KR20060078510A - Liquid crystal display device having compensating circuit and method of applying common voltage to a common electrode - Google Patents

Abstract

The liquid crystal display device according to the present invention includes a liquid crystal panel including a plurality of pixels, the liquid crystal panel including at least one pair of common electrodes and pixel electrodes disposed substantially parallel inside the pixels to apply a transverse electric field, and applied to the common electrodes. It is composed of a common voltage supply circuit that generates a common voltage and compensates the voltage output from the liquid crystal panel to eliminate ripple generated in the liquid crystal panel.

Liquid crystal, common voltage, compensation circuit, ripple, swing structure

Description

Liquid crystal display device having a compensation circuit and a method of applying a common voltage {LIQUID CRYSTAL DISPLAY DEVICE HAVING COMPENSATING CIRCUIT AND METHOD OF APPLYING COMMON VOLTAGE TO A COMMON ELECTRODE}

1 is a view showing a common voltage generation circuit of a conventional liquid crystal display device.

Figure 2 is a simplified diagram showing the structure of a liquid crystal panel according to the present invention.

3 illustrates a common voltage supply circuit according to the present invention.

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 common voltage compensation method including a compensation circuit capable of compensating for common voltage to prevent deterioration of image quality.

Recently, with the development of various portable electronic devices such as mobile phones, PDAs, and notebook computers, there is a growing demand for flat panel display devices for light and thin applications. Such flat panel displays are being actively researched, such as LCD (Liquid Crystal Display), PDP (Plasma Display Panel), FED (Field Emission Display), VFD (Vacuum Fluorescent Display), but mass production technology, ease of driving means, Liquid crystal display devices (LCDs) are in the spotlight for reasons of implementation.

The liquid crystal display device has various display modes according to the arrangement of the liquid crystal molecules. However, the liquid crystal display device of the TN mode is mainly used because of the advantages of easy monochrome display, fast response speed, and low driving voltage. In such a TN mode liquid crystal display device, liquid crystal molecules aligned horizontally with the substrate are almost perpendicular to the substrate when a voltage is applied. Therefore, there is a problem that the viewing angle is narrowed upon application of voltage due to the refractive anisotropy of the liquid crystal molecules.

In order to solve this viewing angle problem, liquid crystal display devices of various modes having wide viewing angle characteristics have recently been proposed, but among them, the liquid crystal display device of the lateral field mode (In Plane Switching Mode) is applied to actual production. It is produced. The IPS mode liquid crystal display device aligns liquid crystal molecules in a plane by forming at least one pair of electrodes (ie, a pixel electrode and a common electrode) arranged in parallel in a pixel to form a transverse electric field substantially parallel to the substrate.

In the IPS mode liquid crystal display device having such a structure, as a thin film transistor disposed in each pixel operates, an image signal is applied to the pixel electrode to form a transverse electric field at a potential difference with a common voltage applied to the common electrode, thereby driving the liquid crystal molecules. will be.

In the IPS mode liquid crystal display device, a scan signal is applied from a gate driver formed separately from or integrally formed with the liquid crystal panel to turn on the thin film transistor, and an image signal is applied from the data driver to the pixel electrode through the thin film transistor. The transverse electric field is generated between the pixel electrodes. At this time, the image signal is applied simultaneously with the turn-on of the thin film transistor, but the common voltage applied to the common electrode is applied to the common electrode through the common voltage generation circuit.

A common voltage supply circuit having such a common voltage compensation circuit is shown in FIG. 1. As shown in the drawing, the common voltage generating circuit includes first and second resistors R1 and R2 connected in series between a power supply voltage Vdd and a ground potential Vss, and the first and second resistors R1. And a variable resistor VR1 connected between the R2s to distribute the power supply voltage Vdd to a desired level and output the common voltage Vcom.

The common voltage Vcom generated from the common voltage generating circuit is applied to the common electrode of the liquid crystal panel 10 and the data signal and the transverse electric field according to the image information applied to the pixel electrode arranged in parallel with the common electrode are applied to the liquid crystal layer. By applying, the liquid crystal molecules of the liquid crystal layer are rotated by dielectric anisotropy to control light transmittance for each pixel.

