JP2001356748A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal display device which can be miniaturized, thinned and inexpensive, which is capable of performing correct gradation expression and which has a function for adjusting the brightness of a display screen. SOLUTION: This display device is has a constitution in which the brightness adjustment of a display screen based on the setting of a brightness adjusting part 23 is possible because the voltage level of a video signal to be supplied to a source circuit 7 is fixed and, besides, the peak-to-peak amplitude of a counter electrode signal changes in accordance with a setting in the brightness adjusting part 23. In the device, a reference changing part 25b shifts the reference value of a broken line approximation characteristic by the changed amount αof the amplitude of the counter electrode signal which is to be adjusted on the basis of the setting in the brightness adjusting part 23, and a level converting part 25a converts the level of the video signal on the basis of this corrected reference value to correct the non-linearity of the light transmittance characteristics of the liquid crystal.

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 or a liquid crystal display in which each pixel is formed in a matrix at the position where a row electrode and a column electrode intersect, and a brightness adjusting function is added. Things.

[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. 12, the above-mentioned TFT-LCD has signal electrodes 52 and gate electrodes 5 arranged orthogonally.
, 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 in a conductive state for each gate electrode 53, and the signal voltage VS of the video signal is changed to the pixel electrode. 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. ing.

As a result, a potential difference is generated between the picture element electrode 54 to which the signal voltage VS is applied and the counter electrode 56 to which the counter voltage VCOM 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 characteristic of the liquid crystal used in the LCD is as shown in FIG. 5, and the light transmittance changes according to the difference between the counter voltage VCOM and the signal voltage VS (hereinafter, referred to as the drive voltage V). Thereby, display according to the video signal is performed.

When a constant voltage is constantly applied to the liquid crystal, the liquid crystal is degraded due to electrolysis and flicker becomes noticeable. Therefore, the polarity of the driving voltage V needs to be inverted at a predetermined cycle. In this case, a method is also conceivable in which the common voltage VCOM of the common electrode signal is set to a constant level and the video signal is switched every one horizontal scanning period.
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, the power consumption of the device increases, and the driver IC used in the source drive circuit 57 has a withstand voltage. Tall ones are needed. Therefore, conventionally, by converting the common electrode signal into an alternating current, the common voltage V serving as the liquid crystal drive voltage V is obtained.
An AC driving method of a counter electrode signal which can reduce the peak-to-peak amplitude of the entire video signal while maintaining the difference between COM and the signal voltage VS is used.

Since the light transmittance characteristics of the liquid crystal depend on the viewing angle, the brightness of the display screen differs between looking up the liquid crystal panel 51 from below 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.
The brightness can be adjusted according to the use state of the liquid crystal display device.

Conventionally, this brightness adjustment is performed by changing the voltage level of the video signal during one horizontal scanning period as shown in FIG. By changing the voltage level of the video signal in this way, the voltage difference between the video signal and the counter electrode signal (that is, the drive voltage V applied to the liquid crystal) changes overall, and as a result, the display screen The brightness changes.

However, as described above, in the case of a TFT-LCD configured to adjust the brightness of the display screen by changing the voltage level of the video signal, changing the voltage level of the video signal inevitably results. Since the peak-to-peak amplitude of the entire video signal changes, the source drive circuit 57
A so-called medium withstand voltage driver having a high withstand voltage is required as a driver IC used for the above. Medium voltage driver IC
Is a low-withstand-voltage driver I which is common in chip size and cost.
C is disadvantageous as compared with C, and thus hinders downsizing and thinning of the TFT-LCD module,
-The cost of the LCD is also increased.

Therefore, the applicant of the present application has solved the above-mentioned problems and has developed a driver IC used in the source drive circuit 57.
In order to make it possible to use a low-voltage driver IC,
As shown in FIG. 4, instead of changing the voltage level of the video signal during one horizontal line period, the potential difference between the video signal and the counter electrode signal is changed by changing the voltage level of the counter electrode signal during one horizontal line period. Then, a method of changing the brightness of the display screen (hereinafter, this method is referred to as a low voltage method) has been proposed (Japanese Patent Laid-Open No. 7-295164). Specifically, as shown in FIG. 15, a brightness control signal corresponding to a desired brightness set by the user in the brightness adjustment unit 72 for setting the brightness of the display screen is output from the counter electrode signal generation circuit. 71 is input. Counter electrode signal generation circuit 7
In No. 1, a polarity inversion signal is amplified by a feedback amplifier circuit (not shown) constituting an amplitude adjustment unit according to a brightness control signal to generate a counter electrode signal. As a result, it is possible to provide a liquid crystal display device having a display screen brightness adjusting function capable of realizing miniaturization, thinning, and cost reduction.

