JP2003122330A - Liquid crystal display device and adjusting method for liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily adjust the gamma characteristic of a liquid crystal display device. SOLUTION: A test control circuit 5 which controls an inverter 3 and a gamma conversion table 4 is provided and adjusts a 2nd set value PA2 of transmissivity of a liquid crystal panel 1 when a 2nd set value PB2 of the illumination rate of a back light 2 is 100% so as to attain coincidence with the luminance when a 1st set value PA1 of transmissivity of the liquid crystal panel 1 is 100% and a 1st set value PB1 of the illumination rate of the back light 2 is equalized to set target panel transmissivity, thereby obtaining a desired gamma characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a method of adjusting the liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display devices have been widely used in C.
Compared to RT (cathode ray tube) display devices, it consumes less power and can be made smaller in shape, and is therefore widely used in portable terminals, computer terminals, and the like. In addition, the color reproducibility and moving image display performance, which have been weak points in the past, have been improved, and recently, they have been widely used in television receivers and the like.

Generally, in a display device, the applied voltage and the displayed brightness are not in a linear relationship. FIG. 2 shows the luminance-voltage characteristics of a typical CRT. This is called a gamma characteristic.

By the way, for television broadcasting, video images, and the like, a signal adapted to the gamma characteristic of a CRT has been conventionally used. In other words, TV broadcasts, video images, etc.
By using the display device having the gamma characteristic shown in, it is possible to display a correct image for the first time.

On the other hand, since the liquid crystal panel is completely different in operating principle from the CRT, the gamma characteristic is naturally different. In a liquid crystal panel, when a voltage is applied to the front and back of the panel containing liquid crystal, liquid crystal molecules move and the polarization characteristics change. Further, by the action of the polarizing plate installed on the surface of the liquid crystal panel, the change in the polarization characteristic is converted into the change in the light transmittance and used for display. In general, the liquid crystal moves slowly in the low voltage region and saturates in the high voltage region, so that the transmittance-voltage characteristic, that is, the gamma characteristic is approximately S-shaped. FIG. 3 shows an example of gamma characteristics of a liquid crystal panel used for a computer terminal, a television receiver and the like. The liquid crystal panel may have a different gamma characteristic from that shown in FIG. 3 due to the difference in material and structure, but in each case, a curve completely different from the gamma characteristic of the CRT is shown. .

In order to approximate the gamma characteristic of the liquid crystal panel to the gamma characteristic of the CRT, it is necessary to convert the voltage of the video signal by some method. This will be described with reference to FIG. In FIG. 4, graph 1 is C shown in FIG.
This is the gamma characteristic of RT. Graph 2 is the gamma characteristic of the liquid crystal shown in FIG. If a non-linear function as shown in graph 3 is prepared and the input voltage is converted into a voltage applied to the liquid crystal panel, a gamma characteristic equivalent to that of a CRT can be realized by combining graph 3 and graph 2.

FIG. 5 shows a transformation of the coordinate axes of the nonlinear function shown in the graph 3 of FIG. Such a non-linear function can be realized, for example, by preliminarily storing the function data in a semiconductor memory, applying an input signal to an address terminal of the semiconductor memory, and taking out a converted output signal from the data terminal. it can.

As an example of the above gamma characteristic adjusting method, there is a method disclosed in Japanese Patent Laid-Open No. 8-320671. In this method, the voltage applied to the liquid crystal panel is set by the contrast adjustment circuit, the brightness adjustment circuit, and the control / data processing circuit, the transmittance of the liquid crystal panel at that time is measured by the measurement unit, and the result is stored in the nonlinear characteristic correction circuit. I will let you. Similarly, the gamma characteristic (voltage-transmittance characteristic) can be obtained by sequentially changing the voltage applied to the liquid crystal panel.

Since the liquid crystal panel does not emit light by itself,
In a general direct-viewing type display device, a fluorescent lamp called a backlight is arranged on the back surface or side surface of the panel for irradiation,
The transmitted light is used for display. Therefore, the brightness of the liquid crystal display device depends on the brightness of the backlight and the transmittance of the liquid crystal panel.

Cold cathode fluorescent tubes that do not use filaments are often used for backlights of liquid crystal display devices. In this cold cathode fluorescent tube, a high frequency voltage is applied to the electrodes provided at both ends to discharge. An inverter is used to generate the high frequency voltage.

