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1. WO2006098527 - METHOD AND APPARATUS FOR CONVERTING GRADATION DATA IN TFT LCD

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]

METHOD AND APPARATUS FOR CONVERTING GRADATION DATA
IN TFT LCD

Technical Field
The present invention relates to an apparatus for driving a thin film transistor liquid crystal display TFT LCD and, more particularly, to a method and an apparatus for converting gradation data in TFT LCD that raises response speed and improves picture quality output of TFT LCD by converting gradation data applied to TFT LCD appropriately.

Background Art
Recently, a liquid crystal display has been widely used among various kinds of display apparatus. The LCD consists primarily of two glass plates, on which transparent electrodes are formed, with some liquid crystal material filled between them. When a predetermined electric field is applied to the transparent electrodes, the electric field arranges and rotates the liquid crystal material in a specific direction so as to control the quantity of lights transmitting the liquid crystal material, thus displaying images. The LCD is classified into a twisted nematic TN LCD, a super twisted nematic STN LCD, etc., in view of displaying method of the LCD. Besides, it is divided roughly into a simple matrix method and an active matrix method, in view of driving method of the LCD. The active matrix LCD is also known as a thin film transistor TFT LCD. The TFT LCD having a transistor located at each pixel intersection can provide high quality images because it drives each pixel using the transistor directly. Accordingly, the TFT LCD has been widely used.
Meanwhile, the LCD may deteriorates vividness of the moving picture since it has a long response time against input data under the influence of cumulative response, that is, since an image of a previous screen does not immediately disappear but is overlapped with a subsequent image,
To solve this problem, the present inventor and applicant have disclosed a method and an apparatus for raising the response speed of the LCD by over-driving the LCD adequately to increase time-sequential variation in the gradation voltage applied to the LCD.
Fig. 1 is a block diagram explaining the basic concept of US Patent Application No. 10/395,663 titled: Method and Apparatus for Converting Gradation Data in STN LCD and PCT Application No. PCT/KR2004/000406 disclosed by the present inventor and the applicant.
The apparatus for converting gradation data as shown in Fig. 1 comprises a processor 10 for processing image data to generate and output gradation data corresponding to respective pixels, an LCD driving part 20 for driving the LCD based on driving signals input, and a data converting apparatus 30 for converting the gradation data input from the processor 10.
The data converting apparatus 30 includes a recording buffer 31 for storing the gradation data input from the processor 10, a frame memory 32 for storing the gradation data for driving the LCD, and a data converting part 33 for converting the gradation data stored in the recording buffer 31 and for storing converted gradation data in the frame memory 32.
In the above configuration, the gradation data corresponding to an image displayed on the LCD at present is stored in the frame memory 32. Then, if new gradation data is input from the processor 10, the data converting part 33 compares the input gradation data with the previous gradation data stored in the frame memory 32, i.e., the gradation data displayed on the LCD at present;
calculates a difference value between them based on the previous gradation data; and converts the input gradation data based on the difference value. That is, according to the conventional apparatus, it is designed to improve the response speed of the LCD by setting forcibly the variation of the gradation values
displayed on the LCD large.
However, the above described apparatus has following drawbacks.
Fig. 2 is a configuration diagram showing an active matrix circuit and a driving circuit of the TFT LCD panel. The TFT LCD panel of Fig. 2 includes a plurality of data lines S (S1 , S2, •■•, Sn) and gate lines G (G1 , G2, •••, Gn), which are crossed with each other as a matrix pattern on a lower glass. On the
respective crossings between the data lines and the gate lines, FETs 40 and cell capacitors 41 are connected with each other to drive the respective pixels of the LCD panel. The gate lines G are connected with gate line driving devices 50 (50-1, ■ ■ •, 50-n) for driving the gate lines and the data lines S are coupled with data line driving devices 60 (60-1 , ••■, 60-n) for outputting gradation signals. Here, the gate line driving device 50 and the data line driving device 60 are established plurally according to the size of the LCD since they are arranged to drive the gate lines and the data lines in the unit of predetermined number.
Meanwhile, since the LCD driving part 20 and the data converting apparatus 30 in Fig. 1 generates and outputs gradation data based on the gradation data input from the processor 10, the LCD driving part 20 and the data converting apparatus 30 organize the data line driving device 60 in Fig. 2 substantially. Accordingly, if applying the elements depicted in Fig. 1 to the LCD, the data converting apparatus 30 in Fig. 1 is provided in each data line driving device 60 and the number of the data converting apparatus 30 is set identical with that of the data line driving device 60.
Besides, the data converting apparatus 30 requires the frame memory 32, which is relatively a high-priced device, in order to execute data conversion.
Accordingly, if applying the apparatus depicted in Fig. 1 to the LCD, the
manufacturing cost of the LCD is increased sharply.

