KR20010112807A - Liquid crystal display device using an alternative common voltage - Google Patents

Abstract

An optical filter comprising a filter substrate (11) and a transparent conductive film (12) for cutting off electromagnetic waves and infrared rays (for example, a transparent conductive film sputter film), provided on the filter substrate (11) by alternately forming silver thin films and zinc oxide thin films into a multilayer structure. The transmissivity of image light outputted from a PDP (1) is a predetermined value (e.g. 60 %) or more and the surface resistance of the transparent conductive film (12) is 3 Omega/cm2 or less. In this way, the cutoff quantity (damping) of electromagnetic waves of a frequency of 30 to 130 MHz leaking from the PDP (1) is a predetermined value (e.g. 10 dB) or more, and the transmissivity of infrared rays of a wavelength of 800 to 1, 000 nm radiated from the PDP is predetermined value (e.g. 10 %) or less. Accordingly, the leakage level of electromagnetic waves leaking from the PDP (1) is below a restricted value, and interference with the operation of remote controllers, optical communication equipment, etc., disposed nearby is prevented by cutting off infrared rays radiated from the PDP (1). When warp of the filter substrate (11) (when it is a synthetic resin substrate, for example) due to heat generated by the discharge of the PDP (1) is a problem, the filter substrate (11) is made of glass (e.g. reinforced glass substrate) to prevent degradation of display quality due to the warp of the optical filter. When corrosion of the transparent conductive film (12) (particularly, a silver thin film) due to the water vapor in the open air is a problem, this corrosion can be prevented by covering the exposed surface of the transparent conductor film (12) with a moisture-proofing film. An AR film (13) is used to prevent reflection of external light so as to prevent the drop of contrast, and an AN film (14) is used to prevent the occurrence of Newton rings (bright and dark concentric circles).

Description

Liquid crystal display using AC common electrode voltage {LIQUID CRYSTAL DISPLAY DEVICE USING AN ALTERNATIVE COMMON VOLTAGE}

The present invention relates to a liquid crystal display device using an alternating current common electrode voltage, and more particularly, to a liquid crystal display device using an alternating current common electrode voltage capable of reducing a flicker phenomenon by outputting a common voltage interworking irregularly with a pixel electrode. It is about.

Recently, display devices are also required to be lighter and thinner in accordance with the light weight and thickness of personal computers and televisions, and according to such demands, flat panel displays such as liquid crystal displays are used instead of cathode ray tubes. Is being developed.

An LCD is a display device that obtains a desired image signal by applying an electric field to a liquid crystal material having an anisotropic dielectric constant injected between old substrates and adjusting the intensity of the electric field to control the amount of light transmitted through the substrate. Such LCDs are typical of portable flat panel displays, and among these, TFT-LCDs using thin film transistors as switching elements are mainly used.

In general, LCDs include a plurality of gate lines that transmit scan signals and data lines that are formed to cross the gate lines, and that transmit image data. The LCD includes a plurality of pixels in a matrix form connected through the gate lines and switching elements. Include.

The method of applying image data to each pixel in such an LCD is as follows.

First, the gate-on signal, which is a scan signal, is sequentially applied to the gate lines to sequentially turn on the switching element connected to the gate line, and at the same time, an image signal (more specifically, a gray level to be applied to the pixel row corresponding to the gate line). Voltage) to each data line. Then, the image signal supplied to the data line is applied to each pixel through the turned-on switching element. At this time, the gate-on signal is sequentially applied to all the gate lines during one frame period to apply the image signal to all the pixel rows, thereby displaying an image of one frame.

FIG. 1 is a pixel equivalent circuit diagram of a general TFT-LCD, and FIGS. 2A to 2B are diagrams for explaining the change in the pixel electrode voltage waveform of FIG.

As shown in FIG. 1, the parasitic capacitor Cgd between the gate and the drain, the parasitic capacitor Cds between the drain and the source, and the overlap capacitor Cov between the data line and the pixel electrode are indicated by dotted lines. At this time, the liquid crystal capacitor Ct and the storage capacitor Cs serve as loads that the TFT must drive.