On the other hand, the light transmittance characteristic of the liquid crystal panel 51 has a unique characteristic as shown in FIG.
In order to perform good gradation expression, it is necessary to perform correction corresponding to the characteristics on the video signal side. Generally, such correction is referred to as gamma correction, and the voltage applied to the liquid crystal is corrected according to the level of the video signal input to the liquid crystal module after the brightness adjustment.

FIG. 8 is a characteristic diagram after correction in which the transmittance is proportional to the drive voltage, which is the voltage applied to the liquid crystal. For example, assuming that the characteristics in FIGS. 7 and 8 are A and B, respectively, the characteristic A may be changed to the characteristic B by performing a correction (B ÷ A). FIG. 9 shows the correction characteristics to be applied based on this concept (hereinafter, referred to as correction characteristics).
By converting the level of the video signal with the correction characteristics, the characteristics of the drive voltage and the transmittance have a proportional relationship shown in FIG. Actually, the light transmittance characteristics of the liquid crystal panel 51 are corrected only approximately in order to simplify the circuit and the like. For example, two inflection points γ1. The level conversion of the video signal is performed by the polygonal line approximation characteristic having γ2. The inflection point voltages γ1 and γ2 of such broken line approximation characteristics are set from a certain reference value of the video signal.

[0016]

By the way, even in a TFT-LCD whose brightness can be varied, a TFT-LCD of a type in which the brightness is varied by changing the voltage level of a video signal during one horizontal line period, As shown in FIG. 16, if the inflection point voltages γ1 and γ2 of the polygonal line approximation characteristic are set from the offset point L of the counter electrode signal which is the reference point of the video signal, even if the voltage level of the video signal changes, The inflection point voltages γ1 and γ2 do not fluctuate even if a voltage change of α occurs, and good gradation expression is possible.

However, the above-mentioned T of the low voltage system
In the FT-LCD, instead of changing the voltage level of the video signal during one horizontal line period, the drive voltage applied to the liquid crystal is changed by changing the amplitude of the counter electrode signal, thereby changing the brightness of the display screen. Figure 1
As shown in FIG. 7, the inflection point voltage γ1 · γ
2 is set from the offset point L of the counter electrode signal, which is the reference point of the video signal, when the amplitude of the counter electrode signal is changed, the inflection point voltage γ1
γ2 moves by the change amount α. As a result, the correction is incomplete, and accurate gradation expression cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to realize a display screen capable of realizing miniaturization, thinning, and cost reduction and capable of accurately expressing gradation. An object of the present invention is to provide a liquid crystal display device having a brightness adjustment function.

[0019]

According to a first aspect of the present invention, there is provided a liquid crystal display device, comprising: a display electrode; and a counter electrode disposed to face the display electrode via a liquid crystal layer. A brightness setting unit for setting brightness of a display screen; a video signal generating means for generating a video signal whose polarity is inverted at a predetermined cycle; and a video for applying a video signal voltage corresponding to the video signal to the display electrode. A signal voltage application unit, and a counter electrode signal generation unit that generates a counter electrode signal whose polarity is inverted in synchronization with an inversion cycle of the video signal and supplies the counter electrode signal to the counter electrode, wherein the counter electrode signal generation unit includes: Based on the setting in the brightness setting unit, while an amplitude adjustment unit that adjusts the peak-to-peak amplitude of the counter electrode signal is provided, the video signal generation unit, the video signal, the video signal was set from a certain reference value, liquid A level conversion unit that performs level conversion with a correction characteristic that corrects the nonlinearity of the transmittance with respect to the applied voltage, and a reference for the correction characteristic by the amplitude change of the common electrode signal that is adjusted based on the setting in the brightness setting unit. A reference variation unit for changing a value is provided.

[0020]

According to the above arrangement, the reference variation unit provided in the video signal generating means is adapted to adjust the reference value of the correction characteristic by the amplitude change of the counter electrode signal adjusted based on the setting in the brightness setting unit. And the level conversion unit of the video signal correction unit converts the level of the video signal with the correction characteristic for correcting the non-linearity of the transmittance with respect to the applied voltage of the liquid crystal based on the corrected reference value. As in the liquid crystal display device of (1), an amplitude adjuster is provided, and instead of changing the voltage level of the video signal, the applied voltage (drive voltage) applied to the liquid crystal is changed by changing the amplitude of the counter electrode signal. Even in the case of a configuration in which the brightness of the display screen is variable, the video signal is accurately corrected so that the transmittance with respect to the applied voltage of the liquid crystal shows linearity without being affected by the amplitude change of the counter electrode signal. It becomes possible, and can be implemented accurate gradation.