In the liquid crystal display device, the high frequency voltage described above is intermittently applied with a waveform as shown in FIG. 7 and the backlight is intermittently turned on to adjust the brightness. As shown in FIG. 6, the brightness of the backlight and the ratio of the lighting period (hereinafter referred to as the lighting ratio) are in a substantially proportional relationship.

[0012]

As described above, since the gamma characteristic of the liquid crystal panel and the gamma characteristic of the CRT are completely different from each other, the conversion of the video signal voltage for displaying the same as the CRT is complicated. In general, semiconductor memory is used for conversion. In addition, gamma characteristics often vary slightly due to variations in liquid crystal panels, so in the production process for consumer products, several types of curves are prepared to match typical gamma characteristics, and due to variations in liquid crystal panels, the closest match It is also done by selecting. Furthermore, the brightness balance of each of the three primary colors of red, green, and blue varies slightly depending on the liquid crystal panel, so when the white balance is adjusted, the voltage for the same brightness is
Each of the three primary colors is different.

Thus, there are various variations,
Since the storage area of the semiconductor memory is also finite, the gamma conversion table is not always adjusted to the optimum value, and even if the white balance is taken at the maximum brightness, the white balance may shift at the intermediate brightness, and the production quality is kept constant. Difficult to keep.

Depending on the purpose of use by the user, it may be desired to set a gamma characteristic different from the standard. However, since the conversion formula is complicated as described above, it is difficult for the user to set the desired gamma characteristic even if the setting of the gamma conversion table is opened to the user.

The present invention has been made in view of the above problems, and an object thereof is to easily obtain a desired gamma characteristic.

[0016]

In order to achieve the above object, a liquid crystal display device of the present invention has a lighting rate control means for controlling the lighting rate of a backlight and a transmittance for controlling the transmittance of a liquid crystal panel. Control means, lighting rate first set value output means for outputting the first set value of the lighting rate of the backlight, and lighting rate second set value output means for outputting the second set value of the lighting rate of the backlight. A transmittance first set value output means for outputting a first set value of the transmittance of the liquid crystal panel, and a transmittance second set value output means for outputting a second set value of the transmittance of the liquid crystal panel, It has means for switching the lighting rate of the backlight and the set value of the transmittance of the liquid crystal panel periodically or manually at the same time.

In order to achieve the above-mentioned object, a method of adjusting a liquid crystal display device according to the present invention comprises a lighting rate control means for controlling a lighting rate of a backlight and a transmittance control for controlling a transmittance of a liquid crystal panel. Means, a lighting rate first set value output means for outputting a first set value of the lighting rate of the backlight, and a lighting rate second set value output means for outputting a second set value of the lighting rate of the backlight. A first transmittance set value output means for outputting a first transmittance set value of the liquid crystal panel, a second transmittance set value output means for outputting a second set transmittance value of the liquid crystal panel, and a back light. In a liquid crystal display device, a first setting value of the transmittance of the liquid crystal panel and a backlight having a switching unit for periodically or manually simultaneously switching the setting value of the lighting rate of the light and the setting value of the transmittance of the liquid crystal panel. The lighting rate of the And the second set value as the default value, the second set value of the transmittance of the liquid crystal panel as a variable value, and the set value of the lighting rate of the backlight and the set value of the transmittance of the liquid crystal panel are set cyclically. At the same time, the second set value of the transmittance of the liquid crystal panel is adjusted so that the screen brightness before and after the switching becomes the same.

In the liquid crystal display device according to the present invention, the first and second set values of the lighting rate of the backlight and the first and second set values of the transmittance of the liquid crystal panel are simultaneously or periodically made manually. By switching, it is possible to adjust the transmittance of the liquid crystal panel and set a desired gamma characteristic.

According to the liquid crystal display device adjusting method of the present invention, the set value of the transmittance of the liquid crystal panel and the set value of the transmittance of the liquid crystal panel are compared with the set value of the transmittance of the backlight. A desired gamma characteristic can be obtained by setting the setting value of the lighting rate of the backlight having the same ratio and adjusting the transmittance of the liquid crystal panel so as to show the same luminance.