The effective value of the voltage actually applied to the liquid crystal is determined by the area between the pixel electrode voltage and the common voltage, and the actual operation of the liquid crystal is determined by the effective value of this voltage so that the area around the common voltage Vcom is symmetrical. It is necessary to adjust the common voltage level.

However, since the dielectric constant of the liquid crystal changes by 2 to 3 times depending on the applied voltage, the magnitude of ΔV also changes according to the image signal. For this reason, only by adjusting the potential Vcom of the common electrode, the effective value of the voltage applied to the liquid crystal cannot be precisely symmetrical, and an optical asymmetric component of 30 kHz is generated, causing the screen to flicker in our eyes. This is called flicker.

In general, the common electrode voltage (or the counter voltage, hereinafter referred to as Vcom) includes a DC voltage application method and a square wave voltage application method. Both of these methods have a fixed Vcom, causing flicker due to panel characteristics change after a reliability test. There is this.

In addition, there is a problem in that the flicker occurs locally according to the top voltage gradient according to the sorting method of the upper and lower panels.

Accordingly, the technical problem of the present invention is to solve such a conventional problem, and to reduce flicker due to a change in characteristics or lack of margin during design and mass production of a liquid crystal display by changing the level of a common voltage applied to the liquid crystal display.

1 is a pixel equivalent circuit diagram of a general TFT-LCD.

2A to 2B are diagrams for explaining the change in the pixel electrode voltage waveform of FIG. 1 described above.

3 is a configuration diagram of a liquid crystal display using an AC common electrode voltage according to an exemplary embodiment of the present invention.

4A to 4C are waveform diagrams for describing waveforms of an AC common voltage output from a voltage generator according to the present invention.

<Description of the symbols for the main parts of the drawings>

100: timing controller 200: gray voltage generator

300: voltage generator 400: data drive

500: gate drive 600: LCD panel

Cgd, Cds: Parasitic Capacitors

According to one aspect of the present invention, a liquid crystal display using an AC type common electrode voltage includes a data drive including a plurality of data drive ICs to output a data voltage, and a gate drive consisting of a plurality of gate drive ICs. A gate controller for outputting, a timing controller for outputting a digital signal for driving the respective data and gate drive ICs, a gray voltage generator for outputting a gray voltage to each of the data drive ICs, and a plurality of pixel electrodes A liquid crystal display device comprising: an LCD panel driven by receiving the data voltage and the gate voltage.

A Von voltage for turning on the gate terminal of the pixel electrode is output to the gate drive, a Voff voltage for turning off the gate terminal is output to the data drive, and an AC type common electrode voltage serving as a reference for the data voltage difference in the TFT is provided. And a voltage generator outputting the data drive.

According to the liquid crystal display device using the AC type common electrode voltage, the common electrode voltage applied to the liquid crystal display device is converted into an AC type common voltage, and the frequency is increased again so that the flicker is not visually recognized at a high speed. can do.

Then, embodiments will be described so that those skilled in the art can easily implement the present invention.

3 is a configuration diagram of a liquid crystal display using an AC common electrode voltage according to an exemplary embodiment of the present invention.

As shown in FIG. 3, the liquid crystal display using the AC type common electrode voltage according to an exemplary embodiment of the present invention includes a timing controller 100, a gray voltage generator 200, a voltage generator 300, and a data drive ( 400), gate drive 500 and LCD panel 600.

The timing controller 100 maintains a high level only during a period in which a vertical synchronization signal Vsync, a frame discrimination signal Vsync, a horizontal synchronization signal Hsync, a line discrimination signal, and data are provided from a graphic controller (not shown). The data enable signal DE and the main clock MCLK are provided to output digital signals for driving the respective data ICs and the gate drive ICs formed in the data drive 400 and the gate drive 500. In this case, the digital signal provided to the data drive 400 includes R, G, and B signals, a horizontal start signal, and a load signal, and the digital signal provided to the gate drive includes a gate clock and a vertical start signal.

The gray voltage generator 200 outputs a gray voltage input to each data drive IC.

