JP3265048B2 - 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 such as a liquid crystal television and a liquid crystal display to which a brightness adjusting function is added.

[0002]

2. Description of the Related Art A TFT (Thin F) is used as a switching element.
Active matrix driving type liquid crystal display device using an ilm transistor (hereinafter referred to as TFT-LCD)
Will be described below as a conventional example.

As shown in FIG. 6, the above-mentioned TFT-LCD comprises signal electrodes 52...
, TFTs 55 arranged in a matrix near each intersection of the signal electrode 52 and the gate electrode 53.
55 are connected to the respective drains of the pixel electrodes 54, and the opposing electrodes 5 are arranged to face the pixel electrodes 54 via the liquid crystal layer.
6 and the like. The above TFT
55 are connected to the signal electrodes 52, and the gates are connected to the gate electrodes 53, respectively. The liquid crystal panel 51 is driven by a source drive circuit 57 connected to the signal electrodes 52 and a gate drive circuit 58 connected to the gate electrodes 53.

A control signal from a control device (not shown) is input to the source drive circuit 57 together with a display signal from a video signal processing circuit to be described later. Based on the sampling pulse, a display signal for one horizontal scanning period is supplied to the sample and hold circuit 60 via the shift register 59,
Are output to the respective signal electrodes 52 through the output buffer 61.

On the other hand, a control signal from the control device is input to the gate drive circuit 58. Based on a control signal synchronized with the horizontal synchronizing signal, the gate O is driven.
The N signal is given to the level shifter 63 while sequentially shifting in the shift register 62. In the level shifter 63, the level of the gate ON signal is converted into the level for turning on the TFT 55, and the gate electrodes 53 are output via the output buffer 64. Is output to

As the gate electrodes 53 are sequentially scanned in this manner, the TFTs 55 on the gate electrodes 53 are turned on for each of the gate electrodes 53, and the signal voltage V _{S of the} display signal is changed to the pixel voltage. Are applied to the electrodes 54.

A counter electrode signal is output from a counter electrode driving circuit (not shown) to a counter electrode 56 disposed opposite to the pixel electrodes 54 via the liquid crystal layer.
_COM is applied.

As a result, a potential difference is generated between the picture element electrode 54 to which the signal voltage V _S is applied and the counter electrode 56 to which the counter voltage V _COM is applied, and the liquid crystal is driven by the electric field. For example, a normally white TFT that normally transmits light but blocks light when voltage is applied
-The light transmittance characteristics of the liquid crystal used in the LCD are as shown in FIG. 11, and the counter voltage V _COM and the signal voltage V _S
(Hereinafter, referred to as a drive voltage V), the light transmittance changes, thereby performing display according to the video signal.

If a constant voltage is constantly applied to the liquid crystal, the liquid crystal deteriorates due to electrolysis and flicker becomes noticeable. Therefore, the polarity of the driving voltage V needs to be inverted at a predetermined cycle. Therefore, usually, as shown in FIG. 9, the common voltage V _COM of the common electrode signal is set to a constant level,
The video signal is switched every one horizontal scanning period. Here, for convenience of explanation, a video signal for displaying a gradation pattern is shown.

However, in the above case, since the peak-to-peak amplitude of the entire video signal increases, the supply voltage to the signal electrodes 52 of the source drive circuit 57 increases, so that the power consumption increases and the source drive circuit 57 A driver IC to be used must have a high withstand voltage.

Therefore, conventionally, as shown in FIG.
By converting the counter electrode signal to an alternating current, the peak-to-peak amplitude of the entire video signal can be reduced while maintaining the difference between the counter voltage V _COM and the signal voltage V _S, which is the driving voltage V of the liquid crystal. An AC drive system is used.

By the way, the light transmission characteristics of the liquid crystal shown in FIG. 11 depend on the viewing angle as shown in FIG.
Therefore, even if the display image is the same, for example, the screen becomes darker when the user looks up the screen from below 30 °, and looks brighter when viewed from above 30 ° than when the viewing angle is 0 °. Therefore, a liquid crystal display device such as a liquid crystal television or a liquid crystal display is usually provided with a brightness adjustment function in order to correct the viewing angle characteristics as described above, and the brightness is adjusted according to the usage state of the liquid crystal display device. Adjustment is possible.

Conventionally, this brightness adjustment is performed by changing the DC level during one horizontal scanning period of the video signal to adjust the drive voltage V. For example, as shown by D in FIG. 8, the display screen becomes brighter when the voltage difference between the video signal and the counter electrode signal (that is, the drive voltage V) is reduced, and as shown by E in FIG. The display screen can be darkened by increasing the voltage difference between the signal and the counter electrode signal.

