JP3183995B2 - Liquid crystal display device and driving method thereof - 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 having a brightness adjusting function, and a method of driving the same.

[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. 11, 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 drive control circuit (not shown) is input to the source drive circuit 57 together with a video signal to be described later. The source drive circuit 57 is based on a sampling pulse of the control signal synchronized with the horizontal synchronization signal. , A video signal for one horizontal scanning period is supplied to the sample-and-hold circuit 60 via the shift register 59, and is output to each of the signal electrodes 52 via the output buffer 61.

On the other hand, a control signal from the drive control circuit is input to the gate drive circuit 58.
On the basis of the control signal synchronized with the horizontal synchronizing signal, the gate ON signal is given to the level shifter 63 while sequentially shifting in the shift register 62, and the level shifter 63 converts the level of the gate ON signal into a level for turning on the TFT 55. Are output to the respective gate electrodes 53 via the output buffer 64.

As the gate electrodes 53 are sequentially scanned in this manner, the TFTs 55 on the gate electrodes 53 are excited into conduction for each gate electrode 53, and the signal voltage V _{S of the} video signal is reduced Are applied to the electrodes 54.

Further, a counter voltage _VCOM of a counter electrode signal generated by a counter electrode signal generation circuit is applied to a counter electrode 56 disposed opposite to the picture element electrodes 54 via the liquid crystal layer. Has become.

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. 6, and the light transmittance changes according to the difference between the counter voltage V _COM and the signal voltage V _S (hereinafter, referred to as the drive voltage V). Thus, display according to the video signal is performed.

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. 15, 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 is increased, the supply voltage to the signal electrodes 52 of the source drive circuit 57 is increased, the power consumption of the device is increased, and the source drive circuit is increased. The driver IC used for the transistor 57 also needs to have a high withstand voltage.

Therefore, conventionally, as shown in FIG.
By converting the counter electrode signal to AC, the liquid crystal driving voltage V
The AC drive method of the counter electrode signal that can reduce the peak-to-peak amplitude of the entire video signal while maintaining the difference between the counter voltage V _COM and the signal voltage V _S is used.

As shown in FIG. 12, the conventional counter electrode signal generation circuit for generating the above-mentioned AC electrode signal has a pulse width generated by the drive control circuit in which the polarity is inverted during one horizontal scanning period. The signal for use (see (b) in FIG. 5) is amplified by a feedback amplifier circuit composed of electric resistors R ₁ and R ₂ and an amplifier 70 to generate a counter electrode signal as shown in FIG. Has become.

Since the light transmission characteristics of the liquid crystal depend on the viewing angle, the brightness of the display screen differs between looking up at the liquid crystal panel 51 from above and looking down from above. 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 of the video signal during one horizontal scanning period, for example, as shown in (a) and (b) of FIG. That is, by changing the DC level of the video signal as described above, the voltage difference between the video signal and the counter electrode signal (that is, the driving voltage V applied to the liquid crystal) is changed overall, and as a result, The brightness of the display screen changes.

[0015]

However, as described above, in the case of a TFT-LCD configured to adjust the brightness of the display screen by changing the DC level of the video signal, the driver used in the source drive circuit 57 A high withstand voltage IC is required.

That is, in the case of a TFT-LCD having no function of adjusting the brightness of the display screen, the dynamic range of the source drive circuit 57 can be obtained by using the above-described AC drive method of the counter electrode signal as shown in FIG. In the light transmittance characteristics, about 4 V at which the light transmittance changes from the maximum to the minimum is sufficient, and a driver IC operating with a 5 V power supply is usually used for the source drive circuit 57. On the contrary,
As described above, the TFT having the function of adjusting the brightness of the display screen by changing the DC level of the video signal
In the case of an LCD, changing the DC level of the video signal necessarily changes the peak-to-peak amplitude of the entire video signal. Even when the peak-to-peak amplitude of the entire video signal is maximized), a driver IC that can output the signal is required.

The above-mentioned conventional TFT having a brightness adjusting function
In the case of an LCD, generally, a driver IC capable of obtaining an output of 10 V _PP is used for the source drive circuit 57.
A driver IC that obtains such an output is called a so-called medium-voltage driver, and is disadvantageous in terms of chip size and cost as compared with a driver IC that operates with a 5 V power supply. And the cost of the TFT-LCD is increased.

SUMMARY OF THE INVENTION 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 device having a display screen brightness adjusting function capable of realizing miniaturization, thinning, and cost reduction, and a driving method thereof. Is to provide.

Another object of the present invention is to achieve a reduction in size, thickness, and cost, and
Contact liquid crystal display device can be best displayed in accordance with the brightness adjustment
And a driving method thereof .

