JP2001083945A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of performing a luminance regulation and preventing a liquid crystal deterioration such as flicker with an inexpensive circuit structure by changing the potential difference between the high level voltage and low level voltage of a scanning signal according to the luminance regulation. SOLUTION: This device comprises a circuit formed of an operational amplifier A1, a VGH forming circuit consisting of resistors R1-R4, an operational amplifier A2, and a VGL forming circuit consisting of resistors R5-R8. The value of luminance regulating voltage is set according to the contrast value set by a luminance regulating means. The circuit having such a structure is provided, whereby the potential different of VGH-VGL is regulated by changing the voltages of VGH and VGL even if the luminance regulation is performed, so that the change of the value ΔV can be suppressed. Accordingly, the value of ΔV can be kept at an optimum value for rationalization of center value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device, and more particularly to a liquid crystal display device which adjusts luminance and prevents liquid crystal deterioration such as flicker.

[0002]

2. Description of the Related Art Hitherto, a liquid crystal display device using a nematic liquid crystal has been widely used as a segment type liquid crystal display device for a clock, a calculator, and the like. Recently, thin,
Taking advantage of features such as light weight and low power consumption, the market is expanding as a variety of displays, including word processors, personal computers, and navigation systems, and more widely. Especially TFT (Thin Film
Active matrix type liquid crystal display devices in which active elements such as transistors are used as switching elements and pixels are arranged in a matrix have attracted attention.

[0003] Such a liquid crystal display device is, for example, a CRT.
Compared to (Cathode Ray Tube), it has the advantages of being much thinner (depth), being easy to be full-color, and having low power consumption. The demand is expanding in a wider field such as a portable television, a space-saving television, and a display device of a digital camera or a digital video camera.

[0004] A conventional transmission type active matrix type liquid crystal display device comprises a translucent active matrix substrate on which an active matrix circuit of TFTs is formed;
The semiconductor device includes a counter substrate provided with a common electrode and opposed to the active matrix substrate, and a liquid crystal sandwiched between the active matrix substrate and the counter substrate.

[0005] A plurality of pixel electrodes are formed in a matrix on the active matrix substrate. The pixel electrodes are usually formed in a row direction and a column direction in a line of several hundreds or more.

A common electrode is formed on the counter substrate so as to face the pixel electrode via the liquid crystal layer.
A voltage is applied to the liquid crystal layer by the pixel electrode and the common electrode. The common electrode is generally formed on substantially the entire surface of the counter substrate.

Further, a plurality of TFTs are formed on the active matrix substrate as active elements as switching means for selectively driving the pixel electrodes, and each TFT is connected to each pixel electrode.

In the above TFT, a gate line is connected to a gate electrode, and a data line is connected to a source electrode. The gate lines and the data lines pass around pixel electrodes arranged in a matrix and are arranged to be orthogonal to each other. The driving of the TFT is controlled by inputting a gate signal through the gate line. Also,
When driving the TFT, a data signal is input to the pixel electrode via the data line.

Here, on the active matrix substrate, each gate line is arranged in a row in the row direction.
FT, and each data line is connected to a TFT arranged in the column direction. In this case, when an image display operation is performed, a gate signal is applied to a gate line to sequentially turn on the TFTs for each row, and a size corresponding to the gradation of each pixel in the turned-on TFT rows. Is applied to each data line, and a voltage is applied to the liquid crystal via the pixel electrode.

In the period when the TFT is on,
The light transmittance of the liquid crystal layer changes according to the magnitude of the voltage applied via the data line, and electric charges are accumulated in the capacitance of the liquid crystal. After the TFT is turned off,
The state in which the light transmittance of the liquid crystal layer has changed due to the charge accumulated in the capacitance is maintained.

The liquid crystal has a property that it deteriorates when a voltage of the same polarity is continuously applied. Therefore, in the liquid crystal display device, the polarity of the voltage applied to the liquid crystal is inverted, for example, for each frame, thereby preventing the deterioration of the liquid crystal.

On the other hand, a switching element such as a TFT has a parasitic capacitance. After the TFT is turned off, the potential of the electrode connected to the TFT is reduced by ΔV due to the parasitic capacitance. That is, when a positive voltage is applied to the liquid crystal, the absolute value of the potential of the electrode decreases by ΔV after the TFT is turned off. , The absolute value of the potential of Δ increases. Since the light transmittance of the liquid crystal changes in accordance with the potential fluctuation between the electrodes, there is a problem that flicker occurs or a liquid crystal deterioration such as screen burn-in occurs in some cases.

Conventionally, in order to prevent such a problem, the voltage between the electrodes after the TFT is turned off is determined by applying a positive voltage or a negative voltage. In this case, an image is displayed by optimizing the center value of the electrode potential in accordance with each gradation so as to be equal to that in the case of the above.

[0014]

Since the active matrix type liquid crystal display device has excellent display performance as described above, it is studied to replace various monitors currently constituted by a CRT with the active matrix type liquid crystal display device. Have been. As described above, in order to use the liquid crystal display device with the same functionality as the CRT, the liquid crystal display device needs to have a brightness adjustment function.

In the case where the liquid crystal display device is configured so that the luminance can be adjusted, when the luminance is changed, ΔV in each gradation also changes. This is because the dielectric constant of the liquid crystal changes according to the absolute value of the voltage applied between the electrodes, and due to this effect, the magnitude of ΔV becomes
This is because the voltage applied between the electrodes changes according to the magnitude of the voltage, that is, the gradation. Therefore, when the brightness can be adjusted, as described above, the TFT
The voltage between the electrodes after the is turned off is equal between the case where the positive voltage is applied and the case where the negative voltage is applied, so that the electrode potential according to each gradation is equal. It is difficult to apply a configuration for displaying an image by optimizing the center value.