Here, a conventional video signal processing circuit having a brightness adjusting function will be described with reference to FIG. The conventional video signal processing circuit basically includes a sync separation circuit 65 for separating a sync signal from a video signal, a pedestal clamp circuit 66 for keeping a pedestal level of the video signal constant,
It comprises an inverting amplifier circuit 67 which amplifies a video signal and inverts every horizontal scanning period, and a brightness setting circuit 68.

In this video signal processing circuit, first,
The original video signal separated from the television signal or the like is input to the sync separation circuit 65 and the pedestal clamp circuit 66. Here, the sync separation circuit 65 forms a gate pulse d for clamping a pedestal level (that is, a black level) portion based on a sync signal separated from an original video signal, and forms a pedestal clamp circuit 66. Output to Further, the pedestal clamp circuit 66
, A brightness adjustment signal e corresponding to a brightness adjustment operation by a user is input from the brightness setting circuit 68.

The pedestal clamp circuit 66 clamps a pedestal level portion in a video signal based on a gate pulse, and further, based on a brightness adjustment signal e input from the brightness setting circuit 68. Apply a DC voltage to the pedestal. Thus, the DC level of the entire video signal is determined. That is, the brightness is adjusted by adjusting the DC level.

Thereafter, the video signal is amplified by the inverting amplifier circuit 67 and inverted every horizontal scanning period to obtain a video signal having a waveform such as D or E in FIG. Can be

[0018]

However, in the above-described conventional configuration, the brightness is adjusted by changing the DC level (DC component) of the video signal, that is, by changing the white level as a whole from the black level. Is effective for correcting the visibility of the image corresponding to the vicinity of the black level based on the viewing angle, but when the brightness setting is changed in the direction of increasing the brightness, the vicinity of the white level is improved. In this case, a problem such as whiteout of the image corresponding to the image may occur. This is because if the brightness setting is changed in the direction in which the image becomes brighter, the entire video signal is shifted in the direction of the white level, so that gradation does not appear in the white level saturation region of the light transmittance characteristic of the liquid crystal. is there. On the other hand, if the brightness setting is changed in the darker direction, then the whole video signal is shifted in the direction of the black level, so that the white level is also reduced, and the dynamic range of the liquid crystal display cannot be used effectively. Problems arise.

The present invention has been made in view of the above, and an object of the present invention is to provide a liquid crystal display having a dynamic range of a liquid crystal display that does not cause whitening loss on a display screen near white when brightness is adjusted. It is an object of the present invention to provide a liquid crystal display device capable of performing a display using the image data effectively and obtaining an optimum display state according to the viewing angle by adjusting the brightness.

[0020]

According to the present invention, there is provided a liquid crystal display device comprising a display electrode to which a display signal for driving a liquid crystal layer based on a video signal is supplied, and a display electrode opposed to the display electrode via the liquid crystal layer. A counter electrode to which a counter electrode signal is supplied;
Brightness adjusting means for adjusting the potential difference between the display electrode and the counter electrode by changing the DC component of the video signal to adjust the brightness of the display screen. This is a normally white type liquid crystal display device that blocks light by applying a voltage, and is characterized by taking the following means in order to solve the above problems.

[0021] That is, the liquid crystal display device, for the brightness setting of the display screen, the brightness setting means for outputting a brightness adjusting signal designating a DC component to the brightness adjustment unit,
An inverting amplifier circuit for amplifying the display signal and inverting the display signal every horizontal scanning period; a white peak detecting means for detecting a white peak of the display signal during one frame period; The amplitude of the display signal is determined based on the output of the white peak detecting means so that the white peak is fixed substantially constant near the white saturation level that maximizes the light transmittance of the liquid crystal, regardless of the brightness adjustment. And amplitude adjusting means for changing the amplitude.

Further, in the above liquid crystal display device, the white peak detecting means is provided downstream of the amplitude adjusting means,
The detection signal is output to the amplitude adjusting means.

[0023]

According to the above arrangement , the DC component of the video signal is adjusted by the brightness adjustment means based on the brightness adjustment signal output from the brightness setting means, so that the liquid crystal layer is adjusted based on the video signal. The potential difference between the display electrode to which the display signal for driving the display electrode is supplied and the counter electrode to which the counter electrode signal is supplied changes, and the transmittance of the liquid crystal interposed between the display electrode and the counter electrode, that is, the display screen Brightness is adjusted.