[0020]

According to the present invention, there is provided a liquid crystal display device, comprising: a display electrode; a counter electrode disposed to face the display electrode via a liquid crystal layer; and a video signal whose polarity is inverted at a predetermined period. A video signal generating means for applying a video signal voltage corresponding to the video signal to the display electrode; a counter electrode signal having a polarity inverted in synchronization with the video signal; A counter electrode signal generating means for supplying an electrode; and a brightness setting unit for setting the brightness of the display screen, wherein the brightness of the display screen can be adjusted according to the setting in the brightness setting unit. In order to solve the above-mentioned problems, the following means are taken.

That is, the peak-to-peak amplitude of the counter electrode signal
An amplitude detecting means for detecting the width, the counter electrode signal generating means, based on the setting in the brightness setting unit,
An amplitude adjusting means for adjusting the peak-to-peak amplitude of the counter electrode signal is provided.

Further, the video signal generating means may be configured to control the amplitude
The peak-to-peak amplitude of the counter electrode signal is adjusted by the adjusting means.
By adjusting the peak-to-peak amplitude of the counter electrode signal
Is smaller than the peak-to-peak amplitude of the video signal.
And the polarity of the liquid crystal driving voltage applied to the liquid crystal layer.
However, the peak-to-peak amplitude of the counter electrode signal is not adjusted.
The opposite depending on the level of the video signal.
If possible, the amplitude detection output of the amplitude detection means
According to the peak-to-peak amplitude of the video signal within one cycle period
And a video signal amplitude adjusting means for reducing the amplitude . Ma
Further, the liquid crystal display device according to the present invention has the configuration of the above invention.
In addition, the video signal amplitude adjusting means further comprises:
Amplitude limiting circuit that limits the amplitude of the signal or video signal
It is preferable to use an amplitude adjustment amplifier to reduce the amplitude of the
No. Further, the driving method of the liquid crystal display device according to the present invention includes
And the display electrode is disposed to face the display electrode via a liquid crystal layer.
To set the brightness of the display screen
LCD with adjustable display screen brightness according to the setting
In the display device driving method, the polarity is inverted at a predetermined cycle.
A video signal corresponding to the video signal.
Voltage is applied to the display electrodes and synchronized with the video signal.
A counter electrode signal whose polarity is inverted is generated and supplied to the counter electrode.
Supply, and based on the brightness setting,
Adjust the peak-to-peak amplitude of the electrode signal, and
The counter electrode is adjusted by adjusting the peak-to-peak amplitude of the signal.
The peak-to-peak amplitude of the signal is the peak-to-peak of the video signal.
By being smaller than the amplitude, the voltage applied to the liquid crystal layer is reduced.
The polarity of the liquid crystal drive voltage is
When the peak amplitude is not adjusted,
If the level can be reversed,
Depending on the peak-to-peak amplitude of the electrode signal,
The feature is to reduce the peak-to-peak amplitude of the video signal
are doing. Also, a method for driving a liquid crystal display device according to the present invention
In the above method, further, the image within one cycle period
When reducing the peak-to-peak amplitude of the signal,
Limit the amplitude of the video signal or reduce the amplitude of the video signal.
Preferably. Note that the peak signal of the video signal voltage is
The peak amplitude is determined by the voltage applied to the liquid crystal layer.
The voltage when changing the light transmittance of
May substantially correspond to the width of change . In addition, the video signal
The DC level of the signal voltage may be fixed. Also on
The amplitude adjusting means comprises a feedback amplifier circuit.
The brightness setting section is operated by the user and the feedback amplification
When the gain of the path is changed,
The peak-to-peak amplitude may be adjusted
No.

[0023]

The liquid crystal drive voltage applied to the liquid crystal layer is a voltage difference between a video signal voltage applied to the display electrode and a counter electrode signal voltage applied to the counter electrode. Here, the brightness adjustment of the display screen is to increase or decrease the liquid crystal driving voltage applied to the liquid crystal layer over the entire screen.

According to the above arrangement, the common electrode signal generating means for generating the common electrode signal whose polarity is inverted in synchronization with the video signal has the amplitude adjusting means, and is based on the setting in the brightness setting section. Thus, the peak-to-peak amplitude of the counter electrode signal can be adjusted. As described above, when the peak-to-peak amplitude of the counter electrode signal changes, the DC of the video signal is changed.
Even if the level (pedestal level) is constant, the liquid crystal drive voltage, which is the voltage difference between the video signal and the counter electrode signal, changes overall, and the brightness of the display screen can be adjusted.

