Patent Publication Number: US-7592992-B2

Title: Inversion method for liquid crystal display

Description:
BACKGROUND 
     The invention relates to liquid crystal display, and in particular, to an inversion method for liquid crystal display. 
       FIG. 1  shows a conventional liquid crystal display  100 . Polarity inversion is a technique used in flat panel display to eliminate image retention caused by longtime DC biasing. The liquid crystal display  100  comprises a pixel array  102 , a plurality of source drivers  104 , and a plurality of gate drivers  106 . The source driver  104  is driven by the timing controller  108  to output data signals, and the gate driver  106  outputs scan signals, thereby the pixel array  102  is driven to display images. Each of the source drivers controls a plurality of pixel columns, and each of the gate drivers controls a plurality of pixel lines, thus forming intersecting sections. The timing controller  108  provides inversion signals POL( 1 H) or POL( 2 H) to the source driver  104  for determining polarity of corresponding pixels. The source driver  104  thereafter generates data voltage of corresponding polarity accordingly to drive the pixels. The value of inversion signals varies with time, thus polarities of adjacent pixels are different. More specifically, polarities of adjacent pixels are at an opposite level. The inversion signal POL( 2 H) represents a period twice than that of inversion signal POL( 1 H). Symbols “+” and “−” denotes polarities of each section in one frame time. The polarity inversion, however, induces certain disadvantages. For example, when the image comprising a specific pattern is input, screen flicker occurs. The specific pattern is referred to as a Killer pattern, caused by panel resistance irregularity, and is unavoidable. 
       FIG. 2  is a timing chart of an inversion signal POL in the conventional liquid crystal display of  FIG. 1 . “GCK” denotes the scan line clock. The inversion signal POL( 1 H) periodically inverts every scan line, and the inversion signal POL( 2 H) every two scan lines. The inversion may resolve the Killer pattern of  FIG. 1 , however, another specific pattern can be found to induce screen flicker for the double period case. Thus periodic inversions always present a weakness. 
     SUMMARY 
     An embodiment of the invention provides an inversion method for use in a liquid crystal display comprising pluralities of pixels. First, at least one inversion signal is provided to determine a polarity. Data voltage is then generated according to the polarity and a data signal. Thereafter, a scan signal is provided to activate a pixel, such that the data voltage generates luminance. The inversion signal is a non-periodic signal. When the scan signal activates the pixel, the inversion signal provides the random alternative of a first level and a second level. 
     When the inversion signal is at the first level, the polarity is determined to be positive. When the inversion signal is at the second level, the polarity is determined to be negative. The first level is a logic 1, and the second level is a logic 0. The pixels are grouped by column, each group comprising at least one column, and the provision of at least one inversion signal comprises providing a plurality of inversion signals to individually determine the polarity of each group. The plurality of inversion signals comprises an odd inversion signal and an even inversion signal. The odd inversion signal determines polarity of odd groups, and the even inversion signal determine polarity of even groups. 
     Also provided is a liquid crystal display, comprising a timing controller, at least one source driver, and at least one gate driver. The timing controller generates a scan signal and a data signal, and provides at least one inversion signal to determine polarity of a data voltage. The source driver, coupled to the timing controller, generates the data voltage according to the inversion signal and the data signal. The gate driver, coupled to the timing controller, generates the scan signal to activate at least one pixel. When the scan signal activates the pixel, the pixel receives the data voltage for illumination. When the pixel is activated, the inversion signal has the random alternative of a first level and a second level. Wiring between the timing controller and the source drivers comprises point-to-point architecture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description, given by way of example and not intended to limit the invention solely to the embodiments described herein, will best be understood in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a conventional liquid crystal display  100 ; 
         FIG. 2  is a timing chart of an inversion signal POL in the conventional liquid crystal display of  FIG. 1 ; 
         FIG. 3  shows an embodiment of a liquid crystal display liquid crystal display  300 ; 
         FIG. 4  shows an embodiment of a liquid crystal display liquid crystal display  400 ; 
         FIG. 5  shows an embodiment of a liquid crystal display liquid crystal display  500 ; and 
         FIG. 6  is a flowchart of the inversion method according to the invention. 
         FIG. 7  is a timing chart similar to  FIG. 2 , illustrating features or aspects of the embodiment shown and described in connection with  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  is an embodiment of a liquid crystal display  300 . The liquid crystal display  300  comprises a pixel array  102 , three gate drivers  106  and four paired source drivers  104  and  114 . The source driver  104  and  114  are identical chips arranged by order, even and odd, each drive corresponding to a plurality of column of pixels. Additionally, the liquid crystal display  300  comprises a timing controller  308  for generating an inversion signal POL, wherein the inversion signal is a non-periodic random signal, comprising random alternatives of logic 0 and logic 1. Through an inverter  302 , the source drivers  104  and  114  receive the inversion signal POL with opposite polarity, such that the corresponding plurality of pixel columns is driven to eliminate the killer pattern effect. 
       FIG. 4  shows an embodiment of a liquid crystal display  400 . The liquid crystal display  400  comprises a pixel array  102 , three gate drivers  106  and eight source drivers  104 . Each source driver  104  drives corresponding plurality column of pixels. Additionally, the liquid crystal display  400  comprises a timing controller  408 , generating eight different inversion signals POL to corresponding source driver  104 , such that the corresponding plurality column of pixels are driven with individual random inversion. During display, the timing controller  408  delivers a scan signal and a data signal to the gate driver  106  and source driver  104 . The source driver  104 , coupled to the timing controller  408 , generates data voltage based on the received inversion signal POL and the data signal, to drive a pixel. The polarity of the data voltage is determined by the inversion signal POL. When the gate driver  106  outputs the scan signal to activate the corresponding pixel in the pixel array  102 , the pixel converts the data voltage to luminance. 
       FIG. 5  shows an embodiment of a liquid crystal display  500 . The liquid crystal display  500  comprises a plurality of source drivers  104  and  114 , arranged by order, even and odd, each coupled to the timing controller  508 . The source drivers  104  and  114  receive different inversion signals. Specifically, the four source drivers  104  are driven by an inversion signal POL(A), and the four source drivers  114  are driven by an inversion signal POL(B). The inversion signal POL(A) and the inversion signal POL(B) may have no relationship, and may be of opposite polarity. Both are non-periodic random signals comprising random alternatives of logic 0 and logic 1, as shown in  FIG. 7 . Random signal generation is achieved by conventional pseudo-random algorithm. The output comprises only two values, logic 0 and logic 1, with equal probability. The eight different inversion signals POL in  FIG. 4 , may be generated by one circuit with eight different random seeds. The inversion is non-periodic, such that flicker never occurs. The timing controller may further avoid flicker by predicting the killer pattern based on the image data, and enhance the image accordingly through specific inversion. The gate driver  106  scans the pixel array  102  line by line, and the source driver  104  inverts the activated pixels according to the inversion signals POL output from the timing controller. 
       FIG. 6  is a flowchart of the inversion method according to the invention. In step  602 , the timing controller provides a random inversion signal POL comprising random alternative of positive and negative polarities. In step  604 , the source drivers  104  and  114  generate data voltages according to data signals delivered from the timing controller and the inversion signal POL. In step  606 , the gate driver  106  provides a scan signal to activate a pixel, and the data voltage generates luminance. The random inversion avoids flicker. 
     The inversion signal may require additional wiring in conventional architecture, thus the invention is more suitable for point-to-point architecture that utilizes a serial data stream to transfer the signals between the timing controller and the source drivers without the need for additional wiring. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.