JP3107444B2 - Liquid crystal display - Google Patents

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,
In particular, the present invention relates to a liquid crystal display device including a variable γ correction circuit that corrects a gradation of a video signal in accordance with a voltage-luminance characteristic of a liquid crystal display device and an input signal amplitude.

[0002]

2. Description of the Related Art A liquid crystal display device can display a plurality of gradations because its luminance changes in accordance with an input voltage.

FIG. 2 shows an example of input voltage-luminance characteristics of a liquid crystal display panel used in a liquid crystal display device. FIG. 2 shows an example of an input voltage-luminance characteristic of a so-called normally black type liquid crystal panel that does not transmit light when no voltage is applied. However, the following description can be similarly applied to a so-called normally white liquid crystal panel that transmits light without applying a voltage.

The input voltage-luminance characteristic of a liquid crystal panel is shown in FIG.
As shown in the example of FIG. On the other hand, a video signal of a television broadcast or the like generally uses a signal corrected in advance so that an input voltage-luminance characteristic shows linearity when an image is displayed on a cathode ray tube. Therefore, when a video signal such as a television broadcast is displayed on the liquid crystal panel at a normal gradation, the characteristics of the output signal with respect to the input signal are indicated by the broken line in FIG. 3 obtained from the voltage-luminance characteristics of the liquid crystal panel. It is necessary to perform correction by a γ correction circuit so as to approximate the characteristics.

As a conventional gamma correction circuit used in a liquid crystal display device, for example, a circuit described in Japanese Patent Application Laid-Open No. 1-154093 is known. In this conventional example, the input / output voltage characteristic shown by the example of the broken line in FIG. 3 is changed by a voltage amplifier circuit in which three types of voltage amplification rates are switched according to the amplitude of the input voltage as shown by the example of the solid line in FIG. It is an approximation.

[0006]

In the above prior art, the amplification factor of the voltage amplification circuit serving as a gamma correction circuit and the point at which the amplification factor is switched are fixed. Therefore, if the amplitude of the video signal is changed in an attempt to change the maximum luminance (the minimum luminance = the maximum luminance in a state where the black level is fixed) of the display image according to the surrounding environment (that is, to change the contrast), No consideration has been given to the point that the gradation cannot be correctly expressed.

As a specific example of the above problem, a so-called in-vehicle display mounted on a car will be described as an example.

The environment in which a vehicle-mounted display is used can be roughly divided into daytime and nighttime. The ambient brightness when using the in-car display during the day,
It is very bright when exposed to direct sunlight. For this reason, in order to make the display easier to see, it is common to use the display with the maximum brightness. On the other hand, since the surroundings are dark at night, the brightness of the display does not need to be as bright as during the day. In some cases, it is required that the luminance be reduced to about one-tenth of the maximum luminance so that the screen is not dazzled.

In general, a liquid crystal display performs display by illuminating a liquid crystal panel with a backlight using a fluorescent tube. In this type of liquid crystal display,
To adjust the brightness, a method of reducing the brightness of the fluorescent tube is considered. However, if the current flowing through the fluorescent tube is reduced in order to lower the luminance of the fluorescent tube, the lighting state becomes unstable, and in some cases, the lighting does not occur.

On the other hand, if the brightness adjustment range is to be further expanded beyond the range that can be adjusted by the fluorescent tube, and, for example, it is desired to display stably even at a brightness of several tenths of the maximum brightness, the A method of reducing the signal amplitude and a method of using the method in combination with the adjustment of the backlight luminance can be considered. However, in the above conventional example, since the voltage amplification rate switching point of the γ correction circuit is fixed, if the amplitude of the video signal is reduced to reduce the luminance, the gradation of the image cannot be correctly expressed. was there.

An object of the present invention is to adjust the amplitude of a signal applied to a liquid crystal panel to adjust the brightness and contrast of a display image, and to always display an image with an appropriate gradation. It is to provide a liquid crystal display device which can be used.

[0012]

According to the present invention, there is provided a liquid crystal panel for receiving a video signal and displaying an image, a device for driving the liquid crystal panel, and a light source for illuminating the liquid crystal panel. And a gamma correction circuit that sets a correction characteristic of a gradation characteristic in accordance with an input voltage-luminance characteristic of a liquid crystal panel and corrects a gradation characteristic of a video signal, and an amplitude of the video signal. Means for setting, for the input video signal, the means for correcting the gradation characteristic according to the set correction characteristic, and corresponding to the setting of the amplitude of the video signal, Means for setting a correction characteristic, and for an input video signal,
Means for determining at least one correction characteristic change point corresponding to the magnitude of the amplitude, and for changing the correction characteristic of the video signal depending on which side the amplitude is before or after the change point. A liquid crystal display device characterized by the above is provided.

The means for changing the correction characteristic presets at least one change point between the maximum value and the minimum value of the amplitude of the input video signal, and sets the amplitude of the input video signal to the change point. It is possible to have a function of changing the correction characteristic depending on whether it is larger or smaller.

The means for correcting the gradation characteristic may include an amplifier circuit.

[0015] The means for setting the correction characteristics may be for setting the amplification factor of the amplifier circuit.

The present invention further comprises means for generating information indicating the setting of the amplitude of the video signal and inserting the information into the video signal, and the gamma correction circuit extracts the information indicating the setting of the amplitude from the video signal. In addition, a configuration may be provided that further includes means for sending to the means for setting the correction characteristics. The means for generating the information indicating the setting of the amplitude of the video signal and inserting the information into the video signal may be, for example, a means for generating a pulse signal subjected to pulse width modulation.

The means for setting the amplitude of the video signal includes:
It may have a circuit for outputting a signal for setting the amplitude of the video signal. The circuit that outputs the signal may have, for example, a variable resistor that divides a power supply voltage.

Further, the means for setting the amplitude of the video signal may include a circuit for detecting the amount of ambient light and outputting a signal for setting the amplitude of the video signal in accordance with the amount of light.

Further, the means for setting the amplitude of the video signal includes an element for detecting the amount of ambient light and a variable resistor, and sets the amplitude of the video signal according to the resistance value of the variable resistor and the amount of light. And a circuit for outputting a signal to be output.

Further, the present invention can further comprise means for adjusting a DC voltage level of a signal applied to the liquid crystal panel. The means for adjusting the DC voltage level of the signal applied to the liquid crystal panel may be, for example, one in which the DC level is selected in correspondence with the setting of the correction characteristic for the means for setting the correction characteristic.

[0021]

The liquid crystal panel is illuminated by a light source.
Upon receiving the video signal, it is driven by a driving device to display an image. At this time, since the input voltage-luminance characteristic of the liquid crystal panel does not match the amplitude characteristic of the video signal, the γ correction circuit sets the correction characteristic of the gradation characteristic in accordance with the input voltage-luminance characteristic of the liquid crystal panel. And correct the gradation characteristics of the video signal.
Here, the brightness of the displayed image is set by means for setting the amplitude of the video signal. For example, luminance can be set by setting a voltage corresponding to the maximum amplitude.

In the γ correction circuit, the gradation characteristic of the input video signal is corrected by the means for correcting the gradation characteristic in accordance with the set correction characteristic. The correction of the gradation characteristics can be performed, for example, by changing the amplification factor when amplifying the video signal.

On the other hand, the means for setting the correction characteristic sets the correction characteristic in accordance with the setting of the amplitude of the video signal. For example, a circuit configuration for setting a plurality of types of amplification factors of an amplification circuit,
It can be selected according to the setting of the amplitude of the video signal. The amplitude of the video signal can be set, for example, by setting the voltage.

The means for changing the correction characteristic of the video signal determines at least one change point of the input video signal in accordance with the set magnitude of the amplitude. At least one change point is defined between the maximum value and the minimum value of the amplitude. Further, this change point is determined according to the magnitude at which the amplitude is set. That is, if the set value of the maximum amplitude is small between the maximum value and the minimum value of the amplitude, it corresponds to a small amplitude, and if it is large, it corresponds to a large amplitude. Therefore, if the setting of the amplitude of the video signal is changed, the position of the changed point will change accordingly.

Before and after the change, different correction characteristics are set. Therefore, the correction characteristics differ depending on whether the amplitude of the video signal is before or after this point. For example, the voltage amplification rate changes.

