This application claims priority to and the benefit of Korean Patent Application No. 10-2011-0123575, filed on Nov. 24, 2011, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field
Exemplary embodiments of the present invention relate to a liquid crystal display.
2. Discussion of the Background
A liquid crystal display, which is one of the most common types of flat panel displays currently in use, includes two panels with field generating electrodes, such as a pixel electrode, a common electrode, and the like, and a liquid crystal layer interposed therebetween. The liquid crystal display generates an electric field in the liquid crystal layer by applying voltage to the field generating electrodes, and determines the orientation direction of liquid crystal molecules of the liquid crystal layer by the generated electric field, thus controlling polarization of incident light so as to display images.
The liquid crystal display may include a thin film transistor that switches application of data voltage and, in the thin film transistor, a current characteristic may be reduced at a low temperature and the data voltage may not be sufficiently charged in the pixel. Further, in the case of a precharge driving mode for compensating a charging time, when an image signal of a mixed color pattern is inputted, a bar line may be shown, thereby deteriorating display quality.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.
An exemplary embodiment of the present invention provides a liquid crystal display including a thin film transistor having an improved current characteristic so that the data voltage may be sufficiently charged in the pixels at low temperature.
Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention.
An exemplary embodiment of the present invention discloses a liquid crystal display, including: pixels; a signal controller receiving an input image signal and an input control signal and outputting a processing image signal and a control signal; and a data driver changing the processing image signal to data voltage on the basis of the control signal to supply the data voltage to the pixel. The data driver causes charges of odd channel data voltage of an odd channel and even channel data voltage of an even channel which have different polarities to be shared based on temperature.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thicknesses of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals in the drawings denote like elements.
It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” or “connected to” another element, it can be directly on or connected to the other element, or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or “directly connected to” another element, there are no intervening elements present. It will be understood that for the purposes of this disclosure, “at least one of X, Y, and Z” can be construed as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XYY, YZ, ZZ).
Referring to
A gray voltage generator 800 generates two gray voltage sets (or reference gray voltage sets) relating to transmittance of the pixel. One set of the two gray voltage sets has a positive value for a common voltage Vcom, and the other set has a negative value.
A gate driver 400 is connected to the gate line of the liquid crystal panel assembly 300 to apply a gate signal configured by combining gate-on voltage Von and gate-off voltage Voff to the gate line.
A data driver 500 is connected to the data line of the liquid crystal panel assembly 300 to select the gray voltage from the gray voltage generator 800 and apply the selected gray voltage to the pixel as data voltage. The gray voltage generator 800 need not supply all voltages for all gray levels. Rather, the gray voltage generator 800 may supply a predetermined number of the reference gray voltages, the data driver 500 divides the reference gray voltages to generate gray voltages for the entire gray scale and select a data signal among the gray voltages.
A signal controller 600 controls the gate driver 400 and the data driver 500.
Each of the drivers 400, 500, 600, and 800 may be directly mounted on the liquid crystal panel assembly 300 in at least one IC chip form or mounted on a flexible printed circuit film (not shown) to be attached to the liquid crystal panel assembly 300 in a tape carrier package (TCP) form. On the contrary, the drivers 400, 500, 600, and 800 may be integrated to the liquid crystal panel assembly 300 together with the signal lines and a thin film transistor switching element. Further, all the drivers 400, 500, 600, and 800 may be integrated in a single chip and in this case, at least one of the drivers 400, 500, 600, and 800 or at least one circuit element configuring the drivers 400, 500, 600, and 800 may be disposed outside the single chip.
The signal controller 600 receives input image signals R, G, and B and an input control signal controlling a display thereof from an external graphic controller (not shown). The input image signals R, G, and B have luminance information of each pixel PX and the luminance has a predetermined number, for example, 1024 (=210), 256 (=28), or 64 (=26)gray levels. Examples of the input control signal include a vertical synchronization signal Vsync, a horizontal synchronizing signal Hsync, a main clock MCLK, a data enable signal DE, and the like.
The signal controller 600 properly processes the input image signals R, G, and B to be suitable for operating the liquid crystal panel assembly 300 and the data driver 500 based on the input image signals R, G, and B and the input control signal. After the signal controller 600 generates a gate control signal CONT1, a data control signal CONT2, a backlight control signal CONT3, and the like, the signal controller 600 transmits the gate control signal CONT1 to the gate driver 400 and outputs the data control signal CONT2 and the processed image signal DAT to the data driver 500. The output image signal DAT has the predetermined number of values (or gray levels) as a digital signal.