To cope with such a problem, Japanese Patent Application Laid-Open No. Hei 7-129127 discloses a driving apparatus for a liquid crystal display device which can prevent the occurrence of flickering even when the contrast of an image to be displayed is changed. Is disclosed. This driving device changes the magnitude of the voltage applied to the liquid crystal in accordance with the contrast of the image, and applies the changed voltage to the liquid crystal with a predetermined polarity and when the changed voltage is applied with a polarity opposite to the predetermined polarity. In addition, the magnitude of the changed voltage is corrected for each polarity so that the absolute value of the voltage between the transparent electrode pairs during the period when the switching element is off is equal.

However, in the case of this driving device, when the changed voltage is applied to the liquid crystal with a predetermined polarity and when the changed voltage is applied with a polarity opposite to the predetermined polarity, the transparent electrode during the period when the switching element is off is applied. A correction circuit is required to correct the magnitude of the changed voltage for each polarity so that the absolute values of the voltages between the pairs become equal. Since the correction circuit having such a function has a complicated circuit configuration, the manufacturing cost and the cost of parts are increased, and the yield and the reliability are reduced.

The present invention has been made to solve the above problems, and its object is to provide an inexpensive circuit configuration.
It is an object of the present invention to provide a liquid crystal display device that can adjust luminance and prevent liquid crystal deterioration such as flicker.

[0019]

In order to solve the above-mentioned problems, a liquid crystal display device according to the present invention comprises a pixel electrode provided in a matrix on an active matrix substrate, and a liquid crystal layer formed on the active matrix substrate. In a liquid crystal display device that displays an image by changing the light transmittance of the liquid crystal by applying a voltage to the liquid crystal between the liquid crystal display and a counter electrode provided on a counter substrate disposed to face the liquid crystal. A switching element connected to each of the pixel electrodes, a scanning electrode driving circuit for supplying a scanning signal to the switching element, and a luminance adjusting unit for adjusting luminance when displaying an image. Wherein the scan electrode drive circuit changes a potential difference between a high-level voltage and a low-level voltage of a scan signal in accordance with brightness adjustment by the brightness adjustment means. To have.

Generally, the potential difference between the pixel electrode connected to the switching element and the counter electrode is reduced by ΔV due to the parasitic capacitance generated in the switching element after the switching element is turned off. Become. Since the light transmittance of the liquid crystal changes with the change in the absolute value of the potential difference between the pixel electrode and the counter electrode, this causes flicker or, in some cases, liquid crystal such as screen burn-in. There is a problem that deterioration occurs.

In order to prevent such a problem, the voltage between the electrodes after the switching element has been turned off is either a case where a positive voltage is applied or a case where a negative voltage is applied. An image is displayed by optimizing the center value of the electrode potential in accordance with each gradation so that the values are equal in each case.

However, when adjusting the brightness,
The amplitude of the source signal and / or the amplitude of the opposing amplitude signal will be changed, which will further change ΔV. This is because the dielectric constant of the liquid crystal changes according to the absolute value of the voltage applied between the pixel electrode and the counter electrode.
This is because it changes according to the magnitude of the potential difference between the electrodes.

On the other hand, according to the above configuration, the scanning electrode driving circuit for changing the potential difference between the high level voltage and the low level voltage of the scanning signal is provided. After the switching element is turned off, the parasitic capacitance generated in the switching element is generated between the gate and the drain of the switching element. Therefore,
According to the magnitude of the difference between the high-level voltage of the scanning signal input from the scanning electrode when the switching element is turned on and the low-level voltage of the scanning signal input from the scanning electrode when the switching element is turned off. As a result, the magnitude of the parasitic capacitance changes. Therefore, even when the luminance is adjusted by the luminance adjusting means, by changing the potential difference between the high-level voltage and the low-level voltage of the scanning signal that determines the magnitude of ΔV, ΔV
Can be suppressed. Therefore, even if the brightness is adjusted, the amount of change in ΔV can be reduced.
, The center value of the electrode potential can be optimized according to each gradation. That is, it is possible to provide a liquid crystal display device which can adjust the luminance and does not cause liquid crystal deterioration such as generation of flicker.

Further, in the liquid crystal display device according to the present invention, in the above configuration, the scan electrode drive circuit generates a high level voltage of a scan signal;
A low-level voltage generation circuit that generates a low-level voltage of the scanning signal; and a change in the potential difference between the high-level voltage and the low-level voltage of the scanning signal changes the value of the output voltage of the high-level voltage generation circuit and / or A configuration may be adopted in which this is performed by changing the value of the output voltage of the low-level voltage generation circuit.

According to the above configuration, by changing the value of the output voltage of the high-level voltage generating circuit and / or the value of the output voltage of the low-level voltage generating circuit, the high-level voltage and the low-level voltage of the scanning signal are changed. Is changed. The high-level voltage generation circuit and the low-level voltage generation circuit are circuits that generate a predetermined DC voltage, and can be configured by a relatively simple circuit. A liquid crystal display device in which liquid crystal deterioration does not occur can be provided.

