KR100867920B1 - Liquid Crystal Display Device - Google Patents

Abstract

A liquid crystal display device capable of efficiently controlling light emitted from a light emitting diode (LED) constituting a backlight is disclosed. The liquid crystal display of the present invention includes a light receiving element capable of detecting the brightness of light output from the backlight. The light receiving element applies a current corresponding to the detected luminance to the light source controller. The light source controller feeds back the current to apply a voltage to the backlight to correct the luminance. Therefore, it is possible to efficiently control the change in the luminance of the backlight.

Backlight, LED, Brightness Control

Description

Liquid crystal display device             

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

FIG. 2 is a pixel circuit diagram of a representative pixel among N_M pixels constituting the liquid crystal display panel illustrated in FIG. 1.

3 is a detailed block diagram illustrating a light source controller of the liquid crystal display shown in FIG. 1.

* Description of reference numbers for the main parts of the drawings *

100: liquid crystal display panel 200: scan driver

300: source driver 400: light source controller

410: D / A converter 420: A / D converter

430: comparator 440: level adjustment unit

500: backlight 600: light receiving element

700: Timing Controller

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of efficiently controlling light emitted from a light emitting diode (LED) constituting a backlight.

Recently, display devices are also required to be lighter and thinner in accordance with the light weight and thickness of personal computers and televisions, and according to such demands, liquid crystal displays (LCDs) instead of cathode ray tubes (CRTs) are required. Flat panel displays (FPDs) are becoming popular.

In general, liquid crystal displays (LCDs) are much thinner, lighter, and consume less power than cathode ray tubes (CRTs), and are already widely used as screen display devices for portable information devices such as mobile phones, computers, and PDAs. It is becoming mainstream in the display field.

Such a liquid crystal display (LCD) has a liquid crystal display panel and a backlight unit arranged on the rear surface thereof. A liquid crystal display panel applies an electric field to a liquid crystal material having an anisotropic dielectric constant injected between two substrates, and adjusts the intensity of the electric field to adjust the amount of light transmitted from an external light source (backlight) to the substrate. By doing so, a desired image is displayed. The backlight unit includes a light source and a plurality of optical members for effectively emitting light from the light source to the liquid crystal display panel. As a light source of the backlight unit, a white LED that outputs white light or a CCFL (Cold Cathode Fluoresence Lamp) is used for a driving method using a color filter, and a red for a field-sequiential driving method. Red, green and blue LEDs are used to sequentially output green, blue and blue light.

LEDs are used more often as light sources of backlight units because they have superior color characteristics compared to CCFLs. In particular, in the field sequential driving method, LED is used as a light source and LED chip containing RLED, GLED, and BLED in one chip is used mainly to emit red, green, and blue colors sequentially. do. Due to the scanning angle limit of the light emitted from the LED chip, two to three LED chips are used as the backlight unit in a general liquid crystal display device.

The LED constituting the backlight of the liquid crystal display as described above has excellent color characteristics, but its light emitting characteristics are slightly unstable. In particular, the light emission characteristic of the LED is changed by time and temperature change. Specifically, the LED has a problem in that the light emission luminance decreases due to changes over time, and the light emission intensity changes due to temperature changes.

The technical problem to be solved by the present invention is a backlight controller of a liquid crystal display device having a feedback (feed-back) system that can effectively control the LED driving voltage by detecting the luminance emitted from the LED constituting the backlight To provide.

According to an aspect of the present invention, there is provided a liquid crystal display including: a liquid crystal display panel having a plurality of pixels formed in an area where a plurality of scan lines and a plurality of data lines intersect, and displaying an image; A scan driver for sequentially applying scan signals through the plurality of scan lines to select the plurality of pixels; A source driver for supplying a data signal to a pixel selected by the scan signal through the plurality of data lines; A backlight unit for irradiating light onto the liquid crystal display panel; A light receiving element for detecting a brightness of light emitted from the backlight unit and outputting a current value corresponding to the brightness; A light source controller for receiving the current value output from the light receiving element and controlling the light emission luminance of the backlight unit; And a timing controller outputting a control signal for controlling operations of the scan driver, the source driver, and the light source controller.