The gate control signal CONT1 includes a scanning start signal STV instructing a scanning start and at least one clock signal controlling an output period of the gate-on voltage Von. The gate control signal CONT1 may further include an output enable signal OE limiting a duration time of the gate-on voltage Von.
The data control signal CONT2 includes a horizontal synchronization start signal notifying a transmission start of the image data for the pixels PX of one row and a load signal instructing the application of the data signal to data lines, and a data clock signal. The data control signal CONT2 may further include an inversion signal inverting a voltage polarity of the data signal with respect to the common voltage Vcom (hereinafter, referred to as a “polarity of the data signal” by shortening “the voltage polarity of the data signal with respect to the common voltage”).
According to the data control signal CONT2 from the signal controller 600, the data driver 500 receives the digital image signal DAT for the pixels PX of one row and selects the gray voltage corresponding to each digital image signal DAT and as a result, converts the digital image signal DAT into an analog data signal and then applies the analog data signal to the corresponding data lines. The number of the gray voltages generated by the gray voltage generator 800 may be the same as the number of the gray levels represented by the digital image signal DAT.
The gate driver 400 applies the gate-on voltage Von to the gate lines according to the gate control signal CONT1 from the signal controller 600 to turn on the switching element connected to the gate lines. Then, the data signal applied to the data lines is applied to the corresponding pixel PX through the turned-on switching element.
A difference between the voltage of the data signal applied to the pixel PX and the common voltage Vcom is represented as charged voltage of the liquid crystal capacitor, in other words, “pixel voltage”. Liquid crystal molecules are arranged differently according to a size of the pixel voltage and accordingly, polarization of light passing through a liquid crystal layer 3 is changed. The change of the polarization is represented as a change in transmittance of light by a polarizer attached to the display panel assembly 300, such that the pixel PX displays luminance represented by the gray of the image signal DAT.
By repeating the process as a unit of 1 horizontal period (also written as “1H” and the same as one period of the horizontal synchronizing signal Hsync and the data enable signal DE), the gate-on voltage Von is sequentially applied to the plurality of gate lines to apply the data signal to the plurality of pixels PX, thereby displaying images of one frame.
One frame ends, the next frame starts, and a state of the inversion signal applied to the data driver 500 is controlled so that a polarity of the data signal applied to each pixel PX is opposite to a polarity of the previous frame (“frame inversion”). In this case, the polarity of the data signal flowing through one data line may be changed according to a characteristic of the inversion signal even in one frame (for example, row inversion and dot inversion) or the polarities of the data signals applied to one pixel row may also be different from each other (for example, column inversion and dot inversion).
Referring to
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A charge sharing technique may be selectively applied to the data driver 500 of the liquid crystal display according to temperature. For example, referring to
On the contrary, in the case where the two dot inversion drive shown in
As an example for selectively applying the charge sharing techniques of
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The low drop output unit receives input voltage Vin to output an output voltage DVDD lower than the input voltage. For example, the input voltage may be 5 V and the output voltage may be 3.3 V.
The signal controller 600 may transmit an inversion signal POL controlling inversion drive to a digital analog converter DAC and may transmit a horizontal synchronizing signal TP to an output buffer. The charge sharing technique may be applied only in a polarity inversion at room temperature on the basis of the inversion signal POL, and the charge sharing technique may be applied every 1 horizontal period (1 H) at a low temperature less than room temperature on the basis of the horizontal synchronizing signal.
The charge share control signal may be transmitted to the output buffer through resistors Ra and Rb. Ra and Rb may be omitted.
The data driver 500 may include an output buffer, a digital analog converter, a data latch, a shift register, and a receiver.
The charge sharing units A and B include a negative temperature coefficient resistor and charge share control signals CSMODE0 and CSMODE1, which are outputted by the negative temperature coefficient resistor, in which a resistance varies according to a temperature, may vary. For example, CSMODE0 is recognized as a high value and CSMODE1 is recognized as a low value at room temperature and in this case, the charge sharing technique of
Referring to
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The liquid crystal display recognizes a mixed color pattern by a pattern detection unit 620 and, when the mixed color pattern is recognized, the data driver 500 increases a charge sharing time and as a result, the charging time of the data voltage increases to prevent a bar line phenomenon.
For example, referring to
The mixed color pattern is a yellow pattern in the example shown in
Referring to
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According to exemplary embodiment of the present invention, it is possible to ensure a sufficient charging time at various temperatures, reduce the occurrence of a bar line, and improve display quality.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
Number | Date | Country | Kind |
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10-2011-0123575 | Nov 2011 | KR | national |