Further, the liquid crystal display device according to the present invention, in the above configuration, further comprises a signal electrode drive circuit for supplying a source signal to the switching element, wherein the signal electrode drive circuit is provided by the brightness adjusting means. A configuration may be employed in which the amplitude of the output source signal is changed according to the brightness adjustment.

According to the above arrangement, the brightness is adjusted by changing the amplitude of the source signal in accordance with the brightness adjustment by the brightness adjusting means, and the potential difference between the high level voltage and the low level voltage of the scanning signal is changed. So
It is possible to provide a liquid crystal display device that can accurately adjust luminance and does not cause liquid crystal deterioration.

Further, the liquid crystal display device according to the present invention, in the above structure, further comprises a counter amplitude signal driving circuit for supplying a counter amplitude signal to the counter electrode, wherein the counter amplitude signal driving circuit is provided with the brightness adjusting means. The amplitude of the opposite amplitude signal to be output may be changed in accordance with the brightness adjustment by.

According to the above configuration, the brightness is adjusted by changing the amplitude of the opposite amplitude signal in accordance with the brightness adjustment by the brightness adjusting means, and the potential difference between the high level voltage and the low level voltage of the scanning signal is reduced. Since it is changed, it is possible to provide a liquid crystal display device in which the brightness can be accurately adjusted and the liquid crystal does not deteriorate.

Further, the liquid crystal display device according to the present invention, in the above structure, further comprises a counter amplitude signal driving circuit for supplying a counter amplitude signal to the counter electrode, wherein the counter amplitude signal driving circuit is provided with the brightness adjusting means. The amplitude of the output opposite amplitude signal may be changed in accordance with the luminance adjustment by, and the low level voltage of the scanning signal may be changed in synchronization with the amplitude of the opposite amplitude signal.

According to the above arrangement, the amplitude of the opposite amplitude signal is changed in accordance with the brightness adjustment by the brightness adjusting means, and the low level voltage of the scanning signal is changed in synchronization with the amplitude of the opposite amplitude signal. I have. Here, for example, when the low level voltage of the scanning signal is a constant DC voltage regardless of the amplitude of the counter amplitude signal, the liquid crystal of the switching element is affected by the capacitance between the gate and the drain of the switching element. Degradation, the insulation between the gate and the drain is broken, or the switching element
There is a possibility that a problem such as generation of a leak current when the FF is formed may be caused. On the other hand, as described above, if the low-level voltage of the scanning signal is changed in synchronization with the amplitude of the opposite amplitude signal, it is possible to suppress the occurrence of the above-described problem.

Although the high level voltage of the scanning signal may be changed in synchronization with the amplitude of the opposite amplitude signal, the switching element may be turned on compared to the time when the switching element is turned off. The duration of the scan signal is extremely short, so that the effect of the high level voltage of the scanning signal is very small. Therefore, as described above, only the low-level voltage of the scanning signal is
With the configuration synchronized with the change in the opposing amplitude signal, the above-described problem can be sufficiently suppressed. Further, since a configuration for changing the high-level voltage of the scanning signal is not required, the configuration can be simplified and the cost can be reduced.

It is to be noted that setting the amplitude potential difference in the change of the low level voltage of the scanning signal to be equal to the amplitude potential difference of the opposite amplitude signal more effectively suppresses the above-described problem. It becomes possible.

Further, in the liquid crystal display device according to the present invention, in the above configuration, when changing the low level voltage of the scanning signal, the level on the high voltage side in the voltage waveform of the low level voltage of the scanning signal is fixed. On the other hand, the low-voltage side of the low-level voltage waveform of the scanning signal may be changed in accordance with a change in the amplitude of the opposite amplitude signal.

According to the above arrangement, the high-voltage level of the low-level voltage waveform of the scanning signal is fixed, while the low-voltage level of the low-level voltage voltage waveform of the scanning signal is set to the opposite amplitude. The low level voltage of the scanning signal is changed by changing the amplitude according to the change in the signal amplitude. That is, the potential difference between the high-level voltage and the low-level voltage of the scanning signal is changed by changing only the low-voltage level in the voltage waveform of the low-level voltage of the scanning signal according to the change in the amplitude of the opposite amplitude signal. Therefore, for example, by applying a diode clipping type circuit using a capacitor and a diode to the low-level voltage generator, the above configuration can be realized. That is, with a simple circuit configuration, it is possible to realize a configuration in which the low-level voltage of the scanning signal is changed in synchronization with the amplitude of the opposite amplitude signal.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

The matrix type display device according to this embodiment is an active matrix type liquid crystal display device provided with a switching element for each pixel. FIG. 6 is a circuit diagram schematically illustrating a schematic configuration of the liquid crystal display device. As shown in FIG. 6, the liquid crystal display device includes a liquid crystal display unit 3, a scan electrode drive circuit 1, a signal electrode drive circuit 2, a counter amplitude signal drive circuit 8, and a brightness adjustment unit 9.

The liquid crystal display unit 3 displays an image based on an input image signal. The liquid crystal display unit 3 encloses liquid crystal for modulating light incident from illumination means such as a backlight, and has pixels 4. Is provided. Hereinafter, the configuration of the liquid crystal display unit 3 will be described in more detail.

The liquid crystal display section 3 includes a light-transmitting active matrix substrate on which an active matrix circuit formed by switching elements is formed, and a counter substrate on which a counter electrode is formed facing the active matrix substrate. And a liquid crystal sandwiched between an active matrix substrate and a counter substrate.

A plurality of pixel electrodes 5 are formed in a matrix on the active matrix substrate. The pixel electrodes 5 are usually formed so as to be several hundreds or more in the row direction and the column direction, respectively.

