2 and the backlight switching circuit 3 with the video signal of each color and the driving signal of the light emitting diodes 8R, 8G, 8B of each color of the backlight 8 for a time T0
An instruction is given to switch at intervals (for example, 60 Hz) as shown in FIG. The details of the switching operation are the same as in the first embodiment, and a description thereof will be omitted.

Next, the illuminance sensor 12 is connected to the liquid crystal display panel 6.
When the control unit 1 detects that the illuminance around the illuminance has decreased below the reference illuminance (for example, illuminance corresponding to nighttime) (low illuminance), the control unit 1 sends the video signal switching circuit 2 and the backlight switching circuit 3 a video of each color. The signal and the drive signal of the light emitting diodes 8R, 8G, 8B of each color of the backlight 8 are instructed to be switched at intervals of T2 (for example, 80 Hz) in which the switching cycle is shorter than at the time of high illuminance as shown in FIG. The details of the switching operation are the same as in the first embodiment, and a description thereof will be omitted.

As described above, in the present embodiment, the flickering of the screen is reduced by controlling the switching frequency of the video signal and the backlight drive signal that are switched synchronously according to the illuminance around the liquid crystal display device. You.

FIG. 4 is an explanatory diagram of a backlight drive signal waveform of a liquid crystal display according to a third embodiment of the present invention.
(A) is a diagram showing the relationship between the running state of the vehicle and the optimum switching frequency,
(B) is a time chart of the backlight drive signal when stopped, and (c) is a time chart of the backlight drive signal during traveling. Hereinafter, description will be made with reference to the drawings. The configuration of the driving circuit of the liquid crystal display device is the same as that of the first embodiment, and the configuration of the liquid crystal display unit 4 is the same as the configuration of the liquid crystal display unit 4 of FIG. I do.

In a liquid crystal display device mounted on a vehicle, when a driver frequently looks away from the liquid crystal display device to look at a rearview mirror, a door mirror, or the like during driving, each color appears to flicker. FIG. 4A is a diagram showing the relationship between the traveling state (stop or traveling) of the vehicle and the switching frequency.
In order to divert the line of sight from the liquid crystal display device, flicker tends to occur, and it is necessary to increase the switching frequency. The liquid crystal display device of the present embodiment changes the switching frequency of the video signal and the backlight as shown in FIGS. 4B and 4C according to the running state of the vehicle in consideration of the characteristics of the human eye. To control.

First, when the vehicle speed sensor 13 detects that the vehicle is in a stopped state, the control unit 1 sends a video signal of each color and a light emission of each color of the backlight 8 to the video signal switching circuit 2 and the backlight switching circuit 3. Diode 8R, 8
G, 8B drive signals are transmitted at time T0 intervals (for example, 60H
In z), an instruction is given to switch as shown in FIG. The details of the switching operation are the same as in the first embodiment, and a description thereof will be omitted.

Next, when the vehicle speed sensor 13 detects that the vehicle is running, the control unit 1 sends a video signal of each color and a video signal of each color of the backlight 8 to the video signal switching circuit 2 and the backlight switching circuit 3. Light emitting diode 8R, 8
The drive signals of G and 8B are instructed to be switched at intervals of a time T3 (for example, 80 Hz) whose switching cycle is shorter than the conventional one, as shown in FIG. The details of the switching operation are the same as in the first embodiment, and a description thereof will be omitted.

As described above, in this embodiment, flicker can be prevented by controlling the switching frequency of the video signal and the backlight drive signal that are switched synchronously according to the running state of the vehicle.

[0033]

As described above, according to the present invention, it is possible to provide a liquid crystal display device which can always obtain good image quality even when the use environment changes in consideration of the properties of liquid crystal.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a drive circuit of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a backlight drive signal waveform of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a backlight drive signal waveform of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a backlight drive signal waveform of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a liquid crystal display unit 4.

FIG. 6 is a block diagram illustrating a configuration of a driving circuit of a conventional liquid crystal display device.

FIG. 7 is a waveform diagram of a backlight driving signal of a conventional liquid crystal display device.

[Explanation of symbols]

11 temperature sensor 2 video output switching circuit 12 illuminance sensor
3... Backlight switching circuit, 13... Vehicle speed sensor, 4.
····· Control unit 6 ····· LCD panel 21 ··· Red video signal circuit 7 ···
... Light guide plate, 22 ... Green video signal circuit,
8... Backlight, 23... Blue video signal circuit, 9.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/34 G09G 3/34 J 3/36 3/36

Claims (3)

[Claims] 1. A liquid crystal display device for displaying a color image by sequentially switching and driving color irradiation light to a liquid crystal display panel at a predetermined frequency for each field, wherein a temperature detecting means for detecting a temperature around the liquid crystal display device. A liquid crystal display comprising: a switching frequency control unit configured to control a switching drive frequency of the color irradiation light to be changed according to a temperature around the liquid crystal display device detected by the temperature detection unit. apparatus. 2. A liquid crystal display device for displaying a color image by sequentially switching and driving color irradiation light to a liquid crystal display panel at a predetermined frequency for each field, wherein an illuminance detecting means for detecting illuminance around the liquid crystal display device. A liquid crystal display comprising: a switching frequency control unit configured to control a switching drive frequency of the color irradiation light to be changed according to the illuminance around the liquid crystal display device detected by the illuminance detection unit. apparatus. 3. A liquid crystal display device for displaying a color image by sequentially switching and driving a color irradiation light at a predetermined frequency for each field with respect to a liquid crystal display panel, wherein: a driving state detecting means for detecting a driving state of the vehicle; A liquid crystal display device comprising: switching frequency control means for controlling to change the driving frequency for switching the color irradiation light in accordance with the traveling state of the vehicle detected by the traveling state detection means.