Here, the above-mentioned liquid crystal display device changes the amplitude of the display signal based on the output of the white peak detecting means for detecting the white peak of the display signal during one frame period. It has amplitude adjustment means, and the white peak of the display signal of each frame is fixed almost constant regardless of brightness adjustment near the white saturation level where the light transmittance of the liquid crystal becomes maximum and the saturation of white display occurs It is supposed to be. Note that, for example, in the case of a liquid crystal having a light transmittance characteristic as shown in FIG. 12, the white saturation level is a voltage level of a video signal corresponding to a white saturation point P in FIG. . In addition, the white peak in one frame period of the display signal is defined as one of the display screens.
This is the level corresponding to the part closest to white on the screen.

For this reason, even if the brightness is adjusted, the portion corresponding to the white level on the screen can always be fixed in the vicinity where the saturation of the white display occurs. Therefore,
Even when the brightness setting is changed in the direction in which the image becomes brighter, the gray level of the display in the vicinity of white is not impaired as in the related art, and the white loss does not occur. Further, even when the brightness setting is changed in the darkening direction, the white level of the display signal is fixed near the white saturation level, so that the dynamic range of the liquid crystal display can be effectively used.

Further, as shown in FIG. 12, the driving voltage V (the voltage difference between the video signal and the counter electrode signal) at which the light transmittance approaches zero greatly changes according to the change of the viewing angle. , The drive voltage V corresponding to the white saturation point P is substantially constant regardless of the viewing angle. Therefore, as described above, by fixing the white level of the display signal near the white saturation level without depending on the brightness adjustment, the best display signal waveform corresponding to the viewing angle can be obtained. Therefore, if the brightness is adjusted in the present liquid crystal display device to correct the viewing angle characteristics, the display state can be adjusted to a display state with good visibility according to the viewing angle.

For example, when the white peak of a video signal during one frame period is a white level, when the DC component of the video signal changes due to brightness adjustment, the white level of the display signal also changes. However, the change in the white level is detected by the white peak detecting means, and the amplitude of the display signal is adjusted by the amplitude adjusting means based on the output of the white peak detecting means. It will be fixed around the white saturation level.
That is, when the white peak in one frame period of the video signal is the white level, the amplitude of the display signal is adjusted in conjunction with the brightness adjustment, and the best display signal waveform according to the viewing angle is obtained. . Further, in this configuration, even when the white peak during one frame period of the video signal is other than the white level, the white peak of the display signal is fixed near the white saturation level.

That is, no matter what video signal is input, the brightest part on the screen can be fixed near the point where white display saturation occurs, and the dynamic range of the liquid crystal display is always utilized to the maximum. Display can be performed.
Therefore, if the brightness is adjusted in the present liquid crystal display device to correct the viewing angle characteristics, for example, even if a video signal having a relatively small amplitude is input as an input signal, the dynamic range of the liquid crystal display is used to the maximum. Therefore, it is possible to adjust to the state with the best visibility according to the state of the viewing angle.

Further, in the above liquid crystal display device, the white peak detecting means is provided downstream of the amplitude adjusting means,
The detection signal is output to the amplitude adjusting means.

Accordingly, the amplitude adjusting means can control the white
Based on the detection signal from the peak detection means, the original video signal
After adjusting the gain of the signal amplitude, adjust the brightness of the video signal.
Output to the adjusting means. Therefore, the above amplitude adjustment
Means based on a detection signal from the white peak detection means.
Video gain by adjusting the gain of the video signal amplitude.
White peak during each frame period of image signal is saturated with white
Can be fixed near the level.

[0031]

[Embodiment 1] An embodiment of the present invention is described below with reference to FIGS.

As shown in FIG. 2, the liquid crystal display device according to this embodiment is an active matrix driving type liquid crystal display device (hereinafter, referred to as a TFT) using a TFT 5 as a switching element.
FT-LCD). Here, a normally white type TFT-LCD that transmits light in a normal state and blocks light by applying a voltage will be described.

The TFT-LCD includes a plurality of TFTs 5.
, A liquid crystal panel 1 including a TFT substrate formed in a matrix, a counter substrate disposed to face the TFT substrate, a liquid crystal layer provided between the TFT substrate and the counter substrate, two deflection plates, and the like. I have. A strip-shaped signal electrode 2 made of a transparent conductive film is provided on a TFT substrate of the liquid crystal panel 1.
And the gate electrodes 3 are arranged orthogonally. Also, T
At each intersection of the signal electrode 2 and the gate electrode 3 on the FT substrate, the above-described TFT 5 and a pixel electrode (display electrode) 4 made of a transparent conductive film are arranged.
Is the signal electrode 2 and the drain is the picture element electrode 4.
And its gate is connected to the gate electrode 3, respectively. In addition, a counter electrode 6 made of a transparent conductive film is formed on the counter substrate.