[0021]

1 to 11 show an embodiment of the present invention.
This will be described below.

As shown in FIG. 2, the liquid crystal display device according to this embodiment is a liquid crystal display device of an active matrix driving system using a TFT 5 as a switching element.
FT-LCD). Here, a normally white type (positive display type) TFT-LC that transmits light in a normal state and blocks the light by applying a voltage is applied.
D 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 (see FIG. 1).

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 VCOM of the electrode signal is applied.

The counter electrode signal generation circuit 21 outputs the polarity inversion signal (see (b) in FIG. 4) generated by the drive control circuit 20 for a pulse width of one horizontal scanning period as shown in FIG. Feedback amplifying circuit (amplitude adjustment unit) 21a comprising electric resistors R1 and R2, variable electric resistor VR and amplifier 22
To generate a counter electrode signal, for example, as shown in FIG. A DC voltage is applied to the plus side input terminal of the amplifier 22, and a polarity inversion signal is inputted to the minus side input terminal thereof through an electric resistor R1.
The output of the amplifier 20 is fed back to its negative input terminal via an electric resistor R2 and a variable electric resistor VR connected in series. Therefore, if the setting of the variable electric resistor VR 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 set value of the variable electric resistor VR is determined by a brightness adjustment unit (brightness setting unit) 23 (see FIG. 1) provided on the outer surface of the device.
) Is set by a brightness control signal corresponding to the brightness set in step (1).

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. 1, 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 at a predetermined cycle (one cycle = 1 horizontal scanning period). A gamma correction unit (video signal correction unit) 25 for performing gamma correction of the video signal;
The data is supplied to the source drive circuit 7.

The gamma correction section 25 performs so-called gamma correction, and includes a level conversion section 25a and a reference variation section 25.
b. The level conversion unit 25a includes the inverting amplification circuit 1
The video signal input from 7 is converted to a reference value of the video signal,
In other words, the level is converted by a polygonal line approximation characteristic having two inflection points γ1 and γ2 as shown in FIG. 10, which is set from the offset point L at the voltage level which is the basic voltage level of the variable counter electrode signal. I have.

Here, the reason for performing gamma correction will be described below. The light transmittance characteristic of the liquid crystal constituting the liquid crystal panel 1 has a unique characteristic as shown in FIGS.
In order to perform good gradation expression, it is necessary to perform so-called gamma correction on the video signal side in accordance with the characteristics. In order to make the characteristic A shown in FIG. 7 like the corrected characteristic B shown in FIG. 8 having a proportional relationship between the driving voltage and the transmittance of the liquid crystal, a correction of (B ÷ A) may be applied. . FIG. 9 shows the correction characteristics to be applied based on this concept. By converting the level of the video signal with the correction characteristics, the characteristics of the drive voltage and the transmittance have a proportional relationship shown in FIG. However, since a circuit capable of multiplying the correction characteristics as shown in FIG. 9 becomes very complicated, a line-line approximation having two inflection points γ1 and γ2 as shown in FIG. The level conversion of the video signal is approximately performed by the characteristic. It should be noted that the number of inflection points γ1 and γ2 may be two or more, in which case it will be more similar to FIG.

On the other hand, the reference variation section 25b is provided with an inflection point γ1 · γ
2 is varied based on a brightness control signal corresponding to the brightness set by the brightness adjustment unit 23. In other words, according to the brightness control signal from the brightness setting unit, the reference value of the polygonal line approximation characteristic is shifted by the change amount α of the counter electrode signal corresponding to the brightness control signal, and the inflection point γ1 · .gamma.2 is translated as shown in FIG. Such a shift of the reference value is necessary because the brightness control signal from the brightness setting unit 23 causes the variable electric resistor V
Since the setting of R is changed and the peak-to-peak amplitude of the counter electrode signal is changed, for example, as shown in (c) to (e) in FIG. 4, the offset point of the counter electrode signal, which is the reference point of the video signal, is changed. This is because L fluctuates, and in the uniform correction from the offset point L, the inflection points γ1 and γ2 fluctuate according to the fluctuation of the offset point L, and correct correction cannot be performed according to the drive voltage.