However, when the common voltage generated in the common voltage generating circuit is applied to the common electrode inside the liquid crystal panel, the waveform is deformed by the resistance or the capacitor inside the liquid crystal panel, and the deformation of the waveform crosses the liquid crystal display device. It was an important cause of torque generation.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and provides a liquid crystal display device and a common voltage application method capable of removing horizontal crosstalk by providing a compensation circuit in a common voltage supply circuit to remove ripples generated in a liquid crystal panel. For the purpose of

In order to achieve the above object, the liquid crystal display device according to the present invention includes a plurality of pixels, the liquid crystal panel including at least a pair of common electrodes and pixel electrodes arranged in substantially parallel inside the pixel to apply a transverse electric field And a common voltage supply circuit generating a common voltage applied to the common electrode and compensating the voltage output from the liquid crystal panel to remove ripples generated in the liquid crystal panel.

The liquid crystal panel includes a plurality of gate lines and data lines arranged vertically and horizontally to define a plurality of pixels, a common line arranged along a gate line to apply a common voltage to a common electrode of a corresponding column, and the common line connected to the outside. And a common voltage supply line for applying a common voltage input from the common line to the common line, wherein the common voltage supply line includes a first common voltage supply line to which an odd common line is connected and a second common line to which an even common line is connected. It consists of a voltage supply line.

The common voltage supply circuit includes a common voltage generating circuit for generating a common voltage and a common voltage compensating circuit for inverting the ripple of the common voltage output from the liquid crystal panel based on the generated common voltage and the common voltage output from the liquid crystal panel. .

At this time, the common voltage generating circuit includes a resistor connected in series between a power supply voltage and a ground potential, a variable resistor connected to the resistor to distribute the power supply voltage to a desired level, and a control signal is input to a non-inverting terminal. Includes a first inverting amplifier which receives a power supply voltage distributed at a desired level and inverts and outputs the input voltage.

In addition, the common voltage compensation circuit includes a first inverting amplifier for inverting and amplifying the ripple output from the liquid crystal panel, and a pushple amplifier for amplifying the voltage including the inverted ripple. The method comprises the steps of: generating a common voltage; and a ripple of the common voltage output from the liquid crystal panel comprising a plurality of pixels and having at least one pair of common electrodes and pixel electrodes disposed substantially parallel within the pixels to apply a transverse electric field; Inverting amplification and applying a common voltage including the inverted ripple to the common electrode of the liquid crystal panel.

The present invention provides a common voltage supply circuit. In the present invention, a common voltage compensation circuit is provided in the common voltage supply circuit to compensate for variations in the common voltage so that the common voltage always applied to the liquid crystal panel is applied.

In general, the common voltage applied to the common electrode of the liquid crystal panel generates ripple due to the resistance and the capacitor inside the liquid crystal panel. In the present invention, such a ripple is effectively eliminated so that a voltage set at all times is applied to the common electrode of the liquid crystal panel. In particular, the present invention provides a common voltage supply circuit applied to an IPS mode liquid crystal display device having a swing structure in which a common voltage is alternately applied to a common electrode of odd-numbered column pixels and a common electrode of even-numbered column pixels.

Unlike the dot-inversion method used in the swing type IPS mode liquid crystal display device, the common voltage is divided by horizontal lines and the vertical signal is AC-driven (that is, the common voltage is applied by separating the odd and even numbers). do). Therefore, even if the variation of the output voltage of the image signal is reduced compared with the conventional structure, the lateral electric field of the desired intensity can be obtained, and thus power consumption can be reduced. According to the present invention, power consumption can be reduced by providing a common voltage supply circuit of an IPS mode liquid crystal display device having a swing structure.

Hereinafter, a liquid crystal display device according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a view schematically showing the structure of a liquid crystal display device according to the present invention. As shown in the figure, the liquid crystal display device of the present invention has a liquid crystal panel 101 in which a plurality of pixels are formed to realize an actual image, and a gated TCP (Taped Carrier Package) attached to an outer portion of the liquid crystal panel 101. 131 and data TCP 133 and a printed circuit board 142 and 144 connected to the liquid crystal panel 101 through the TCP 131 and 133.

In the liquid crystal panel 101, a plurality of gate lines 103 and a data line 105 are vertically and horizontally disposed to define a plurality of pixels, and a thin film transistor 110 is disposed in each pixel. In the pixel, the pixel electrode 115 and the common electrode 116 are disposed to be substantially parallel to form a transverse electric field. In this case, as a swing structure of the liquid crystal panel 101, the thin film transistor 110 of one pixel and the thin film transistor 110 of an adjacent pixel are connected to different gate lines 103. That is, the thin film transistor 110 of one pixel is connected to the gate line of the pixel, while the thin film transistor 110 of the adjacent pixel is connected to the gate line of the front end.