That is, in the liquid crystal display device, since the DC level of the video signal can be kept constant, the dynamic range of the video signal voltage applying means for applying a video signal voltage corresponding to the video signal to the display electrode is provided. For example, in the light transmittance characteristic of the liquid crystal shown in FIG. 6, for example, about 4 V at which the light transmittance changes from the maximum to the minimum is sufficient. A low-voltage driven driver IC can be used.

As described above, the liquid crystal display device has a smaller chip size and lower cost than the conventionally used medium-voltage driver IC, despite having the function of adjusting the brightness of the display screen. Driver IC with low voltage drive
Therefore, the size, thickness, and cost can be reduced.

By changing the amplitude of the counter electrode signal, if the peak-peak amplitude of the counter electrode signal becomes smaller than the peak-peak amplitude of the video signal, for example, as shown in FIG. Inversion of the polarity of the liquid crystal drive voltage, which is the voltage difference between the video signal and the counter electrode signal, occurs.
The image portion, which should be a bright portion, becomes dark.

Here, according to the above configuration, the peak-to-peak amplitude of the counter electrode signal generated by the counter electrode signal generation means is detected by the amplitude detection means, and the peak-peak amplitude of the counter electrode signal is detected by the video signal. the Rukoto a smaller than the peak-peak amplitude, the polarity of liquid crystal driving voltage is reversed
In such a case, by the video signal amplitude adjusting means,
Since the peak-to-peak amplitude of the video signal within one cycle period is reduced according to the amplitude detection output of the amplitude detection means, it is possible to avoid reversal of the polarity of the liquid crystal drive voltage and it should be a bright part. The problem that the image portion becomes dark can be solved.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic structure of an embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 2, the present liquid crystal display device is a liquid crystal display device of an active matrix driving system using a TFT 5 as a switching element (hereinafter referred to as a TFT-LCD).
). Here, a normally white (positive display 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. This source drive circuit 7
Is supplied with power from a power supply device (not shown), and a video interface (hereinafter referred to as video I
/ F) and a control signal from the drive control circuit 20.

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 drive control circuit 20 is input.

The counter electrode 6, which is disposed opposite to the picture element electrodes 4 via the liquid crystal layer, has a counter electrode signal generation circuit (counter electrode signal generation means) 21 shown in FIG. The counter voltage V _COM of the electrode signal is applied.

The counter electrode signal generation circuit 21 converts the polarity inversion signal (see (b) in FIG. 5) generated by the drive control circuit 20 with a pulse width of one horizontal scanning period into an electric resistor R _3. Amplify by a feedback amplifying circuit (amplitude adjusting means) 21a including R ₄ , variable electric resistor VR and amplifier 22 to generate, for example, a counter electrode signal as shown in (c) of FIG. The positive input terminal of the amplifier 22 DC voltage is applied, the polarity inversion signal is inputted via an electrical resistor R ₃ to the negative input terminal. And
The output of the amplifier 2 2 series-connected electrical resistor R
It is fed back to its negative input terminal via ₄ and the variable electric resistor VR. Therefore, the variable electric resistor V
If the setting of R is changed, the output of the amplifier 22, that is, the peak-to-peak amplitude of the counter electrode signal can be changed, for example, as shown in (c) to (e) in FIG.
The setting of the variable electric resistor VR is made possible by operating a brightness adjusting unit 23 (see FIG. 3) provided on the outer surface of the device.

The TFT-LCD has a video I / F (video signal generating means) 19 for processing an input video signal separated from a television signal or the like to generate a video signal having a waveform suitable for driving the liquid crystal. . As shown in FIG. 3, the video I / F 19 has a pedestal clamp circuit 16 for keeping the pedestal level of the video signal constant, and inverts the polarity of the video signal in a predetermined cycle (one cycle = 1 horizontal scanning period). And an inverting amplifier circuit 17. The video I / F
The video signal generated at 19 is supplied to the source drive circuit 7.

Further, the TFT-LCD is provided with a synchronization separation circuit 24 for separating a synchronization signal from an input video signal, and the source drive circuit 7 and the gate drive circuit 8 based on the synchronization signal from the synchronization separation circuit 24. A drive control circuit that generates various signals such as a control signal for controlling the operation, a polarity inversion signal supplied to the counter electrode signal generation circuit 21, and a gate pulse for clamping a pedestal level portion in a video signal. 20.