Further, the TFT-LCD includes a synchronization separation circuit 24 for separating a synchronization signal from an input video signal, and a synchronization driving circuit for separating the source driving circuit 7 and the gate driving 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. 1, first, an original video signal separated from a television signal or the like is input to a video I / F 19 and a synchronization 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 of the video signal is always kept constant in the pedestal clamp circuit 16,
Further, the polarity is inverted at a constant cycle in the inverting amplifier circuit 17, so that 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 inverting amplifier circuit 17 (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 output from the inverting amplifier 17 is input to a gamma correction unit 25,
At 5a, the level is converted by a polygonal line approximation characteristic having inflection points γ1 and γ2 as shown in FIG. At this time, the inflection point voltages γ1 and γ2 of the polygonal line approximation characteristic used in the level converter 25a are changed by the reference value change by the reference changer 25b, as shown in FIG.
However, since the voltage is changed from the offset point L of the common electrode signal, it is held without being affected by the voltage change of the common electrode signal.

Thereafter, 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, and a video signal for one horizontal scanning period is generated based on a sampling pulse of the control signal synchronized with the horizontal synchronization signal. As shown in FIG. 2, the sample-and-hold circuit 1
0 to each signal electrode 2 via the output buffer 11.
Output to ...

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 in a conductive state for each gate electrode 3, and the signal voltage VS of the video signal is changed to the pixel electrode. 4.

On the other hand, 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. Here, when the brightness adjustment unit 23 is operated by the user in the counter electrode signal generation circuit 21,
A brightness control signal is input from the brightness adjustment unit 23, and the setting of the variable electric resistor VR of the counter electrode signal generation circuit 21 shown in FIG. The gain changes, and counter electrode signals having different peak-to-peak amplitudes are generated and output as shown in, for example, (c) to (e) of FIG. 4 according to the desired brightness. The counter electrode signal generated in this way is supplied to the counter electrode 6 disposed opposite to the picture element electrodes 4 via the liquid crystal layer.

Thus, the pixel electrode 4 to which the signal voltage VS 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. In the present TFT-LCD, since the voltage level of the video signal (see (a) in FIG. 4) supplied to the source drive circuit 7 is fixed, the amplitude of the counter electrode signal changes as described above. As a result, the voltage difference between the video signal and the counter electrode signal (that is, the drive voltage V applied to the liquid crystal) changes as a whole, and as a result, brightness display according to the change in the counter electrode signal is performed. Become.

The waveforms of the signals shown in (a) to (e) in FIG. 4 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. 4 and the counter electrode signals shown in (c) to (e) of FIG. 4 are compared with the timing at which the signal voltage VS and the counter voltage VCOM are applied to the liquid crystal layer. In FIG. 6, (a)
To (c).

As described above, the TFT-LCD of this embodiment
The gamma provided in the video I / F 19 has a configuration in which the peak-to-peak amplitude of the common electrode signal generated by the common electrode signal generation circuit 21 changes according to the brightness control signal from the brightness adjustment unit 23. The reference variation unit 25b of the correction unit 25 shifts the reference value of the polygonal line approximation characteristic by the amplitude change amount α of the counter electrode signal adjusted based on the setting in the brightness adjustment unit 23, and uses the corrected reference value as a reference. The level converter 25a converts the level of the video signal to correct the nonlinearity of the transmittance with respect to the applied voltage of the liquid crystal.

Therefore, instead of changing the voltage level of the video signal as in the TFT-LCD of this embodiment,
Even in the case where the driving voltage applied to the liquid crystal is changed by changing the amplitude of the counter electrode signal, and the brightness of the display screen is changed, the driving of the liquid crystal is not affected by the change in the amplitude of the counter electrode signal. The video signal can be accurately corrected so that the transmittance with respect to the voltage shows linearity, and accurate gradation expression can be performed.

As a result, the TFT-LCD of this embodiment is
It is possible to realize a reduction in size, thickness, and cost, and to have a function of adjusting the brightness of a display screen capable of accurately expressing gradation.

In each of the above embodiments, the positive display type TFT-LCD has been described. However, it is needless to say that the present invention can also 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.