Thus, even when the amplitude of the video signal is reduced in order to lower the luminance, for example, the voltage amplification rate switching point and the voltage amplification rate of the γ correction circuit change in conjunction with this, and an appropriate gradation Display can be performed.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a first embodiment of the liquid crystal display device of the present invention, and uses the liquid crystal panel voltage-luminance characteristic example of FIG. 2 and the input / output characteristic example of the gamma correction circuit of FIGS. The operation will be described. FIG. 1 is a block diagram showing a configuration example of a first embodiment of a liquid crystal display device according to the present invention having a function of performing variable γ correction.

In FIG. 1, the liquid crystal display device according to the present embodiment has a video chroma circuit 1 having a contrast adjusting function and γ correction for the R, G, B primary color signals.
A correction circuit 2 and a polarity inversion circuit 4 for converting the primary color signal into an alternating current
A synchronization separation circuit 5 for separating a synchronization signal from a video signal,
It has a liquid crystal panel 9, a horizontal driver 7 and a vertical driver 8 for driving the liquid crystal panel 9, a control circuit 6 for controlling the driving of the horizontal driver 7 and the vertical driver 8, and a backlight 10 for illuminating the liquid crystal panel 9. . Also,
The liquid crystal display device according to the present embodiment functions as a means for setting the amplitude of a video signal, a variable resistor 11 and a power supply 12 for generating a voltage signal for contrast adjustment and γ change, and a video signal (FIG. 1 has an input terminal 100 (indicated by Video).

In FIG. 1, a video signal input from an input terminal 100 is input to a video chroma circuit 1.
The video chroma circuit 1 processes an input video signal and outputs R, G, B primary color signals. The primary color signal is input to the γ correction circuit 2, and is amplified by an amplification unit in the γ correction circuit 2 to an amplitude required for driving the liquid crystal panel 9.

The gamma correction circuit 2 corrects the gradation characteristics of the input video signal in accordance with the set correction characteristics, and sets the correction characteristics in accordance with the setting of the amplitude of the video signal. And at least one correction characteristic change point corresponding to the magnitude of the amplitude of the input video signal, and according to which side the amplitude is before or after the change point, Means for changing the correction characteristic. As a configuration for realizing these means, the γ correction circuit 2 includes a circuit portion that functions as an amplifier 2a that amplifies a primary color signal, although it is not always possible to clearly distinguish the circuit, And a circuit part functioning as a variable γ correction unit 3 for performing γ correction.
The γ correction circuit 2 has a characteristic of an output signal to an input signal, for example, such that an image is displayed at an appropriate gradation on a liquid crystal panel 9 having a voltage-luminance characteristic as shown in the example of FIG.
For example, the amplitude characteristic of the primary color signal is corrected so as to have the characteristic shown by the solid line in FIG. It should be noted that the characteristics indicated by the broken lines in FIG. 3 are ideal, and the characteristics indicated by the solid lines are set so that the input / output characteristics of the γ correction circuit 2 are as close to the ideal characteristics as possible. The output of the γ correction circuit 2 is input to the polarity inversion circuit 4. In general, since the liquid crystal panel 9 needs to be driven by an AC signal, the polarity inversion circuit 4 converts the primary color signal into AC.

On the other hand, the video signal input from the input terminal 100 is also input to the sync separation circuit 5. The synchronization separation circuit 5 separates the horizontal synchronization signal H and the vertical synchronization signal V from the video signal and sends them to the control circuit 6. The control circuit 6 controls a control signal group CPLS necessary for controlling the horizontal driver 7 and the vertical driver 8 based on the applied horizontal synchronization signal H and vertical synchronization signal V.
Is generated and supplied to the horizontal driver 7 and the vertical driver 8.

The primary color signal group RV converted by the polarity inversion circuit 4 is supplied to the horizontal driver 7. The horizontal driver 7 applies the AC primary color signal group RV to the liquid crystal panel 9 according to the timing of the plurality of control signal groups CPLS input from the control circuit 6. The vertical driver 8
In accordance with the timing of the control signal group CPLS input from the control circuit 6, a scanning signal is applied to the liquid crystal panel 9 to scan the liquid crystal panel 9. As a result, an image is displayed on the liquid crystal panel 9. The backlight 10 is, for example, an illuminating device for the liquid crystal panel 9 using a fluorescent tube as a light source, so that an image displayed on the liquid crystal panel 9 can be viewed.

The liquid crystal display device described above may require so-called dimming, which changes the brightness of the display screen in accordance with the surrounding environment, depending on the application. That is, for example, an in-vehicle liquid crystal display device displays a bright screen in the daytime so that it is easy to see even under sunlight, and displays the display screen so that it is not dazzled at night (in some cases, about one-tenth of the maximum brightness). Until darkening is required. In order to darken the display screen, a method of darkening the backlight 10 can be considered. However, if the current flowing through the fluorescent tube is reduced in order to darken the fluorescent tube, which is the light source of the backlight 10, the lighting becomes unstable or does not light at all. For this reason, it is difficult to realize a luminance of about several tenths of the maximum luminance as described above using only the fluorescent tube. On the other hand, since the transmittance of the liquid crystal panel 9 changes depending on the magnitude of the applied voltage, in the embodiment shown in FIG. It is carried out.

In the embodiment shown in FIG. 1, the amplitude of the primary color signal output from the video chroma circuit 1 changes according to the voltage applied from the variable resistor 11. That is, the variable resistor 11 corresponds to a knob for adjusting the contrast of the displayed image. As a result, the amplitude of the primary color signal output from the video chroma circuit 1 changes, and the light transmittance of the liquid crystal panel 9 changes, so that the brightness and contrast of the display image can be changed.

Here, an output voltage is applied from the variable resistor 11 to the γ correction circuit 2 together with the video chroma circuit 1. When the voltage applied from the variable resistor 11 has a predetermined value, the γ correction circuit 2 turns off the amplification factor of the amplifier 2a at points P1 and P2 in the input / output voltage characteristic example shown in FIG. Be replaced. When the voltage applied from the variable resistor 11 is changed, the amplitude of the primary color signal output from the video chroma circuit 1 is changed, and in accordance with this, as shown in the example of FIG. Amplifier 2a
The point at which the amplification factor is switched changes to P1 'and P2', and the input / output characteristics also change as shown in the figure.

As a result, the brightness of the image displayed on the liquid crystal panel 9 can be easily adjusted to a low brightness which is difficult to realize only by adjusting the brightness of the backlight 10, and γ is adjusted in accordance with the change in the amplitude of the primary color signal. Since the amplitude characteristics of the output signal of the correction circuit 2 can always be changed so as to match the display characteristics of the liquid crystal panel 9, appropriate gradation display can be performed.

FIG. 5 shows an example of the configuration of the γ correction circuit 2. The operation will be described with reference to the input / output characteristics examples of FIGS. Note that a similar circuit is provided for each of the three primary colors of R, G, and B in the γ correction circuit.
Only the color components are shown. The same applies to the following embodiments.

In FIG. 5, 14, 18 and 21 are transistors, 15-1 to 15-n, 16-1 to 16-n, 1
Reference numerals 7-1 to 17-n, 19, 20, and 22 denote resistors; 110, a variable resistor; 23, an output terminal of an amplified and gamma-corrected primary color signal; 13, a voltage level detection circuit;
0 and 170 are switch circuits, and Vcc and Vbb are power supply terminals.

The switch circuits 150, 160, 170
Each of the plurality of switch elements 150-1 to 150-n,
160-1 to 160-n and 170-1 to 170-n. These include resistors 15-1 to 15-n and 16-1 to 16-n.
16-n and 17-1 to 17-n are connected. Each of the switch elements 150-1 to 150-n, 160-1 to 16
For example, 0-n and 170-1 to 170-n are turned on when the applied control voltage is at "H" level, and are turned off when at "L" level.

The transistor 14 has a switch circuit 150
One of the resistors 15-1 to 15-n selected by the switch 15-i is connected to the emitter, and the resistors 160-1 to 160-160 selected by the switch circuit 160.
Any one of the resistors 16-i of -n is connected to the collector. The transistor 21 has a collector grounded, and forms an emitter follower together with the resistor 22. The collector of transistor 14 is connected to the base of transistor 21. These constitute at least a part of the amplifier circuit section 2a.

The primary color signal output from the video chroma circuit 1 whose contrast voltage is set by the variable resistors 11 and 110 is applied to the base of the transistor 14. The primary color signal input to the base of the transistor 14 is supplied to resistors 15-1 to 15-15 by switch circuits 150 and 160, whose operations are controlled by the voltage level detection circuit 13.
-N and an amplification factor determined by the ratio of one resistor selected from each of the resistors 16-1 to 16-n (assuming that the resistor 15-i having the resistance value R1 and the resistor 16-i having the resistance value R2 are selected). The amplification factor is amplified by R2 / R1), output from the collector terminal of the transistor 14, and
1 is applied to the base.