A counter electrode 7 is formed on the counter substrate so as to face the pixel electrodes 5 via the liquid crystal layer. The pixel electrodes 5 and the counter electrode 7 apply a voltage to the liquid crystal layer. Is applied. A predetermined voltage is supplied to the counter electrode 7 from the counter amplitude signal drive circuit 8. In addition,
The counter electrode 7 is generally formed on substantially the entire surface of the counter substrate.

As an active element for selectively driving the pixel electrodes 5, a plurality of switching elements 6 are formed on the active matrix substrate, and are connected to the respective pixel electrodes 5. The above switching element 6
For example, a three-terminal transistor, a two-terminal diode, or the like can be used, but in this embodiment,
As the switching element 6, a thin film transistor (TF
T).

In each of the switching elements 6, a scanning electrode G is connected to a gate portion, and a signal electrode S is connected to a source portion. Scan electrode G ... and signal electrode S ...
Are arranged so as to pass around the pixel electrodes 5 arranged in a matrix and to be orthogonal to each other. Each scan electrode G is connected to the scan electrode drive circuit 1, while
Each signal electrode S is connected to the signal electrode drive circuit 2.

The switching element 6 is driven and controlled by inputting a scanning signal via the scanning electrode G. When the switching element 6 is driven, a video signal is input to the pixel electrode 5 via the signal electrode S.

Here, on the active matrix substrate, each scanning electrode G is connected to switching elements 6 arranged in a row direction, and each signal electrode S
Are the switching elements 6 arranged side by side in the column direction.
It is assumed that they are connected to ... In this case, the image display operation is performed as follows. First, the scan electrode drive circuit 1
Scan electrodes G are sequentially selected for each row, and an ON signal is applied to the selected scan electrodes G. The switching element 6 connected to the scanning electrode G to which the ON signal is applied switches between the signal electrode S and the pixel electrode 5 to a conductive state.
At this time, a signal voltage sent from the signal electrode drive circuit 2 to the signal electrode S is applied to the pixel electrode 5 based on the input video signal. In other words, when the scan electrode G is selected by the scan electrode drive circuit 1, the pixel 4 on this line
.. Are written with a signal voltage based on the video signal.

In accordance with the above signal voltage, a voltage is applied to the liquid crystal between the pixel electrodes 5 and the counter electrode 7, and the alignment state of the liquid crystal changes. As a result, the light transmittance of the liquid crystal changes, and an image based on the image signal is displayed on the display screen including the pixels 4 arranged in a matrix. At the same time, charge is accumulated in the capacitance of the liquid crystal,
After the switching element 6 is turned off, the state in which the light transmittance of the liquid crystal changes due to the electric charge accumulated in the capacitance is maintained.

In the liquid crystal display device having the above configuration, the brightness is adjusted by the source signal applied to the pixel electrode 5 and the counter electrode 7 in accordance with the output from the brightness adjusting means 9.
This is performed by changing the voltage applied to the liquid crystal according to the opposing amplitude signal applied to the liquid crystal. Since the liquid crystal has the property of deteriorating when a voltage of the same polarity is continuously applied, in the above liquid crystal display device, the polarity of the voltage applied to the liquid crystal by the source signal and the opposite amplitude signal is increased. Is inverted for each frame, for example, to prevent the deterioration of the liquid crystal.

On the other hand, as described above, the switching element 6 composed of a TFT or the like has a parasitic capacitance. The potential difference between the pixel electrode 5 connected to the switching element 6 and the counter electrode 7 is reduced by ΔV due to the parasitic capacitance after the switching element 6 is turned off. That is, when a positive voltage is applied to the liquid crystal, the absolute value of the potential difference decreases by ΔV after the TFT is turned off, and when a negative voltage is applied, the absolute value of the potential difference is reduced. The value increases by ΔV. Since the light transmittance of the liquid crystal changes with the change in the absolute value of the potential difference between the pixel electrode 5 and the counter electrode 7, flicker occurs due to the change, and in some cases, screen burn-in occurs. There is a problem that the liquid crystal is deteriorated.

After the switching element 6 is turned off,
The parasitic capacitance generated in the switching element 6 is generated between the gate and the drain of the switching element 6. Therefore, the high-level voltage VGH of the scanning signal input from the scanning electrode G when the switching element 6 is turned on, and the low-level voltage VGL of the scanning signal input from the scanning electrode G when the switching element 6 is turned off. The magnitude of the parasitic capacitance changes in accordance with the magnitude of the difference between. That is, the magnitude of ΔV changes according to the magnitude of the potential difference obtained by VGH−VGL.

Further, even if the amplitude of the source signal and the amplitude of the opposite amplitude signal are changed, ΔV will change. This is because the dielectric constant of the liquid crystal is higher than the pixel electrode 5 and the counter electrode 7.
This is because the magnitude of ΔV varies according to the magnitude of the potential difference between the electrodes due to this effect.

As described above, the liquid crystal display device according to the present embodiment has a luminance adjustment function, and ΔV changes by performing the luminance adjustment. In the voltage applied between the electrodes, an intermediate voltage value between the positive polarity voltage value and the negative polarity voltage value is referred to as a center value, and the potential difference between the pixel electrode 5 and the counter electrode 7 is defined as the center value. The optimum center value that minimizes the change in the absolute value changes with the change in ΔV. Therefore, in the liquid crystal display device according to the present embodiment, the change in ΔV is suppressed by adjusting the magnitude of the potential difference obtained by VGH−VGL that determines the magnitude of ΔV.