[0048]

As described above, the liquid crystal display device according to the first aspect of the present invention comprises a display electrode, a counter electrode disposed to face the display electrode via a liquid crystal layer, and a brightness setting of the display screen. A video signal generating unit for generating a video signal whose polarity is inverted at a predetermined cycle; a video signal voltage applying unit for applying a video signal voltage corresponding to the video signal to the display electrode; A counter electrode signal generation unit that generates a counter electrode signal whose polarity is inverted in synchronization with a signal inversion cycle and supplies the counter electrode signal to the counter electrode, wherein the counter electrode signal generation unit performs setting in the brightness setting unit. An amplitude adjustment unit that adjusts the peak-to-peak amplitude of the counter electrode signal based on the video signal, the video signal generation unit converts the video signal into a transmittance of a liquid crystal applied voltage set from a certain reference value. A level conversion unit that performs level conversion with a correction characteristic that corrects linearity, and a reference variation unit that changes the reference value of the correction characteristic by an amplitude change of the common electrode signal that is adjusted based on the setting in the brightness setting unit. Is provided.

Therefore, like the liquid crystal display device of the present invention, the driving voltage applied to the liquid crystal is provided by providing amplitude adjusting means and converting the amplitude of the counter electrode signal instead of changing the voltage level of the video signal. Can be changed to change the brightness of the display screen, accurate gradation expression can be implemented. Thereby, the liquid crystal display device of the present invention
In spite of having the function of adjusting the brightness of the display screen, it is possible to achieve a reduction in size, a reduction in thickness, and a reduction in cost, and an effect that accurate gradation expression can be performed.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, in which a TFT-
FIG. 3 is a block diagram illustrating a configuration of a main part in signal processing of 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 circuit diagram showing a counter electrode signal generation circuit in the TFT-LCD.

FIG. 4 is a timing chart showing a video signal, a polarity inversion signal, and a counter electrode signal in the TFT-LCD.

FIG. 5 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. 6 is a waveform diagram showing waveforms of a video signal and a counter electrode signal in the TFT-LCD.

FIG. 7 is a graph showing light transmittance characteristics of a liquid crystal.

FIG. 8 is a graph showing light transmittance characteristics of a liquid crystal after correction.

FIG. 9 is a graph showing a correction characteristic for correcting a light transmittance characteristic of a liquid crystal.

FIG. 10 is a graph showing a polygonal line approximation characteristic actually used as a correction characteristic.

FIG. 11 is an explanatory diagram showing a shift of an inflection point position of gamma correction in the TFT-LCD.

FIG. 12 shows a conventional example, and shows a conventional TFT-L
FIG. 2 is an explanatory diagram illustrating a configuration of a liquid crystal panel and a drive unit of the CD.

FIG. 13 is a waveform chart showing waveforms of a video signal and a counter electrode signal in a conventional system.

FIG. 14 is a waveform diagram showing waveforms of a video signal and a counter electrode signal of a low voltage system.

FIG. 15 is a block diagram showing a brightness adjusting mechanism of a display screen in the low-voltage TFT-LCD.

FIG. 16 is an explanatory diagram showing an inflection point position of the conventional gamma correction with respect to the liquid crystal driving voltage.

FIG. 17 is an explanatory diagram showing an inflection point position of the conventional gamma correction with respect to the liquid crystal applied voltage when the brightness is adjusted by changing the amplitude of the counter electrode signal.

[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) 20 Drive control circuit 21 Counter electrode signal generation circuit ( Counter electrode signal generation means) 23 brightness adjustment unit (brightness setting unit) 25 gamma correction unit 25a level conversion unit 25b reference variation unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H093 NA16 NA31 NA51 NB01 NC22 NC23 NC34 ND54 5C006 AA16 AC11 AC25 AF46 BB16 FA46 FA55 FA56 5C080 AA10 BB05 DD30 EE29 FF11 JJ02 JJ04 JJ05

Claims (1)

[Claims] 1. A display electrode, a counter electrode disposed to face the display electrode via a liquid crystal layer, a brightness setting unit for setting brightness of a display screen, and a video signal whose polarity is inverted at a predetermined cycle. A video signal generating means for generating; a video signal voltage applying means for applying a video signal voltage corresponding to the video signal to the display electrode; and a counter electrode signal having a polarity inverted in synchronization with an inversion cycle of the video signal. And a counter electrode signal generating means for supplying the counter electrode signal to the counter electrode, wherein the counter electrode signal generating means has an amplitude adjuster for adjusting a peak-to-peak amplitude of the counter electrode signal based on the setting in the brightness setting section. On the other hand, the video signal generating means includes a level for converting the level of the video signal by a correction characteristic for correcting the non-linearity of the transmittance with respect to the applied voltage of the liquid crystal, which is set from a certain reference value. A liquid crystal display, comprising: a switching unit; and a reference changing unit that changes a reference value of the correction characteristic by an amplitude change of the counter electrode signal adjusted based on the setting in the brightness setting unit. apparatus.