Patent Document

BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to liquid crystal displays (LCDs), and more particularly, to a liquid crystal display device having modified image signals and a method of modifying same. 
   2. Description of the Related Art 
   Liquid crystal displays (LCDs) are widely used as flat display devices. LCDs comprise a liquid crystal panel having two opposing substrates (e.g. a thin film transistor (TFT) and a color filter (CF) substrate) and a liquid crystal layer disposed between the two opposing substrates. 
   LCDs display image data in response to movement of liquid crystal material caused by voltages applied from external source. However, since the movement of the liquid crystal material does not reach a desired level in a certain time period (e.g. in one frame), the LCD device, especially a device that has many moving images, cannot display the desired data exactly in a frame as known in the art. Several attempts have been made to solve this problem, such as driving methods that are used to raise a response time of the liquid crystal material (e.g. dynamic capacitance compensation (DCC) method). The DCC method compares image signals for a previous frame and image signals for the current frame, and generates new modified signals according to results of the comparison. In other words, when a level of the image signal for the current frame is more than that of the image signal for the previous frame, the DCC method generates a new modified signal that is at a higher level than the image signal for the current frame, and vice versa. However, one drawback to the DCC method is that the LCDs display different images even at the same gray level, i.e., a level of the image signal, by variation in temperature. 
   SUMMARY OF THE INVENTION 
   The present invention provides a liquid crystal display (LCD) device and a method of modifying image signals that can improve a response time of liquid crystal material by minimizing modification errors of the image signals in consideration of non-linearity of the inherent liquid crystal material using varying temperatures. 
   In one embodiment, a liquid crystal display (LCD) device comprises a liquid crystal panel assembly; a sensor, the sensor senses temperature; an image signal modifying portion, the image signal modifying portion receiving image signals and the temperature, calculating a plurality of reference data for modification for image signals for previous and current frames with respect to the temperature using coefficients of quadratic equation, and generating modified images signals according to the plurality of the reference data for modification; and a data driving portion, the data driving portion converting the modified image signals into data voltages and supplying the data voltages to the liquid crystal panel assembly. 
   Further, a method of modifying image signals comprises sensing temperature; calculating reference data for modification for image signals for previous and current frames with respect to the temperature using coefficients of quadratic equation; and generating modified image signals by an interpolation method using the reference data for modification. 
   These and other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments thereof, which is to be read in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantage points of the present invention will become more apparent by describing in detailed embodiments thereof with reference to the accompanying drawings, in which: 
       FIG. 1  is a block diagram of a liquid crystal display (LCD) device according to exemplary embodiments; 
       FIG. 2  is an equivalent circuit diagram for a pixel in the LCD device of  FIG. 1  in accordance with exemplary embodiments; 
       FIG. 3  is a graphical view of sample DCC data corresponding to image signals applied for previous frame and image signals for current frame, and temperature in accordance with exemplary embodiments; 
       FIG. 4  is a graphical view of sample DCC data corresponding to image signals applied for the current frame and the temperature when an image signal for the previous frame is “0” in accordance with exemplary embodiments; 
       FIG. 5  is a graphical view of a method of modifying DCC data using varying temperatures in accordance with exemplary embodiments; 
       FIG. 6  is a block diagram of an image signal modifying portion in accordance with exemplary embodiments; 
       FIG. 7  is a graphical view of a sample of a look-up table (LUT) in accordance with exemplary embodiments; and 
       FIG. 8  is a prospective view of a method of modifying the image signals for the LCD of  FIG. 1  in accordance with exemplary embodiments. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter the embodiments of the present invention will be described in detail with reference to the accompanied drawings. 
     FIG. 1  is a block diagram of a liquid crystal display (LCD) device in accordance with exemplary embodiments, and  FIG. 2  is an equivalent circuit diagram for a pixel in the LCD device of  FIG. 1  in accordance with exemplary embodiments. 
   As shown in  FIG. 1 , an LCD device  1000  comprises a liquid crystal panel assembly  300 , a gate drive portion  400 , a data drive portion  500 , a gamma voltage portion  800 , a signal control portion  600 , and a temperature sensor  900 . 
