KR20040062099A - Field sequential color liquid crystal display device and driving method thereof - Google Patents

Abstract

The present invention relates to a field sequential driving liquid crystal display and a driving method thereof, which can prevent luminance unevenness due to temperature change by adjusting a lighting period of a lamp in proportion to temperature. An embodiment of the present invention includes a backlight controller including a thermistor for sensing a temperature and a pulse width modulator for determining a pulse width based on the sensed temperature to adjust a lighting period of a lamp.

Description

Field sequential driving liquid crystal display and its driving method {FIELD SEQUENTIAL COLOR LIQUID CRYSTAL DISPLAY DEVICE AND DRIVING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a field sequential driving method in which one frame is divided into three subframes and driven.

In the liquid crystal display device, a TFT substrate on which a thin film transistor (TFT), which is a switch element, is formed, and a color filter substrate on which a color filter is formed, are maintained at regular intervals, and liquid crystal is injected therebetween. Configured liquid crystal panel. However, such a liquid crystal display device has a disadvantage in that luminance is low because light is lost while passing through the color filter. In order to solve such a decrease in light efficiency, a field sequential driving method has been proposed.

The liquid crystal display of the field sequential driving method has no color filter and has a sequential backlight that sequentially emits colors of red (R), green (G), and blue (B). The sequential backlight may include a red lamp, a green lamp, and a blue lamp, and each lamp may be configured as a light emitting diode (LED). The conventional field sequential liquid crystal display device time-divides one frame into three sub-frames, and additionally mixes red, green, and blue light in each sub-frame to display colors.

1 is a graph showing temperature vs. brightness characteristics of LEDs.

As shown in the figure, the LED is degraded as the temperature increases. Therefore, when the LED is used as a backlight of the liquid crystal display, a phenomenon in which the brightness of the screen changes with temperature changes occurs. Therefore, when the LED is used as a backlight of the liquid crystal display, the brightness of the displayed screen is changed according to the temperature change of the surrounding environment.

A common way to overcome this characteristic of LEDs is to sense the temperature with a thermistor to control the current applied to the LEDs. However, there are many limitations in applying this method to the field sequential driving liquid crystal display. In the field sequential driving liquid crystal display, since the LED blinks only for a short period, the maximum allowable current is applied to the LED in order to secure the luminance during this period. Therefore, there is a problem that can no longer increase the amount of current applied to the LED.

An object of the present invention is to provide a field sequential driving liquid crystal display and a driving method thereof for displaying an image of the same brightness regardless of temperature change in order to solve the above problems.

Other features and objects of the present invention will be described in detail in the configuration and claims of the invention below.

1 is a graph showing temperature vs. brightness characteristics of LEDs.

2 is a side sectional view showing a field sequential driving liquid crystal display device according to an embodiment of the present invention;

3 is a block diagram showing a driving circuit of the field sequential driving liquid crystal display according to the embodiment of the present invention;

4A and 4B are waveform diagrams showing driving waveforms of a field sequential driving liquid crystal display according to an exemplary embodiment of the present invention.

*** Explanation of symbols for the main parts of the drawing ***

200: first transparent substrate 205: TFT substrate

210: gate insulating film 220: organic film

250: pixel electrode 260: second transparent substrate

265: upper substrate 290: liquid crystal layer

300: black matrix 310: thin film transistor

330: contact hole 350: planarization film

360: common electrode 400: liquid crystal panel

410: data driver 420: gate driver

430: timing controller 440: backlight controller

450: sequential backlight 452: red lamp

454: green lamp 456: blue lamp

460: thermistor

In order to achieve the above object, the present invention provides a method comprising: dividing a frame into three subframes representing red, green, and blue; A sensing step of sensing a temperature; And a display step of displaying one of red light, green light, and blue light in each subframe in a lighting period proportional to the temperature.

The displaying step may include generating a control clock having a pulse width proportional to a temperature; And displaying one of red light, green light, and blue light during the same period as the pulse width of the control clock.

Red light, green light and blue light are characterized in that repeatedly irradiated in a certain order.

The present invention also provides a timing controller for dividing a frame into three subframes displaying red, green, and blue, and rearranging and outputting input image data. A sequential backlight for irradiating any one of red light, green light, and blue light after a predetermined time elapses in each subframe; A thermistor for sensing temperature; And a backlight controller configured to set an irradiation period of red light, green light, and blue light to be proportional to the temperature.