The light source controller includes an A / D converter for converting a current value output from the light receiving element into a digital signal; A comparator for comparing the digital signal converted by the A / D converter with a reference emission control signal and outputting a deviation signal; A level adjusting unit for receiving the deviation signal output from the comparator and outputting a corrected emission control signal by multiplying a correction coefficient; And a D / A converter configured to receive the corrected emission control signal output from the level adjuster, convert the converted light emission signal into an analog voltage, and apply the converted light to the backlight unit.

The light receiving element is one selected from cadmium sulfide, a photo transistor and a photo diode.

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

1 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of a representative pixel of the liquid crystal display shown in FIG. 2.

Referring to FIG. 1, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 100, a scan driver 200, a source driver 300, a light source controller 400, a backlight unit 500, and a light receiving device. 600 and timing controller 700.

In the liquid crystal display panel 100, a plurality of scan lines S1 -Sn and a plurality of data lines D1 -Dm that are insulated from and intersect with each other are arranged, and the signal lines S1 -Sn and D1 -Dm are arranged. It includes a plurality of pixel circuits (P11-Pnm) connected to each of the crossing areas.

Referring to FIG. 2, a representative pixel circuit 110 among the pixel circuits P11 -Pnm is illustrated in FIG. 2. Each pixel circuit 110 includes a switching transistor 10 and a liquid crystal capacitor connected thereto. C _LC ) and a storage capacitor (Cst).

The switching transistor 10 is a three-terminal device, the gate terminal and the source terminal of which are connected to the scan line Sn and the data line Dm, respectively, and the drain terminal of which is connected to the liquid crystal capacitor C _LC and the storage capacitor Cst. And turn on the scan signal transmitted through the scan line Sn to transfer the data voltage Vd transmitted through the data line Dm.

The liquid crystal capacitor C _LC has a pixel electrode (not shown) and a common electrode (not shown) connected to the drain terminal of the switching transistor 10 as two electrodes, and has a liquid crystal layer filled between the two electrodes. Accordingly, the liquid crystal capacitor C _LC has liquid crystal molecules having a transmittance corresponding to the voltage difference between the data voltage applied to the pixel electrode and the common voltage Vcom applied to the common electrode.

The storage capacitor Cst is formed by overlapping a storage electrode (not shown) and a pixel electrode with an insulator interposed therebetween, and the storage electrode is connected to the common electrode to apply a common voltage Vcom. Therefore, the storage capacitor Cst stores the electric charge corresponding to the voltage difference between the data voltage applied to the pixel electrode and the common voltage Vcom applied to the common electrode and supplies the charge to the liquid crystal capacitor C _LC for a predetermined time. do. Referring to the circuit operation of FIG. 2, when a scan signal is applied to the scan line Sn and the switching transistor 10 is turned on, the data voltage Vd supplied to the data line Dm is transferred through the switching transistor 10. Is applied to the electrode. Then, an electric field corresponding to the difference between the pixel voltage Vp and the common voltage Vcom applied to the pixel electrode is applied to the liquid crystal (equivalently represented by the liquid crystal capacitor in FIG. 2), and thus transmittance corresponding to the intensity of the electric field. To allow light to pass through. In this case, the storage capacitor Cst serves to maintain an electric field corresponding to the difference between the pixel voltage Vp and the common voltage Vcom for one frame or one field.

Referring back to FIG. 1, the scan driver 200 sequentially applies a scan signal to a plurality of pixel circuits P11 -Pnm connected to the plurality of scan lines S1 -Sn, and thus scan lines to which the scan signal is applied. The pixel circuit connected to is turned on.

The source driver 300 generates a gray voltage having a size corresponding to the R, G, and B data, and generates R, G, B gray voltages to the pixel circuit selected by the scan signal through a plurality of data lines D1 -Dm. Is applied.