[0019]

DETAILED DESCRIPTION OF THE INVENTION A description will be given below with reference to the drawings. Figure 1
FIG. 1 is a block diagram of a liquid crystal display device showing an embodiment of the present invention. In FIG. 1, 1 is a liquid crystal panel, 2 is a backlight, 3 is an inverter, 4 is a gamma conversion table,
Reference numeral 5 is a test control circuit, and 6 is a video circuit. In the test control circuit 5, PA1 is the first set value output of the transmittance of the liquid crystal panel, PA2 is the second set value output of the transmittance, and PB1 is the first setting of the lighting rate of the backlight. A value output, PB2 is a second set value output of the lighting rate of the backlight. Specifically, PA1, PA2, PB1, P
B2 is composed of, for example, a logic circuit register, and a control microcomputer that controls the entire liquid crystal display device (not shown in FIG. 1) sets necessary control values at each stage of gamma adjustment and retains those control values. And output. Reference numeral 51 is a parameter switching control circuit, which is used for the PA1, PA2, and P.
B1 and PB2 can be switched arbitrarily. Further, the PA1 or PA2 output is applied to the gamma conversion table 4, and the gamma conversion table 4 outputs a voltage corresponding to the applied set value to the liquid crystal panel 1 to define the transmittance of the liquid crystal panel 1. Further, the PB1 or PB2 output is applied to the inverter 3 to control the lighting rate of the backlight.

Therefore, the PA1 and PA2, PB1
The brightness of the liquid crystal display device can be changed by arbitrarily switching between PB2 and PB2.

As shown in FIG. 9, the adjusting method of the liquid crystal display device according to the present invention sets the first set value of the lighting rate of the backlight to 60% of the maximum lighting rate, and sets the first transmittance of the liquid crystal panel to the first value. When the first set value is 100% of the maximum transmittance and the second set value of the lighting rate of the backlight is 100% of the maximum lighting rate, the second set value of the transmittance of the liquid crystal panel is set to the maximum transmittance. This is an application of the fact that the apparent brightness is the same when the ratio is 60%. Therefore, the first and second set values of the lighting rate of the backlight and the first set value of the transmittance of the liquid crystal panel are known values, and the second set value of the transmittance of the liquid crystal panel is changed. hand,
If the apparent brightness matches, the second set value of the transmittance of the liquid crystal panel becomes 60% of the maximum transmittance.

The test control circuit 5 simultaneously switches the set value for the lighting rate of the backlight and the set value for the transmittance of the liquid crystal panel in a constant cycle. From the viewpoint of the response speed of the inverter and the visibility, the switching cycle is suitably, for example, a fraction of a second to 1 second. Further, when the manual adjustment is performed at the time of user adjustment, the switching can be performed regardless of the above cycle.

Next, the adjustment procedure will be described. Here, a case is considered in which the gamma characteristic as shown by the solid line in FIG. 8 is matched. It is assumed that the adjustment of the maximum input value has already been completed. Also, the maximum input value is 10
The input value is expressed as a ratio with respect to the maximum value. The characteristics of the solid line in FIG. 8 are as follows: input 80%, brightness 61%, input 60%, brightness 33%, input 40%, brightness 13%.
It looks like.

First, when adjusting the brightness of 80% input to 61%, the first set value (PA1) of the transmittance of the liquid crystal panel in FIG. 1 is 100% and the first set value of the backlight lighting rate ( PB1) is set to 61% and the second set value (PB2) is set to 100%. The second set value (PA2) of the transmittance of the liquid crystal panel is an arbitrary value.

When the test control circuit 5 of FIG. 1 operates, first, the first set value (PA1 = 100%) of the transmittance of the liquid crystal panel is set in the gamma conversion table 4, and the first lighting rate of the backlight is set in the inverter 3. Is set (PB1 = 61%). The operation at this time is at point A in FIG. 8 because the brightness of the backlight is reduced. Next, in the gamma conversion table 4, the second set value of the transmittance of the liquid crystal panel (PA2)
However, the second set value of the lighting rate of the backlight (PB2 = 100%) is given to the inverter 3. The operation at this time is visually the same brightness, that is, the point B in FIG.
The second set value (PA2) of the liquid crystal transmittance is adjusted. The second set value (PA2) of the transmittance of the liquid crystal at this time becomes the set value of the gamma conversion table 4 for the input 80%.

Similarly, when adjusting the luminance of 60% input to 33%, the first set value (PA
1) is 100%, the first setting value (PB1) of the lighting rate of the backlight is 33%, and the second setting value (PB2) is 60%.
Set to. Here, the second set value PA2 of the transmittance of the liquid crystal panel is adjusted so that the brightness is visually the same. The second set value PA2 of the transmittance of the liquid crystal panel at this time
Is the set value of the gamma conversion table 4 for input 60%.