FIG. 1 shows a high-level voltage VGH and a low-level voltage V
FIG. 3 is a circuit diagram schematically illustrating a circuit that generates a GL. As shown in FIG. 1, this circuit includes an operational amplifier A1, and a VGH generating circuit including resistors R1, R2, R3, and R4, and an operational amplifier A2 and a VGL generating circuit including resistors R5, R6, R7, and R8. ing.

First, the VGH creation circuit will be described.
The inverting input terminal of the operational amplifier A1 is connected via a resistor R2 to
The brightness adjustment voltage output from the brightness adjustment means 9 is input. The value of the brightness adjustment voltage is set according to the contrast value set by the brightness adjustment means 9. Further, the output from the output terminal of the operational amplifier A1 is input to the inverting input terminal of the operational amplifier A1 via the resistor R1.

On the other hand, the DC voltage 1 is input to the non-inverting input terminal of the operational amplifier A1 via the resistor R3.
Further, the non-inverting input terminal of the operational amplifier A1 is grounded via the resistor R4. Then, the high-level voltage VGH of the scanning signal is output from the output terminal of the operational amplifier A1.

In the VGH generating circuit having such a configuration, the reference value of the voltage of the VGH is set by the DC voltage 1 and the ratio between the resistors R3 and R4. Then, in the operational amplifier A1, the reference value of the VGH voltage is amplified by − (R1 / R2) × the luminance adjustment voltage (not necessarily the inversion amplification). In other words, the voltage for the amplification changes with the change in the brightness adjustment voltage, and as a result, V
The voltage of GH will change.

Next, the VGL creation circuit will be described.
The inverting input terminal of the operational amplifier A2 is connected via a resistor R6 to
The brightness adjustment voltage has been input. Furthermore, operational amplifier A
The output from the output terminal of the operational amplifier A2 is input to the inverting input terminal 2 via a resistor R5.

On the other hand, the DC voltage 2 is input to the non-inverting input terminal of the operational amplifier A2 via the resistor R7.
Further, the non-inverting input terminal of the operational amplifier A2 is grounded via the resistor R8. Then, the low-level voltage VGL of the scanning signal is output from the output terminal of the operational amplifier A2.

In the VGL generating circuit having such a configuration, the reference value of the voltage of VGL is set by the DC voltage 2 and the ratio between the resistors R7 and R8. Then, in the operational amplifier A2, the reference value of the VGL voltage is amplified by-(R5 / R6) × luminance adjustment voltage.
That is, the voltage of the amplification changes with the change of the brightness adjustment voltage, and the voltage of VGL changes accordingly.

With the circuit having the above configuration, even when the brightness is adjusted, VGH and VG
By changing the voltage of L, the potential difference composed of VGH-VGL is adjusted, and the change of the value of ΔV can be suppressed. Therefore, it is possible to maintain the value of ΔV at an optimal value for optimizing the center value.

In the above configuration, both the VGH generating circuit and the VGL generating circuit are provided, and VGH and VGL are provided.
VGH-V
Although the potential difference composed of GL was adjusted, only one of the VGH creation circuit and the VGL creation circuit was provided, and the VG
A configuration in which the voltage value of only one of H and VGL is changed may be used. Even in such a configuration, VG
Since the potential difference composed of H-VGL can be adjusted, it is possible to suppress a change in the value of ΔV.

FIG. 2 shows a source signal power source generating circuit for adjusting the luminance by changing the amplitude of the source signal in the signal electrode driving circuit 2 in addition to the VGH generating circuit and VGL generating circuit shown in FIG. 1 is a circuit diagram schematically showing a circuit including: In the configuration shown in FIG. 2, the grayscale power supply V for the source signal is used as the source signal power generation circuit.
A circuit for generating 0 and V5 is provided. This source signal power generation circuit includes an operational amplifier A3, a resistor R9
A circuit for generating a gradation power supply V0 including R10, R11, R12 and a variable resistor VR1, an operational amplifier A4, resistors R13, R14, R15, R16, and a variable resistor V
And a circuit for generating a gradation power supply V5 composed of R2.

The above-mentioned gradation power supply V0 indicates the power supply level of the gradation voltage indicating the black level gradation, and the gradation power supply V5 indicates the power supply level of the gradation voltage indicating the white level gradation. Shall be shown. In the configuration shown in FIG.
Although a circuit for generating the gray scale power supplies V0 and V5 is described, actually, the gray scale power supplies V1 to V4 indicating the gray scale are described.
Is further provided. Also,
The number of gray scale power supplies is not limited to this, and the same configuration is obtained even when an arbitrary number of gray scale power supplies are provided. As described above, by setting the power supply voltage by using a plurality of gray-scale power supplies, it is possible to appropriately set the γ characteristic in the relationship between the voltage applied to the liquid crystal and the light transmittance of the liquid crystal.

First, a circuit for generating the gradation power supply V0 will be described. The inverting input terminal of the operational amplifier A3 has a resistor R
The luminance adjustment voltage is input via the resistor 11 and the resistor R9 in series. The value of the brightness adjustment voltage is set according to the contrast value set by the contrast adjustment means provided in the liquid crystal display device. Further, the output from the output terminal of the operational amplifier A3 is input to the inverting input terminal of the operational amplifier A3 via the resistors R10 and R9 in series. Further, a polarity inversion signal is input to the inverting input terminal of the operational amplifier A3 via the resistor R12.