The voltage generator 300 outputs a Von voltage for turning on the gate terminal of the pixel electrode to the gate drive, and outputs a Voff voltage for turning off the gate terminal to the data drive, and the AC common which serves as a reference for the data voltage difference in the TFT. Output the voltage to the data drive.

The data drive 400 includes a plurality of data drive ICs G1, G2, G3,..., And receives the R, G, B signals, the horizontal start signal, and the load signal from the timing controller 100, and the gray level. The gray voltage is received from the voltage generator 200 to output the data voltage to the data line of the LCD panel 600.

The gate drive 500 includes a plurality of gate drive ICs S1, S2, S3,..., And receives a gate clock and a vertical start signal from the timing controller 100, and drives the gate from the voltage generator 300. The on-voltage Von, the gate driving off Voff, and the common voltage Vcom are provided to output the gate voltage to the gate line of the LCD panel 600.

The LCD panel 600 includes a plurality of pixel electrodes, and is driven by receiving a plurality of data voltages provided from the data drive 400 and a plurality of gate voltages provided from the gate drive 500 to correspond to R, G, and B. Display the image for the data.

An embodiment of the waveform of the common electrode voltage output from the voltage generator 300 according to the present invention will be described.

4A to 4C are waveform diagrams for describing waveforms of an AC common voltage output from a voltage generator according to the present invention.

4A is a diagram for describing a waveform of a common electrode voltage input by using one half of the pixel electrode voltage Vds as one period according to an exemplary embodiment of the present invention.

As shown in FIG. 4A, a sine wave instead of a direct current voltage is applied to the common electrode voltage, so that the area between the pixel electrode voltage and the common electrode voltage can be more accurately symmetrical.

FIG. 4B is a diagram for describing a waveform of a common electrode voltage input using a half cycle of the pixel electrode voltage Vds as two cycles according to another exemplary embodiment of the present invention.

As shown in FIG. 4B, a square wave instead of a direct current voltage is applied to the common electrode voltage, so that the area between the pixel electrode voltage and the common electrode voltage can be more accurately symmetrical.

FIG. 4C is a diagram for describing waveforms of a common electrode voltage input with n cycles of 1/2 of the pixel electrode voltage Vds according to another exemplary embodiment of the present invention.

As shown in FIG. 4C, a random wave instead of a direct current voltage is applied to the common electrode voltage, so that the area between the pixel electrode voltage and the common electrode voltage can be more accurately symmetrical.

The frequencies of each of the sinusoidal, square, and random waves shown in FIGS. 4A to 4C must satisfy the following equation.

here, Is the inversion frequency of the common electrode voltage Vcom, Is the inverting frequency of the pixel electrode voltage Vds.

As described above, sine waves, square waves, and random waves have been described as examples, but sawtooth waves, ramp waves, and the like may be used as waveforms of the common electrode voltage.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

As described above, the flicker speeds up by converting the common electrode voltage applied to the LCD panel of the liquid crystal display device into an alternating voltage and artificially increasing the frequency of the converted common electrode voltage. You can make it impossible to recognize it visually.

Claims (3)

A data drive consisting of a plurality of data drive ICs for outputting a data voltage, a gate drive consisting of a plurality of gate drive ICs for outputting a gate voltage, and a timing for outputting a digital signal for driving the respective data and gate drive ICs A liquid crystal display comprising a control unit, a gray voltage generator for outputting a gray voltage to each of the data drive ICs, and an LCD panel including a plurality of pixel electrodes to receive and drive the data voltage and the gate voltage. , A Von voltage for turning on the gate terminal of the pixel electrode is output to the gate drive, a Voff voltage for turning off the gate terminal is output to the data drive, and an AC type common electrode voltage serving as a reference for the data voltage difference in the TFT is provided. A voltage generator outputting the data drive Liquid crystal display using an AC type common electrode voltage, characterized in that it comprises a. The method of claim 1, wherein the AC common electrode voltage, An alternating current waveform including any of a square wave, a sine wave, a sawtooth wave, and a ramp waveform, wherein the liquid crystal display device uses the AC common electrode voltage. The frequency of the AC-type common electrode voltage, (here, Is the inversion frequency of the common electrode voltage, Is an inverted frequency of the pixel electrode).