Disclosure of Invention
Accordingly, the present invention is designed in consideration of the above described drawbacks and an object of the present invention is to provide a method and an apparatus for converting gradation data in TFT LCD that can generate gradation data for driving LCD efficiently, not applying an additional frame memory.
To accomplish the above object, there is provided a method for converting gradation data in TFT LCD in accordance with a first aspect of the present invention comprising the steps of: inputting gradation data corresponding to one scan line from outside; receiving and storing gradation values corresponding to a present image from cell capacitors mounted on an LCD panel; converting gradation data values input from outside based on the two gradation values; and driving the LCD panel based on the converted gradation data.
Besides, the step of converting gradation data converts the input gradation data values to increase a difference more between the gradation data values input from outside and the gradation data values stored in the capacitors.
To accomplish the above object, there is provided an apparatus for converting gradation data in TFT LCD comprising: a first storing means for storing gradation data input from outside; an analog/digital converting means, connected with respective data lines of an LCD panel, for converting voltage values on the data lines into digital data; a second storing means for storing data values output from the analog/digital converting means; a data converting means for converting data values stored in the first storing means based on data values stored in the first and second storing means and for storing converted data values in a gradation driving means; and a gradation driving means for driving the LCD panel based on the data values stored by the data converting means.
In addition, the data converting means converts the data values stored in the first storing means to increase a difference more between the data values stored in the first storing means and the data values stored in the second storing means.

Brief Description of Drawings
Fig. 1 is a block diagram showing a conventional apparatus for converting gradation data;
Fig. 2 is a configuration diagram illustrating an active matrix circuit and a driving circuit constituting an LCD panel;
Fig. 3 is a block diagram depicting an apparatus for converting gradation data in TFT LCD in accordance with a preferred embodiment of the present invention;
Fig. 4 a flowchart for explaining the operation of elements depicted in Fig. 3; and
Fig. 5 is a timing diagram for illustrating the operation of elements depicted in Fig. 3.