Here, the switch circuit 170 connected to the emitter of the transistor 14 is connected to the voltage level detection circuit 1
According to the detection result of No. 3, any one of the plurality of switches becomes conductive, and any one of the resistors 17-1 to 17-n is connected to the emitter of the transistor 14. Resistance 17-1 to 1
The transistor 18 having 7-n connected to the emitter has an emitter voltage of the transistor 14 equal to the value V1 shown in FIG.
The base voltage is set by the resistors 19 and 20 so that the cut-off state is set when the voltage is smaller than V1 and the active state is set when the voltage is larger than V1. Thus, when the transistor 18 is in the cutoff state, the transistor 14
Is determined only by the resistors selected from the resistors 15-1 to 15-n and the resistors selected from the resistors 16-1 to 16-n. On the other hand, when the transistor 18 is in an active state, the voltage amplification factor is a parallel resistance of a resistor selected from the resistors 15-1 to 15-n and a resistor selected from the resistors 17-1 to 17-n, It is determined by a ratio with a resistor selected from the resistors 16-1 to 16-n.

The input / output characteristics of the transistor 14 described above are, for example, as shown by the solid line in FIG. That is, the output voltage amplitude at the time of the maximum amplitude IA of the input signal is OA, and the slope of the input / output characteristic changes at the point P1.

As described above, the primary color signal whose amplitude characteristic has been corrected is output via the transistor 21 to the output terminal 2.
3 is output.

Next, the case where the contrast voltage applied to the video chroma circuit 1 is changed by the variable resistor 11 will be described.

When the contrast voltage applied to the video chroma circuit 1 is changed by changing the resistance of the variable resistor 11, the amplitude of the primary color signal applied to the base of the transistor 14 changes. Also, the voltage applied to the base of the transistor 18 changes, and the voltage level detection circuit 1
The voltage applied to 3 changes. From this, the switching elements selected in the switching circuits 150, 160, and 170 whose operations are controlled by the voltage level detection circuit 13 are switched. As a result, the voltage at which the operation state of the transistor 18 switches changes, and the transistor 1
4 also changes.

For this reason, the input / output characteristics of the transistor 14 are, for example, as shown in the example of FIG. That is, the output voltage amplitude at the time of the maximum amplitude IB of the input signal is OB (IB <IA, OB <OA), and the point at which the amplification factor of the transistor 14 switches is PB.

As described above, by reducing the amplitude of the primary color signal and changing the point at which the amplification factor of the transistor 14 changes and the amplification factor, for example, the ideal correction curve shown by the broken line in FIG. ing.

As described above, the transistor 14
The luminance and contrast of the displayed image can be changed by changing the amplitude of the primary color signal input to the LCD, and the point at which the amplification factor changes and the amplification factor are changed in accordance with the display characteristics of the liquid crystal panel 9 to change the image. Can be appropriately expressed.

FIG. 8 shows a specific configuration example of the voltage level detection circuit 13 shown in FIG. 5, and its operation will be described with reference to FIG.

In FIG. 8, 13-1 to 13-5 are resistors, 13-6 to 13-9 are comparators for comparing voltages, 13-10 to 13-13 are AND circuits, and 13-14.
13-16 are inverters, and 13-17 to 13-20 are output terminals for selection signals. The voltage level detection circuit of FIG. 8 has four output terminals 13-17 to 13-20, and switch circuits 150 and 16 each having four switches.
0,170.

In FIG. 8, voltages divided by resistors 13-1 to 13-5 are respectively applied to comparators 13-6.
13-9. Comparators 13-6 to 13
-9 is the voltage applied from the variable resistor 11 and the resistor 13-
The voltage is divided by 1 to 13-5 and compared with the applied voltage,
The voltage applied from the variable resistor 11 is
When the voltage is divided by -5 and becomes higher than the voltage applied to each comparator, an "H" level signal is output. When the voltage applied from the variable resistor 11 is lower, "L" is output.
It outputs a level signal. The signals output from the four comparators are AND circuits 13-10 to 13
-13 and an inverter 13-14 to 13-16.

The logic circuit includes comparators 13-6 to 13-6.
Output terminals 13-17 to 13-20 according to the output of 3-9
Operate so that only one of them attains the "H" level. For example, when all the outputs of the comparators 13-6 to 13-9 are at the "H" level, only the output terminal 13-17, which is the output of the AND circuit 13-10, becomes the "H" level, and the inverter 13-14 outputs "H". The output terminals 13-18 to 13-20, which are the outputs of the AND circuits 13-11 to 13-13 to which the L-level signal is applied, all have the "L" level.

By using the voltage level detection circuit as described above, the switch circuits 150, 160, 170
Can be controlled. Note that FIG. 8 illustrates an example in which a logic circuit is configured by an AND circuit and an inverter. However, another logic element may be used as long as the result is logically the same. In the example of FIG. 8, an example in which a switch circuit having four switches is controlled has been described. However, the number of comparators for comparing the voltage divided by the resistor with the voltage of the variable resistor 11 is increased, and the logic circuit is increased. Is configured to correspond to the number of comparators, so that a switch circuit having more switches can be controlled. For example, when five switches are controlled, the number of comparators can be made to correspond to the number of logic circuits by using a five-input AND circuit.

In the examples shown in FIGS. 5, 6 and 7,
An example using a so-called normally black liquid crystal panel in which light does not pass through when no voltage is applied to the liquid crystal panel 9 has been described. However, the present invention can be applied to a so-called normally white liquid crystal panel in which light is transmitted without applying a voltage to the liquid crystal panel. Therefore, another example using a normally white liquid crystal panel will be described below.

FIG. 9 shows an example of correction characteristics for displaying an image with an appropriate gradation on a normally white liquid crystal panel.
FIG. 10 shows a configuration example of a variable γ correction circuit applied to a normally white liquid crystal panel.

A broken line in FIG. 9 is an example of an ideal correction characteristic obtained from the display characteristic of the liquid crystal panel. In the figure,
The solid line is an example of the approximate correction characteristic obtained by the variable γ correction circuit shown in FIG. In FIG. 9 and FIGS. 11 and 12, which will be described later, the brightness of the display image becomes minimum (that is, black display) when the output voltage is the maximum. Does not change, and the minimum value changes.

In FIG. 10, the gamma correction circuit has the same components as the gamma correction circuit shown in FIG. 5, for example, a level detection circuit 13, switch circuits 150, 160 and 170, variable resistors 11 and 110, and the like. It has a transistor 24 and a resistor 25.

The transistor 24 is an NPN transistor. This transistor 24 has an emitter voltage of the transistor 14 opposite to that of the transistor 18 in FIG.
Is smaller than V1 and the cutoff state is set. That is, when the emitter voltage of the transistor 14 is lower than V1, the gain of the transistor 14 increases when the emitter voltage of the transistor 14 is lower than V1, and decreases when the emitter voltage of the transistor 14 is higher than V1. As a result, the input / output characteristics of the base input signal and the collector output signal of the transistor 14 become, for example, as shown by the solid line in FIG. 9 with respect to the ideal input / output characteristics shown by the broken line in FIG.

Next, by changing the output voltage of the variable resistor 11,
The case where the amplitude of the primary color signal output from the video chroma circuit 1 is reduced will be described.

When the output voltage of the variable resistor 11 is changed, the point at which the operation state of the transistor 24 switches is changed. Further, since the voltage detected by the voltage level detection circuit 13 changes, the switch circuits 150, 160, and 170 whose operations are controlled by the voltage level detection circuit 13
The switching elements respectively selected inside are switched.
As a result, the point at which the amplification factor of the transistor 14 changes changes, and the switch circuits 150, 160, 1
70 changes the resistance value of the resistor connected to the transistor 14. For this reason, the input / output characteristics of the transistor 14 change from the state of the example of FIG. 9, for example, as shown by the example of the solid line in FIG. 11.

In FIG. 11, the minimum voltage of the output signal is OB
(OB> OA) shows an example in which the point at which the amplification factor changes is set to PB. Thus, the brightness and contrast of the display image can be changed by changing the amplitude of the video signal, and the image can be displayed with an appropriate gradation.

Next, the operation of the above-described first embodiment of the present invention will be described in more detail by giving specific circuit constants. Note that the following description is basically the same for other embodiments described later for performing γ correction using an amplifier circuit.