The liquid crystal panel 1 is driven by a source drive circuit 7 connected to the signal electrodes 2 and a gate drive circuit 8 connected to the gate electrodes 3.

The source drive circuit 7 basically includes a shift register 9, a sample and hold circuit 10, and an output buffer 11. The source drive circuit 7 is supplied with power from a power supply device (not shown), and receives a video signal from a video signal processing circuit described later and a control signal from a control device (not shown). I have.

The gate drive circuit 8 basically includes a shift register 12, a level shifter 13, and an output buffer 14. This gate drive circuit 8 includes:
Power is supplied from the power supply device, and a control signal from the control device is input.

The counter electrode 6, which is disposed opposite to the picture element electrodes 4 via the liquid crystal layer, has a counter voltage V of a counter electrode signal output from a counter electrode driving circuit (not shown).
_COM is applied.

The TFT-LCD processes an original video signal separated from a television signal or the like, and generates a video signal (display signal described in claims) to be supplied to the source drive circuit 7. It has a circuit. This video signal processing circuit basically has, as shown in FIG.
Sync separation circuit 1 for separating sync signal from original video signal
5, an amplitude adjustment amplifier (amplitude adjustment means) 19 for adjusting the gain of the amplitude of the video signal, a pedestal clamp circuit (brightness adjustment means) 16 for keeping the pedestal level of the video signal constant, and amplifying the video signal In addition, an inverting amplifier circuit 17 for inverting a video signal every one horizontal scanning period, and a brightness adjustment terminal on the outer surface of the device for setting the brightness of the display screen according to the brightness adjustment operation by the user. Brightness setting circuit (brightness setting means) 18.

The operation of the TFT-LCD in the above configuration will be described below.

First, an original video signal separated from a television signal or the like is processed in a video signal processing circuit,
Are supplied to the source drive circuit 7 shown in FIG. The operation of the video signal processing circuit will be described later in detail.

A control signal from a control unit (not shown) is input to the source drive circuit 7 together with the video signal (display signal) processed by the video signal processing circuit. Based on the sampling pulse, a video signal for one horizontal scanning period is provided to the sample and hold circuit 10 via the shift register 9 and is output to each signal electrode 2 via the output buffer 11.

A control signal from the control device is input to the gate drive circuit 8, and the gate ON signal sequentially shifts in the shift register 12 based on the control signal synchronized with the horizontal synchronization signal. The level is supplied to the level shifter 13, and the level of the gate ON signal is converted into a level for turning on the TFT 5 in the level shifter 13.
It is output to each gate electrode 3... Via the output buffer 14.

As the gate electrodes 3 are sequentially scanned in this manner, the TFTs 5 on the gate electrodes 3 are excited in a conductive state for each gate electrode 3, and the signal voltage V _{S of the} video signal is changed to the pixel voltage. Are applied to the electrodes 4.

On the other hand, a counter electrode signal whose polarity is inverted every horizontal scanning period is output to the counter electrode 6 from the counter electrode drive circuit as shown by C in FIG. That is, the above-described counter electrode 6, which is the picture element electrode 4 ... and oppositely arranged with the liquid crystal layer, the counter voltage V _COM of the common electrode signal is adapted to be applied.

As a result, a potential difference is generated between the picture element electrode 4 to which the signal voltage V _S is applied and the counter electrode 6 to which the counter voltage V _COM is applied, and the liquid crystal is driven by the electric field so that the above-mentioned image is displayed. Display according to a video signal (display signal) output from the signal processing circuit is performed.

The operation of the video signal processing circuit will now be described in detail.

As shown in FIG. 1, first, the original video signal is input to the sync separation circuit 15 and the amplitude adjustment amplifier 19. Here, the synchronization separation circuit 15
By separating the horizontal synchronizing signal from the original video signal and delaying the horizontal synchronizing signal by a predetermined time by a delay circuit (not shown), a pedestal level (that is, black level) portion in the video signal is clamped. A gate pulse a is formed, and this gate pulse a is output to the pedestal clamp circuit 16.

On the other hand, a brightness adjustment operation (brightness setting of a display screen) by a user is enabled by a brightness adjustment terminal provided on the outer surface of the apparatus.
Thus, a brightness adjustment signal b corresponding to the brightness adjustment operation by the user is output to the amplitude adjustment amplifier 19 and the pedestal clamp circuit 16.