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

As shown in FIG. 3, first, an original video signal separated from a television signal or the like is input to a video I / F 19 and a sync separation circuit 24. here,
The sync separation circuit 24 separates the horizontal and vertical sync signals from the original video signal and outputs these sync signals to the drive control circuit 20. The drive control circuit 20 forms a gate pulse for clamping the pedestal level portion in the video signal by delaying the horizontal synchronization signal from the synchronization separation circuit 24 by a predetermined time by a delay circuit (not shown). The pulse is output to the pedestal clamp circuit 16 of the video I / F 19.

In the video signal input to the video I / F 19, the pedestal level portion in the video signal is always kept constant in the pedestal clamp circuit 16.
Further, when the polarity is inverted at a constant period in the inverting amplifier circuit 17, the waveform becomes, for example, as shown in FIG. Here, the level difference between the black level and the white level of the video signal output from the video I / F 19 (that is, the peak-to-peak amplitude of the entire video signal) depends on the light transmittance characteristic of the liquid crystal shown in FIG. The transmittance is set to about 4 V, which changes from the maximum to the minimum. The video signal formed by the video I / F 19 is supplied to the source drive circuit 7.

A control signal from the drive control circuit 20 is input to the source drive circuit 7 together with the video signal. Based on a sampling pulse of the control signal synchronized with the horizontal synchronization signal, the source drive circuit 7 performs one horizontal scanning period. As shown in FIG. 2, the video signal is supplied to a sample-and-hold circuit 10 via a shift register 9, and is output to each signal electrode 2 via an output buffer 11.

A control signal from the drive control circuit 20 is input to the gate drive circuit 8. Based on the control signal, the gate ON signal is sequentially shifted in the shift register 12 to the level shifter 13. And the level of the gate ON signal in the level shifter 13 is T
The signal is converted to a level at which the FT 5 is turned on, and is output to each of the gate electrodes 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 into conduction for each gate electrode 3, and the signal voltage V _{S of the} video signal is reduced Are applied to the electrodes 4.

In the drive control circuit 20, based on the synchronization signal from the synchronization separation circuit 24, as shown in (b) of FIG. This is output to the counter electrode signal generation circuit 21. The counter electrode signal generation circuit 21 amplifies the polarity inversion signal according to the setting of the variable electric resistor VR in the feedback amplifier circuit shown in FIG. The generated counter electrode signal is generated. Then, the above-mentioned counter electrode signal is supplied to the counter electrode 6 arranged to face the picture element electrodes 4 through the liquid crystal layer.

Thus, the pixel electrode 4 to which the signal voltage V _S of the video signal is applied and the counter voltage V of the counter electrode signal
_A potential difference is generated between the counter electrode 6 to which _COM is applied and the liquid crystal is driven by the electric field, so that display according to the video signal is performed.

Here, the adjustment of the brightness of the display screen in the TFT-LCD will be described below.

The operation of adjusting the brightness of the display screen is performed by using a brightness adjusting section 23 (see FIG. 3) provided on the outer surface of the apparatus. That is, when the brightness adjustment unit 23 is operated by the user, the setting of the variable electric resistor VR of the common electrode signal generation circuit 21 shown in FIG. As a result, the gain of the feedback amplifier circuit changes, and, for example, counter electrode signals having different peak-peak amplitudes are obtained as shown in (c) to (e) of FIG.

In the present TFT-LCD, the source driving circuit 7
Since the DC level of the video signal (see (a) in FIG. 5) supplied to the video signal is fixed, as described above, the amplitude of the counter electrode signal changes, thereby causing a difference between the video signal and the counter electrode signal. The voltage difference (that is, the driving voltage V applied to the liquid crystal) changes overall, and as a result, the brightness of the display screen changes.

The waveforms of the signals shown in (a) to (e) in FIG. 5 are the waveforms at the timing when they are supplied to the source drive circuit 7, and the sampling at the source drive circuit 7 By the hold operation, the video signal is changed to the picture element electrode 4 ...
Are shifted by one horizontal scanning period from this. The video signal shown in (a) of FIG. 1 and the counter electrode signals shown in (c) to (e) of FIG. 1 are applied to the liquid crystal layer by applying a signal voltage V _S and a counter voltage V _COM to the liquid crystal layer. If shown at the same time, (a) in FIG.
To (c).

As described above, in the present TFT-LCD, the DC level of the video signal (see (a) in FIG. 5) generated by the video I / F 19 and supplied to the source drive circuit 7 is fixed. At the same time, the peak-to-peak amplitude of the counter electrode signal generated by the counter electrode signal generation circuit 21 is changed according to the setting in the brightness adjustment unit 23, whereby the setting is based on the setting of the brightness adjustment unit 23. The brightness of the display screen can be adjusted.