A common line 117 connected to the common electrode 116 is disposed along the pixel column to apply a common voltage to the common electrode 116. In addition, the first common voltage supply line 120 and the second common electrode supply line 122 are disposed in the outer region of the liquid crystal panel 101. The first and second common voltage supply lines 120 and 122 are disposed on both sides of the liquid crystal panel 101, respectively, and are connected to the odd common line 117 and the even common line 117, respectively. The common voltage is alternately applied to the common electrode and the common electrode of the even-numbered column pixels.

Meanwhile, gate pads 104 and data pads 106 are formed at ends of the gate line 103 and the data line 105, respectively. The gate pad 104 and the data pad 106 are connected to the terminals of the gate driver 132 and the data driver 134 mounted on the gate TCP 131 and the data TCP 133, respectively, and scan signals. And an image signal are input. Although not shown in the drawing, the PCBs 142 and 144 are provided with a control unit for applying a control signal to the gate driver 132 or the data driver 134 and a common voltage supply unit for supplying a common voltage.

In the liquid crystal display device configured as described above, as the scan signal is applied from the gate driver 132, the thin film transistor 110 is turned on, and an image signal applied from the data driver 134 is pixelated through the thin film transistor 110. Is applied to the electrode 115. At the same time, a common voltage is applied to the common electrode 116 through the common voltage supply line 120 to form a transverse electric field between the pixel electrode 115 and the common electrode 116.

Both ends of the first and second common voltage supply lines 120 and 122 are provided with input terminals 120a and 122a through which a common voltage is input and output terminals 122a and 122b through which a common voltage is output. The input terminals 120a and 120b are connected to an output terminal of a common voltage supply circuit for applying a common voltage to apply a common voltage to the liquid crystal panel, and the output terminals 122a and 122b are connected to a common voltage compensation circuit to compensate for the common voltage. do.

3 is a diagram illustrating a common voltage supply circuit having a common voltage compensation function according to the present invention. In the swing-type IPS mode liquid crystal display device, since a signal is separately applied to the odd common line and the even common line, a common voltage supply circuit for supplying a common voltage to the odd common line and a common voltage to the even common line Each common voltage supply circuit must be provided to supply. However, the structure of the common voltage supply circuit for the odd-numbered common lines and the common voltage supply circuit for the even-numbered common lines is substantially the same, and there is a difference only in that the control signal is input inverted. Therefore, in the following description, only one common voltage supply circuit has been described.

As shown in FIG. 3, the common voltage supply circuit of the present invention includes a common voltage generation circuit 110 and a common voltage compensation circuit 120.

The common voltage generating circuit 110 is connected to the resistor R1 connected in series between the power supply voltage Vdd and the ground potential Vs, and is connected to the resistor R1 to distribute the power supply voltage Vdd to a desired level. A control signal is input to the variable resistor VR1 and the inverting terminal, and a power voltage Vdd distributed at a desired level is input to the non-inverting terminal, and the first and the inverted amplification is output through the resistor R2 and the capacitor C1. Inverting amplifier 113 is configured.

The control signal is a signal in which low and high (for example, 0 V and 3.3 V) are alternately alternately. As the control signal is input, the first inverting amplifier 113 alternately alternates the signal for each control signal R 3 / R 2. Inverted and amplified to the common line 117 can be output.                     

In addition, the common voltage compensating circuit 120 receives the common voltage Vcom output from the common voltage generating circuit 110 as a non-inverting terminal through the resistor R4 and receives the common voltage supply line of the liquid crystal panel 101. The second inverting amplifier 123 in which the output voltage output through the output pads 120b and 120b of the 120 and 122 is input through an inverting terminal, and two transistors Q1 and Q2 are configured. The output voltage is input to the common gate, the source of the first transistor is connected to the power supply voltage (Vdd), the drain is connected to the source of the second transistor (Q2), the drain of the second transistor (Q2) is the ground potential And a push amplifier that amplifies the input voltage connected to the Vss and inputs the input voltage through the input pads 120a and 122a of the common voltage supply lines 120 and 122 through the resistor R7.

The voltage output through the output pads 120b and 122b of the common voltage supply lines 120 and 122 causes ripple, which is an AC component, due to the resistance of the liquid crystal panel 101 and the capacitor component. The common terminal including the ripple is input to the inverting terminal of the second inverting amplifier 123.

