KR20080072435A - Driving circuit for liquid crystal display device - Google Patents

Abstract

A driving circuit of an LCD(Liquid Crystal Display) device is provided to prevent flicker and image sticking thereof by compensating for voltages according to temperature variation. A driving circuit of an LCD(Liquid Crystal Display) device includes a timing controller(31), gate and data drivers(32,33), an LCD panel(34), and a DC/DC(Direct Current) converter(35). The timing controller outputs control signals for controlling gate and data drivers. The gate driver supplies scan pulses to gate lines of the LCD panel using gate high and low voltages from the DC/DC converter. The data driver supplies data signals to the data lines of the LCD panel. The LCD panel driven by the data signals and the scan pulses displays images. The DC/DC converter generates driving voltages for respective units of a system and compensates for the gate high and low voltages according to temperature variation of the LCD panel when the gate high and low voltages are generated from switching transistors of the LCD panel.

Description

DRIVING CIRCUIT FOR LIQUID CRYSTAL DISPLAY DEVICE}

1 is a waveform diagram of a gate low and high voltage.

2 is a waveform diagram of a current-voltage characteristic graph of a transistor according to temperature change.

3 is a block diagram of a driving circuit of a liquid crystal display device according to the present invention;

FIG. 4 is a detailed block diagram of the DC / DC converter in FIG. 3. FIG.

5 is a graph showing an example of the compensation output of the gate low and high voltage according to the present invention.

6 is an exemplary table of a lookup table applied to the present invention.

*** Description of the symbols for the main parts of the drawings ***

31: Timing control 32: Gate driver

33: data driver 34: liquid crystal panel

35: DC / DC converter 41: Initial setting value output part

42: temperature sensor 43: lookup table

44: operation processing unit 45: gate voltage compensation unit

46: gate voltage output unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for properly controlling a switching operation of a transistor, which is a liquid crystal cell driving element, in accordance with a temperature change in a liquid crystal display. The driving circuit of the liquid crystal display device is adapted to be output.

Recently, with the development of information technology (IT), the importance of the display as a visual information transmission medium is further emphasized, and in order to preoccupy a major position in the future, it is necessary to satisfy requirements such as low power consumption, thinning, light weight, and high quality.

Liquid crystal display, which is a typical display device of flat panel display, displays an image by using optical anisotropy of liquid crystal. Cathode ray tube due to thin, small size, low power consumption and high quality It is being developed as a major product of flat panel display that can replace CRT.

In general, a liquid crystal display device is a display device in which image information is individually supplied to pixels arranged in a matrix, and a desired image is displayed by adjusting light transmittance of the pixels. Accordingly, the liquid crystal display includes a liquid crystal panel in which pixels, which are the smallest unit for implementing an image, are arranged in an active matrix form, and a driving unit for driving the liquid crystal panel. Since the LCD does not emit light by itself, a backlight unit is provided to supply light to the LCD.

Briefly explaining the driving principle of the liquid crystal display, the system supplies the digital video data, the vertical / horizontal synchronization signal and the clock signal to the timing controller, and the timing controller uses the signals input from the system to provide the gate driver. A gate control signal for controlling and a data control signal for controlling the data driver are generated, the digital video data is sampled, rearranged, and supplied to the data driver. The liquid crystal panel is driven by the gate driver and the data driver to display an image of the video data.

The liquid crystal display device is provided with a DC / DC converter for supplying a DC voltage required for each part of the system. The DC / DC converter supplies a driving voltage to the data driver, supplies a power terminal voltage Vcc to each system part, and supplies a gate low voltage VGL and a gate high voltage VGH to the gate driver.

The gate low voltage VGL and the gate high voltage VGH are voltages supplied to a gate of a transistor TFT, which is a switching element for driving respective pixels arranged in a matrix on a liquid crystal panel. The timing is output.

In this case, a section in which the gate high voltage VGH is output is a gate-on section, in which a data voltage is charged to the pixel. In addition, the section in which the gate low voltage VGL is output is a gate-off section, in which the voltage charged in the gate-on section is maintained.

The gate high voltage VGH and the gate low voltage VGL are output as fixed values preset by the DC / DC converter.

FIG. 2 is a graph illustrating current-voltage characteristics of the transistor TFT. As shown in FIG. 2, it can be seen that the characteristic graph changes with temperature. That is, when setting the gate high voltage VGH and the gate low voltage VGL in the DC / DC converter, the current-voltage characteristic graph of the transistor TFT is assumed to be a characteristic graph G21. However, when the temperature is increased, the current-voltage characteristic graph of the transistor TFT is changed to the characteristic graph G22. On the contrary, when the temperature is lowered, the current-voltage characteristic graph of the transistor TFT is changed to the characteristic graph G23. Is changed.

Therefore, when the temperature is changed, the switching control operation of the transistor TFT is not accurately performed, which makes it difficult to accurately transmit the data voltage (pixel voltage) to the pixel through the transistor TFT.