For this reason, the dynamic range of the source drive circuit 7 is sufficient to be about 4 V where the light transmittance changes from the maximum to the minimum in the light transmittance characteristics of the liquid crystal shown in FIG. For example, a low-voltage driver IC that operates with a 5 V power supply can be used. Thus, the present TFT-LCD
Has a display screen brightness adjustment function,
Compared with a conventionally used medium-voltage driver IC, it can be manufactured using a low-voltage driven driver IC having a smaller chip size and lower cost, so that miniaturization, thinning, and cost reduction can be realized. Yes, TFT-L
The range of use of the CD module is expanded.

By the way, in the above TFT-LCD,
In the normal case, the peak-to-peak amplitude of the video signal falls within the peak-to-peak amplitude of the counter electrode signal, for example, as shown in (a) and (b) of FIG. When the brightness is adjusted in the direction of darkening the display screen, no problem occurs because the peak-to-peak amplitude of the counter electrode signal increases as shown in (b) of FIG. When the brightness is adjusted in the direction of increasing the brightness, (c) in FIG.
As shown in the figure, the peak-to-peak amplitude of the counter electrode signal becomes smaller than the peak-to-peak amplitude of the video signal, and the image corresponding to the white level and the level near the white level in the video signal (that is, the image portion which should be a bright portion) ), But the problem of darkening occurs. This is because, when the peak-to-peak amplitude of the counter electrode signal becomes smaller than the peak-to-peak amplitude of the video signal, a part of the video signal that is normally at a level lower than the level of the counter electrode signal (white level and the vicinity of white level) Level) becomes higher than the level of the counter electrode signal, so that the picture element electrodes 4 to which the video signal voltage of the white level and a level near the white level is applied.
The polarity of the drive voltage V applied to the liquid crystal layer between the liquid crystal layer and the counter electrode 6 is opposite to that in the normal state. In such a portion, the display becomes darker as the video signal level approaches the white level. It is because.

Accordingly, the brightness of the display screen can be adjusted by adjusting the peak-to-peak amplitude of the counter electrode signal.
In the FT-LCD, a TFT-LCD that optimizes operating conditions for brightness adjustment and can avoid inconveniences such as darkening of a bright portion will be described in the following first and second embodiments.

[0055] An embodiment of Example 1 the present invention will be described with reference mainly to FIGS. 7 and 8, is as follows. The components having the same configuration as above are denoted by the same reference numerals, and description thereof will be omitted.

The TFT as the liquid crystal display device of this embodiment
The LCD has the same configuration as the above-described TFT-LCD except for the video I / F and the drive control circuit. As shown in FIG. 7, a video I / F (video signal generating means) 1 according to the present embodiment.
9 'is provided with an amplitude limiting circuit (video signal amplitude adjusting means) 25 was not on the video I / F19. In this embodiment, the counter electrode signal generated by the counter electrode signal generation circuit 21 is input to a drive control circuit 20 'as an amplitude detecting means, and the drive control circuit 20' generates a peak-to-peak amplitude of the counter electrode signal. Is detected. When the peak-to-peak amplitude of the counter electrode signal becomes smaller than 4 V _PP, which is the peak-to-peak amplitude of the video signal, the drive control circuit 20 ′ generates an amplitude control signal corresponding to the peak-to-peak amplitude of the counter electrode signal. Video I /
The signal is output to the amplitude limiting circuit 25 of F19 '. Incidentally, the drive control circuit 20 ', except that outputs an amplitude control signal by detecting the peak-to-peak amplitude of the counter electrode signal has the same structure as the drive control circuit 20.

The amplitude limiting circuit 25 includes an inverting amplifier 1
7, before the polarity inversion processing of the video signal is performed, based on the amplitude control signal from the drive control circuit 20 ',
This limits (cuts) the amplitude of the video signal.

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 the video I / F 19 ′ and the synchronization separation circuit 2.
4 will be input. Here, based on the synchronization signal separated by the synchronization separation circuit 24, the drive control circuit 2
At 0 ', various control signals are generated and output to the source drive circuit 7, gate drive circuit 8, counter electrode signal generation circuit 21, video I / F 19' and the like.

The counter electrode signal generation circuit 21 amplifies the polarity inversion signal (see (b) in FIG. 5) from the drive control circuit 20 'in accordance with the setting of the brightness adjustment unit 23. The counter-electrode signals converted into AC as shown in (c) to (e) of FIG. 5 are generated. Then, the above-described counter electrode signal is supplied to the counter electrode 6 and also input to the drive control circuit 20 '.

The drive control circuit 20 'detects the peak-to-peak amplitude of the counter electrode signal, and when the peak-to-peak amplitude becomes smaller than 4 V _PP , the drive control circuit 20' outputs the amplitude control signal corresponding to the peak-to-peak amplitude. Output to the amplitude limiting circuit 25 of the video I / F 19 '.