The amplitude adjustment amplifier 19 adjusts the gain of the amplitude of the original video signal based on the brightness adjustment signal b input from the brightness setting circuit 18 as described later. The video signal is output to a pedestal clamp circuit 16 as brightness adjustment means.

The pedestal clamp circuit 16 clamps the pedestal level portion in the video signal based on the gate pulse a input from the sync separation circuit 15 and receives the signal from the brightness setting circuit 18. A DC voltage is applied to the pedestal based on the brightness adjustment signal b. Thus, the DC level of the entire video signal is determined, and a video signal corresponding to the brightness setting in the brightness setting circuit 18 is obtained. Specifically, the higher the brightness setting in the brightness setting circuit 18 is, the higher the DC level of the video signal is.

Here, the amplitude adjusting amplifier 19 will be described. In this embodiment, the amplitude adjustment of the video signal by the amplitude adjustment amplifier 19 is performed in conjunction with the adjustment of the DC level (DC component) of the video signal of the pedestal clamp circuit 16. In other words, the amplitude adjustment amplifier 19 that performs gain adjustment of the amplitude of the video signal based on the brightness adjustment signal b is set so that the brightness setting in the brightness setting circuit 18 is set to be brighter (that is, the video is adjusted). The higher the DC level of the signal is, the lower the gain is set. As shown in FIG.
Even if the C level changes, the white level of the video signal acts to be substantially constant, whereby the white level of the video signal becomes the white saturation level (light of the liquid crystal) at which the light transmittance of the liquid crystal is maximized. (Level corresponding to white saturation point P in transmittance characteristic curve)
Fixed around V _S0 .

FIG. 4 shows the case where the driving voltage V (signal voltage V _S
Those with the voltage difference between the opposing voltage V _COM) and with showing the viewing angle dependence of the liquid crystal light transmittance characteristics showing the relationship between the liquid crystal light transmittance shows the relationship between the light transmittance characteristic and the video signal waveform is there. As shown in the figure, the drive voltage V at which the light transmittance approaches zero changes greatly according to the change of the viewing angle, but the drive voltage V ₀ corresponding to the white saturation point P at which the light transmittance becomes maximum.
Is substantially constant regardless of the viewing angle. Therefore, by fixing the white level of the video signal to the vicinity of the white saturation level V _S0 irrespective of the brightness adjustment as in the present embodiment, the best video signal waveform according to the viewing angle can be obtained.

As described above, the video signal whose amplitude has been adjusted by the amplitude adjusting amplifier 19 and whose DC level has been adjusted by the pedestal clamp circuit 16 is supplied to the inverting amplifier circuit 17.
, And is amplified by the inverting amplifier circuit 17 and inverted every horizontal scanning period. Thereby, for example, a video signal (display signal) having a waveform like A or B in FIG. 3 is formed. Then, when this video signal is supplied to the source drive circuit 7, display according to the video signal is performed on the liquid crystal panel 1 as described above.

As described above, the TFT-LCD of this embodiment
Is the DC of the video signal by the pedestal clamp circuit 16.
An amplitude adjustment amplifier 19 for adjusting the amplitude of the video signal in conjunction with the level adjustment is provided. Even if the DC level (DC component) of the video signal changes, the white level of the video signal is changed to the white saturation level V. It is configured to be fixed near _S0 .

For this reason, in the TFT-LCD of this embodiment, even if the setting of the brightness is changed in the direction of increasing the brightness, the gray level of the display near white is deteriorated as in the related art, and the white area is lost. There is no. Further, even when the brightness setting is changed in the darkening direction, the white level of the video signal is fixed near the white saturation level, so that the dynamic range of the liquid crystal display can be used effectively.

Further, as shown in FIG. 4, the white saturation point P of the light transmittance characteristic curve of the liquid crystal is substantially constant irrespective of the viewing angle, so that it does not depend on the brightness adjustment as in this embodiment. By fixing the white level of the video signal near the saturation level V _S0 , the best video signal waveform according to the viewing angle can be obtained. Therefore, when the brightness is adjusted for correcting the viewing angle characteristics in the TFT-LCD of this embodiment, high display quality can be obtained.