As described above, in the conventional liquid crystal display device, the gate low and high voltages are output at fixed values regardless of the temperature change. Therefore, when the temperature is changed, the switching control operation of the transistor is not performed accurately. It was difficult to properly transfer the data voltage to the pixel. As a result, crosstalk, flicker, and afterimage are generated, thereby degrading image quality.

Accordingly, an object of the present invention is to provide a driving circuit for properly compensating and outputting voltages when a gate low and high voltage is output to a gate of a transistor which is a liquid crystal cell driving element.

The present invention for achieving the above object is a timing controller for outputting various control signals for controlling the drive of the gate driver and the data driver; A gate driver for supplying scan pulses to the gate lines on the liquid crystal panel using gate low and high voltages output from the DC / DC converter; A data driver supplying a data signal to each data line on the liquid crystal panel; A liquid crystal panel driven by the data signal and the scan pulse to display an image; And a DC / DC converter for generating various driving voltages required by each part of the system and properly compensating for the temperature change when outputting the gate low and high voltages of the switching transistor on the liquid crystal panel. do.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a block diagram showing an embodiment of a driving circuit of a liquid crystal display according to the present invention. As shown in FIG. 3, various control signals for controlling the driving of the gate driver 32 and the data driver 33 are provided. An output timing controller 31; A gate driver 32 supplying scan pulses to the gate lines of the liquid crystal panel 34 by using the gate low and high voltages output from the DC / DC converter 35; A data driver 33 for supplying a data signal to each data line of the liquid crystal panel 34; A liquid crystal panel (34) driven by the data signal and the scan pulse to display an image; The DC / DC converter 35 generates various driving voltages required by each part of the system and compensates and outputs the gate low, high voltage VGL, and VGH appropriately according to the temperature change.

FIG. 4 is a detailed block diagram showing an embodiment of the DC / DC converter 35. As shown therein, an initial setting value output unit 41 for outputting initially set gate low and high voltage values; A temperature sensor 42 for detecting a temperature change around the transistor on the liquid crystal panel 34 and outputting a detection signal accordingly; A look-up table (43) storing a compensation value for compensating the initially set gate low and high voltage values according to the detection signal; If the temperature detected by the temperature sensor 42 is different from the initial temperature at the time of setting the gate low and high voltage values, the calculation processor 44 reads out the compensation voltage value from the lookup table 43 and outputs the compensation voltage value. Wow; The gate voltage compensator 45 outputs the compensated gate low and high voltage values by adding the compensation voltage values output from the operation processor 44 to the gate low and high voltage values output from the initial value output unit 41. )Wow; The gate voltage compensator 45 is configured to generate and output gate low, high voltages VGL, and VGH having levels corresponding to gate low and high voltage values.

Referring to Figures 5 and 6 attached to the operation of the present invention configured as described above in detail as follows.

The timing controller 31 may include a gate control signal GDC for controlling the gate driver 32 and a data control signal for controlling the data driver 33 using a vertical / horizontal synchronization signal and a clock signal supplied from the system. DDC). In addition, the timing controller 31 samples the digital video data RGB input from the system, rearranges the digital video data RGB, and supplies the data to the data driver 33.

The gate driver 32 sequentially supplies a gate on signal (scan pulse) VGH to the gate lines G1 to Gn in response to the gate control signal GDC input from the timing controller 31. Horizontal lines of the liquid crystal panel 34 to which data is supplied are selected.

The data driver 33 converts the digital video data RGB into a data voltage (analog gamma compensation voltage) corresponding to the gray scale value in response to the data control signal DDC input from the timing controller 31. The converted data voltage is supplied to the data lines D1 to Dm on the liquid crystal panel 34.

The liquid crystal panel 34 includes a plurality of liquid crystal cells Clc that are arranged in a matrix at the intersection of the data lines D1 to Dm and the gate lines G1 to Gn. The data signal and the gate-on signal are driven to display an image.

The DC / DC converter 35 converts the high potential common voltages VDD voltage, VCOM voltage, gate low, high (off, on) voltage (VGL), and (VGH) using the power terminal voltage (VCC) provided from the system. Occurs.

For reference, in the above description, the data driver 33 and the gate driver 32 are separately installed from the liquid crystal panel 34. However, in recent years, each of them is directly mounted on the liquid crystal panel 34 by packaging technology. Is in.

When the DC / DC converter 35 outputs the gate low, high voltage VGL, and VGH, the DC / DC converter 35 properly compensates and outputs the temperature according to the temperature change around the transistor TFT on the liquid crystal panel 34. The process will be described in more detail with reference to FIG. 4 as follows.

The initial value output unit 41 outputs initial values of the gate low, high voltages VGL, and VGH that are initially set. When the initial value is set, the temperature around the transistor TFT on the liquid crystal panel 34 is set. The characteristic graph G41 of FIG. 5 is applied as a current-voltage characteristic graph of the transistor TFT at this time. Therefore, the initial gate low voltage VGL set in the initial set value output section 41 is Vg8, and the gate high voltage VGH is Vg21.

Thereafter, the operation processor 44 periodically checks the temperature change around the transistor TFT on the liquid crystal panel 34 through the temperature sensor 42, and when it is determined that the temperature is changed, the gate low and high voltage ( VGL) and (VGH) are outputted.