On the other hand, the video signal input to the video I / F 19 ′ is output to the amplitude limiting circuit 25 after the pedestal level is determined in the pedestal clamp circuit 16. Here, when the peak-to-peak amplitude of the counter electrode signal is 4 V _PP or more, the amplitude of the video signal is not limited by the amplitude limiting circuit 25, and the video signal is not = 1 horizontal scanning period)
The polarity is reversed by, for example, (a) in FIG.
As shown in, the same waveform as the above.

On the other hand, when the peak-to-peak amplitude of the counter electrode signal is smaller than 4 V _PP , the amplitude limiting circuit 25
In, the amplitude of the video signal is cut in accordance with the amplitude control signal from the drive control circuit 20 '. In this case, as the peak-to-peak amplitude of the counter electrode signal is smaller, the limit level in the amplitude limiter 25 is set lower, and the white level cut of the video signal is larger. After this, the video signal
By inverting the polarity every one horizontal scanning period in the inverting amplifier circuit 17, for example, as shown in FIG. 8, the waveform in which the peak-to-peak amplitude A of the video signal in one cycle period is smaller than that in the normal state is obtained. Become.

This video signal is supplied to the source drive circuit 7
(See FIG. 1), as described above ,
Display according to the video signal is performed on the liquid crystal panel 1 (see FIG. 1).

As described above, the TFT-LCD of this embodiment is generated by the video I / F 19 '
The DC level of the video signal supplied to the counter electrode signal is fixed, and the peak-to-peak amplitude of the counter electrode signal generated by the counter electrode signal generation circuit 21 changes according to the setting in the brightness adjustment unit 23. The drive control circuit 20 'detects the peak-to-peak amplitude of the counter electrode signal, and the video I / F 19' outputs an amplitude detection output (amplitude control signal) from the drive control circuit 20 '. And an amplitude limiting circuit 25 for reducing the peak-to-peak amplitude of the video signal within one cycle period by cutting the amplitude of the video signal based on the video signal. only when it becomes smaller than 4V _PP is the peak-peak amplitude of the configuration of the amplitude of the video signal is cut in accordance with the peak-peak amplitude of the counter electrode signal

Thus, in addition to the above effects, even when the brightness is adjusted in the direction of increasing the brightness of the display screen, the polarity of the drive voltage V applied to the liquid crystal layer may be reversed from that in the normal state. This avoids the problem that the image portion, which should be a bright portion, becomes dark.

Embodiment 2 Another embodiment of the present invention will be described below mainly with reference to FIGS. 9 and 10. Components having the same configuration as in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The TFT as the liquid crystal display device of this embodiment
The LCD is the same as the TFT of Example 1 except for the video I / F.
It has the same configuration as the LCD. As shown in FIG. 9, a video I / F (image signal generation means) 19 of the present embodiment ", the upper
In place of the amplitude limiting circuit 25, an amplitude adjusting amplifier (video signal amplitude adjusting means) 26 for reducing the amplitude of a video signal based on an amplitude control signal from a drive control circuit 20 'as an amplitude detecting means is provided. I have.

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

As in the first embodiment, the brightness adjustment unit 23
The counter electrode signal generated by the counter electrode signal generation circuit 21 in accordance with the setting is supplied to the counter electrode 6 and input to the drive control circuit 20 '. The drive control circuit 20 '
Detects the peak-to-peak amplitude of the counter electrode signal, and when the peak-to-peak amplitude is smaller than 4 V _PP , sends an amplitude control signal corresponding to the peak-to-peak amplitude to the video I / F 19 ″ for amplitude adjustment. Output to the amplifier 26.

Here, when the peak-to-peak amplitude of the counter electrode signal is 4 V _PP or more, the video signal is not reduced by the amplitude adjusting amplifier 26 and the video signal is kept constant in the inverting amplifier circuit 17. By inverting the polarity in a cycle (one cycle = 1 horizontal scanning period), a waveform similar to the above is obtained, for example, as shown in FIG.

On the other hand, when the peak-to-peak amplitude of the common electrode signal is smaller than 4 V _PP , the amplitude of the video signal is reduced by the amplitude control amplifier 26 to the drive control circuit 20 ′.
Is reduced in accordance with the amplitude control signal from. In this case, the smaller the peak-to-peak amplitude of the common electrode signal, the larger the reduction ratio of the video signal is set in the amplitude adjustment amplifier 26. Thereafter, the video signal is inverted at a constant period in the inverting amplifier circuit 17, so that, for example, as shown in FIG.
However, the waveform becomes smaller than usual.