FIG. 30 is a circuit diagram specifically showing the number of switches and circuit constants of the switch circuits 150, 160, 170 in the circuit of the embodiment shown in FIG.
FIG. 31 shows the input / output characteristics of the gamma correction circuit. FIG. 31 shows a state where the maximum input voltage amplitude and the output voltage amplitude are divided into four at the switching point P2 of the correction curve, the maximum amplitude point of the correction curve, and the switching point P1 of the correction curve, respectively. The divided sections are A, B, C, and D for the input voltage and a, b, c, and d for the output voltage, from the lower voltage side. In addition, the input voltage indicates an input voltage that is actually input and a difference voltage that contributes to a change in amplitude. In the present embodiment, the point P1 indicates the position when the voltage at the point X in FIG. 31 is 2V, and the point P2 indicates the position when the voltage at 1.7V is 1.7V.

In FIG. 31, R2 (1.2 kΩ) and R1
(1.8 kΩ), R4 (5.1 kΩ) and R3 (5.6 kΩ) as resistors selected by the switch circuit 160,
R6 (1.5 kΩ) and R5 (6.2 kΩ) are provided as resistors selected by the switch circuit 170, and R7 (1.5 kΩ) and R8 (1 kΩ) are set as resistors for setting the base voltage of the transistor 18. Provided. The variable resistor 11 has a variable range of 0 to 11 kΩ. In the present embodiment, the variable terminal is 3.9 kΩ.
Is set to The power supply is set to Vcc = 5V and Vbb = -13.5V.

With these settings, the gamma correction circuit of this embodiment realizes two types of correction curves by the switch circuits 150, 160 and 170. That is, the resistors R2, R4 and R6 are selected in the correction curve by the switch circuits 150, 160 and 170,
In the correction curve, the resistances R1, R3 and R5
Is selected. As a result, the correction curve is switched so that the voltage applied to the level detection circuit 13 becomes a correction curve shown in FIG. 31 when the voltage is higher than 4.25 V and a correction curve when the voltage is lower.

In the sections A, B and C of the correction curve, the input voltage amplitude, the output voltage amplitude and the ratio between the input voltage and the output voltage up to the switching point are as follows: A + B + C = 0.55 V a + b + c = 2.5 V 5 ÷ 0.55 ≒ 4.5. On the other hand, the amplification factor in this section of the gamma correction circuit of the present embodiment is R4 ＲR2 = 5.1 kΩ ÷ 1.2 kΩ = 4.25.

In the section D of the correction curve,
The input voltage amplitude, the output voltage amplitude, and the ratio between the input voltage and the output voltage up to the switching point are as follows: D = 0.15V d = 1.1V 1.1 ÷ 0.15 ≒ 7.3 On the other hand, the amplification factor in this section of the gamma correction circuit of the present embodiment is obtained by increasing the parallel resistance value of the resistors R2 and R6 by (R2‖R
When expressed as 6), R4 ÷ (R2‖R6) = 5.1 kΩ ÷ 0.667 kΩ ≒ 7.6.

As described above, in the correction curve, the sections A, B, and C and the section D substantially realize the required amplification factor.

In the section A of the correction curve, the input voltage amplitude, the output voltage amplitude, and the ratio between the input voltage and the output voltage up to the switching point are as follows: A = 0.2V a = 0.7V 0.7 ÷ 0. 2 = 3.5. On the other hand, the amplification factor in this section of the gamma correction circuit of the present embodiment is as follows: R3５R1 = 5.6 kΩ ÷ 1.8 kΩ ≒ 3.1.

In the section B of the correction curve,
The input voltage amplitude, the output voltage amplitude, and the ratio between the input voltage and the output voltage up to the switching point are as follows: B = 0.2V b = 0.8V 0.8 ÷ 0.2 ≒ 4 On the other hand, the amplification factor in this section of the gamma correction circuit of the present embodiment is obtained by increasing the parallel resistance value of the resistors R1 and R5 by (R1‖R
When expressed as 5), R3 ÷ (R1‖R5) = 5.6 kΩ ÷ 1.395 kΩ ≒ 4.

As described above, in the correction curve, both the section A and the section B substantially realize the required amplification factor.

As described above, according to this embodiment, two types of γ correction curves can be realized depending on whether the input voltage is above or below the switching point.
In the description using FIG. 0 and FIG. 31, an example has been described in which the correction characteristic approximated by the variable γ correction circuit 3 has only one point at which the amplification factor is switched. Good. For example, in the configuration example of the variable γ correction circuit shown in FIG.
7-n, a plurality of circuits each including the transistors 18 and 25, the resistors 19 and 20, and the switch circuit 170 may be provided in parallel. In such a circuit configuration, by setting the cutoff voltage of each parallel circuit including the transistors 18 and 25 and the resistors 19 and 20 to be different from each other, the amplification factor is changed according to the cutoff of each circuit. Are provided. Thus, a plurality of change points of the input / output voltage characteristics are provided, and characteristics closer to an ideal correction curve can be approximated.

As an example, FIG. 12 shows an example of input / output characteristics of a variable γ correction circuit having two amplification rate switching points. As shown in the example of FIG.
With this arrangement, it is possible to obtain an approximate characteristic closer to an ideal correction characteristic than the input / output characteristic example of FIG.

Next, a second embodiment of the present invention will be described. FIG. 13 shows the configuration of the second embodiment of the present invention.
In the present embodiment, γ correction is performed by a method different from that of the first embodiment.

In this embodiment, as shown in FIG. 13, a video chroma circuit 1, a gamma correction circuit 2, a polarity inversion circuit 4
, A synchronization separation circuit 5, a control circuit 6, and a horizontal driver 7.
, A vertical driver 8, a liquid crystal panel 9, a backlight 10, a variable resistor 11 and a power supply 12. This embodiment has the same configuration as that of the first embodiment except that the configuration of the γ correction circuit 2 is different. Therefore, the description here will focus on the differences.

As shown in FIG. 13, the gamma correction circuit 2 used in the present embodiment is not necessarily clearly divided on the circuit, but a part functioning as the amplification circuit unit 2a and a variable gamma correction unit 3 It has a functioning portion and a portion functioning as a pulse width control circuit 26 for controlling these portions.

FIG. 14 shows a specific configuration example of the gamma correction circuit 2. FIG. 15 shows an example of the operation waveform. The configuration and operation will be described with reference to these drawings.

In FIG. 14, the γ correction circuit 2 includes a multivibrator 27, a clock generation circuit 28, a pulse generation circuit 29, an AND circuit 30, an inverter 31, Shift register 32 and D flip-flops 33-1 to 3-3
3-n. The switch circuit 150 (the switch element 15)
0-1 to 150-n), 160 (switch element 160-
1-160-n) and 170 (switch element 170-
1 to 170-n), transistors 18 and 24, and resistors 19, 20 and 25 used for setting the γ change point. Further, similarly to the one shown in FIG. 10, the transistor 1
4, 21 and a resistor 22.

The multivibrator 27 generates a pulse MBO whose pulse width changes according to the voltage applied from the variable resistor 11 in synchronization with the vertical synchronizing signal V, for example.
It is applied to the AND circuit 30 and the inverter 31. The AND circuit 30 receives the clock signal C from the clock generation circuit 28.
LK is also applied, and a signal that is the logical product of the pulse MBO and the clock signal CLK is applied to the shift register 32. The pulse signal PLS from the pulse generation circuit 29 is also applied to the shift register 32. The shift register 32 has n output terminals, and outputs a signal SF obtained by shifting the pulse signal PLS by the clock signal CLK.
1 to SFn are output.

The signals SF1 to SFn are applied to D flip-flops 33-1 to 33-n, respectively. The output signal IMBO of the inverter 31 is applied to the clock terminals of the D flip-flops 33-1 to 33-n. The D flip-flops 33-1 to 33-n latch the signal applied from the shift register 32 in synchronization with the rise of the signal applied to the clock terminal, and transmit the signal to the output terminal. D flip-flop 33-1
To 33-n are output from the switch elements 150-1 to 150-1.
50-n, 160-1 to 160-n and 170-1 to
170-n.

