JPH06348235A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To make it possible to freely adjust the gradation characteristics of the liquid crystal display device at all times. CONSTITUTION:The gradation voltage generating circuit of the liquid crystal display device is composed of plural fixed resistors R1, R2, R3,...R14 connected in series between a reference voltage VH of a high potential and a reference voltage V2 of a low potential and voltage varying means VR2 to VR5 which vary the voltages at the connection points among these fixed resistors between the reference voltage VH of the high potential and the reference voltage VL of the low potential so that the voltages at the connection points among the fixed resistors are formed as gradation signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-tone liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device has been attracting attention as a flat panel display, and a multi-tone liquid crystal display device has been developed and put into practical use from the tendency of high image quality in both monochrome and color.

FIG. 4 shows a schematic structure of a conventional multi-gradation liquid crystal display device of the active matrix driving system, where 1 is an X signal line X _1, X ₂ , X ₃ , ... X _m and a Y signal line. Y ₁ ,
A liquid crystal panel provided with a thin film transistor (TFT) at an intersection with Y ₂ , Y ₃ ... Y _n , 2 selects one grayscale signal from a plurality of grayscale signals based on a data signal of an image to be displayed. Then, a horizontal driver 3 for outputting to the X signal line of the liquid crystal panel 1, a vertical driver 3 for outputting a gate signal as a scanning signal for scanning the liquid crystal panel 1 to the Y signal line of the liquid crystal panel 1, and a plurality of gradation voltages 4 To generate gradation signals V _{0 to} V
_{This is} a gradation voltage generation circuit that outputs ₇ (for 8 gradations). In addition to the gradation signals V _{0 to} V ₇ , the horizontal driver 2 has a vertical synchronizing signal S _v and a data signal S of an image to be displayed.
_d , the start signal S _s is input, the gate voltage V _G is applied to the vertical driver 3, and the horizontal synchronizing signal _Sh and the clock signal CLK are input.

When a plurality of grayscale signals V _{0 to} V ₇ output from the grayscale voltage generation circuit 4 are input to the horizontal driver 2, the horizontal driver 2 outputs one grayscale signal based on the data signal S _d. Is stored as a gradation signal for one line, and the gradation signal is output to the liquid crystal panel 1 by the vertical synchronizing signal S _v and the start signal S _s . This gradation signal is supplied to the drain terminal of the thin film transistor of the liquid crystal panel 1.

On the other hand, the Y signal line Y from the vertical driver 3
_{1, Y 2, Y 3,} ··· Y n is connected to the gate terminals of the liquid crystal panel 1 TFT, horizontal sync signal S _h in synchronization with the gate signal generated based on the clock signal the scanning signal As a result, the thin film transistors connected to the respective Y signal lines are sequentially turned on. One screen is completed when the gate signals are supplied to all the Y signal lines.

FIG. 5 shows an example of the circuit configuration of the gradation voltage generating circuit 4 shown in FIG. In this example, eight kinds of gradation signals V _{0 to} V ₇ are output in order to express eight gradations, but 16 kinds of gradation voltage levels are generated because of AC drive.

The gradation voltage generating circuit 4 has 14 fixed resistors R ₁ , R ₂ , R ₃ ... R ₁₄ between two reference voltages V _H and V _L (V _H > V _L ). And one variable resistor VR ₁
Are connected in series, and different voltages V _0H , V _1H , V _2H ... V _7H and V _0L , V obtained from the connection point between these fixed resistors and the connection point between the fixed resistor and the variable resistor are connected.
_1L, a switch 10 for switching the reverse polarity voltage (eg V _0H and V _0L) at the same potential among the V _2L ··· V _7L,
A buffer circuit 11 is connected in series corresponding to each switch 10. When the switch 10 is switched in synchronization with the horizontal synchronizing signal, the gradation signals V _{0 to} V ₇ of opposite polarities are alternately obtained in the form of a rectangular wave. For example, the gradation signal V ₀ is a rectangular wave with voltage levels V _0H and V _0L . The gradation expression is determined by the voltage level of the gradation signal.

[0008]

In the above-mentioned conventional liquid crystal display device, the voltage level of the grayscale signal that determines the grayscale characteristic is for voltage division connected in series between the reference voltages _VH and _VL . Since it is determined by the resistance values of the fixed resistors R _{1 to} R ₁₄ , once designed and the device is assembled, the gradation characteristics cannot be arbitrarily changed thereafter.

However, in a color television or a display of a personal computer, the appearance of colors may change depending on the angle at which the user looks at the screen (called the viewing angle). In such a case, the gradation of the image is changed. It may be desired to adjust the color appearance to an optimum state by adjustment, but there is a problem that the conventional liquid crystal display device cannot do so. Further, in the final stage of manufacturing, it is not possible to correct the product variation of the liquid crystal panel or the tone variation due to the manufacturing error of the voltage dividing fixed resistance value.

The present invention has been made in view of the above points, and it is an object of the present invention to make it possible to freely adjust the gradation characteristics of a liquid crystal display device at any time.

[0011]

In order to achieve the above-mentioned object, the present invention connects a gray scale voltage generating circuit of a liquid crystal display device in series between a high potential reference voltage and a low potential reference voltage. Connected between the fixed resistors, and a plurality of fixed resistors, and a voltage varying means for varying the voltage at the connection point between the fixed resistors between the high-potential reference voltage and the low-potential reference voltage. The voltage at the point is used as the gradation signal.

[0012]

According to the present invention, by adjusting the voltage varying means, the voltage between the fixed resistors can be changed to a value different from the voltage determined by the fixed resistors, so that the gradation voltage can be changed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

The schematic structure of the liquid crystal display device according to the present invention is the same as that shown in FIG. 4, and therefore is not shown. However, the gradation voltage generating circuit of the liquid crystal display device of the present invention is as shown in FIG. The gradation voltage generating circuit shown in FIG. 1 is assumed to generate gradation signals V _{0 to} V ₇ for 8-gradation display. The gradation voltage generating circuit includes fixed resistors R _{1 to} R between the reference voltages V _H and V _L.
14 and the variable resistor VR ₁ are connected in series, and the variable resistors VR ₂ , VR ₃ , VR ₄ and VR ₄ are connected in series,
The operational amplifier 12 is connected between the connection point between the fixed resistors R ₂ and R ₃ and the variable resistance VR _2, and the operational amplifier 13 is connected between the connection point between the fixed resistors R ₅ and R ₆ and the variable resistance VR _3. The operational amplifier 14 is connected between the connection point between the fixed resistors R ₁₀ and R ₁₁ and the variable resistor VR _4, and the operational amplifier 15 is connected between the connection point between the fixed resistors R ₁₃ and R ₁₄ and the variable resistor VR _5. Connect the fixed resistor and the fixed resistor and the variable resistor V
Different voltages V _0H , V _1H , V obtained from the connection point with R _1.
Corresponding to the switch 10 for switching the voltage (for example, V _0H and V _0L ) of the same potential and the opposite polarity from among _2H ... V _7H and V _0L , V _1L , V _2L ... V _7L And a buffer circuit 11 are connected in series.

In this gradation voltage generating circuit, the reference voltage V _H is output as it is to the gradation voltage V _0H , and the gradation voltage V 0
_The voltage divided by the fixed resistor R ₁ is output to _1H , but the grayscale voltages V _2H , V _3H , and V _4H depend on the output voltage of the operational amplifier 12, and are connected to the input side of this operational amplifier 12. The output voltage changes depending on the resistance value of the variable resistor VR ₂ . That is, the gradation voltages V _2H , V _3H , and V _4H can be adjusted by adjusting the resistance value of the variable resistor VR ₂ . Similarly, a variable gray scale voltage V _5H by adjusting the resistance values of the resistors VR _3, V _6H, can adjust the V _7H, gradation voltages V _4L by adjusting the resistance value of the variable resistor VR ₄ , V _3L , V _2L can be adjusted, and the gradation voltage V _1L can be adjusted by adjusting the resistance value of the variable resistor VR ₅ . The gradation voltages V _7L , V _6L , and V _5L can be adjusted by the variable resistor VR ₁ .

As described above, the variable resistors VR ₁ , VR ₂ , VR
By adjusting the resistance values of ₃ , VR ₄ and VR ₅ , the voltage level of the gradation signal, that is, the gradation voltage can be arbitrarily adjusted, and the gradation characteristics can be freely changed.

As shown in FIG. 2, for example, the gradation characteristic is γ.
When (gamma) = 3 is set, the gradation characteristic is γ =
To change to 4, the following adjustment is made to the gradation voltage when the gradation characteristic is γ = 3.

The gradation voltage V _{2H is set} to 0. V by the variable resistor VR ₂ .
Lower 25V.

The gradation voltage V _{5H is set} to 0. V by the variable resistor VR ₃ .
Lower 125V.

The gradation voltage V _{7L is set} to 0. by the variable resistor VR ₁ .
Raise 125V.

The gradation voltage V _{4L is set} to 0. by the variable resistor VR ₄ .
Raise 25V.

The result is shown as "the present invention" in FIG. 2, and a gradation characteristic close to the gradation characteristic set as γ = 4 from the beginning can be obtained.

FIG. 3 shows a gradation voltage generating circuit of a liquid crystal display device as another embodiment of the present invention. The gradation voltage generating circuit of this embodiment generates a gradation signal of 16 gradations, and like the gradation voltage generating circuit shown in FIG. 1, it divides between the reference voltages V _H and V _L. Fixed resistors for pressure R ₁ , R ₂ , R
₃ , ... R ₂₇ , R ₂₈ and variable resistor VR ₁ are connected in series, and variable resistors VR ₂ , VR ₃ , VR ₄ , V
R ₅ is connected in series, and operational amplifiers 16, 17, 18 and 19 are connected between these two series circuits as shown in the figure,
Different voltages V _0H , V _1H , V _2H obtained from the connection point between the fixed resistors and the connection point between the fixed resistor and the variable resistor VR _1.
A switch 10 for switching between voltages having the same potential but opposite polarities (for example, V _0H and V _0L ) among V _15H and V _0L , V _1L , V _2L, ... V _15L , and a buffer circuit corresponding to each switch 10. 11 and 11 are connected in series.

According to this circuit, the voltage levels of the gradation voltages V _{4H to} V _9H can be changed by adjusting the resistance value of the variable resistor VR ₂ , and the resistance value of the variable resistor VR ₃ can be adjusted. Can change the voltage levels of the gradation voltages V _{10H to} V _{15H, and} the voltage levels of the gradation voltages V _{9L to} V _4L can be changed by adjusting the resistance value of the variable resistor VR _4. it is possible to change the voltage level of the gradation voltages V _3L ~V _1L by adjusting the resistance value of the resistor VR _5. The gradation voltages V _{15L to} V _10L can be adjusted by the variable resistor VR ₁ .

As described above, the variable resistors VR ₁ , VR ₂ , VR
It is shown in FIG. 1 that the voltage level of the gradation signal, that is, the gradation voltage can be arbitrarily adjusted by adjusting the resistance values of ₃ , VR ₄ and VR ₅ , and the gradation characteristics can be freely changed. Same as the embodiment.

In the above two embodiments, the operational amplifier is used for adjusting the gradation voltage, but the present invention is not limited to this, and a circuit or element whose output voltage can be changed by external adjustment such as a DC / DC converter is used. be able to. Further, the present invention can be applied to any liquid crystal display device, either monochrome or color, and the driving method thereof is not limited to the active matrix driving method or the AC driving method.

[0027]

As described above, according to the present invention,
Since the gradation voltage can be changed freely even after the liquid crystal display device is assembled, variations in gradation characteristics due to variations in the product of the liquid crystal panel or variations in the resistance value of the fixed resistor for voltage division, etc. Also, it can be arbitrarily corrected.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a gradation voltage generating circuit of a liquid crystal display device as an embodiment of the present invention.

FIG. 2 shows a result of adjusting gradation characteristics of the liquid crystal display device according to the present invention.

FIG. 3 is a circuit diagram of a gradation voltage generating circuit of a liquid crystal display device as another embodiment of the present invention.

FIG. 4 is a block diagram showing a schematic configuration of the present invention and a conventional liquid crystal display device.

FIG. 5 is a circuit diagram of an example of a grayscale voltage generation circuit of a conventional liquid crystal display device.

[Explanation of symbols]

1 liquid crystal panel 2 horizontal driver 3 vertical driver 4 gray scale voltage generation circuit 10 switch 11 buffer circuit V ₀ , V ₁ , V ₂ ... V ₇ gray scale signal R ₁ , R ₂ , ... R ₁₄ fixed resistance VR ₁ , VR ₂ , VR ₃ , VR ₄ , VR ₅ variable resistors

Claims (5)

[Claims] 1. A liquid crystal panel having an X signal line and a Y signal line, and one gradation signal is generated based on a data signal of an image to be displayed from a plurality of gradation signals output from a gradation voltage generation circuit. In the liquid crystal display device including a horizontal driver for selecting and outputting to the X signal line of the liquid crystal panel, and a vertical driver for outputting a scanning signal of the liquid crystal panel to the Y signal line of the liquid crystal panel, the grayscale voltage generating circuit includes A plurality of fixed resistors connected in series between a high-potential reference voltage and a low-potential reference voltage, and a voltage at a connection point between the fixed resistors as the high-potential reference voltage and the low-potential reference voltage. A liquid crystal display device which outputs a voltage at a connection point between the fixed resistors as a gradation signal. 2. The liquid crystal display device according to claim 1, wherein a variable resistor is connected in series with a plurality of fixed resistors of the gradation voltage generating circuit. 3. A variable resistor, wherein the voltage variable means is connected between a high-potential reference voltage and a low-potential reference voltage, and one input terminal is connected to a voltage variable terminal of the variable resistor and an output terminal. 2. The liquid crystal display device according to claim 1, further comprising an operational amplifier connected to a predetermined connection point between the plurality of fixed resistors. 4. The liquid crystal display device according to claim 1, wherein the voltage at the connection point between the fixed resistors is output as a gradation signal via a buffer circuit. 5. A plurality of sets of grayscale voltages having the same potential and opposite polarities are generated at the connection points by the plurality of fixed resistors, and each grayscale is synchronized with a predetermined repeating cycle of a data signal of an image to be displayed. The liquid crystal display device according to claim 1, wherein a switch that alternately switches the polarities of the voltages is connected to the preceding stage of the buffer circuit.