As described above, the liquid crystal display device according to the present invention
Provides a display signal that drives the liquid crystal layer based on the video signal.
The display electrode supplied is paired with the display electrode via a liquid crystal layer.
And a counter electrode to which a counter electrode signal is supplied.
The display power is changed by changing the DC component of the video signal.
Adjust the potential difference between the electrode and the counter electrode to adjust the brightness of the display screen.
Brightness adjustment means for adjusting brightness.
Therefore, even if the DC component of the video signal changes, the display signal
The white level of the signal is the white saturation that maximizes the light transmittance of the liquid crystal
The brightness adjustment means so that it is almost fixed near the level.
The amplitude of the above display signal changes in conjunction with the brightness adjustment operation of
It may be configured to include an amplitude adjusting unit for converting the amplitude.

According to the above arrangement, the brightness adjusting means
By adjusting the DC component of the video signal,
A display signal that drives the liquid crystal layer based on the video signal is supplied.
Between the display electrode and the counter electrode to which the counter electrode signal is supplied.
The potential difference between the display electrode and the counter electrode
The liquid crystal transmittance, that is, the brightness of the display screen is adjusted.
You.

The liquid crystal display device has the brightness
The amplitude of the display signal is linked to the brightness adjustment operation of the adjustment means.
The amplitude of the video signal
The white level of the display signal changes even if the DC component of
White saturation at which light transmittance is maximized and white display saturation occurs
It is almost fixed near the level.

Therefore, the liquid crystal display device has a display screen.
Even if the brightness is adjusted, the white level on the screen
Fix the corresponding part near the saturation of the white display.
Brightness can be adjusted accordingly.
Even if the setting is changed, the display near white
There is no loss of gradation and loss of white. Ma
Also, even if you change the brightness setting in the darker direction,
As before, the white saturation level is maintained without changing the white level.
The liquid crystal display dynamic lens
Can be used effectively. And this liquid crystal display
If the device adjusts the brightness to correct the viewing angle characteristics,
It can be adjusted to a display state with good visibility according to the corner
It produces effects such as

Embodiment 2 Another embodiment of the present invention will be described below with reference to FIG. Components having the same configuration as in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The liquid crystal display of this embodiment has the same configuration as that of the TFT-LCD of the first embodiment except for the video signal processing circuit. As shown in FIG. 5, the video signal processing circuit of the present embodiment basically includes a sync separation circuit 15, an amplitude adjustment amplifier 19 'as amplitude adjustment means, and a pedestal clamp circuit 16 as brightness adjustment means. And the inverting amplifier circuit 1
7, a brightness setting circuit 18, and a white peak detecting circuit 20 as white peak detecting means.

The white peak detecting circuit 20 detects a white peak in one frame period of the video signal output from the pedestal clamp circuit 16, and outputs a detection signal c to the amplitude adjusting amplifier 19 '. . here,
The white peak during one frame period of the video signal is a level corresponding to the portion of one display screen which is closest to white, in other words, the white peak detection circuit 20.
Detects the maximum value of the signal voltage of the video signal output from the pedestal clamp circuit 16 during one frame period.

The amplitude adjusting amplifier 19 ′, based on the detection signal c from the white peak detecting circuit 20, determines the white peak of the video signal of each frame as the white saturation level at which the light transmittance of the liquid crystal becomes maximum. The gain of the amplitude of the video signal is adjusted so as to be substantially fixed near V _S0 (see FIG. 4).

The operation of the TFT-LCD in the above configuration will be described below.

First, an original video signal separated from a television signal or the like is supplied to a synchronization separation circuit 15 and an amplitude adjustment amplifier 1.
9 '. Here, the sync separation circuit 15 outputs a gate pulse a for clamping a pedestal level (that is, a black level) portion in the video signal to the pedestal clamp circuit 16 as in the first embodiment. Further, a brightness adjustment signal b corresponding to a brightness adjustment operation by a user is input from the brightness setting circuit 18 to the pedestal clamp circuit 16.

The amplitude adjustment amplifier 19 'adjusts the gain of the amplitude of the original video signal based on a detection signal c from a white peak detection circuit 20, which will be described later, and then applies the video signal to the pedestal clamp circuit. 16 is output.

The pedestal clamp circuit 16 clamps the pedestal level portion in the video signal based on the gate pulse a input from the sync separation circuit 15 and receives the pedestal signal from the brightness setting circuit 18. A DC voltage is applied to the pedestal based on the brightness adjustment signal b to determine the DC level of the entire video signal. Thereafter, the video signal output from the pedestal clamp circuit 16 is output to the white peak detection circuit 20 and the inverting amplification circuit 17.
Is input to

The white peak detection circuit 20 detects a white peak during one frame period of the video signal, and outputs a detection signal c to the amplitude adjustment amplifier 19 '. And
The amplitude adjustment amplifier 19 ′ is connected to the white peak detection circuit 2.
By adjusting the gain of the amplitude of the video signal based on the detection signal c from 0, the pedestal clamp circuit 16
The white peak in each frame period of the video signal output from is substantially fixed near the white saturation level V _S0 .