The switch elements 150-1 to 150-
n, 160-1 to 160-n and 170-1 to 170
The signal -n is turned on when the applied signal is at "H" level and turned off when it is at "L" level. FIG.
5, the output signal IMBO of the inverter 31 is
Of the output signals of the shift register 32, SFi (1 ≦ i ≦
n) rises during the “H” level period. Therefore, among the output signals of the D flip-flops 33-1 to 33-n, only the output of the D flip-flop 33-i becomes "H" level, and all the other output signals of the D flip-flops become "L" level. Become. As a result, only the switch element 150-i, the switch element 160-i, and the switch element 170-i are turned on, and the other switch elements are turned off. At this time, the amplification factor of the transistor 14 is represented by the ratio (Ri2) of the parallel resistance (R1) of the resistors 15-i and 17-i to the resistance 16-i (R2).
/ Ri1). Note that the output MBO of the multivibrator 27 and the output PLS of the pulse generation circuit 29 are signals repeatedly output at a constant cycle, and the cycle is, for example, synchronized with the vertical scanning cycle of the video signal.

On the other hand, by changing the output voltage of the variable resistor 11, the amplitude of the primary color signal output from the video chroma circuit 1 changes, and the voltage at which the operation state of the transistor 24 switches changes. Therefore, the variable resistor 1
By changing the output voltage of No. 1, the brightness and contrast of the image displayed on the liquid crystal panel can be adjusted by changing the amplitude of the primary color signal. Further, the voltage at which the operation state of the transistor 24 is switched is adjusted, and the multivibrator 27
Switch elements 150-1 to 150-n, 160-1 to 160 by adjusting the pulse width of pulse MBO output from
-N and one of 170-1 to 170-n are turned on to form resistors 15-1 to 15-n and 16-1 to 16-16.
By selecting one of -n and 17-1 to 17-n, the amplitude characteristic of the primary color signal applied to the liquid crystal panel 9 can always be set to match the display characteristic of the liquid crystal panel 9. Thus, an image can always be displayed with an appropriate gradation.

Next, a third embodiment of the present invention will be described. FIG. 16 shows a third embodiment of the present invention. In the present embodiment, γ correction is performed by another method different from the first and second embodiments.

In this embodiment, as shown in FIG. 16, a video chroma circuit 1, a gamma correction circuit 2, and a polarity inversion circuit 4
, A synchronization separation circuit 5, a control circuit 6, and a horizontal driver 7.
, A vertical driver 8, a liquid crystal panel 9, a backlight 10, and a setting circuit 39. This embodiment is different from the first embodiment in that the configurations of the γ correction circuit 2 and the setting circuit 39 are different.
It has the same configuration as the first and second embodiments. Therefore, the description here will focus on the differences.

As shown in FIG. 16, the gamma correction circuit 2 used in this embodiment is not necessarily clearly divided on the circuit, but a part functioning as the amplifier circuit 2a and a variable gamma correction And a portion functioning as the count control circuit 26. The setting circuit 39 used in the present embodiment includes the count control circuit 38.
Is a circuit that gives data to The amplification circuit unit 2a and the variable γ correction unit 3 are controlled by the count control circuit 38 and the setting circuit 39.
Control.

FIG. 17 shows a specific configuration example of the amplifying section 2a, the variable γ correction section 3, the count control circuit 38, and the setting circuit 39, and the operation will be described with reference to the operation waveform example of FIG. .

In FIG. 17, the setting circuit 39 includes a voltage setting circuit 40 and a count value setting circuit 41. The voltage setting circuit 40 has a circuit similar to the circuit including the power supply 12 and the variable resistor 11 described above, and can set a voltage. The count value setting circuit 41 sets a count value corresponding to the set voltage.
Although not shown, the count value setting circuit 41 includes a voltage-count value conversion unit that sets a count value corresponding to the set voltage, and a change in the set voltage.
A control circuit for setting a count value, setting the count value in the counter 42, and activating the counter 4; Instead of changing the set voltage, the count value may be set periodically, for example, in synchronization with a vertical synchronization signal, and the setting to the counter 42 and the activation of the counter 42 may be performed. .

In FIG. 17, the gamma correction circuit 2
The part functioning as the count control circuit 38 includes a counter 42, a clock generation circuit 28, and a delay circuit 43.
, A pulse generation circuit 29, a shift register 32, and D
Flip-flops 33-1 to 33-n. Also,
The switch circuit 150 (switch elements 150-1 to 150-n), 1
60 (switch elements 160-1 to 160-n) and 1
70 (switch elements 170-1 to 170-n), transistors 18, 24, and resistors 19, 20, and 25 used for setting a γ change point. Further, FIG.
As shown in FIG. 7, transistors 14 and 21 and a resistor 22 are provided as a portion functioning as the amplifier circuit section 2a.

The counter 42 includes a count value setting circuit 41
The count value is preset by setting. When activated by the count value setting circuit 41, the counter 42 counts the value set by the count value setting circuit 41 based on the signal DCLK obtained by delaying the clock signal CLK from the clock generation circuit 28 by the delay circuit 43. When the counting is completed, an output signal RCO is output,
It is applied to the clock terminals of the D flip-flops 33-1 to 33-n. The counter 42 can change the timing at which the output signal RCO is output by changing the setting of the count value.

On the other hand, the clock signal CLK from the clock generation circuit 28 and the pulse signal PLS from the pulse generation circuit 29 are applied to the shift register 32. Note that the delay time of the delay circuit 43 is equal to the input clock signal CL.
It is set to a time within one cycle of K. The shift register 32 sequentially shifts the pulse signal PLS according to the delayed clock signal CLK and shifts the shifted signal SF.
1 to SFn are applied to the D flip-flops 33-1 to 33-n, respectively.

D flip-flops 33-1 to 33-n
Latches the signals SF1 to SFn applied to the data terminals from the output of the shift register 32 at the rising edge of the output signal RCO of the counter 42 applied to the clock terminal. Thereby, the D flip-flops 33-1 to 3-3 are output.
3-n output terminals to switch elements 150-1 to 150
-N, 160-1 to 160-n and 170-1 to 17
The level of the signal applied to 0-n changes.

Since the shift register 32 operates with a clock signal having the same cycle as that of the counter 42, the output signals SF1 to SFn of the shift register 32 have substantially the same pulse width as the pulse width of the output signal RCO of the counter 42. Width, and the output signals SF1 to SF1 of the shift register 32
One of SFn is output at a timing corresponding to the output signal RCO of the counter 42.

The operation waveform example of FIG. 18 shows an example in which SFi of the output signal of the shift register 32 is output at a timing substantially corresponding to the output signal RCO of the counter 42. Since the counter 42 operates with the signal DCLK obtained by delaying the clock signal CLK, the rising edge of the output signal RCO coincides with the shift register 32
Is slightly delayed from the rise of the output signal SFi. Therefore, the output signal SFi of the shift register 32 is reliably latched as an input signal. Thereby, the shift register 3
D flip-flop 3 latching the output signal SFi
Only the output of 3-i becomes "H" level, and the outputs of the other D flip-flops remain at "L" level.

Thus, the switching elements 150-1 to 150-1
50-n, 160-1 to 160-n and 170-1 to
150-i, 160-i and 170 out of 170-n
Only -i conducts and the other switches are non-conducting.
Thus, the switch elements 150-1 to 150-
n, 160-1 to 160-n and 170-1 to 170
When one of −n is selected, the amplification factor of the transistor 14 is determined.

The voltage setting circuit 40 sets the voltage applied to the base of the transistor 18 to the count value setting circuit 4.
1, whereby the voltage applied to the contrast terminal of the video chroma circuit 1 is adjusted to change the amplitude of the primary color signal, thereby changing the brightness and contrast of the display image. Also, as in the example shown in FIG. 14, by changing the voltage at which the operating state of the transistor 24 changes between the active state and the cutoff state, the amplitude characteristic of the primary color signal applied to the liquid crystal panel 9 is reduced. Since the setting can be made to match the display characteristics of the panel 9, an image can always be displayed with an appropriate gradation.

As described above, in the embodiment of FIG. 16, the count control circuit 38 and the setting circuit 39 can arbitrarily set the amplification factor of the amplifier circuit section 2a and the amplitude characteristic switching point of the variable γ correction section 3. , The brightness and contrast of the display image can be changed, and the image can always be displayed with an appropriate gradation.

Next, a fourth embodiment of the present invention will be described. FIG. 19 shows the configuration of the fourth embodiment of the present invention.
In the present embodiment, γ correction is performed by a method different from the above embodiments.