The backlight controller may include a pulse width modulator, and the pulse width modulator may generate a control clock having a pulse width corresponding to an irradiation period of light.

The present invention also provides a timing controller for dividing a frame into three subframes displaying red, green, and blue, and rearranging and outputting input image data. Thermistor whose resistance decreases with increasing temperature; A backlight controller receiving a resistance value from the thermistor and generating a control clock having a pulse width inversely proportional to the resistance value; And a sequential backlight for irradiating any one of red light, green light, and blue light in synchronization with the control clock after a predetermined time has elapsed for each subframe.

The backlight controller may include a pulse width modulator, and the pulse width of the control clock is determined by the pulse width modulator.

The sequential backlight is preferably composed of three kinds of light emitting diodes displaying red, green, and blue.

According to the field sequential driving liquid crystal display of the present invention configured as described above, even when the temperature changes, it is possible to maintain uniform luminance.

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

2 is a side sectional view showing a field sequential driving liquid crystal display according to an embodiment of the present invention.

As described above, the field sequential driving liquid crystal display has no color filter and includes a sequential backlight 450 including a red lamp 452, a green lamp 454, and a blue lamp 456. The lamps 452, 454, and 456 are composed of LEDs.

The lower substrate 205 and the upper substrate 265 are bonded together with the liquid crystal layer 290 filled in the cell gap d to form a liquid crystal panel. The backlight 450 is sequentially provided below the lower substrate 205.

In the lower substrate 205, a TFT 310 is formed on each of the pixel areas on the first transparent substrate 200 to apply and block a signal voltage to the pixel electrode. The TFT 310 is a gate electrode 312 to which a gate signal is applied, a semiconductor layer 314 that is activated in response to the gate signal to form a channel, and n ⁺ doped to form the channel 314. Active layer 316 formed on both sides of the upper side, a gate insulating film 210 that electrically isolates the active layer 316 and the gate electrode 312, and a data signal formed on the active layer 316. A source electrode 318 that is input and a drain electrode 320 that applies a data signal input to the source electrode 318 to the pixel electrode 250 as the semiconductor layer 314 is activated. The organic layer 220 is formed on the TFT 310 to protect the source electrode 318 and the drain electrode 320 and to provide a high opening ratio. The organic layer 220 on the drain electrode 320 is etched to form a contact hole 330, and the drain electrode 320 and the pixel electrode 250 are electrically connected to each other through the contact hole 330. Connected.

A black matrix 300 is formed on the upper substrate 265 at the boundary of each pixel of the second transparent substrate 260. As described above, the field sequential driving liquid crystal display has no color filter. The planarization film 350 is formed on the surface of the upper substrate 265 for a gentle step. In addition, indium tin oxide (ITO) is deposited on the surface of the planarization film 350 using the common electrode 360 to apply a voltage to the liquid crystal layer 290 together with the pixel electrode 250 of the TFT substrate 310.

The sequential backlight 450 emits red (R), green (G), and blue (B) light in a predetermined order to irradiate the liquid crystal panel. The sequential backlight 450 includes a red lamp 452, a green lamp 454, and a blue lamp 456 that emit light of red (R), green (G), and blue (B) in a certain order. Unlike the backlight that irradiates the conventional white light, the sequential backlight 450 of the field sequential driving method does not need a color filter because it displays a color in itself. Since there is no color filter, transmittance is increased, thereby improving brightness.

3 is a block diagram illustrating a driving circuit of a liquid crystal display according to an exemplary embodiment of the present invention.

The liquid crystal panel 400 in which a plurality of data wires and a gate wire intersect and a TFT is formed at an intersection thereof, a data driver 410 for supplying data to the data wires of the liquid crystal panel 400, and a liquid crystal panel 400 of the liquid crystal panel 400. A gate driver 420 for supplying a gate pulse GP to the gate wiring, a timing controller 430 to which image data and a control signal are supplied, a red lamp 452, a green lamp 454, and a blue color And a backlight controller 440 for driving the sequential backlight 450 having the lamp 456, and a thermistor 460 for sensing a temperature to control the lighting period of each lamp 452, 453, 456. .

The TFT formed at the intersection of the data line and the gate line of the liquid crystal panel 400 supplies the data voltage to the liquid crystal cell in response to the gate pulse GP from the gate driver 420. The source electrode of the TFT is connected to the data wiring, and the drain electrode is connected to the pixel electrode of the liquid crystal cell. The gate electrode of the TFT is connected to the gate wiring.