Best Mode for Carrying Out the Invention
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.
First, the basic concept of the present invention will be described hereinafter.
Referring to Fig. 2, in order to display an image on an LCD panel, a data line driving device 60 outputs a predetermined gradation voltage, while a gate line driving device 50 is selecting a specific gate line G. A driving signal output from the gate line driving device 50 turns on the FETs 40 connected with corresponding gate line, then, gradation data output from the data line driving device 60, more precisely, gradation voltages corresponding to gradation values are charged in cell capacitors 41 coupled with corresponding data line through the FETs 40. And, each pixel is driven according to the voltage charged in corresponding cell capacitor 41.
The above described operation proceeds continuously and repeatedly to the respective gate lines G in turn so as to display a predetermined moving picture on the LCD panel.
In the above configuration, the cell capacitor 41 established on each pixel has a charged voltage value corresponding to gradation data displayed through corresponding pixel. That is, the charge voltages of the respective cell capacitors 41 correspond to the gradation data displayed on the LCD panel at present.
Accordingly, the gradation voltage stored in the cell capacitor 41 has the same value substantially with the gradation data stored in the frame memory 32 depicted in Fig. 1.
The present invention doesn't apply an additional frame memory 32, but uses the voltage values charged in the cell capacitors 41 established on the respective pixel of the LCD panel, differently from the conventional apparatus depicted in Fig. 1. Like this, it is unnecessary to equip an additional frame memory in the data line driving device 60 for driving LCD panel, thus reducing the manufacturing cost of the LCD panel, more concretely, the data line driving device 60 sharply.
Fig. 3 is a block diagram depicting an apparatus for converting gradation data in TFT LCD in accordance with a preferred embodiment of the present invention. In Fig. 3, only one gate line driving device 50 and data line driving device 70 each are depicted and the elements substantially identical with those described in Fig. 2 have the same reference numerals.
In Fig. 3, the gate line driving device 50 is connected with a plurality of gate lines G and the data line driving device 70 is coupled with a plurality of data lines S in the same manner with Fig. 2.
The data line driving device 70 includes a recording buffer 71 , a gradation driving part 72, an analog/digital converting part 73, a latch part 74, a data converting part 75 and a delay circuit 76.
The recording buffer 71 temporarily stores gradation data input from an external processor 10 in the same manner with Fig. 1.
An input end of the gradation driving part 72 is connected with an output end of the data converting part 75 and output ends of the gradation driving part 72 are coupled with a plurality of data lines S on the LCD panel. The gradation driving part 72 outputs gradation voltages corresponding to gradation data to be displayed on the LCD panel through the respective data lines S in the same manner with the LCD driving part 20 in Fig. 1. Then, the gradation voltages output from the gradation driving part 72 are charged in the cell capacitors 41 established on the respective pixels.
Input ends of the analog/digital converting part 73 are connected with the respective data lines S and output ends of the analog/digital converting part 73 are coupled with the latch part 74 as input ends. The analog/digital converting part 73 is driven by a line pulse input from the external processor 10. If the line pulse input through the delay circuit 76 from the external processor 10 is increased to a high level for example, the analog/digital converting part 73 executes
analog/digital conversion for converting the voltage levels of the data lines S into digital data and output the converted data. Then, if ending the digital conversion against input analog signals, the analog/digital converting part 73 outputs an A/D conversion end signal EOC. The EOC signal output from the analog/digital converting part 73 is input to the data converting part 75 and, at the same time, to the latch part 74 as a latch signal.
Input ends of the latch part 74 are connected with the output ends of the analog/digital converting part 73 and an output end of the latch part 74 is coupled with an input end of the data converting part 75. If the A/D conversion end signal EOC is input from the analog/digital converting part 73, the latch part 74 latches data output from the analog/digital converting part 73 to output to the data converting part 75.

The delay circuit 76 delays the line pulse signal input from the external processor 10 for a predetermined time and inputs the line pulse signal to the analog/digital converting part 73. The delay circuit 76 is to match the data conversion operation of the analog/digital converting part 73 with a gate driving signal output from the gate line driving device 50.
The gate line driving device 50 operates, not depicted in Fig. 3, according to the line pulse input from the external processor 10. That is, the data line driving device 50 outputs a gate driving signal for driving a specific gate line G, if the line pulse is input from the external processor 10. The gate line driving device 50 outputs the gate driving signal for driving subsequent gate lines in turn, every time when the line pulse is input.
As described with reference to Fig. 2, when a specific gate line G is driven by the gate line driving device 50, the FETs 40 coupled with corresponding gate line G are turned on and, at the same time, the respective cell capacitors 41 are electrically coupled with the data lines S. Here, electric charges charged in the cell capacitors 41 are output through the turned-on FETs 40 and the data lines S. The gradation voltages output as described above are converted into digital data by the analog/digital converting part 73 and forwarded to the latch part 74.
Accordingly, the latch part 74 stores a series of gradation data corresponding to the gate line G selected by the gate line driving device 50 and, the stored gradation data have substantially the same value with the gradation data displayed on the LCD panel at present.