For example, considering the case where the white peak in one frame period of the video signal is the white level, if the brightness setting in the brightness setting circuit 18 changes, the video output from the pedestal clamp circuit 16 will change. The DC level of the signal changes, and thus the white level of the video signal also changes. This change in the white level is detected by the white peak detection circuit 20 and the amplitude is determined based on the output of the white peak detection circuit 20. The amplitude of the video signal is adjusted by the adjustment amplifier 19 ', and the white level becomes the white saturation level V.
It will be almost fixed near _S0 . That is, 1 of the video signal
When the white peak during the frame period is at the white level, a video signal waveform similar to that of the first embodiment can be obtained. Further, in this embodiment, even when the white peak during one frame period of the video signal is other than the white level, the white peak is substantially fixed near the white saturation level V _S0 , and the liquid crystal display The dynamic range can be used to the maximum, and the visibility of the display screen is further improved.

As described above, the amplitude adjustment amplifier 19 '
And the pedestal clamp circuit 16
The video signal whose pedestal level has been adjusted in step (1) is amplified in the inverting amplifier circuit 17 and is inverted every horizontal scanning period. The video signal (display signal) is supplied to the source drive circuit 7 (see FIG. 1), so that the liquid crystal panel 1 (see FIG. 1) as described in the first embodiment.
Is displayed in accordance with the video signal.

As described above, the liquid crystal display device of the present embodiment provides a white peak detecting circuit 20 for detecting a white peak of a video signal during one frame period, and an image based on the output of the white peak detecting circuit 20. An amplitude adjustment amplifier 19 'for adjusting the amplitude of the signal is provided, and the video signal of each frame is fixed such that the white peak of the video signal of each frame is substantially fixed near the white saturation level at which the light transmittance of the liquid crystal is maximized. An amplitude adjusting means for changing the amplitude is provided, and the white peak during each frame period of the video signal is substantially fixed near the white saturation level V _S0 .

As a result, the liquid crystal display device of this embodiment is
The same effect as that of the TFT-LCD of the first embodiment can be obtained. In addition, no matter what video signal is input, the brightest part on the screen can be fixed in the vicinity of the occurrence of white display saturation, and the display always makes full use of the dynamic range of the liquid crystal display. be able to.
Therefore, when performing brightness adjustment for correcting viewing angle characteristics in the liquid crystal display device of the present embodiment, for example, even if a video signal having a relatively small amplitude is input as an input signal, the dynamic range of the liquid crystal display is maximized. Therefore, it is possible to adjust to the state with the best visibility according to the state of the viewing angle, and high display quality can be obtained.

In the above embodiment, the normally white type TFT-LCD has been described. However, the present invention can be applied to a normally black type, and a dynamic driving method using no switching element such as a TFT, or It can also be applied to a static drive type. The embodiments described above are intended to clarify the technical contents of the present invention, and should not be construed as being limited to such specific examples in a narrow sense. Various changes can be made within the scope.

[0075]

As described above, the liquid crystal display device according to the present invention has the display electrode to which the display signal for driving the liquid crystal layer is supplied based on the video signal, and the display electrode facing the display electrode via the liquid crystal layer. A counter electrode to which a counter electrode signal is supplied;
Brightness adjusting means for adjusting the potential difference between the display electrode and the counter electrode by changing the DC component of the video signal to adjust the brightness of the display screen. A normally white liquid crystal display device that blocks light by applying a voltage, wherein the brightness adjusting device outputs a brightness adjustment signal for designating a DC component to the brightness adjusting means for setting the brightness of a display screen. Setting means;
An inverting amplifier circuit for amplifying the display signal and inverting the display signal every horizontal scanning period; a white peak detecting means for detecting a white peak of the display signal during one frame period; The amplitude of the display signal is determined based on the output of the white peak detecting means so that the white peak is fixed substantially constant near the white saturation level that maximizes the light transmittance of the liquid crystal, regardless of the brightness adjustment. And amplitude adjustment means for changing the amplitude.

Therefore, irrespective of the brightness adjustment of the display screen or the input of any video signal, the brightest part on the screen can be fixed near the saturation of white display. It is possible to always perform a display that makes full use of the dynamic range of the liquid crystal display.