The timing controller 330 divides one frame into three subframes of red (R), green (G), and blue (B), and supplies a control signal for driving the liquid crystal panel 400 to the data driver 410 and the gate driver. Supply to 420. When the liquid crystal display is driven at 60 Hz, one frame is displayed for 16.7 ms and each sub frame is displayed for 5.56 ms, one third thereof.

To this end, the timing controller 430 rearranges the image data supplied from a graphic controller (not shown) such as a computer for each of red (R), green (G), and blue (B). The image data rearranged by the timing controller 430 is supplied to the data driver 410. In addition, the timing controller 430 generates a data control signal and a gate control signal at frequencies necessary for the field sequential driving method. The data control signal is supplied to the data driver 410 including a source shift clock SSC, a source output enable SOE, a polarity inversion signal POL, and the like. The gate control signal is supplied to the gate driver 420 including a gate start pulse GSP, a gate shift clock GSC, a gate output enable GOE, and the like. In addition, the timing controller 430 controls the backlight controller 440 such that the red lamp 452, the green lamp 454, and the blue lamp 456 are sequentially driven when data is completely supplied to the liquid crystal cell.

The backlight controller 440 receives temperature information from the thermistor 460 and includes a pulse width modulator therein. The thermistor 460 is a resistance whose resistance value changes sensitively to temperature change. In the exemplary embodiment of the present invention, the thermistor 460 uses a negative temperature characteristic thermistor whose resistance value decreases as the temperature rises. The temperature may be sensed by measuring the resistance value, and the resistance value is transmitted to the timing controller 430 as temperature information. The pulse width modulator of the backlight controller 440 that receives the temperature information from the thermistor 460 is pulse width modulated (PWM) and inversely proportional to the resistance value of the thermistor 460 (proportional to temperature). Adjust the pulse width of the clock that controls the lighting period of the < RTI ID = 0.0 > That is, as the temperature increases, the pulse width of the clock increases, and accordingly, the lighting periods of the lamps 452, 454, and 456 also increase.

After sampling the data according to the data control signal from the timing controller 430, the data driver 310 latches the sampled data line by line and converts the latched data into a gamma voltage. do.

The gate driver 420 may generate a shift register sequentially generating the gate pulse GP in response to the gate start pulse GSP among the gate control signals from the timing controller 430, and the voltage of the gate pulse GP. And a level shifter for shifting the voltage to a voltage level suitable for driving the liquid crystal cell. The timing controller 430 supplies the gate start pulse GSP to the gate driver 420 as a control signal. The gate driver 420 generates the gate pulse GP in response to the gate start pulse GSP.

4A and 4B are waveform diagrams showing driving waveforms of a field sequential driving liquid crystal display according to an exemplary embodiment of the present invention.

4A is a waveform diagram at the time of low temperature driving, and FIG. 4B is a waveform diagram at the time of high temperature driving. The temperature of the liquid crystal display device is affected not only by the heat generated by itself, but also by the surrounding environment.

The field sequential driving liquid crystal display divides one frame into three subframes as shown in the figure. Each subframe is displayed for 5.56 ms as described above, during which a gate pulse GP is generated by the gate driver by a gate start pulse supplied from the timing controller. The subframe is divided into a scan section ST, a response section RT1 and RT2, and a lamp lighting section FT1 and FT2.

The scan period ST is a period in which the gate pulse GP is applied to the TFT, and a data voltage is applied to the pixel electrode in response to the gate pulse GP. In the reaction sections RT1 and RT2, the liquid crystal is applied to the data voltage applied thereto, and the applied data voltage is kept constant. When a voltage is applied to the liquid crystal, the liquid crystal moves in the direction of the long axis in the direction of the electric field in proportion to the magnitude of the voltage. The time required for the liquid crystal is the reaction periods RT1 and RT2. After passing through the reaction sections RT1 and RT2, the liquid crystal can transmit light at a desired transmittance. The transmittance of the liquid crystal is kept constant during the lighting sections FT1 and FT2. At this time, the lamp is turned on so that light passes through the liquid crystal to display a desired color.