   The liquid crystal panel assembly  300  comprises multiple display signals (e.g. gate lines GL 1 -GL n  and data lines DL 1 -DL m ) and arrayed in a matrix. The gate lines GL 1 -GL n  deliver gate signals and the data lines DL 1 -DL m  deliver data signals. As shown in  FIG. 2 , each pixel  2000  has a switching element Q connected to a gate line and a data line of the gate lines GL 1 -GL n  and data lines DL 1 -DL m , a liquid crystal capacitor C lc , and optionally a storage capacitor C st . The switching element Q is formed on a lower substrate  100  and has three terminals. The liquid crystal capacitor C lc  represents a capacitor that a liquid crystal layer  3  is disposed between the pixel electrode  190  and a common electrode  270 . The common electrode  270  is formed on an upper substrate  200 . Further, the common electrode  270  may be formed on the lower substrate  100 . The storage capacitor C st  represents a capacitor where a separate signal line (not shown) formed on the lower substrate  100  overlaps the pixel electrode  190 . Further, the storage capacitor C st  may form a capacitor where the pixel electrode  190  overlaps a previous gate line. 
   The gamma voltage portion  800  includes two groups of gamma voltages, for example, one group has higher voltages and another group has lower voltages than a common voltage. The number of the gamma voltages provided may be adjustable based on the resolution of the LCD. 
   The gate drive portion  400  includes a plurality of gate drivers GDI 1 -GDI p  (not shown) and the gate drivers GDI 1 -GDI p  are connected to the gate lines GL 1 -GL n . The gate drive portion  400  applies a gate signal to the gate lines GL 1 -GL n  in order to turn on and off the switching elements Q. Further, the gate drive portion  400  may be formed on the lower substrate  100 . 
   The data drive portion  500  includes a plurality of data drivers DDI 1 -DDI q  (not shown) and the data drivers DDI 1 -DDI q  are connected to the data lines DL 1 -DL m . The data drive portion  500  applies a desired image signal to the data lines DL 1 -DL m  by selecting a certain gamma voltage corresponding to image signals from the gamma voltage portion  800 . The gate drivers GDI 1 -GDI p  and the data drivers DDI 1 -DDI q  may be formed by attaching a TCP (Tape Carrier Package)(not shown) to the liquid crystal panel assembly  300 , and may be directly mounted on the lower substrate  100 , for example, COG (Chip On Glass). 
   The temperature sensor  900  senses a temperature T of the liquid crystal panel assembly  300  and outputs the temperature to the signal control portion  600 . The temperature sensor  900  may be mounted on the liquid crystal panel assembly  300  and may be implemented by a TFT applied to the liquid crystal panel assembly  300 . The temperature sensor  900  may use a leakage current of the TFT as the value corresponding to the temperature T. 
   The signal control portion  600  comprises a image signal modifying portion  650 , and controls operation of the gate drive portion  400  and the data drive portion  500 . The image signal modifying portion  650  modifies input image signals R, G, B for improving a response time of liquid crystal material according to the input image signals R, G, B from a graphic controller (not shown) and temperature from the temperature sense portion  900 . 
   Turning now to  FIG. 1 , operation of the LCD device  1000  will now be described in accordance with exemplary embodiments. 
   The signal control portion  600  receives an input control signals (Vsync, Hsync, Mclk, DE) from a graphic controller (not shown) and input image signals (R, G, B) and generates image signals (R′, G′, B′), gate control signals CONT 1 , and data control signals CONT 2  in response to the input control signals and the input image signals. Further, the signal control portion  600  sends the gate control signals CONT 1  to the gate drive portion  400  and the data control signals CONT 2  to the data drive portion  500 . The gate control signals CONT 1  include STV indicating start of one frame, CPV controlling an output timing of the gate on signal, and OE indicating an ending time of one horizontal line, etc. The data control signals CONT 2  include STH indicating start of one horizontal line, TP or LOAD instructing an output of data voltages, RVS or POL instructing polarity reverse of data voltages with respect to a common voltage, etc. 
   The data drive portion  500  receives the image signals R′, G′, B′ from the signal control portion  600  and outputs the data voltages by selecting gamma voltages corresponding to the image signals R′, G′, B′ according to the data control signals CONT 2 . The gate drive portion  400  applies the gate on signal according to the gate control signals CONT 1  to the gate lines and turns on the switching elements Q connected to the gate lines. 
   Turning now to  FIGS. 3-8 , a method of modifying image signals of the LCD device  1000  will now be described in accordance with exemplary embodiments. 
     FIG. 3  is a graphical view of DCC data according to image signals for previous frame and image signals for current frame, and temperature,  FIG. 4  is a graphical view of DCC data according to the image signals for the current frame and the temperature when an image signal for the previous frame is “0”, and  FIG. 5  is a graphical view of a method of modifying DCC data with respect to the temperature according to an exemplary embodiment.  FIG. 6  is a block diagram of an image signal modifying portion according to an exemplary embodiment,  FIG. 7  is a graphical view of an example of a look-up table (LUT) according to an exemplary embodiment, and  FIG. 8  is a prospective view of a method of modifying the image signals according to an exemplary embodiment. 