The video signal is supplied to the source driving circuit 7
(See FIG. 1), as described above ,
Display according to the video signal is performed on the liquid crystal panel 1 (see FIG. 1).

As described above, the TFT-LCD of this embodiment is generated by the video I / F 19 '
The DC level of the video signal supplied to the counter electrode signal is fixed, and the peak-to-peak amplitude of the counter electrode signal generated by the counter electrode signal generation circuit 21 changes according to the setting in the brightness adjustment unit 23. The peak-to-peak amplitude of the counter electrode signal is detected by the drive control circuit 20 ', and the video I / F 19 "outputs an amplitude detection output (amplitude control signal) from the drive control circuit 20'. , The amplitude of the video signal within one horizontal scanning period is reduced by reducing the amplitude of the video signal, and the amplitude of the video signal within one horizontal scanning period is reduced. Only when the peak-to-peak amplitude becomes smaller than 4 V _{PP, the} amplitude of the video signal is reduced in accordance with the peak-to-peak amplitude of the counter electrode signal.

As a result, in addition to the above effects, even when the brightness is adjusted in the direction of increasing the brightness of the display screen, the polarity of the drive voltage V applied to the liquid crystal layer may be reversed from that in the normal state. This avoids the problem that the image portion, which should be a bright portion, becomes dark.

In the first embodiment, since a part of the video signal is cut (maintained at a constant level) to reduce the peak-to-peak amplitude of the video signal within one horizontal scanning period, the video signal is cut. In the shaded portion, the tone does not appear, but no gradation is produced. On the other hand, in the present embodiment, since the peak-to-peak amplitude of the video signal within one horizontal scanning period is reduced by reducing the entire video signal, the gradation is not impaired.

In each of the above embodiments, a positive display type TFT-LCD has been described. However, it is needless to say that the present invention can be applied to an active display type, and a dynamic driving method using no switching element such as a TFT. Alternatively, the present invention 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.

[0078]

As described above, in the liquid crystal display device according to the present invention, the common electrode signal generating means for generating the common electrode signal whose polarity is inverted in synchronization with the video signal is based on the setting in the brightness setting section. And an amplitude adjusting means for adjusting the peak-to-peak amplitude of the counter electrode signal.

Therefore, the brightness of the display screen can be adjusted while the DC level of the video signal is kept constant. Therefore, the video signal voltage applying means for applying the video signal voltage corresponding to the video signal to the display electrode includes: A low-voltage driver IC can be used. As described above, although the present liquid crystal display device has the function of adjusting the brightness of the display screen, the chip size is smaller and the cost is lower than that of the conventionally used medium-voltage driver IC. Driver I
Since it can be formed using C, there is an effect that the size, thickness and cost can be reduced.

Further, the liquid crystal display device according to the present invention includes amplitude detecting means for detecting the peak-to-peak amplitude of the counter electrode signal, and the video signal generating means for generating the video signal has the peak-to-peak amplitude of the counter electrode signal. by Rukoto a smaller than the peak-peak amplitude of the video signal, the liquid crystal drive
A configuration having video signal amplitude adjusting means for reducing the peak-to-peak amplitude of a video signal within one cycle period according to the amplitude detection output of the amplitude detecting means when the polarity of the voltage can be reversed. It is.

Therefore, the reversal of the polarity of the liquid crystal drive voltage when the brightness is adjusted in the direction of increasing the brightness of the display screen can be avoided, so that the image portion that should be bright does not become dark. There is an effect that an optimal display according to the brightness adjustment can be performed.

[Brief description of the drawings]

FIG. 1 is a waveform diagram showing waveforms of a video signal and a counter electrode signal in a TFT-LCD having a basic configuration according to an embodiment of the present invention.

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 block diagram showing a configuration of a main part of the TFT-LCD.

FIG. 4 is an electronic circuit diagram showing a counter electrode signal generation circuit in the TFT-LCD.

FIG. 5 is a timing chart showing a video signal, a polarity inversion signal, and a counter electrode signal in the TFT-LCD.

FIG. 6 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, and showing a relationship between the light transmittance characteristic and a video signal waveform.

FIG. 7 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 the LCD.

FIG. 8 is a waveform diagram showing waveforms of a video signal and a counter electrode signal when the peak-peak amplitude of the counter electrode signal is smaller than the peak-peak amplitude of the video signal in the TFT-LCD.

FIG. 9 shows another embodiment of the present invention, in which a TFT is used.
FIG. 2 is a block diagram illustrating a configuration of a main part of an LCD.