The backlight unit 500 irradiates the liquid crystal display panel 100 with light for a predetermined time. In the field sequential driving method, the backlight includes a red light emitting diode (RLED), a green light emitting diode (GLED), and a blue light emitting diode (BLED) which sequentially output red (R), green (G), and blue (B) light. do. The backlight unit 500 may use an LED chip in which a red light emitting diode (RLED), a green light emitting diode (GLED), and a blue light emitting diode (BLED) are included in one chip. The LED chip may be embedded in the LED chip as well as R, G, and B three LEDs, and depending on each LED brightness. In addition, two or more LED chips may be used due to the limitation of the emission scan angle of each LED. In general liquid crystal display, two to three LED chips are used in the backlight unit. In addition, in the color filter method, the backlight unit 500 may be configured of a white light emitting diode (WLED) or a CCFL (Cold Cathode Fluoresence Lamp) that outputs white (W) light. Hereinafter, the backlight unit including the R, G, and B LEDs will be described as an example.

The photo-detector 600 detects the luminance of the light emitted from the backlight unit 500 and outputs a current value corresponding to the luminance to the light source controller 400. The light receiving device 600 may be a cadmium sulfide (CDS), a photo transistor, or a photodiode capable of measuring photon flux or optical power by converting the energy of photons absorbed into the device into a form capable of measuring the energy. The light receiving device 600 may be positioned between the backlight unit 500 and the liquid crystal display panel 100. In addition, the LED chip constituting the backlight unit 500 or the liquid crystal display panel 100 may be positioned. In the case of the field-sequential driving type liquid crystal display, since the red, green, and blue light emitting diodes are time-divided and sequentially emit light, the luminance values of three colors R, G, and B can be detected using one light receiving element 600. have.

The light source controller 400 feeds back this value based on the current value detected by the light receiving element 600 to correct the voltage after comparison, thereby forming a red light emitting diode (RLED) constituting the backlight unit 500. The lighting of the green light emitting diode (GLED) and the blue light emitting diode (BLED), the light emission intensity, the brightness, and the like are controlled. A feedback control system of the light source controller 400 will be described in detail with reference to FIG. 3 to be described later.

The timing controller 700 includes R, G, and B image signals R, G, and B data and an input control signal such as a vertical synchronization signal Vsync and a horizontal synchronization signal Hysnc from an external graphic controller (not shown). ) Is provided. The timing controller 500 appropriately processes the image signals R, G, and B data based on the input image signals R, G, and B data and the input control signal in accordance with operating conditions of the liquid crystal display panel 100. After generating the scan control signal Sg, the data control signal Sd, the light source control signal Sb, and the like, the scan control signal Sg is sent to the scan driver 200, and the data control signal Sd is transmitted to the data driver. And outputs a light source control signal Sb to the light source controller 700.

As described above, the liquid crystal display according to the exemplary embodiment of the present invention detects the luminance of the R, G, and B light sources emitted from the backlight unit 500 by the light receiving element 600, and feeds the result back to the light source controller 400. The deviation of the light source from the backlight unit 500 may be controlled by correcting the deviation compared to the initially set luminance.

Hereinafter, the configuration and operation of the backlight unit 500, the photo-detector 600, and the light source controller 400 of the liquid crystal display according to the exemplary embodiment of the present invention will be described in detail with reference to FIG. 3.

3 is a detailed block diagram illustrating a light source controller of a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the light source controller 400 of the liquid crystal display according to the exemplary embodiment of the present invention may include a D / A converter (Digital-Analog Converter: 410), an A / D converter (Analog-Digital Converter: 420), and a comparator. A comparator 430 and a level adjusting unit 440.

The D / A converter 410 converts the emission control signal Sc, which is a digital signal output from the timing controller, or the emission control signal Sc, which is a level adjusted digital signal output from the level adjustment unit 440 by the feedback system, to an analog signal. After conversion to the red light emitting diode (RLED), the green light emitting diode (GLED) and the blue light emitting diode (BLED) constituting the backlight unit 500, the red voltage (V _R ), the green voltage (V _G ), The blue voltage V _B is sequentially applied.