In detail, in the field sequential driving liquid crystal display according to the exemplary embodiment of the present invention, when the R data voltage is supplied to the liquid crystal cell in response to the gate pulse GP during the scan period ST in the first subframe of one frame, Responds to the R data voltage. The liquid crystal passes through the reaction sections RT1 and RT2 to reach the desired transmittance of the liquid crystal. At this time, the red lamp R is turned on during the lighting sections FT1 and FT2 so that red light is transmitted through the liquid crystal cell. Accordingly, red light is displayed at a desired transmittance in the liquid crystal cell to which the R data voltage is supplied in the first subframe of the first frame.

In the same manner, the second subframe and the third subframe are driven to display the green light and the blue light at a desired transmittance, and to realize colors by the combination of the three colors.

In the embodiment of the present invention, the lighting sections FT1 and FT2 of the respective lamps are controlled by the thermistor and the backlight controller, and the reaction sections RT1 and RT2 are also adjusted accordingly.

4A and 4B show control clocks CLK1 and CLK2 whose amplitude is modulated by the pulse width modulator of the timing controller. The lighting sections FT1 and FT2 are synchronized with the pulse widths of the control clocks CLK1 and CLK2. Since the pulse width of the control clock CLK2 when driving at high temperature is wider than the pulse width of the control clock CLK1 when driving at low temperature, the lamp lighting section FT2 at high temperature is the lamp lighting section FT1 at low temperature. Becomes larger. When the lamp is driven at a high temperature, the lamp is turned on faster than at a low temperature. Liquid crystals have a low viscosity at high temperatures, resulting in a faster reaction rate and a shorter reaction time. That is, the reaction section RT1 at the time of low temperature driving is smaller than the reaction section RT2 at the time of high temperature driving. Therefore, at a high temperature, even if the lamp lighting section FT2 is increased, the reaction section RT2 is reduced, so that an image can be displayed at a desired transmittance.

By increasing the lighting period FT at a high temperature, the luminance of the displayed image is increased, thereby compensating for the decrease in luminance due to the temperature increase due to the LED itself. The pulse widths of the control clocks CLK1 and CLK2 that are modulated with temperature should be determined in consideration of the temperature vs. luminance characteristics of the LEDs.

While many details are set forth in the foregoing description, it should be construed as an illustration of preferred embodiments rather than to limit the scope of the invention. Therefore, the scope of the invention should not be defined by the described embodiments, but should be defined by the claims and the equivalents of the claims.

As described above, the field sequential driving liquid crystal display according to the embodiment of the present invention prevents the luminance change due to the temperature change by changing the lighting period of the LED according to the temperature change. In other words, the temperature is sensed using a thermistor, and the backlight controller determines the lighting period of the LED based on the temperature, thereby ensuring luminance uniformity according to temperature.

Claims (9)

A dividing step of dividing one frame into three subframes representing red, green, and blue; A sensing step of sensing a temperature; And And a display step of displaying one of red light, green light, and blue light in each subframe in a lighting period proportional to the temperature. The method of claim 1, wherein the displaying step, Generating a control clock having a pulse width proportional to the temperature; And And displaying one of red light, green light, and blue light for a period equal to the pulse width of the control clock. The method of claim 1, wherein the red light, the green light, and the blue light are repeatedly irradiated in a predetermined order. A timing controller dividing one frame into three subframes displaying red, green, and blue, and rearranging and outputting input image data; A sequential backlight for irradiating any one of red light, green light, and blue light after a predetermined time elapses in each subframe; A thermistor for sensing temperature; And And a backlight controller configured to set an irradiation period of red light, green light, and blue light in proportion to the temperature. The apparatus of claim 4, wherein the backlight controller comprises a pulse width modulator, And the pulse width modulator generates a control clock having a pulse width corresponding to an irradiation period of light. A timing controller dividing one frame into three subframes displaying red, green, and blue, and rearranging and outputting input image data; Thermistor whose resistance decreases with increasing temperature; A backlight controller receiving a resistance value from the thermistor and generating a control clock having a pulse width inversely proportional to the resistance value; And And a sequential backlight for irradiating any one of red light, green light, and blue light in synchronization with the control clock after a predetermined time has elapsed for each subframe. The apparatus of claim 6, wherein the backlight controller comprises a pulse width modulator, And the pulse width of the control clock is determined by the pulse width modulator. 7. The field sequential driving liquid crystal display according to claim 4 or 6, wherein the sequential backlight comprises three kinds of light emitting diodes displaying red, green, and blue. 7. The field sequential driving liquid crystal display according to claim 4 or 6, wherein the sequential backlight repeatedly irradiates red light, green light, and blue light in a predetermined order.