In addition, the signal generated from the common voltage generation circuit 110 is input to the non-inverting terminal of the second inverting amplifier 123. Accordingly, the second inverting amplifier 123 inverts and outputs only the ripple component of the input common voltage Vcom with a gain of R6 / R5. Ripple inverted means that the AC component ripple is reversed. Therefore, the common voltage Vcom compensated by the compensation circuit 120 and input to the liquid crystal panel 101 includes a ripple inverted from the common voltage output from the liquid crystal panel 101. Therefore, when the compensated common voltage Vcom is input to the liquid crystal panel 101, the inverted ripple of the common voltage Vcom to which the ripple generated by the resistance and capacitor components of the liquid crystal panel 101 is input and its phase are different. By canceling, the common voltage of the pure direct current component is applied to the common electrode of the liquid crystal panel 101.

As described above, the present invention is applied to an IPS mode liquid crystal display device having a swing structure in which a common voltage is alternately applied to common electrodes in odd-numbered columns and common electrodes in even-numbered columns, respectively. The image is displayed by alternately applying a common voltage with ripples removed (i.e., compensated). However, the present invention is not limited to this swing structure but may be applied to an IPS mode liquid crystal display device having a general structure.

As described above, in the present invention, by providing a common voltage supply circuit with a compensation circuit for removing ripples generated in the liquid crystal panel, it is possible to effectively prevent deterioration in image quality by always applying a compensated common voltage in the liquid crystal panel. .

Claims (14)

A liquid crystal panel including a plurality of pixels, the liquid crystal panel including at least one pair of common electrodes and pixel electrodes disposed substantially parallel in the pixels to apply a transverse electric field; And a common voltage supply circuit for generating a common voltage applied to the common electrode and compensating a voltage output from the liquid crystal panel to remove ripples generated in the liquid crystal panel. The liquid crystal panel of claim 1, wherein A plurality of gate lines and data lines arranged vertically and horizontally to define a plurality of pixels; A common line arranged along the gate line to apply a common voltage to a common electrode of a corresponding column; And And a common voltage supply line connected to the common line to apply a common voltage input from the outside to the common line. The method of claim 2, wherein the common voltage supply line, A first common voltage supply line to which an odd common line is connected; And And a second common voltage supply line to which the even common line is connected. The method of claim 3, wherein signals are alternately applied to a common electrode connected to an odd common line and a common electrode connected to an even common line through the first common voltage supply line and the second common voltage supply line. Liquid crystal display device. The method of claim 3, wherein the common voltage supply circuit, A first common voltage supply circuit for applying a first common voltage to a common electrode connected to an odd-numbered common line through a first common voltage supply line; And And a second common voltage supply circuit for applying a second common voltage to a common electrode connected to an even-numbered common line through a second common voltage supply line. 6. The liquid crystal display device according to claim 5, wherein the first common voltage and the second common voltage are inverted in phase. The method of claim 1, wherein the common voltage supply circuit, A common voltage generating circuit for generating a common voltage; And And a common voltage compensating circuit for inverting and outputting a ripple of the common voltage output from the liquid crystal panel based on the generated common voltage and the common voltage output from the liquid crystal panel. The method of claim 7, wherein the common voltage generation circuit, A resistor connected in series between the supply voltage and the ground potential; A variable resistor connected to the resistor to distribute the power supply voltage to a desired level; And And a first inverting amplifier to which a control signal is input to the inverting terminal and a power supply voltage distributed to a desired level is input to the inverting terminal to invert and amplify the input voltage. 10. The liquid crystal display of claim 8, wherein the first inverting amplifier alternately inverts and amplifies a signal for each vertical synchronization signal. The method of claim 7, wherein the common voltage compensation circuit, A first inverting amplifier inverting and amplifying the ripple output from the liquid crystal panel; And And a push amplifier for amplifying a voltage including the inverted ripple. The liquid crystal display device of claim 10, wherein the inverted ripple is opposite in phase to the ripple generated in the liquid crystal panel. 12. The liquid crystal display device according to claim 11, wherein the inverted ripple is input to the liquid crystal panel to cancel the ripple generated from the liquid crystal panel. Generating a common voltage; Inverting and amplifying the ripple of the common voltage output from the liquid crystal panel including the pixel electrode and at least one pair of common electrodes and pixel electrodes disposed in substantially parallel inside the pixels; And A common voltage application method comprising applying a common voltage including an inverted ripple to a common electrode of a liquid crystal panel. The method of claim 13, wherein the ripple applied to the common electrode is canceled from the ripple generated in the liquid crystal panel.

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