In this embodiment, as shown in FIG. 19, a video chroma circuit 1, a gamma correction circuit 2, and a polarity inversion circuit 4
, A synchronization separation circuit 5, a control circuit 6, and a horizontal driver 7.
, A vertical driver 8, a liquid crystal panel 9, a backlight 10, a variable resistor 11 and a power supply 12. This embodiment has the same configuration as that of the second embodiment except that the configuration of the γ correction circuit 2 is different. Therefore, the description here will focus on the differences.

As shown in FIG. 19, the γ correction circuit 2 used in the present embodiment is not necessarily clearly divided on the circuit, but it functions as an amplifier circuit section 2a and a variable γ correction section 3. Amplifying circuit 2a and variable γ based on the functioning part and the value or amplitude of the applied voltage
It has a portion that functions as a voltage value control circuit 44 that controls the correction unit 3.

FIG. 20 shows a specific configuration example of the gamma correction circuit 2. The configuration and operation of this embodiment will be described with reference to FIG.

In FIG. 20, the γ correction circuit 2 includes a variable resistor 11 as a part functioning as a voltage value control circuit 44.
And an A / D conversion circuit 45 for converting a voltage set by the power supply 12 into a digital signal, and output lines 46-1 to 46-n
And an output line 46 according to the value of the digital signal.
Selection circuit 46 for selecting any one of -1 to 46-n
And The switch circuit 150 (switch element 150-1) serves as a portion functioning as the variable γ correction section 3.
To 150-n), 160 (switch elements 160-1 to 160-1)
60-n) and 170 (switch elements 170-1 to 170-1)
70-n), and transistors 18, 24 and resistors 19, 20, and 25 used for setting the γ change point.
Further, similarly to the one shown in FIG.
a, the transistors 14 and 21
And a resistor 22.

The A / D conversion circuit 45 converts the voltage applied from the resistor 11 into a digital signal and applies the digital signal to the selection circuit 46. The selection circuit 46 outputs "H" to one of the output lines 46-1 to 46-n according to the applied digital signal.
A low level signal is output, and an "L" level signal is output to the remaining output lines. Thereby, the switching element 150
-1 to 150-n, 160-1 to 160-n, and 1
One each is selected from 70-1 to 170-n. That is, by changing the output voltage of the resistor 11, the amplification factor of the transistor 14 can be arbitrarily set.

By adjusting the amplitude of the output primary color signal of the video chroma circuit 1 by changing the output voltage of the resistor 11, the brightness and contrast of the displayed image can be changed, and the operating state of the transistor 24 becomes active. By setting the voltage that switches between the state and the cutoff state arbitrarily, the gradation characteristics of the displayed image can be set so that the image is always displayed with an appropriate gradation.

A specific configuration example of the selection circuit 46 is shown in FIG.
Shown in In FIG. 21, 45 is a 3-bit A / D conversion circuit, 46-1 to 46-8 are output lines, and 46-9 to 46-
20 is an inverter, and 46-21 to 46-28 are AND circuits.

The 3-bit A / D conversion circuit 45 has three outputs and outputs a signal of "L" level or "H" level according to the applied voltage value. Eight selections can be made by combining these three outputs. For example, when all eight output lines are at "H" level, only the output line 46-8 of the selection circuit 46 is at "H" level, and all the remaining output lines are at "L" level.
Only output line 46-8 can be selected.

In the selection circuit 46 shown in FIG. 21, the output line 46-1 depends on the combination of the inverter and the AND circuit.
Although an example of selecting .about.46-8 is shown, a combination of different logic circuits may be used as long as the result is logically the same. If the A / D conversion circuit 44 has a larger number of bits, the selection circuit can have more outputs.

Next, a fifth embodiment of the present invention will be described. FIG. 22 shows the configuration of the fifth embodiment of the present invention.
In the present embodiment, γ correction is performed by a method different from the above embodiments.

The present embodiment is an example in which a signal source for supplying a video signal and the liquid crystal display device according to the present invention are substantially integrated. That is, in this embodiment, as shown in FIG. 22, a signal source 51 for supplying a video signal,
A chroma circuit 1, a gamma correction circuit 2, a polarity inversion circuit 4,
A synchronization separation circuit 5, a control circuit 6, a horizontal driver 7,
Vertical driver 8, liquid crystal panel 9, backlight 10
And a variable resistor 11 and a power supply 12. This embodiment has the same configuration as the above embodiments, except that the signal source 51 is provided and the configuration of the γ correction circuit 2 is different. Therefore, the description here will focus on the differences.

As shown in FIG. 22, the signal source 51 includes a video signal generator 510 and a control signal generator / inserter 511. The control signal generation / insertion unit 511 generates a control signal to be supplied to the variable γ control circuit 52 and inserts it into the video signal sent from the video signal generation unit 510. Here, the generated control signal is changed according to the voltage set by the variable resistor 11. For example, the pulse width is changed.

The gamma correction circuit 2 used in the present embodiment, although not necessarily clearly divided on the circuit, a part functioning as the amplifier circuit part 2a, a part functioning as the variable gamma correction part 3, and an application circuit. It has a portion functioning as a variable γ control circuit 52 that controls the amplifier circuit section 2a and the variable γ correction section 3 based on the value or amplitude of the voltage to be applied.

The portion functioning as the variable γ control circuit 52 has, for example, a configuration as shown in the example of FIG. 23, and a signal extraction timing for generating a timing signal PUP for giving a control signal extraction timing based on a vertical synchronization signal. A generation circuit 522 and an amplification circuit 523 that amplifies a control signal input when the analog switch 521 is turned on.
And a pulse width control circuit 26 that determines a pulse width based on the extracted control signal. Analog switch 5
21 conducts only when the timing signal PUP is at "H" level.

The pulse width control circuit 26 is the same as that shown in FIG. Further, a portion functioning as the amplifier circuit portion 2a and a portion functioning as the variable γ correction portion 3 are the same as those shown in FIG.

The operation of this embodiment will be described with reference to FIGS. 22, 23, and 24.

In FIG. 22, control signal generation / insertion unit 5
Reference numeral 11 denotes a pulse width (or a pulse position, a pulse amplitude, or the like) depending on the output voltage of the variable resistor 11 at a specific portion in, for example, a vertical blanking period in the video signal input from the video signal generation unit 510. Is inserted as a control signal. The video signal waveform into which the control pulse is inserted is, for example, as shown in the operation waveform example of FIG. The video signal into which the control pulse has been inserted is input to the variable γ control circuit 52 together with the video chroma circuit 1 and the synchronization separation circuit 5. The variable γ control circuit 52 controls the analog switch 521 by the output signal PUP of the sampling timing generation circuit 522, and makes the analog switch 521 conductive only when the signal PUP is at “H” level. Thus, only the control pulse inserted into the video signal is extracted and amplified to a required amplitude by the amplifier circuit 523, and the extracted control pulse is sent to the pulse width control circuit 26.

Thus, the pulse width control circuit 26
The control of the amplifier circuit section 2a and the variable γ correction section 3 is performed. The γ correction is the same as in the embodiment shown in FIG.

In this embodiment, an example is shown in which the pulse width control circuit 26 used in the embodiment of FIG. 13 is used to control the amplifier circuit section 2a and the γ correction section 3. However, other than this, the same effect can be obtained by using a count value control circuit as shown in the embodiment of FIG.

As described above, by changing the output voltage of the variable resistor 11, the amplitude and the contrast of the display image can be changed by changing the amplitude of the output primary color signal of the video chroma circuit 1, and the control inserted in the video signal. Pulses are extracted by the variable γ control circuit 52 and controlled by the amplification circuit unit 2a and the variable γ correction unit 3, thereby obtaining
As described in the embodiment of FIG. 21, the amplitude characteristic of the primary color signal to be displayed is corrected so as to match the display characteristic of the liquid crystal panel 9, so that an image can always be displayed with an appropriate gradation.

Next, a sixth embodiment of the present invention will be described. FIG. 25 shows the configuration of the sixth embodiment of the present invention.
This embodiment is different from the above embodiments in that the amplitude of the primary color signal is adjusted using an external light detection circuit.

This embodiment is an example in which a signal source for supplying a video signal and the liquid crystal display device according to the present invention are substantially integrally formed as in the fifth embodiment. That is,
In the present embodiment, as shown in FIG. 25, a signal source 51 for supplying a video signal, a video chroma circuit 1, a gamma correction circuit 2
, A polarity inversion circuit 4, a synchronization separation circuit 5, and a control circuit 6.
, A horizontal driver 7, a vertical driver 8, a liquid crystal panel 9, a backlight 10, and an external light detection circuit 53. The present embodiment is different from the fifth embodiment in that the amplitude of the primary color signal is adjusted and the control signal to be inserted into the video signal is set using an external light detection circuit 53 instead of the variable resistor 11. It has a similar configuration and operates similarly.