On the other hand, the DC voltage 3 is input to the non-inverting input terminal of the operational amplifier A3 via the variable resistor VR1. Then, the gradation power supply V0 for the source signal is output from the output terminal of the operational amplifier A3.

In the circuit for generating the gradation power supply V0 having such a configuration, the reference DC voltage of the gradation power supply V0 is set by the variable resistor VR1 and the DC voltage 3. Then, in the operational amplifier A3, the polarity inversion signal is amplified according to the change in the brightness adjustment voltage, and the brightness is adjusted by this.

Next, a circuit for generating the gradation power supply V5 will be described. The inverting input terminal of the operational amplifier A4 has a resistor R
The luminance adjustment voltage is input via the resistor 15 and the resistor R13 in series. Further, the output from the output terminal of the operational amplifier A4 is connected to the inverting input terminal of the operational amplifier A4 by the resistor R1.
4 and a resistor R13 in series. Further, a resistor R is connected to the inverting input terminal of the operational amplifier A4.
A polarity inversion signal is input via a line 16.

On the other hand, the DC voltage 4 is input to the non-inverting input terminal of the operational amplifier A4 via the variable resistor VR2. Then, the gray scale power supply V5 for the source signal is output from the output terminal of the operational amplifier A4.

In the circuit for generating the gradation power supply V5 having such a configuration, the reference DC voltage of the gradation power supply V5 is set by the variable resistor VR2 and the DC voltage 4. Then, in the operational amplifier A4, the polarity inversion signal is amplified according to the change in the brightness adjustment voltage, and the brightness is adjusted by this.

As described above, the gradation power supply for the source signal is generated, and the VGH generation circuit and the VGL generation circuit generate the high-level voltage V
GH and the low level voltage VGL are generated. Thus, even when the brightness is adjusted by changing the amplitude of the source signal, the potential difference between VGH-VGL is adjusted by changing the voltages of VGH and VGL, and the change in the value of ΔV is suppressed. It becomes possible. Therefore, it is possible to maintain the value of ΔV at an optimal value for optimizing the center value.

FIG. 3 shows that, in addition to the VGH generating circuit and the VGL generating circuit shown in FIG. 1, the opposite amplitude signal driving circuit 8 changes the amplitude of the opposite amplitude signal in a state where the amplitude of the source signal is fixed. FIG. 2 is a circuit diagram schematically illustrating a circuit including a counter amplitude signal generation circuit for performing luminance adjustment. The counter amplitude signal generating circuit includes an operational amplifier A5, resistors R17, R18, R19, R20, and a variable resistor VR3.

The inverting input terminal of the operational amplifier A5 has a resistor R
A luminance adjustment voltage is input via a resistor 19 and a resistor R17 in series. The value of the brightness adjustment voltage is set according to the contrast value set by the contrast adjustment means provided in the liquid crystal display device. Further, the output from the output terminal of the operational amplifier A5 is input to the inverting input terminal of the operational amplifier A5 via the resistors R18 and R17 in series. Further, a polarity inversion signal is input to the inverting input terminal of the operational amplifier A5 via the resistor R20.

On the other hand, the DC voltage 5 is input to the non-inverting input terminal of the operational amplifier A5 via the variable resistor VR3. Then, a counter amplitude signal is output from the output terminal of the operational amplifier A5.

In the counter amplitude signal generating circuit having such a configuration, the reference DC voltage of the counter amplitude signal is set by the variable resistor VR3 and the DC voltage 5. Then, in the operational amplifier A5, the polarity inversion signal is amplified according to the change in the brightness adjustment voltage, and the brightness is adjusted accordingly.

As described above, the opposite amplitude signal is generated, and the high-level voltage VGH and the low-level voltage VGL of the scanning signal are generated in the VGH generation circuit and the VGL generation circuit. Thus, even when the brightness is adjusted by changing the amplitude of the opposite amplitude signal, the potential difference between VGH-VGL is adjusted by changing the voltages of VGH and VGL, and the change in the value of ΔV is suppressed. It is possible to do. Therefore, it is possible to maintain the value of ΔV at an optimal value for optimizing the center value.

FIG. 4 shows a gate-off voltage that changes in synchronization with a change in the amplitude of the opposing amplitude signal, that is, a low-level voltage VGL of the scanning signal when the amplitude of the opposing amplitude signal is changed by brightness adjustment. FIG. 2 is a circuit diagram illustrating an outline of a circuit. This circuit includes a capacitor C1 and a diode D1, and one electrode of the capacitor C1 includes:
The opposite amplitude signal is input. The other electrode of the capacitor C1 is connected to the anode side of the diode D1 and outputs a voltage as VGL. The DC voltage 6 is input to the cathode side of the diode D1. Note that a ceramic capacitor, an electrolytic capacitor, or the like is used as the capacitor C1.

In the circuit having the above-described configuration, in order to make the opposite amplitude signal a floating gate, the opposite amplitude signal is input to the capacitor C1 and the DC voltage 6 is input via the diode D1. Re-biased. This makes it possible to output a VGL that changes in synchronization with a change in the amplitude of the opposite amplitude signal, that is, a floating VGL. As described above, the bias method of changing only the DC level of the amplitude of the input signal by the configuration including the capacitor and the diode is called a diode clip method.

