Patent Application
20050275612
1. Field of the Invention
The present invention relates to liquid crystal display (LCD), and more specifically, to an LCD capable of reducing the influence of flicker phenomenon.
2. Description of the Prior Art
LCDs having a plurality of transistors and capacitors forming an array can display vivid images and are widely used throughout the world. The LCD panels, due to light weight, low power consumption, and absence of radiation, have increasingly replaced traditional CRT monitors and are also used extensively in portable electrical devices such as notebook computers and personal digital assistants, etc.
An LCD display includes two indium tin oxide sheets of glass (ITO glass) sandwiching a liquid crystal layer comprising liquid crystal molecules. One of the glass layers serves as a pixel electrode while the other as a common electrode. The alignment of the sandwiched liquid crystal molecules is changed as the voltage across the two electrodes changes. Therefore, various gray levels are resulted based on different light incidence conditions provided by different alignments of the liquid crystal molecules.
In general, as is well known in the art, the voltage across the two electrodes can be of two polarities. A voltage of the pixel electrode larger than that of the common electrode indicates a positive polarity, and inversely, a voltage of the common electrode larger than that of the pixel electrode indicates a negative polarity. If absolute values of the voltage differences across the two electrodes are the same, no matter which of the voltage value of the pixel electrode or that of the common electrode is higher, an identical gray level is obtained. However, as a matter of fact, voltage difference values across the two electrodes with opposite polarities result in opposite alignments of the liquid crystal molecules.
From a viewpoint of long-term averaging effect, if the voltage across the two electrodes appears to be either of the two polarities more often than the other polarity, an average DC constituent of a value other than zero across the two electrodes will be resulted, causing a voltage-drifting phenomenon to a common voltage Vcom on the common electrode. Consequently, the alignment of the liquid crystal molecules fails to follow the control of the designated control voltage, resulting in displaying incorrect gray levels. In an extreme case, if the unbalance between the two polarities lasts for too long a time, it is possible, even after the unbalance is removed, that the liquid crystal molecules cannot be correctly controlled according to applied electrical field, due to spoiled electrical characteristics.
As a result, in order to prevent the common voltage Vcom from experiencing the voltage-drifting phenomenon as the voltage applied across the two electrodes leans toward either of the polarities, the voltages across the two electrodes are designed to periodically switch between positive polarity and negative polarity. As shown in
Please refer to
Nevertheless, under certain situations, a well-known phenomenon called “flicker” occurs when certain periodic input display data is combined with conventional periodic switch modes. Take pixel toggling as an example, in an extreme case, if a periodic data flow (FF, 00, FF, 00, . . . ) is inputted repeatedly, as is obvious to a skilled artisan in this art, the voltage applied across the two electrodes will predominantly appear in the direction of one of the polarities (positive polarity illustrated in
It is therefore one of the objectives of the claimed invention to provide a Liquid Crystal Display (LCD) and method thereof, capable of reducing the influence of flicker phenomenon to improve the quality of image display.
According to embodiments of the present invention, a method for controlling a display device to display an image is disclosed. The method includes the steps of receiving a display data flow, generating a polarity signal, generating a gray-scale signal based on the polarity signal and the display data flow, and driving a pixel unit to display the image based on the gray-scale signal. The polarity signal is substantially DC-balanced.
According to embodiments of the present invention, a display apparatus is also disclosed. The display apparatus includes a plurality of pixel units and a logic unit for receiving a display data flow. The logic unit comprises a polarity signal generator for generating a polarity signal and a plurality of polarity mixers for generating a gray-scale signal based on the polarity signal and the display data flow to drive the plurality of pixel units.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Please refer to
The scan line driver 16 subsequently sends a turn-on voltage through the scan lines 102 to turn on each row of the transistors 22. As the transistor 22 turns on, the logic unit 14 transmits the designated gray-scale signals for each image pixel unit 12 to the pixel electrode 24 through the data line 101, so that the storage capacitor Cs will charge to a desired voltage value. After the image pixel unit 12 at the last line has finished charging, the scan line driver 16 will go back and start a new cycle of charging from the first line. Taking an LCD with 60 Hz refresh frequency as an example, the display time for each frame is about 1/60=16.67 ms. In other words, the scan line driver 16 will recharge each line approximately every 16.67 ms. The alignment of the liquid crystal molecules in the liquid crystal layer 25 is changed based on a difference between the gray-scale signal and the common voltage value Vcom. The storage capacitor Cs is used to maintain the voltage difference as the transistor 22 is turned off, until the corresponding transistor 22 turns on again.
Please note that the functional block diagram of the LCD 10 and the structure diagram of the image pixel unit 12 shown in
Please refer to
In this embodiment of the present invention, in order to achieve the goal of maintaining the voltage across two electrodes of each image pixel unit 12 to be of zero DC constituent in the long run, the polarity signal generator 32 is used for generating substantially DC-balanced polarity signals, i.e., the number of times that the positive polarity appears in the polarity signal is around the same number of times that the negative polarity appears in the polarity signal for a given long period of time. As one embodiment, the polarity signal generator 32 can be a random signal generator, which selects to output the positive polarity or the negative polarity in a randomly fashion. In another embodiment, the polarity signal generator 32 can also be implemented to, within different time periods, select different sequences from a plurality of DC-balanced polarity sequences. As shown in
A skilled person in this art should understand that the sequences shown in
Utilizing the present inventive method, the polarity of gray-scale signals to be received by each pixel unit is more even, so that the possibility of occurrence of flicker phenomenon will be reduced.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 093117195 | Jun 2004 | TW | national |