Although not shown, the external light detection circuit 53 includes a light amount detection unit for detecting brightness and a voltage setting unit for outputting a voltage signal based on the detection signal. The external light detection circuit 53 detects the surrounding brightness (light amount) by a light amount detection unit, and the voltage setting unit applies the voltage to the video chroma circuit 1 so as to change the amplitude of the primary color signal according to the brightness. The contrast adjustment voltage to be set. Also,
The control signal generation / insertion unit 511 changes the setting of the pulse to be inserted into the video signal according to the voltage corresponding to the brightness.

As a result, as in the case of the embodiment shown in FIG. 22, the brightness and contrast of the display image can be changed, and the image can always be displayed with the optimum gradation.

Next, a seventh embodiment of the present invention will be described. FIG. 26 shows the configuration of the seventh embodiment of the present invention.
In the present embodiment, γ correction is performed by a method different from that of the first embodiment.

In this embodiment, as shown in FIG. 26, a video chroma circuit 1, a gamma correction circuit 2, a polarity inversion circuit 4
, A synchronization separation circuit 5, a control circuit 6, and a horizontal driver 7.
, A vertical driver 8, a liquid crystal panel 9, a backlight 10, a variable resistor 11 and a power supply 12. In this embodiment, the operation timing of the variable γ correction unit 3 is controlled by the control circuit 6.
The second embodiment has the same configuration as that of the first embodiment except that the DC voltage level is adjusted together with the amplitude of the primary color signal by controlling with a control signal BCP applied from the first embodiment.
Therefore, the description here will focus on the differences.

As shown in FIG. 26, the gamma correction circuit 2 used in the present embodiment is not necessarily clearly divided on the circuit, but a portion functioning as the amplifier circuit section 2a, a variable gamma
It has a portion functioning as the correction unit 3.

FIG. 27 shows a specific configuration example of the amplifier circuit section 2a and the variable γ correction section 3 of FIG. 26, based on which the configuration and operation will be described.

In FIG. 27, 53 is a capacitor, 54
Is a switch circuit, 55-1 to 55-n and 56 are resistors, 57 is a switch, 58 is a power supply, and 59 is a control signal BC.
P input terminal. Other components are the same as those of the first embodiment.
This is the same as the embodiment.

In the configuration example shown in FIG. 27, the amplitude characteristic of the primary color signal can be set in accordance with the display characteristic of the liquid crystal panel 9 by adjusting the voltage of the variable resistor 11 as in the embodiment of FIG. . Further, the switch circuit 54 is controlled by the voltage level detection circuit 13 to supply a primary color signal to the capacitor 53 via the transistor 21 which is an emitter follower. By passing through the capacitor 53, the DC voltage level of the primary color signal is temporarily lost.

A switch 57 is input from the input terminal 59.
, A control signal BCP is applied. The control signal BCP
Is a signal which becomes “H” level only during a specific period, for example, a horizontal blanking period of a video signal. Switch 5
7 conducts only while the applied control signal BCP is at the “H” level. On the other hand, in the switch circuit 54 controlled by the voltage level detection circuit 13, only one of the n switches conducts, and, for example, the resistor 55-i is selected. Thus, when the switch 57 is turned on,
The DC voltage level of the primary color signal that has passed through the capacitor 53 is reset to a value determined by the resistors 55-i and 56, and is output from the output terminal 23.

As described above, the brightness of the displayed image changes by adjusting the DC voltage level of the primary color signal.
In this case, the darkest black level in the display image also changes, and the black luminance can be adjusted to a desired value. That is,
For example, in the case where external light is reflected on the surface of the liquid crystal panel 9 under strong external light during the day, the dark portion of the image is prevented from being blackened by the reflected light to make it difficult to see. , The brightness of black can be set to be relatively high. Conversely, at night, the surroundings are dark, so that the brightness of the display image is adjusted by adjusting the amplitude of the video signal and the brightness of black is set to be dark, as described in the embodiment of FIG. The contrast can be prevented from being reduced.

The resetting of the DC voltage level of the primary color signal described above is performed in conjunction with the adjustment of the variable resistor 11. As a result, the amplitude of the primary color signal and the DC voltage level can be simultaneously controlled, so that even if the brightness of the display image is changed by adjusting the amplitude of the primary color signal in accordance with the surrounding environment (the state of external light), That is, it is possible to prevent the gradation of the display image from deteriorating.

Next, an eighth embodiment of the present invention will be described. FIG. 28 shows the configuration of the eighth embodiment of the present invention.
In each of the above embodiments, the amplitude characteristic correction of the primary color signal output from the video chroma circuit is performed by an analog circuit,
An image is displayed on the liquid crystal panel 9 using analog signals. On the other hand, in the present embodiment, an example is shown in which the primary color signal is processed by a gamma correction circuit composed of a digital circuit, and an image is displayed on the liquid crystal panel 9 using the digital signal.

FIG. 28 is a block diagram showing an eighth embodiment of the present invention. In this embodiment, the video chroma circuit 1, the gamma correction circuit 200, the level detection circuit 13, and the synchronization separation circuit 5
Control circuit 6, digital horizontal driver 700,
Vertical driver 8, liquid crystal panel 9, backlight 10
And a variable resistor 11 and a power supply 12. This embodiment is different from the above embodiments in that the variable γ correction circuit performs digital processing. Therefore, the description here will focus on the differences.

In FIG. 28, the γ correction circuit 200
Primary color signals DB, DG, and DR provided for three primary colors of R, G, and B and converted into digital signals are output. Each γ correction circuit 200 includes an A / D conversion circuit 60, data conversion circuits 61-1 to 61-n composed of, for example, a ROM, and a switch circuit 62.

As the horizontal driver 7, a digital horizontal driver 700 corresponding to a digital signal is used.

In such a configuration, the primary color signal output from the video chroma circuit 1 is
Is converted into a digital signal by the data conversion circuit 61.
-1 to 61-n. The digital signal is R
The data is applied as an address signal to the data conversion circuits 61-1 to 61-n, which are OMs. Data conversion circuits 61-1 to 6
1-n outputs correction data stored in advance at an address corresponding to the address signal as a signal whose amplitude characteristic has been corrected.

The switch circuit 62 includes the level detection circuit 13
Is controlled by The level detection circuit 1
3 turns on only one of the n switches of the switch circuit 62 based on the output voltage of the variable resistor 11. Thereby, the data conversion circuits 61-1 to 61-
Any one of n is selected. As a result, the selected output signal (the primary color signal D converted into a digital signal)
B, DG, DR) are applied to the digital horizontal driver 700 to display an image.

In the embodiment shown in FIG.
Is applied to the contrast adjustment terminal of the video / chroma circuit 1, so that the output voltage of the variable resistor 11 is changed as in the embodiment of FIG.
The amplitude of the primary color signal can be changed. Further, by controlling the switch circuit 62 with the voltage level detection circuit 13,
A data conversion circuit that performs amplitude characteristic correction corresponding to the amplitude of the primary color signal can be selected.

As a result, the brightness and contrast of the display image can be adjusted, and the image can be displayed with an appropriate gradation.

Next, a ninth embodiment of the present invention will be described. FIG. 29 shows the configuration of the ninth embodiment of the present invention.
In each of the above embodiments, the brightness adjustment is performed by the variable resistor, the voltage setting circuit, or the external light detection circuit. The present embodiment is an example in which automatic light control and manual light control are combined.

FIG. 29 shows a configuration diagram of the ninth embodiment of the present invention. In this embodiment, a video chroma circuit 1, a gamma correction circuit 2, a polarity inversion circuit 4, a synchronization separation circuit 5, a control circuit 6, a horizontal driver 7, a vertical driver 8, a liquid crystal panel 9, It has a backlight 10 and a dimming circuit. This embodiment is configured similarly to the first embodiment except that a dimming circuit is provided instead of the variable resistor. Therefore,
Here, the description will focus on the differences.

The dimming circuit of the present embodiment is configured such that the optical sensor PT and the resistor r are connected in series and the variable resistor RM is connected in series, and is configured to divide the voltage of the power supply 12. The optical sensor PT is composed of, for example, a photodiode.

According to such a configuration, for example, the variable resistor RM is set so that the brightness becomes easy to see in a certain brightness.
Adjust In this state, when the brightness of the environment changes, the resistance of the optical sensor PT changes, and the shared voltage changes. As a result, the output voltage of the dimming circuit changes.