FIG. 10 is a waveform diagram showing waveforms of a video signal and a counter electrode signal when the peak-peak amplitude of the counter electrode signal is smaller than the peak-peak amplitude of the video signal in the TFT-LCD.

FIG. 11 shows a conventional example, and is an explanatory diagram showing a configuration of a liquid crystal panel and a driving unit thereof in a TFT-LCD.

FIG. 12 is an electronic circuit diagram showing a counter electrode signal generation circuit in the TFT-LCD.

FIG. 13 is a waveform diagram showing waveforms of a video signal and a counter electrode signal in the TFT-LCD.

FIG. 14 is a waveform diagram showing a waveform of a video signal in the TFT-LCD.

FIG. 15 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.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 Signal electrode 3 Gate electrode 4 Pixel electrode (display electrode) 5 TFT 6 Counter electrode 7 Source drive circuit 8 Gate drive circuit 19 Video interface (video signal generation means) 19 'Video interface (video signal generation means) 19 "Video interface (video signal generating means) 20 Drive control circuit 20 'Drive control circuit (amplitude detecting means) 21 Counter electrode signal generating circuit (counter electrode signal generating means) 21a Feedback amplifier circuit (amplitude adjusting means) 23 Brightness adjusting section 25 Amplitude limiting circuit (Video signal amplitude adjusting means) 26 Amplitude adjusting amplifier (Video signal amplitude adjusting means)

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G09G 3/36 G02F 1/133 550 G09G 3/20

Claims (6)

(57) [Claims] A display electrode; a counter electrode disposed to face the display electrode via a liquid crystal layer; a video signal generating means for generating a video signal whose polarity is inverted at a predetermined cycle; A video signal voltage applying means for applying a video signal voltage to the display electrode; a counter electrode signal generating means for generating a counter electrode signal whose polarity is inverted in synchronization with the video signal and supplying the counter electrode signal to the counter electrode; A brightness setting unit for setting the brightness of the display device, wherein the brightness of the display screen can be adjusted according to the setting in the brightness setting unit .
Comprises amplitude detection means that, the counter electrode signal generating means,
An amplitude adjusting means for adjusting the peak-to-peak amplitude of the counter electrode signal based on the setting in the brightness setting section is provided.
And the video signal generating means adjusts the amplitude.
Adjust the peak-to-peak amplitude of the above counter electrode signal by means
The peak-to-peak amplitude of the counter electrode signal
To be smaller than the peak-to-peak amplitude of the video signal
Thus, the polarity of the liquid crystal driving voltage applied to the liquid crystal layer is
If the peak-to-peak amplitude of the counter electrode signal is not adjusted
May be reversed depending on the level of the video signal.
The amplitude detection output of the amplitude detection means.
The peak-to-peak amplitude of the video signal within one period
The liquid crystal display device characterized in that it possess a video signal amplitude adjusting means for fence. 2. The video signal amplitude adjusting means according to claim 1 , wherein
An amplitude limiting circuit for limiting the amplitude.
The liquid crystal display device according to claim 1. 3. The video signal amplitude adjusting means according to claim 1 , wherein
It is an amplitude adjustment amplifier that reduces the amplitude.
The liquid crystal display device according to claim 1. 4. A display electrode comprising : a display electrode;
And a counter electrode disposed to face the display screen, and the brightness of the display screen
By setting, the brightness of the display screen according to the setting
In an adjustable liquid crystal display device driving method, a video signal whose polarity is inverted at a predetermined cycle is generated, and a video signal voltage corresponding to the video signal is applied to the display electrode.
In addition, the counter electrode signal whose polarity is inverted in synchronization with the video signal is
Generate and supply to the counter electrode and , based on the brightness setting, the peak of the counter electrode signal.
Adjust the peak amplitude, and adjust the peak-peak amplitude of the counter electrode signal.
The peak-to-peak amplitude of the counter electrode signal is
The peak amplitude is smaller than the peak amplitude of
The polarity of the liquid crystal drive voltage applied to the liquid crystal layer is
When the peak-to-peak amplitude of the pole signal is not adjusted
If the level can be reversed depending on the level of the video signal
In this case, according to the peak-to-peak amplitude of the counter electrode signal,
Reduce the peak-to-peak amplitude of the video signal within one period
A method of driving a liquid crystal display device. 5. A peak-to-peak shake of a video signal within one cycle period.
When reducing the width, limit the amplitude of the video signal
5. The method of driving a liquid crystal display device according to claim 4, wherein
Law. 6. A peak-to-peak shake of a video signal within one period.
When reducing the width, reduce the amplitude of the video signal
5. The method of driving a liquid crystal display device according to claim 4, wherein
Law.