By repeating this operation, a series of values of the second set value (PA2) for each input is obtained.
The brightness curve obtained by the gamma conversion table 4 is obtained.

As described above, the present invention takes advantage of the fact that the lighting rate of the backlight exhibits a linear characteristic and is easily controllable, and conventionally requires a highly accurate measuring instrument and complicated work. The setting of the gamma characteristic curve can be easily realized.

[0029]

As described above, in the liquid crystal display device of the present invention, the first and second set values of the lighting rate of the pair of backlights and the first and second set values of the transmittance of the liquid crystal panel are set. The brightness of the liquid crystal display device can be changed by arbitrarily switching the value and the value.

Further, according to the adjusting method of the liquid crystal display device of the present invention, the set value of the transmittance of the liquid crystal panel is set with respect to the set value of the lighting rate of the backlight and the set value of the transmittance of the liquid crystal panel. A desired gamma characteristic can be obtained by setting a setting value of the lighting rate of the backlight having the same ratio as the above and adjusting the setting value of the transmittance of the liquid crystal panel so as to show the same luminance.

Further, since the gamma adjustment can be released to the user, it is possible to see the display contents in each desired color tone.

[Brief description of drawings]

FIG. 1 is a block diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of gamma characteristics of a CRT.

FIG. 3 is a diagram showing an example of gamma characteristics of a liquid crystal panel.

FIG. 4 is an explanatory diagram of gamma characteristic conversion.

FIG. 5 is a diagram showing an example of gamma correction coefficients.

FIG. 6 is a diagram showing an example of a luminance vs. lighting ratio characteristic of a backlight.

FIG. 7 is a diagram showing an example of an oscillation waveform of an inverter.

FIG. 8 is a diagram showing a process of correction.

FIG. 9 is an explanatory diagram of display brightness of a liquid crystal display device.

[Explanation of symbols] 1 LCD panel 2 backlight 3 inverter 4 Gamma conversion table 5 Test control circuit 6 video circuits 51 Parameter switching control circuit PA1 Output the first set value of the transmittance of the liquid crystal panel PA2 Output the second set value of the transmittance of the liquid crystal panel PB1 Output the first set value of the lighting rate of the backlight. PB2 Output the second set value of the lighting rate of the backlight

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 9/30 H04N 9/30 F term (reference) 2H093 NA58 NC42 NC53 ND06 ND07 5C006 AA22 AF46 AF52 EA01 5C060 DB00 HD01 JA14 5C080 AA10 CC03 EE28 JJ02 JJ04 JJ05

Claims (2)

[Claims] 1. A lighting rate control means (3) for controlling a lighting rate of a backlight (2), a transmittance control means (4) for controlling a transmittance of a liquid crystal panel (1), and a backlight (2). Lighting rate first set value output means (PB1) for outputting the first set value of the lighting rate, and second lighting rate second set value output means for outputting the second set value of the lighting rate of the backlight (2). (PB2), a transmittance first set value output means (PA1) for outputting a first set value of the transmittance of the liquid crystal panel (1), and a second set value of the transmittance of the liquid crystal panel (1). Switching for outputting the second transmittance setting value output means (PA2), the lighting rate setting value of the backlight (2) and the transmittance setting value of the liquid crystal panel (1) at the same time periodically or manually A liquid crystal display device comprising means (51). 2. A lighting rate control means (3) for controlling a lighting rate of a backlight (2), a transmittance control means (4) for controlling a transmittance of a liquid crystal panel (1), and a backlight (2). Lighting rate first set value output means (PB1) for outputting the first set value of the lighting rate, and second lighting rate second set value output means for outputting the second set value of the lighting rate of the backlight (2). (PB2), a transmittance first set value output means (PA1) for outputting a first set value of the transmittance of the liquid crystal panel (1), and a second set value of the transmittance of the liquid crystal panel (1). A second transmittance set value output means (PA2) for outputting and a switching means (51) for switching the set value of the lighting rate of the backlight and the set value of the transmittance of the liquid crystal panel simultaneously or manually at the same time. In the liquid crystal display device having, the point of the backlight (2) The first and second set values of the rate and the first set value of the transmittance of the liquid crystal panel (1) are fixed, and the lighting rate of the backlight (2) and the transmittance of the liquid crystal panel (1) are fixed. LCD panel (1) so that the screen brightness before and after switching, which is visually recognized or measured by the LCD panel brightness measurement device, is the same.
2. A method for adjusting a liquid crystal display device, comprising: increasing or decreasing a second set value of the transmittance.