The A / D converter 420 receives a current corresponding to the luminance of the R, G, B LED light detected by the light receiving device 600, converts the current into a digital value, and outputs the converted current to the comparator 430.

The comparator 430 compares the emission control reference value Sb of the R, G, and B LEDs already set by the timing controller 700 with the luminance detection value Sf output from the A / D converter 420, and thereby the deviation signal. (Sk) is generated, and the deviation signal Sk is applied to the level adjusting unit 440.

The level adjusting unit 440 receives the deviation signal Sk output from the comparator 430 and multiplies the correction coefficient to adjust the level of the emission control signal, and adjusts the level-adjusted control signal Sc to the D / A converter. 410). In this case, the D / A converter 410 receives the level-adjusted control signal Sc and converts the corrected light emitting diode voltage to apply the voltage to the light emitting diode to emit light.

In the liquid crystal display according to the exemplary embodiment of the present invention, the light emitting device 600 detects the light emission luminance of the LED and feeds it back to the light emission controller, thereby emitting light of the light emitting diode according to time or temperature change. The change can be corrected.

In the above, although an embodiment of the present invention has been described, the scope of the present invention is not limited to the above embodiment, and a person having ordinary knowledge in the art to which the present invention belongs can easily modify or change the following claims. Substituted ones are also within the scope of the present invention.

The liquid crystal display according to the exemplary embodiment of the present invention as described above detects the luminance of the R, G, and B light emitting diodes (LEDs) in the light receiving element and feeds them back to the light source controller to emit light according to time or temperature change. There is an effect that it is possible to correct the change in the light emission luminance of the diode.

Claims (6)

A liquid crystal display panel having a plurality of pixels formed in an area where a plurality of scan lines and a plurality of data lines intersect, and displaying an image; A scan driver for selecting the plurality of pixels by applying a scan signal through the plurality of scan lines; A source driver for supplying a data signal to a pixel selected by the scan signal through the plurality of data lines; A backlight unit for irradiating light onto the liquid crystal display panel; A light receiving element positioned between the backlight unit and the liquid crystal display panel and configured to detect a luminance of light emitted from the backlight unit and output a current value corresponding to the luminance; A light source controller for receiving the current value output from the light receiving element and controlling the light emission luminance of the backlight unit; And A timing controller configured to output a control signal for controlling operations of the scan driver, the source driver, and the light source controller, The light source controller An A / D converter for converting a current value output from the light receiving element into a digital signal; A comparator for comparing the digital signal converted by the A / D converter with a reference emission control signal and outputting a deviation signal; A level adjusting unit for receiving the deviation signal output from the comparator and outputting a corrected emission control signal by multiplying a correction coefficient; And And a D / A converter configured to receive the corrected emission control signal output from the level adjuster, convert the converted light emission signal into an analog voltage, and apply the converted light to the backlight unit. delete The method of claim 1, wherein the light receiving element And a selected one of cadmium sulfide, a photo transistor, and a photo diode. The method of claim 3, wherein The backlight unit, A liquid crystal display comprising red, green, and blue LEDs that sequentially emit red, green, and blue light. The method of claim 3, wherein The backlight unit, A liquid crystal display comprising a white LED or a white cathode fluorescent lamp (CCFL) that emits white light. The method of claim 1, Each pixel, A switching transistor connected to a gate terminal of the scan line and turned on the scan signal to transfer a data voltage; A liquid crystal capacitor having a pixel electrode connected to a drain terminal of the switching transistor, a common electrode connected to a common voltage line Vcom, and having a transmittance corresponding to a voltage difference between the test voltage or the data voltage and the common voltage; And And a storage capacitor connected to the liquid crystal capacitor in parallel to store charge corresponding to a voltage difference between the test voltage or the data voltage and the common voltage.

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