That is, the brightness is set in the direction of increasing the brightness.
Even if it is changed, the gradation of the display near white as in the past
There is no loss of whiteness. Also, dark
Even if you change the brightness setting in the direction
Around the white saturation level without changing the white level
Is fixed to the
It can be used effectively. Further, even when a video signal having a relatively small amplitude is input as an input signal, a display image with very high visibility can be obtained. Soshi
Brightness adjustment for correcting the viewing angle characteristics with this LCD.
The display state with good visibility according to the viewing angle
And the like.

In the liquid crystal display device according to the present invention, as described above, the white peak detecting means is provided after the amplitude adjusting means, and outputs a detection signal to the amplitude adjusting means.

Therefore, the amplitude adjusting means is provided with
The video signal based on the detection signal from the
By adjusting the gain of the width, each frame of the video signal can be adjusted.
The white peak during the program period around the white saturation level
It has the effect that it can be done.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, in which a TFT-
FIG. 2 is a block diagram illustrating a configuration of a main part of a video signal processing circuit in the LCD.

FIG. 2 is an explanatory diagram showing a configuration of a liquid crystal panel and a driving unit thereof in the TFT-LCD.

FIG. 3 is a waveform diagram showing waveforms of a video signal and a counter electrode signal in the TFT-LCD.

FIG. 4 is an explanatory diagram showing a viewing angle dependency of a light transmittance characteristic of a liquid crystal showing a relationship between a driving voltage and a light transmittance of a liquid crystal, and showing a relationship between the light transmittance characteristic and a video signal waveform.

FIG. 5, showing another embodiment of the present invention, is a block diagram illustrating a configuration of a main part of a video signal processing circuit in a liquid crystal display device.

FIG. 6 illustrates a conventional example, and is an explanatory diagram illustrating a configuration of a liquid crystal panel and a driving unit thereof in a TFT-LCD.

FIG. 7 is a block diagram showing a configuration of a main part of a video signal processing circuit in the conventional TFT-LCD.

FIG. 8 is a waveform chart showing waveforms of a video signal and a counter electrode signal in the TFT-LCD.

FIG. 9 is a waveform chart showing waveforms of a counter electrode signal and a video signal in a normal driving method in which a counter voltage is at a constant level.

FIG. 10 is a waveform chart showing waveforms of a counter electrode signal and a video signal in the AC drive method of the counter electrode signal.

FIG. 11 is an explanatory diagram showing a light transmittance characteristic of a liquid crystal showing a relationship between a driving voltage and a light transmittance of a liquid crystal.

FIG. 12 is an explanatory diagram showing a viewing angle dependency of a light transmittance characteristic of a liquid crystal.

[Explanation of symbols]

Reference Signs List 1 liquid crystal panel 2 signal electrode 3 gate electrode 4 picture element electrode (display electrode) 5 TFT 6 counter electrode 7 source drive circuit 8 gate drive circuit 16 pedestal clamp circuit (brightness adjusting means) 17 inverting amplifier circuit 18 brightness setting circuit ( Brightness setting means) 19 Amplitude adjustment amplifier (amplitude adjustment means) 19 'Amplitude adjustment amplifier (amplitude adjustment means) 20 White peak detection circuit (White peak detection means) b Brightness adjustment signal c Detection signal V _S0 White saturation level

Claims (1)

(57) [Claims] 1. A display for driving a liquid crystal layer based on a video signal.
A display electrode to which a signal is supplied, and a display electrode which is disposed to face the display electrode via a liquid crystal layer;
Display by changing the DC component of the video signal and the counter electrode to which the signal is supplied
Adjust the potential difference between the electrode and the counter electrode to
Brightness adjustment means for adjusting the brightness, while transmitting light at normal times, blocking the light by applying a voltage.
In the normally white type liquid crystal display device to be turned off, the brightness adjustment means is used for setting the brightness of the display screen.
A brightness setting that outputs a brightness adjustment signal that specifies the DC component
Means for amplifying the display signal and displaying each horizontal scanning period.
An inverting amplifier circuit for inverting a signal; and detecting a white peak of the display signal during one frame period.
The white peak of the display signal of each frame is the light transmittance of the liquid crystal.
Irrespective of the brightness adjustment near the white saturation level that maximizes
The output of the white peak detecting means is fixed so that
An amplitude control that changes the amplitude of the display signal based on the force
Adjusting means, and the white peak detecting means is provided after the amplitude adjusting means.
Provided at the stage and outputting a detection signal to the amplitude adjusting means
A liquid crystal display device, characterized in that: