KR100830096B1 - Liquid crystal display device and driving method thereof - Google Patents

Abstract

The present invention relates to a liquid crystal display device and a driving method thereof in which a user can adjust a desired viewing angle and contrast ratio.

The liquid crystal display according to the present invention includes a DC voltage source for generating a DC voltage, and a voltage level adjuster for connecting the DC voltage source to a variable resistance value and adjusting the DC voltage to a desired voltage level according to the resistance value. .

According to the present invention, the liquid crystal display forms at least one of the divided resistors for determining the reference supply voltage value as a variable resistor. Accordingly, the reference supply voltage can be accurately obtained with the variable resistor. In addition, the reference supply voltage which can be varied can be adjusted to the desired contrast ratio and viewing angle.

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY DEVICE AND DRIVING METHOD THEREOF}             

1 is a block diagram showing a conventional liquid crystal display device.

FIG. 2 is a circuit diagram illustrating a DC-DC converter of the LCD shown in FIG. 1.

3 is a circuit diagram illustrating a DC-DC converter of a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 4 is a circuit diagram illustrating a common voltage generator generated by a reference supply voltage of the DC-DC converter shown in FIG. 3.

FIG. 5 is a circuit diagram illustrating a gamma voltage generation unit generated by a reference supply voltage of the DC-DC converter shown in FIG. 3.

FIG. 6 is a circuit diagram illustrating a luminance change caused by the common voltage generator and the gamma voltage generator shown in FIGS. 4 and 5.

7 is a waveform diagram showing a viewing angle and contrast ratio according to the present invention;

8 is a flowchart illustrating a process of obtaining a viewing angle and contrast ratio desired by a user of a liquid crystal display according to the present invention.

<Description of Symbols for Main Parts of Drawings>

1: Digital Video Card 2: Control Unit

3: data driver 4: liquid crystal panel

5 gate driver 6 DC-DC converter

7: gamma voltage generator 8: common voltage generator

10,20: Switching Regulator IC

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof in which a user can adjust a desired viewing angle and contrast ratio.

In general, a liquid crystal display (“LCD”) displays an image by adjusting light transmittance of liquid crystal cells according to a video signal. Among the liquid crystal display devices, an active matrix type in which switching elements are provided for each liquid crystal cell is suitable for displaying a moving image. In an active matrix type LCD, a thin film transistor (hereinafter, referred to as TFT) is mainly used as a switching element.

As shown in FIG. 1, a driving device of a liquid crystal display device includes a digital video card 1 for converting analog data into digital video data and a data driver for supplying video data to data lines DL of the liquid crystal panel 4. (3), a gate driver 5 for sequentially driving the gate lines GL of the liquid crystal panel 4, a control unit 2 for controlling the data driver 3 and the gate driver 5; DC-DC converter 6 for generating a voltage for driving the gate driver 5, the data driver 3, the controller 2, the gamma voltage generator 7, the common voltage generator 8, and the like. It is provided.

The digital video card 1 converts an analog input video signal into digital video data and detects a synchronization signal included in the video signal.

The DC-DC converter 6 converts the DC voltage of a predetermined range input from the power supply unit (not shown) into a DC voltage having a predetermined size and outputs the DC voltage.

The control unit 2 supplies the digital video data of red (R), green (G) and blue (B) from the digital video card 1 to the data driver 3. In addition, the controller 2 generates the dot clock Dclk and the gate start pulse GSP using the horizontal / vertical synchronization signals H and V input from the digital video card 1 to generate the data driver 3 and the data driver 3. The timing of the gate driver 5 is controlled. The dot clock Dclk is supplied to the data driver 3, and the gate start pulse GSP is supplied to the gate driver 5.

The gate driver 5 includes a shift register (not shown) that sequentially generates scan pulses in response to the gate start pulse GSP input from the controller 2, and a level suitable for driving the voltage of the scan pulses to drive the liquid crystal cell. And a level shifter (not shown) for shifting to a low speed. In response to the scan pulse input from the gate driver 5, video data on the data line DL is supplied to the pixel electrode of the liquid crystal cell Clc by the TFT.

A dot clock Dclk is input to the data driver 3 together with video data of red (R), green (G), and blue (B) from the control unit 2. The data driver 3 latches the red (R), green (G), and blue (B) digital video data in synchronization with the dot clock (Dclk), and then the latched data is transferred from the gamma voltage generator (7). Correction is performed according to the generated gamma voltage Vγ. The data driver 3 converts the data corrected by the gamma voltage Vγ into analog data and supplies the data lines DL by one line.

In the liquid crystal panel 4, liquid crystal is injected between two glass substrates, and the gate lines GL and the data lines DL are formed to be perpendicular to each other on the lower glass substrate. A TFT for selectively supplying an image input from the data lines DL to the liquid crystal cell Clc is formed at the intersection of the gate lines GL and the data lines DL. For this purpose, the gate line GL is connected to the gate terminal of the TFT, and the data line DL is connected to the source terminal of the TFT.

Referring to FIG. 2, the DC-DC converter 6 includes a switching regulator IC 10, first to third resistors R1, R2, and R3, and first to third capacitors C1, C2, and C3. ), An inductor (L), and a diode (D).

The first and second resistors R1 and R2 are voltage divider resistors, and the reference supply voltage Vdd is determined according to the voltage divider resistance ratios of the first and second resistors R1 and R2. The first and second capacitors C1 and C2 are bypass capacitors, and charge or discharge current to smooth the voltage. The diode D is a reverse flow prevention diode and allows a bias current to flow toward the reference supply voltage Vdd.

The switching regulator IC 10 generates a reference supply voltage Vdd whose voltage level is determined according to the divided resistance ratios of the first and second resistors R1 and R2.

When the reference supply voltage Vdd is changed due to a change in the input voltage Vin, some of the voltages discharged from the second capacitor C2 may cause an RC circuit composed of the third capacitor C3 and the third resistor R3. It is fed back to the switching regulator IC (10). The duty cycle of the variable input reference supply voltage is changed to compensate for the reference supply voltage Vdd.

The reference supply voltage Vdd generated by the DC-DC converter including the switching regulator IC 10 is determined by the ratio of the first and second resistors R1 and R2, which are divided voltage resistors, as shown in Equation (1).

Since the first and second resistors R1 and R2 have a fixed value, the reference supply voltage Vdd generated by the divided resistance ratio of the first and second resistors R1 and R2 is also fixed.

However, the first and second resistors R1 and R2 may have different errors from the design values. Due to this error, the reference supply voltage Vdd affected by the first and second resistors R1 and R2 is different from the design value. For example, when the design resistance value of the first resistor R1 is 10 dB, the maximum resistance may be 9 to 11 dB if the maximum error rate is ± 10%. If an error occurs in the first and second resistors R1 and R2, the reference supply voltage Vdd does not obtain an accurate value and has an approximate value. In addition, the reference supply voltage Vdd formed by the divided resistance ratio of the first and second resistors R1 and R2, which are fixed resistors, is fixed so that the gamma voltage Vγ generated by the divided voltage of the reference supply voltage and the common voltage ( Vcom) is also fixed. Accordingly, the viewing angle and contrast ratio are also fixed due to the fixed reference supply voltage Vdd, thereby preventing a user from obtaining a desired viewing angle and contrast ratio.

Accordingly, it is an object of the present invention to provide a liquid crystal display device and a driving method thereof in which a user can adjust a desired viewing angle and contrast ratio.

In order to achieve the above object, a liquid crystal display device according to an embodiment of the present invention is a direct current voltage source for generating a direct current voltage, and a direct current-to-direct current conversion for adjusting and outputting the direct current voltage to a desired voltage level according to a variable resistance value. The DC-DC converter includes a first capacitor connected between an input terminal and a base voltage of the DC-DC converter, an inductor connected to the input terminal and the DC-voltage source, and a reference supply voltage by a variable resistor. A voltage level regulator for varying and outputting a voltage, a diode connected between the inductor and the voltage level regulator, and a voltage discharged according to a change in a reference supply voltage output from the voltage level regulator; A switching unit for changing the duty cycle of the output unit and outputting the duty cycle to the voltage level regulator; To the feedback portion of the voltage discharged from the regular switching a third capacitor and a third resistor which is connected between the voltage level adjuster and a switching unit configuring the RC circuit.
The voltage level regulator includes first and second resistors connected in parallel between an output terminal of the switching unit generating a DC voltage and a base voltage, and a second capacitor connected between the first resistor and the base voltage, The first resistor or the second resistor is characterized in that the variable resistor.

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In order to achieve the above object, a method of driving a liquid crystal display according to the present invention includes adjusting the DC voltage to a desired voltage level by adjusting a resistance value of the DC-DC converter, and gamma according to the adjusted voltage level. Varying the voltage or the common voltage, varying the voltage applied across the liquid crystal due to the variable gamma voltage or common voltage, increasing or decreasing the twist angle of the liquid crystal according to the voltage applied across the liquid crystal; And increasing or decreasing the light transmittance according to the twist angle of the liquid crystal to be increased or decreased, and adjusting the contrast ratio and the viewing angle according to the increase and decrease of the light transmittance.

Other objects and features of the present invention in addition to the above objects will become apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 3 to 8.

Referring to FIG. 3, the DC-DC converter according to the present invention includes a switching regulator IC 20, a first resistor R1, which is a variable resistor, second and third resistors R2 and R3, and first to third converters. The third capacitor C1, C2, C3, the inductor L, and the diode D are formed.

The first and second resistors R1 and R2 are formed between the output terminal of the switching regulator IC 20 generating the DC voltage and the base voltage. The first resistor R1 is formed of a variable resistor. The reference supply voltage Vdd may be adjusted to a value desired by the user according to the divided resistance ratios of the first and second resistors R1 and R2. The first capacitor C1 is connected between the input terminal of the DC-DC converter and the base voltage, and the second capacitor C2 is connected between the first resistor R1 and the base voltage GND. The first and second capacitors C1 and C2 are bypass capacitors, and charge or discharge the voltage to smooth the voltage. The diode D is a reverse flow prevention diode and allows a bias current to flow toward the reference supply voltage Vdd. This diode D is connected between the inductor L and the first resistor R1. The third capacitor C3 and the third resistor R3 are connected between the switching regulator IC 20 and the ground voltage GND to form an RC circuit.

When the reference supply voltage Vdd of the output terminal is changed, a part of the voltage discharged from the second capacitor C2 passes through the RC circuit composed of the third capacitor C3 and the third resistor R3. Feedback is input. The duty cycle of the variable input reference supply voltage Vdd is changed to compensate and output the reference supply voltage Vdd.

As shown in Equation 1, the reference supply voltage is determined based on the divided resistance ratios of the first and second resistors R1 and R2 connected in series in the DC-DC converter.

When at least one of the first and second resistors R1 and R2 is formed as a variable resistor, the reference supply voltage Vdd can be varied and the voltages generated due to the reference supply voltage Vdd are shown in FIGS. 4 and 5. The gamma voltage Vγ and the common voltage Vcom, which are output voltages of the shown gamma voltage generation circuit and the common voltage generation circuit, may also be varied.

For example, as shown in FIG. 6, the first to third reference supply voltages Vdd1 to Vdd3 are generated by varying the reference supply voltage Vdd. Accordingly, a plurality of first to third gamma voltages GMAAn to GMACn and first to third common voltages Vcom1 to Vcom3 are generated to correspond to the first to third reference supply voltages Vdd1 to Vdd3.

Based on the second reference supply voltage Vdd2, the value of the second reference supply voltage Vdd2 is greater than the value of the first reference supply voltage Vdd1 and smaller than the value of the third reference supply voltage Vdd3.

Accordingly, the potential difference between the first common voltage Vcom1 corresponding to the first reference supply voltage Vdd1 and the first gamma voltage GMAAn is equal to the second common voltage Vcom2 corresponding to the second reference supply voltage Vdd2. ) And lower than the potential difference between the second gamma voltage GMABn and the LCD in the normally white mode, the image is displayed at a brightness close to white. In addition, the potential difference between the third common voltage Vcom3 corresponding to the third reference supply voltage Vdd3 and the third gamma voltage GMACn corresponds to the second common voltage Vcom2 corresponding to the second reference supply voltage Vdd2. The image is displayed with a brightness close to black higher than the potential difference between the second gamma voltage and the GMABn. That is, by changing the reference supply voltage Vdd, the potential difference between the gamma voltage GMA and the common voltage Vcom is varied so that each of the liquid crystal cells selectively expresses a specific luminance gray value.

Due to such fluctuations in brightness, contrast ratio and viewing angle also fluctuate. This will be described with reference to FIG. 7 as follows. Here, the horizontal axis of FIG. 7 represents a viewing angle, the vertical axis represents a contrast ratio, UD represents up and down, LR represents left and right, and numbers 5, 7, 7, 8.8 and 8.4 represent reference supply voltages Vdd, respectively.

As the reference supply voltage Vdd increases, the upper, lower, left and right contrast ratios increase, the upper and lower viewing angles gradually increase, and the left and right viewing angles gradually decrease. As the reference supply voltage Vdd decreases, the upper, lower, left and right contrast ratios decrease, the vertical viewing angle gradually decreases, and the left and right viewing angles gradually increase. Accordingly, the viewing angle and contrast ratio desired by the user may be set according to the increase and decrease of the reference supply voltage Vdd.

Referring to FIG. 8, the DC-DC converter converts the reference supply voltage Vdd into a first resistor R1, which is a variable resistor, as shown in FIG. 8. The common voltage Vcom and the gamma voltage Vγ are variable due to Vdd. (S2) The effective voltage between the pixel electrode and the common electrode generated by the variable common voltage Vcom and the gamma voltage Vγ. The voltage applied to the both ends of the liquid crystal in the liquid crystal panel is varied (S3). Accordingly, the twist angle of the liquid crystal increases or decreases according to the variable amounts of the common voltage Vcom and the gamma voltage Vγ. The light transmittance through the liquid crystal panel is increased or decreased by increasing or decreasing the twist angle. (S5) The luminance is increased or decreased according to the increased or decreased light transmittance (S6). That is, the viewing angle desired by the user by changing the reference supply voltage Vdd. It is possible to obtain a contrast ratio.

As described above, the liquid crystal display according to the exemplary embodiment of the present invention forms at least one of the divided resistors for determining the reference supply voltage value as the variable resistor. Accordingly, the reference supply voltage can be accurately obtained with the variable resistor. In addition, the reference supply voltage which can be varied can be adjusted to the desired contrast ratio and viewing angle.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (4)

DC voltage source for generating a DC voltage, It includes a DC-DC converter for adjusting the DC voltage to the desired voltage level according to the variable resistance value and outputs the DC voltage. The DC-DC converter, A first capacitor connected between an input terminal of the DC-DC converter and a ground voltage; An inductor connected to the input terminal and the DC voltage source; A voltage level regulator for outputting a variable supply of reference voltage by a variable resistor; A diode connected between the inductor and the voltage level regulator; A switching unit configured to receive a voltage discharged according to a change in the reference supply voltage output from the voltage level regulator, change a duty cycle of the reference supply voltage, and output the changed voltage to the voltage level regulator; And a third capacitor and a third resistor connected between the voltage level regulator and the switching unit to form an RC circuit to feed back the voltage discharged from the voltage level regulator to the switching unit. delete The method of claim 1, The voltage level regulator, First and second resistors connected in parallel between an output terminal of the switching unit for generating a DC voltage and a ground voltage; A second capacitor connected between the first resistor and a base voltage, And the first resistor or the second resistor is a variable resistor. A driving method of a liquid crystal display device comprising a DC voltage source for generating a DC voltage and a DC-DC converter for adjusting the DC voltage to a desired voltage level according to a variable resistance value. Adjusting the DC voltage to a desired voltage level by adjusting a resistance value of the DC-DC converter; Changing a gamma voltage or a common voltage according to the adjusted voltage level; Changing the voltage applied across the liquid crystal due to the variable gamma voltage or common voltage; Increasing or decreasing the twist angle of the liquid crystal according to the voltage applied across the liquid crystal; Increasing or decreasing the light transmittance according to the torsion angle of the liquid crystal to be increased or decreased; And adjusting a contrast ratio and a viewing angle according to the increase and decrease of the light transmittance.

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