FIG. 5 shows a voltage waveform of VGL output by the circuit having the above configuration. As shown in FIG.
The voltage raised by the DC voltage 6 clipped by the diode D1 is equal to the floating VGL.
Of the high-voltage side of the voltage waveform of FIG.
Voltage. Then, an amplitude of the VGL that swings in a floating state below this High voltage is generated with the same potential difference as the amplitude potential difference due to the opposite amplitude signal.

In FIG. 5, VA is the width of the voltage clipped by the diode D1, VB is the amplitude of the voltage of the opposite amplitude signal, and VC is the DC level of VGL due to the change in the voltage of the opposite amplitude signal. The change width (VD) of (center value) is VGL due to a change in the voltage of the opposite amplitude signal.
The amplitude of the voltage amplitude is shown.

In the circuit as described above, when the amplitude of the opposite amplitude signal increases due to the luminance adjustment, only the low-voltage level in the VGL voltage waveform, that is, only the Low voltage decreases. As a result, the center value of VGL decreases. Conversely, when the amplitude of the opposing amplitude signal decreases, only the Low voltage increases, thereby increasing the center value of VGL.

As described above, according to the circuit shown in FIG. 4, when the amplitude of the opposite amplitude signal increases in accordance with the luminance adjustment, the center value of VGL decreases, and when the amplitude of the opposite amplitude signal decreases, VGL decreases. Will be higher. Therefore, even if the potential of VGH is fixed, the potential difference between VGH and VGL is adjusted, so that the value of ΔV can be properly corrected.

As another example of the bias method, there is a resistance division method. In this method, the input DC voltage is the center value of the output amplitude voltage. That is, when this method is applied to the above configuration, when the amplitude voltage of the opposite amplitude signal changes, the amplitude of VGL also changes, but its DC level (center value) does not change. Therefore, since the center value of VGL itself does not change, it is impossible to adjust the potential difference between VGH-VGL.

[0082]

As described above, the liquid crystal display device according to the present invention is arranged so that pixel electrodes provided in a matrix on an active matrix substrate are opposed to the active matrix substrate via a liquid crystal layer. In a liquid crystal display device that changes the light transmittance of the liquid crystal by applying a voltage to the liquid crystal between the counter electrode provided on the counter substrate and displays an image, the liquid crystal display device is connected to each of the above pixel electrodes. A switching element, a scanning electrode driving circuit for supplying a scanning signal to the switching element, and a luminance adjusting unit for adjusting luminance when displaying an image, the scanning electrode driving circuit, In this configuration, the potential difference between the high-level voltage and the low-level voltage of the scanning signal is changed in accordance with the brightness adjustment by the brightness adjustment unit.

Thus, even when the brightness is adjusted by the brightness adjusting means, the change in ΔV is achieved by changing the potential difference between the high-level voltage and the low-level voltage of the scanning signal that determines the magnitude of ΔV. Can be suppressed. Therefore, even if the luminance is adjusted, the amount of change in ΔV can be reduced, and the center value of the electrode potential can be optimized according to each gradation so as to be suitable for the value of ΔV. That is, there is an effect that it is possible to provide a liquid crystal display device capable of adjusting luminance and free from deterioration of liquid crystal such as generation of flicker.

Further, in the liquid crystal display device according to the present invention, the scan electrode drive circuit includes a high level voltage generation circuit for generating a high level voltage of the scan signal, and a low level voltage generation circuit for generating a low level voltage of the scan signal. A change in the potential difference between the high-level voltage and the low-level voltage of the scanning signal changes the value of the output voltage of the high-level voltage generation circuit and / or the value of the output voltage of the low-level voltage generation circuit Alternatively, the configuration may be performed by the following.

Thus, in addition to the effects of the above configuration, the high-level voltage generation circuit and the low-level voltage generation circuit are circuits for generating a predetermined DC voltage, and can be configured by relatively simple circuits. Therefore, it is possible to provide a liquid crystal display device in which the brightness is adjusted and the liquid crystal is not deteriorated by an inexpensive circuit configuration.

Further, the liquid crystal display device according to the present invention further comprises a signal electrode drive circuit for supplying a source signal to the switching element, wherein the signal electrode drive circuit is adapted to perform brightness adjustment by the brightness adjustment means. , The amplitude of the output source signal may be changed.

Thus, in addition to the effect of the above configuration, the luminance is adjusted by changing the amplitude of the source signal according to the luminance adjustment by the luminance adjusting means, and the high-level voltage and the low-level voltage of the scanning signal are adjusted. This makes it possible to provide a liquid crystal display device in which the brightness can be accurately adjusted and the liquid crystal display device is free from deterioration of the liquid crystal.

Further, the liquid crystal display device according to the present invention further comprises a counter amplitude signal drive circuit for supplying a counter amplitude signal to the counter electrode, wherein the counter amplitude signal drive circuit responds to brightness adjustment by the brightness adjustment means. Thus, the amplitude of the output opposite amplitude signal may be changed.

Thus, in addition to the effect of the above configuration, the brightness is adjusted by changing the amplitude of the opposite amplitude signal in accordance with the brightness adjustment by the brightness adjusting means, and the high level voltage and low level of the scanning signal are adjusted. Since the potential difference from the voltage is changed, it is possible to accurately adjust the luminance and to provide a liquid crystal display device in which liquid crystal deterioration does not occur.

Further, the liquid crystal display device according to the present invention, in the above structure, further comprises a counter amplitude signal driving circuit for supplying a counter amplitude signal to the counter electrode, wherein the counter amplitude signal driving circuit is provided with the brightness adjusting means. The amplitude of the output opposite amplitude signal may be changed in accordance with the luminance adjustment by, and the low level voltage of the scanning signal may be changed in synchronization with the amplitude of the opposite amplitude signal.