   Herein, Image signals for the current frame indicate image signals for the nth frame, Gn and image signals for the previous frame indicate image signals for (n−1)th frame, Gn−1. 
   Referring to  FIG. 3 , DCC data Gr indicate modified data satisfying a desired response time with respect to the image signals for previous and current frames, Gn−1, Gn, and is previously set by experimental results. Further, the DCC data Gr have different modified image signals even in the same gray levels as the temperature of the LCD device varies. When the image signal for previous frame, Gn−1 is “0” gray level and the image signal for current frame Gn is “48” gray level, and the temperature T is x 1 , the DCC data, Gr is y 1 . When the temperature T is x 2 , the DCC data, Gr is y 2 , and the temperature T is x 3 , the DCC data, Gr is y 3 . When TP 1  (x 1 , y 1 ), TP 2  (x 2 , y 2 ), and TP 3  (x 3 , y 3 ) are connected, variations in the DCC data, Gr with respect to the temperature T as shown in  FIG. 4 . 
   In accordance with exemplary embodiments, the DCC data, Gr, as shown in  FIG. 4 , have non-linear characteristics at less than about 20° C. and linear characteristics at more than about 20° C. In this embodiment, a method of modifying image signals include calculating modified image signals Gn′ using the DCC data, Gr of the non-linear characteristics. The DCC data Gr is stored in a look-up table and correspond to a combination of upper bits of the image signals for previous and current frames, Gn−1, Gn, for example, 17×17 or 9×9 combination. The method includes using the DCC data, Gr as references of the DCC data. The method further includes calculating modified image signals Gn′ by a piecewise quadratic interpolation (PQI) using the DCC data Gr occurring as a result of the temperature modification for a combination of the remaining bits except for the upper bits of the image signals. 
   Turning now to  FIG. 5 , a method of modifying image signals (R′, G′, B′) using the PQI will now be described in accordance with exemplary embodiments. 
   Modified image signals Gn′ with respect to any temperature x between TP 1  (x 1 , y 1 ), TP 2  (x 2 , y 2 ), TP 3  (x 3 , y 3 ), TP 4  (x 4 , y 4 ), and TP 5  (x 5 , y 5 ) may be calculated as follows. Herein, x 1  to x 5  refer to reference temperatures used in calculating the modified image signals, and y 1  to y 5  are DCC reference data with respect to each of the reference temperatures, x 1  to x 5 . A distance between the reference temperatures gets narrower in the temperature section that is less than about 20° C., for example and gets wider in the temperature section that is more than about 20° C., for example, and thus a memory (now shown) storing values of the look-up table may be effectively used. For example, the reference temperatures, x 1  to x 5  may be set as 0° C., 10° C., 20° C., 30° C., 35° C., and 50° C., respectively. Further, the reference temperatures, x 1  to x 5  may be set according to the size of the memory and the temperature of DCC data, Gr, etc. 
   First, a coefficient of quadratic equation, X 1  (p 1 , p 2 , p 3 ), which connects three points, i.e. TP 1 , TP 2 , and TP 3 , is obtained as follows.
 
 y=p   1   x   2   +p   2   x+p   3   [Equation 1]
 
   If Eq. 1 is described as vector, it becomes AX 1 =B. In case of A=[x 1   2 , x 1 , 1; x 2   2 , x 2 , 1; x 3   2 , x 3 , 1], B=[y 1 ; y 2 ; y 3 ], and X 1 =[p 1 , p 2 , p 3 ], X 1  may be obtained as follows.
 
X 1 =A −1 B  [Equation 2]
 
   Reference data for modification at temperature x between TP 1  and TP 3  may be obtained by the Equation 1. In the same way, a coefficient of quadratic equation, X 2 , which connects three points, i.e. TP 2 , TP 3 , TP 4  may be obtained. In other words, reference data for modification at temperature x between TP 2  and TP 4  may be obtained by a coefficient of quadratic equation, X 2 . Further, a coefficient of quadratic equation, X 3 , which connects three points, i.e. TP 3 , TP 4 , TP 5  may be obtained. In other words, reference data for modification at temperature x between TP 3  and TP 5  may be obtained by a coefficient of quadratic equation, X 3 . 
   The reference data for modification between TP 2  and TP 3  may be obtained by one of the coefficients of quadratic equation, X 2  and X 3 . However, the reference data for modification may be obtained by a coefficient closer to measured values by comparing calculated values by X 1  and X 2  using Least Square Approximation method with the measured values. In this way, the reference data for modification between TP 3  and TP 4  may be obtained by one of coefficients of quadratic equation, X 2  and X 3 . As a result, the reference data for modification between TP 1  and TP 5  may be more approximated to the measured values as the number of the reference temperatures increases. 