When the A/D conversion end signal EOC is output from the analog/digital converting part 73, the data converting part 75 generates new gradation data based on the gradation data input from outside and stored in the recording buffer 71 and the gradation data stored in the latch part 74, i.e., the gradation data display on the LCD panel at present. The newly generated gradation data is applied to the gradation driving part 72 and will be displayed on the LCD panel. Besides, if ending the data conversion, the data converting part 75 outputs a data conversion end signal DCC, which is applied to the gradation driving part 72.
Next, the operations of the apparatus having the above configuration will be described hereinafter with reference to Figs. 4 and 5.
Fig. 4 a flowchart for explaining the operation of the data line driving device 70 and Fig. 5 is a timing diagram for illustrating the gate driving signal for driving the gate lines G (G1 , G2, • ••, Gn), the line pulse input from the external processor 10, the output signal of the delay circuit 76, the A/D conversion end signal EOC output from the analog/digital converting part 73 and the data conversion end signal DCC output from the data converting part 75.
In Fig. 3, the external processor 10 inputs a series of gradation data to be displayed on the LCD panel to the data line driving device 70 (ST1). The input gradation data is stored in the recording buffer 71. Here, the gradation data is input in the unit of one scan line. Like this, if ending the data input for one scan line portion, the processor 10 inputs a predetermined horizontal synchronization signal, i.e., the line pulse signal.

If the line pulse signal is input from the processor 10, the gate line driving device 50 outputs a gate driving signal correspondingly. Then, the FETs 40 corresponding to the gate line G are turned on and, at the same time, the respective cell capacitors 41 are electrically coupled with the data lines S. Here, the gate line G driven by the gate driving signal corresponds to the gradation data stored in the recording buffer 71.
The line pulse signal input from the processor 10 is supplied through the delay circuit 76 with the analog/digital converting part 73. Then, the analog/digital converting part 73 executes analog/digital conversion against data values on the data lines S. If ending the digital conversion, the analog/digital converting part 73 outputs an A/D conversion end signal EOC of high level, for example. Then, the latch part 74 latches data values output from the analog/digital converting part 73, synchronizing with the A/D conversion end signal EOC. Accordingly, voltage values of the respective cell capacitor 41 corresponding to the one scan line selected by the gate line G are charged in the latch part 74. That is, the previous gradation data values corresponding to the gate line G are stored in the latch part 74 (ST2).
When the A/D conversion end signal EOC is output from the analog/digital converting part 73, the data converting part 75 compares the gradation data of one scan line portion, which is stored in the recording buffer 71 and will be newly displayed, with the data values of one scan line portion, which is stored in the latch part 74 and displayed on the LCD panel at present, to execute data conversion (ST3). Here, the operation and the method for converting gradation data are the same with those of US Patent Application No. 10/395,663 titled:
Method and Apparatus for Converting Gradation Data in STN LCD and PCT Application No. PCT/KR2004/000406 disclosed by the present inventor and the applicant. That is, the data converting part 75 converts the gradation data stored in the recording buffer 71 to increase a difference more between the new gradation data stored in the recording buffer 71 and the previous gradation data stored in the latch part 74. If ending the data conversion, the data converting part 75 outputs converted gradation data to the gradation driving part 72 and, at the same time, outputs a data conversion end signal DCC, thus storing the new gradation data in a buffer, not depicted, of the gradation driving part 72. (ST4).
If the new gradation data is input from the data converting part 75 and stored, the gradation driving part 72 outputs gradation voltages corresponding to the gradation data stored in the buffer through the respective data lines S. The output gradation voltages are charged in the cell capacitors 41 through the FETs 40 turned on by the gate driving signal.
The above described operation proceeds continuously and repeatedly to all scan lines on the LCD panel in turn so as to display a predetermined moving picture on the LCD panel.
In the above described embodiment, the gradation data conversion is executed based on the voltage values charged in the cell capacitors 41.
Accordingly, it is unnecessary to equip an additional frame memory for converting gradation data, differently from the conventional one, thus reducing the
manufacturing cost of the LCD panel, more concretely, the data line driving device 60 sharply.
It will be apparent to those skilled in the art that various modifications and variations can be made in the method and apparatus for converting gradation data in TFT LCD of the present invention without departing from the spirit or 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.

Industrial Applicability
According to the present invention, it is possible to embody a method and an apparatus for converting gradation data in TFT LCD that can generate gradation data for driving LCD efficiently, not applying an additional frame memory.