Thus, in addition to the effect of the above configuration, for example, the gate portion of the switching element, which is generated when the low level voltage of the scanning signal is a constant DC voltage regardless of the amplitude of the opposite amplitude signal, is obtained. Degradation of the liquid crystal occurs due to the effect of the capacitance between the drain part, or the insulation between the gate part and the drain part is broken,
This has the effect of suppressing the occurrence of problems such as the occurrence of leakage current when the switching element is turned off.

Further, in the liquid crystal display device according to the present invention, in the above configuration, when changing the low level voltage of the scanning signal, the level on the high voltage side in the voltage waveform of the low level voltage of the scanning signal is fixed. On the other hand, the low-voltage side of the low-level voltage waveform of the scanning signal may be changed in accordance with a change in the amplitude of the opposite amplitude signal.

Thus, in addition to the effects of the above-described configuration, by applying a simple circuit configuration, for example, a diode clipping type circuit using a capacitor and a diode to the low-level voltage generation unit, the scanning signal low level can be obtained. There is an effect that a configuration in which the level voltage is changed in synchronization with the amplitude of the opposite amplitude signal can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram schematically illustrating a circuit for generating a high-level voltage VGH and a low-level voltage VGL of a scanning signal provided in a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram schematically showing a circuit including a source signal power generation circuit in addition to the VGH generation circuit and the VGL generation circuit shown in FIG. 1;

FIG. 3 is a circuit diagram schematically showing a circuit including a counter amplitude signal generation circuit in addition to the VGH generation circuit and the VGL generation circuit shown in FIG. 1;

FIG. 4 is a circuit diagram schematically showing a circuit for generating a low-level voltage VGL having a floating gate when the amplitude of a counter amplitude signal is changed by luminance adjustment.

FIG. 5 is a waveform chart showing a voltage waveform of VGL output by the circuit shown in FIG. 4;

FIG. 6 is a circuit diagram schematically illustrating a schematic configuration of the liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Scan electrode drive circuit 2 Signal electrode drive circuit 3 Liquid crystal display part 4 Pixel 5 Pixel electrode 6 Switching element 7 Counter electrode G Scan electrode S Signal electrode A1-A6 Operational amplifier R1-R20 Resistance VR1-VR3 Variable resistance C1 Capacitor D1 Diode

Continued on the front page F-term (reference) 2H093 NA16 NB07 NB11 NB12 NC03 NC09 NC11 NC18 NC21 NC34 ND07 ND10 ND12 ND35 ND47 5C006 AA22 AC02 AC24 AC25 AC28 AF51 AF52 BB16 BC03 BC06 BC13 BF24 BF25 BF42 EC05 EC09 FA23 DD33 DD05 EE28 FF12 GG05 JJ02 JJ03 JJ04 KK02

Claims (6)

[Claims] An image display device comprising: a pixel electrode provided in a matrix on an active matrix substrate; and a counter electrode provided on a counter substrate disposed to face the active matrix substrate via a liquid crystal layer. In a liquid crystal display device that displays an image by changing the light transmittance of the liquid crystal by applying a voltage to the liquid crystal, a switching element connected to each of the pixel electrodes, and a scanning signal to the switching element A scanning electrode driving circuit for supplying the image signal, and a luminance adjusting unit for adjusting luminance when displaying an image. The scanning electrode driving circuit controls a high level of a scanning signal according to the luminance adjustment by the luminance adjusting unit. A liquid crystal display device wherein a potential difference between a level voltage and a low level voltage is changed. 2. The scanning electrode driving circuit according to claim 1, further comprising: a high level voltage generating circuit for generating a high level voltage of the scanning signal; and a low level voltage generating circuit for generating a low level voltage of the scanning signal. The change in the potential difference between the high-level voltage and the low-level voltage is performed by changing the value of the output voltage of the high-level voltage generation circuit and / or the value of the output voltage of the low-level voltage generation circuit. The liquid crystal display device according to claim 1. 3. A signal electrode driving circuit for supplying a source signal to the switching element, wherein the signal electrode driving circuit changes an amplitude of an output source signal in accordance with luminance adjustment by the luminance adjusting means. 3. The liquid crystal display device according to claim 1, wherein 4. An apparatus according to claim 1, further comprising a counter amplitude signal driving circuit for supplying a counter amplitude signal to said counter electrode, wherein said counter amplitude signal driving circuit adjusts the brightness by said brightness adjusting means.
3. The liquid crystal display device according to claim 1, wherein the amplitude of the output opposite amplitude signal is changed. 5. An apparatus according to claim 1, further comprising a counter amplitude signal driving circuit for supplying a counter amplitude signal to said counter electrode, wherein said counter amplitude signal driving circuit adjusts the brightness by said brightness adjusting means.
2. The liquid crystal display device according to claim 1, wherein the amplitude of the output opposite amplitude signal is changed, and the low level voltage of the scanning signal is changed in synchronization with the amplitude of the opposite amplitude signal. 6. When changing the low-level voltage of the scanning signal, the high-voltage level of the low-level voltage waveform of the scanning signal is fixed, while the low-level voltage of the low-level voltage waveform of the scanning signal is fixed. 6. The liquid crystal display device according to claim 5, wherein the level on the side is changed according to a change in the amplitude of the opposite amplitude signal.