   The reference data for modification between TP 1  and TP 5  may be obtained by the coefficient of quadratic equation, X 1  between TP 1  and TP 3  and the coefficient of quadratic equation, X 3  between TP 3  and TP 5 . Accordingly, the number of parameters stored in the LUT may be reduced and thus the size of the memory may be reduced. 
   Accordingly, all the coefficients of quadratic equation with respect to a combination of the remaining bits of the image signals for previous and current frames Gn−1, Gn are obtained by the PQI and stored in the LUT. Then, the reference data for modification are calculated with respect to the image signals for previous and current frames Gn−1, Gn and temperature T, and modified image signals Gn′ are generated by the reference data for modification. 
   An image signal modifying portion for the LCD device will be described in detail with reference to the accompanying drawings. 
   As shown in  FIG. 6 , the image signal modifying portion  650  comprises a signal receiving portion  610 , a memory  620 , a look-up table (LUT)  630 , and an operation processing portion  640 . The image signal modifying portion  650  may be installed in the signal control portion  600 . The LUT  630  and the operation processing portion  640  receive temperature T from a sensor  900 . 
   The signal receiving portion  610  receives input image signals Gm from a signal source (not shown) and converts the input image signals Gm into image signals Gn. The signal receiving portion  610  supplies the image signals Gn to the memory  620 , the LUT  630 , and the operation processing portion  640 . 
   The memory  620  supplies image signals for previous frame, Gn−1 previously stored to the LUT  630  and the operation processing portion  640 , and stores image signals for current frame, Gn from the signal receiving portion  610 . The memory  620  stores image signals by a frame and may be affixed to the image signal modifying portion  650 . Further, the memory  620  comprises a frame memory, etc, for example. 
   Referring to  FIG. 7 , the LUT  630  has 17×17 (or 9×9) matrix. Lows and columns of the matrix indicate the image signals for the previous and current frames, Gn−1, Gn, respectively, and parameters, P 1 , P 2 , P 3 , P 4  for the reference temperatures are stored at intersecting points of the lows and columns of the matrix. The LUT  630  receives the image signals for previous and current frames, Gn−1, Gn and the temperature T, and supplies parameters, P 1 , P 2 , P 3 , P 4  to the operation processing portion  640 . The LUT  630  may be affixed to the image signal modifying portion  650 . In this embodiment, since the LUT  630  stores coefficients of quadratic equation according to the number of the temperatures, the size of the LUT  630  may be reduced. 
   The operation processing portion  640  comprises a first operation portion  642  and a second operation portion  644 . The first operation portion  642  calculates reference data for modification corresponding to the image signals for previous and current frames, Gn−1, Gn and the temperature T using the PQI. The second operation portion  644  receives reference data for modification from the first operation portion  642 , and calculates modified image signals Gn′ with respect to the Gn−1 and the Gn using linear interpolation, etc. 
   Operation of the operation processing portion  640  will be described in more detail with reference to  FIGS. 7 and 8 . 
   Referring to  FIGS. 7 and 8 , when an image signal for previous frame Gn−1 is “40” gray level, an image signal for current frame Gn is “216” gray level, and a temperature T is x, a point corresponding to these conditions is marked as TP in  FIG. 8 . In this case, the reference data for modification for the image signal for previous frame Gn−1 are “32” and “48” gray levels, the reference data for modification for the image signal for current frame Gn are “208” and “224”, and the reference temperatures are x 2  and x 3 . The first operation portion  642  receives coefficients of quadratic equation, P 1 =[P 11 , P 12 , P 13 ], P 2 =[P 21 , P 22 , P 23 ], P 3 =[P 31 , P 32 , P 33 ], P 4 =[P 41 , P 42 , P 43 ], at the temperature (x 2 , x 3 ) with respect to a combination of the reference data for modification, (32, 208), (48, 208), (32, 224), (48, 224) from the LUT  630 , and calculates the reference data for modification, y 00 ′, y 01 ′, y 10 ′, and y 11 ′ with respect to the temperature x. The second operation portion  644  calculates modified image signals Gn′ according to the reference data for modification y 00 ′, y 01 ′, y 10 ′, and y 11 ′ from the first operation portion  642 . 
   In this embodiment, the modified image signals Gn′ are calculated by the four combinations of the reference data for modification for the image signals for previous and current frames, Gn−1, Gn, but may be calculated by three or two combinations of the reference data for modification according to any interpolation method. 
   Consequently, the present invention may reduce the size of the memory by calculating modified image signals with respect to the temperature using PQI and improve the display quality of the LCD device by calculating modified image signals considering variation in the temperature. 
   Having described the embodiments of the present invention and its advantages, it should be noted that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by appended claims.

Technology Category: g