For example, when the operation processor 44 checks the temperature change around the transistor TFT on the liquid crystal panel 34 through the temperature sensor 42 at an arbitrary point in time, the temperature is increased and the transistor ( If it is found that the current-voltage characteristic graph of the TFT is changed to the characteristic graph G42 or the characteristic graph G43, the compensation values of the gate low, high voltage VGL, and VGH accordingly are obtained from the lookup table 43. Will read and print.

The lookup table 43 may be implemented in various forms, and FIG. 6 illustrates one embodiment. That is, the compensation value of the gate low voltage VGL is divided into temperature rise / fall and stored at each address. Likewise, the compensation value of the gate high voltage VGH is divided into temperature rise / fall and The address is stored at.

For example, when the operation processor 44 checks the temperature as described above, the current temperature is changed from the reference temperature to the high temperature, so that the current-voltage characteristic graph of the transistor TFT is shown in the characteristic graph G41. If it is determined to have been changed to G42, the compensation value of the gate low, high voltage VGL, and VGH according to the lookup table 43 is read out and output.

Accordingly, the gate voltage compensator 45 outputs the gate low voltage VGL output from the operation processor 44 to the initial value of the initially set gate low voltage VGL output from the initial value output unit 41. The compensation value of is added and output. As a result, the gate voltage output unit 46 generates and outputs Vg7 as the gate low voltage VGL corresponding to the value of the gate low voltage VGL compensated by the gate voltage compensator 45.

In addition, the gate voltage compensator 45 outputs the gate high voltage VGH output from the operation processor 44 to an initial value of the initially set gate high voltage VGH output from the initial value output unit 41. The compensation value of is added and output. As a result, the gate voltage output unit 46 generates and outputs Vg20 at the gate high voltage VGH corresponding to the value of the gate high voltage VGH compensated by the gate voltage compensator 45.

As another example, when the operation processor 44 checks the temperature as described above, the current temperature is changed from the reference temperature to the low temperature so that the current-voltage characteristic graph of the transistor TFT is characterized by the characteristic graph G41. When it is determined that the graph G43 has been changed, the compensation values of the gate low, high voltage VGL, and VGH are read from the lookup table 43 and output.

Accordingly, the gate voltage compensator 45 outputs the gate low voltage VGL output from the operation processor 44 to the initial value of the initially set gate low voltage VGL output from the initial value output unit 41. The compensation value of is added and output. Accordingly, the gate voltage output unit 46 generates and outputs Vg9 as the gate low voltage VGL corresponding to the value of the gate low voltage VGL compensated by the gate voltage compensator 45.

In addition, the gate voltage compensator 45 outputs the gate high voltage VGH output from the operation processor 44 to an initial value of the initially set gate high voltage VGH output from the initial value output unit 41. The compensation value of is added and output. Accordingly, the gate voltage output unit 46 generates and outputs Vg22 as the gate high voltage VGH corresponding to the value of the gate high voltage VGH compensated by the gate voltage compensator 45.

As described in detail above, in the present invention, when the gate low and high voltages are output to the gate of the transistor which is the liquid crystal cell driving device, the voltages are properly compensated for according to the temperature change, thereby outputting the characteristics of the transistor due to the temperature change. This has the effect of preventing the occurrence of crosstalk, flicker, afterimage, and the like.

Claims (5)

A timing controller for outputting various control signals for controlling the driving of the gate driver and the data driver; A gate driver for supplying scan pulses to each gate line on the liquid crystal panel using gate low and high voltages output from the DC / DC converter, and a data driver for supplying a data signal to each data line on the liquid crystal panel; A liquid crystal panel driven by the data signal and the scan pulse to display an image; It is composed of DC / DC converter which generates various driving voltages needed in each part of the system and compensates the voltages according to the temperature change of the liquid crystal panel when outputting the gate low and high voltage of the switching transistor on the liquid crystal panel. A driving circuit for a liquid crystal display device, characterized in that. The DC / DC converter of claim 1, wherein An initial setting value output unit configured to output an initially set gate low and high voltage value; A temperature sensor which detects a temperature change around the transistor on the liquid crystal panel and outputs a detection signal accordingly; A look-up table storing a compensation value for compensating the gate low and high voltage values initially set according to the detection signal; An arithmetic processing unit for reading out a compensation voltage value corresponding to the detection signal from the lookup table and outputting the readout value; A gate voltage compensator for outputting the compensated gate low and high voltage values by adding a compensation voltage value output from the operation processor to the gate low and high voltage values output from the initial value output unit; And a gate voltage output unit configured to generate and output gate low and high voltages corresponding to gate low and high voltage values output from the gate voltage compensator. The driving circuit of claim 2, wherein the lookup table is configured by dividing the compensation values of the gate low and high voltages at temperature rise / fall and storing them at respective addresses. 3. The driving circuit of claim 2, wherein the temperature sensor detects a temperature change around the transistor on the liquid crystal panel at a predetermined cycle. 2. The driving circuit of claim 1, wherein the section of the gate low voltage is a gate-off section and the section of the gate high voltage is a gate-on section.

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