Therefore, according to the present embodiment, the user can manually adjust the brightness as desired, and in this state, the brightness is automatically adjusted even if external light changes. This is, for example, in an environment such as a vehicle such as an automobile where the brightness constantly changes during traveling,
Since there is no need to manually adjust the luminance, there is an advantage that the burden on the driver is reduced. Therefore, this embodiment is particularly suitable for a liquid crystal display device mounted on a vehicle such as an automobile.

This embodiment is not limited to the first embodiment, and can be applied to other embodiments as they are or after being modified.

[0147]

According to the present invention, the brightness and contrast of a display image can be adjusted by adjusting the amplitude of a signal applied to the liquid crystal panel, and the amplitude characteristic of the signal applied to the liquid crystal panel can be adjusted by the voltage-voltage of the liquid crystal panel. Since the image can be adjusted according to the luminance characteristics, an image can always be displayed with an appropriate gradation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention.

FIG. 2 is a graph showing an example of an input voltage-luminance characteristic of a liquid crystal panel.

FIG. 3 is an explanatory diagram showing an example of input / output voltage characteristics of a γ correction circuit.

FIG. 4 is an explanatory diagram showing another example of input / output voltage characteristics of the variable γ correction circuit.

FIG. 5 is a circuit diagram showing a configuration example of a variable γ correction circuit.

FIG. 6 is an explanatory diagram showing another example of input / output characteristics of the variable γ correction circuit.

FIG. 7 is an explanatory diagram showing another example of input / output characteristics of the variable γ correction circuit.

FIG. 8 is a circuit diagram illustrating a configuration example of a voltage level detection circuit.

FIG. 9 is an explanatory diagram showing another example of input / output characteristics of the variable γ correction circuit.

FIG. 10 is a circuit diagram showing another configuration example of the variable γ correction circuit.

FIG. 11 is an explanatory diagram showing another example of the input / output characteristics of the variable γ correction circuit.

FIG. 12 is an explanatory diagram showing another example of input / output characteristics of the variable γ correction circuit.

FIG. 13 is a block diagram showing a configuration of a second example of the present invention.

FIG. 14 is a circuit diagram showing a specific configuration example of a pulse width control circuit.

15 is an operation waveform diagram for explaining the operation of the circuit in FIG.

FIG. 16 is a block diagram showing a configuration of a third example of the present invention.

FIG. 17 is a block diagram showing a configuration showing a specific configuration example of a count control circuit.

FIG. 18 is an operation waveform diagram for explaining the operation of the circuit in FIG. 17;

FIG. 19 is a block diagram showing a configuration of a fourth embodiment of the present invention.

20 is a configuration diagram showing a specific configuration example of a voltage value control circuit in FIG. 19;

FIG. 21 is a circuit diagram showing a specific configuration example of a selection circuit in FIG. 20;

FIG. 22 is a block diagram showing a configuration of a fifth example of the present invention.

FIG. 23 is a block diagram showing a configuration showing a specific configuration example of a variable γ control circuit in FIG. 22;

FIG. 24 is an operation waveform diagram showing an example of operation waveforms in the configuration example of FIG. 22;

FIG. 25 is a block diagram showing a configuration of a sixth example of the present invention.

FIG. 26 is a block diagram showing a configuration of a seventh embodiment of the present invention.

FIG. 27 is a circuit diagram showing a configuration example of a variable γ correction circuit in FIG. 26;

FIG. 28 is a block diagram showing a configuration of an eighth embodiment of the present invention.

FIG. 29 is a block diagram showing a configuration of a ninth embodiment of the present invention.

FIG. 30 is a circuit diagram showing a more specific configuration by adding circuit constants to the circuit configuration in the first embodiment of the present invention.

FIG. 31 is a graph showing input / output characteristics of a γ correction circuit when the above specific circuit is used.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Video chroma circuit, 2 ... Gamma correction circuit, 2a ... Amplifier circuit part, 3 ... Variable gamma correction part, 4 ... Polarity inversion circuit, 5 ...
Sync separation circuit, 6 ... control circuit, 7: horizontal driver, 8 ...
Vertical driver, 9 ... liquid crystal panel, 10 ... backlight,
11, 110: Variable resistor, 14, 18, 21, 24: Transistor, 15-1 to 15-n, 16-1 to 16-
n, 17-1 to 17-n, 19, 20, 22, 25 ...
Resistance: 12, power supply, 13: voltage level detection circuit, 26:
Pulse width control circuit, 27 multivibrator, 28
Clock generation circuit, 29 ... pulse generation circuit, 30 ... AN
D circuit, 31 ... inverter, 32 ... shift register, 3
3-1 to 33-n D flip-flops, 35-1 to 3-3
5-n, 37-1 to 37-n switch, 38 count control circuit, 42 counter, 43 delay circuit, 44
Voltage value control circuit, 51: signal source, 53: external light detection circuit,
60: A / D conversion circuit, 150, 160, 170: switch circuit. 150-1 to 150-n, 160-1 to 16
0-n, 170-1 to 170-n ... switch elements.

────────────────────────────────────────────────── ─── front page of the continuation (72) inventor Mayumi Igarashi Kanagawa Prefecture, Totsuka-ku, Yokohama-shi Yoshida-cho, 292 address Hitachi, Ltd. video media research house (58) investigated the field (Int.Cl. ^7, DB name) H04N 5 / 66 G09G 3/36

Claims (13)

(57) [Claims] 1. A liquid crystal display device comprising: a liquid crystal panel that receives a video signal and displays an image; a device that drives the liquid crystal panel; and a light source that illuminates the liquid crystal panel. In addition, a gamma correction circuit for setting the correction characteristic of the gradation characteristic and correcting the gradation characteristic of the video signal, and means for setting the amplitude of the video signal, wherein the gamma correction circuit Means for correcting the gradation characteristic of the video signal according to the set correction characteristic; means for setting the correction characteristic in accordance with the setting of the amplitude of the video signal; And at least one correction characteristic change point is determined in accordance with the magnitude of, and depending on which side the amplitude is before or after this change point,
Means for changing a correction characteristic of a video signal. 2. The apparatus according to claim 1, wherein said means for changing the correction characteristic sets at least one change point between the maximum value and the minimum value of the amplitude of the input video signal in advance, and A liquid crystal display device having a function of changing a correction characteristic depending on whether the amplitude of the change is larger or smaller than the change point. 3. A liquid crystal display device according to claim 1, wherein the means for correcting the gradation characteristic has an amplifier circuit. 4. A liquid crystal display device according to claim 3, wherein the means for setting the correction characteristic is for setting an amplification factor of an amplifier circuit. 5. The apparatus according to claim 1, further comprising means for generating information indicating the setting of the amplitude of the video signal and inserting the information into the video signal, wherein the gamma correction circuit indicates the setting of the amplitude from the video signal. A liquid crystal display device further comprising means for extracting information and sending the information to means for setting correction characteristics. 6. A liquid crystal display device according to claim 1, wherein the means for setting the amplitude of the video signal has a circuit for outputting a signal for setting the amplitude of the video signal. 7. The liquid crystal display device according to claim 6, wherein the circuit for outputting a signal has a variable resistor for dividing a power supply voltage. 8. A circuit according to claim 1, wherein the means for setting the amplitude of the video signal detects a surrounding light amount and outputs a signal for setting the amplitude of the video signal in accordance with the light amount. A liquid crystal display device comprising: 9. The device according to claim 1, wherein the means for setting the amplitude of the video signal includes an element for detecting the amount of light in the surroundings, and a variable resistor, and the variable amount of the variable resistor corresponds to the resistance value and the light amount. A liquid crystal display device having a circuit for outputting a signal for setting the amplitude of a video signal. 10. A liquid crystal display device according to claim 7, wherein said variable resistor is capable of changing its resistance in response to an external manual operation. 11. A liquid crystal display device according to claim 5, wherein the means for generating information indicating the setting of the amplitude of the video signal and inserting the information into the video signal generates a pulse signal subjected to pulse width modulation. 12. The liquid crystal display device according to claim 1, further comprising means for adjusting a DC voltage level of a signal applied to the liquid crystal panel. 13. A device according to claim 12, wherein the means for adjusting the DC voltage level of the signal applied to the liquid crystal panel selects the DC level in correspondence with the setting of the correction characteristic for the means for setting the correction characteristic. A liquid crystal display device.