KR101035988B1 - Display device - Google Patents

Abstract

The present invention relates to a display device.

According to an embodiment of the present invention, a display device including at least one light emitting diode includes a switching element having an input terminal connected to one end of the light emitting diode, a PWM driver connected to a control terminal of the switching element, And at least one of the switching device, the PWM driving unit, and the constant current driving unit is a separate module.

In this way, the design can be simplified and the cost can be reduced.

Display device, light source part, light emitting diode, module, PWM, driving part, constant current

Description

Display device {DISPLAY DEVICE}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a display device, and more particularly, to a display device capable of simplifying a design and reducing a cost.

2. Description of the Related Art A general liquid crystal display (LCD) includes two display panels having pixel electrodes and a common electrode, and a liquid crystal layer having a dielectric anisotropy therebetween. The pixel electrodes are arranged in the form of a matrix and connected to a switching element such as a thin film transistor (TFT), and are supplied with a data voltage one row at a time. The common electrode is formed over the entire surface of the display panel and receives a common voltage. The pixel electrode, the common electrode, and the liquid crystal layer between the pixel electrode and the common electrode form a liquid crystal capacitor in a circuit view, and the liquid crystal capacitor together with the switching device connected thereto constitutes a pixel unit.

In such a liquid crystal display device, a voltage is applied to the two electrodes to generate an electric field in the liquid crystal layer, and the intensity of the electric field is adjusted to adjust the transmittance of light passing through the liquid crystal layer to obtain a desired image. The light at this time may be an artificial light source or a natural light separately. In case of using a separate light source, the brightness of the entire screen is adjusted by adjusting the ratio of the lighting time and the light time of the light source.

As such a light source, a cold cathode fluorescent lamp (CCFL) or a light emitting diode (CCFL) is used.

Although CCFL has the advantage of relatively low cost, it is always powered, consumes a lot of power, exhibits color reproducibility of about 70% as compared with CRT, and is pointed out as a disadvantage of environmental problems due to the addition of mercury. Accordingly, researches on light emitting diodes (LEDs) as alternative light sources capable of solving these problems have been actively conducted.

In other words, the light emitting diode can divide a certain region of the screen and drive only the divided regions individually, thereby improving the contrast ratio and power consumption, as well as achieving 100% color reproducibility and being environmentally friendly.

On the other hand, the driving unit for driving such a light emitting diode is formed of a chip in the form of an integrated circuit, and such a chip is separately manufactured within a range that satisfies the voltage current tolerance of the individual product. In other words, it means you can only use the chip for that product. The range of voltage and current varies depending on the number of LEDs, but it can not be used for products with different numbers. In this case, the driving chip is very expensive, and the cost of manufacturing a separate chip for each individual product leads to a cost increase.

SUMMARY OF THE INVENTION The present invention provides a display device capable of simplifying a design and reducing manufacturing costs.

According to an aspect of the present invention, there is provided a display device including at least one light emitting diode, including: a switching device having an input terminal connected to one end of the light emitting diode; And a constant current driving unit connected to an output terminal of the switching device. At least one of the switching device, the PWM driving unit, and the constant current driving unit is a separate module.

According to another aspect of the present invention, there is provided a display apparatus including a display panel assembly including a plurality of pixels arranged in a matrix form, and a light source unit including at least one light emitting diode and supplying light to the display panel assembly, The light source unit includes a switching element having an input terminal connected to one end of the light emitting diode, a PWM driving unit connected to a control terminal of the switching element, and a constant current driving unit connected to an output terminal of the switching element, At least one of the device, the PWM driver, and the constant current driver is a separate module.

In this case, the PWM driver may output a voltage control signal or a current control signal.

The PWM driver may further include a pull-up resistor having one end connected between the PWM driver and the control terminal of the switching device and the other end connected to a predetermined bias voltage when the PWM driver outputs a current control signal.

The constant current driving unit may control the current flowing in the light emitting diode to flow constantly.

Furthermore, the driving apparatus may further include an external resistor connected to the outside of the constant current driving unit.

In addition, the constant current driver may have two or more connected in parallel to the output terminal of the switching element, and the magnitude of the current flowing through the light emitting diode may be increased in proportion to the number of the constant current drivers.

The breakdown voltage of the switching device may be greater than the voltage applied to the light emitting diode.

Meanwhile, the switching device may be a semiconductor device such as a MOSFET or a BJT.

In this way, since the driving unit made up of individual modules is provided instead of a chip that can be used only for a specific display device, specifications corresponding to the display device can be appropriately added, so that it is possible to easily design various display devices having different numbers of light emitting diodes, Can be saved.

The embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

First, a display device according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2, and a liquid crystal display device will be described as an example.

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

1, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal panel assembly 300, a gate driving unit 400, a data driving unit 500, a data driving unit 500, A backlight unit 900 for emitting light to the liquid crystal panel assembly 300, and a signal controller 600 for controlling the backlight unit 900.

The liquid crystal panel assembly 300 includes a plurality of signal lines G ₁ -G _n and D ₁ -D _m and a plurality of pixels PX connected to the signal lines G ₁ -G _n and D ₁ -D _m arranged in the form of a matrix . 2, the liquid crystal panel assembly 300 includes lower and upper display panels 100 and 200 facing each other and a liquid crystal layer 3 interposed therebetween.

The signal lines G ₁ -G _n and D ₁ -D _m include a plurality of gate lines G ₁ -G _n for transferring gate signals (also referred to as "scan signals") and a plurality of data lines D ₁ -D _m ). The gate lines G _{1 to} G _n extend in a substantially row direction and are substantially parallel to each other, and the data lines D _{1 to} D _m extend in a substantially column direction and are substantially parallel to each other.

Each of the pixels (PX), for instance the i-th (i = 1, 2, ... , n) gate line (G _i) and the j-th (j = 1, 2, ... , m) data line (D pixels (PX) connected to _j) includes a switching element (Q) and a liquid crystal capacitor (liquid crystal capacitor) (Clc) and a storage capacitor (storage capacitor) (Cst) connected thereto is connected to the signal line (G _i, D _j) . The storage capacitor Cst can be omitted if necessary.

The switching element Q is a three terminal element such as a thin film transistor provided in the lower panel 100. The control terminal is connected to the gate line G _i and the input terminal is connected to the data line D _j And the output terminal is connected to the liquid crystal capacitor Clc and the storage capacitor Cst.

The liquid crystal capacitor Clc has the pixel electrode 191 of the lower panel 100 and the common electrode 270 of the upper panel 200 as two terminals and the liquid crystal layer 3 between the two electrodes 191 and 270, . The pixel electrode 191 is connected to the switching element Q and the common electrode 270 is formed on the entire surface of the upper panel 200 to receive the common voltage Vcom. 2, the common electrode 270 may be provided on the lower panel 100. At this time, at least one of the two electrodes 191 and 270 may be linear or bar-shaped.

The storage capacitor Cst serving as an auxiliary capacitor of the liquid crystal capacitor Clc is formed by superimposing a separate signal line (not shown) and a pixel electrode 191 provided on the lower panel 100 with an insulator interposed therebetween, A predetermined voltage such as the common voltage Vcom is applied to the separate signal lines. However, the storage capacitor Cst may be formed by overlapping the pixel electrode 191 with the previous gate line immediately above via an insulator.

On the other hand, in order to implement color display, each pixel PX uniquely displays one of primary colors (space division), or each pixel PX alternately displays a basic color (time division) So that the desired color is recognized by the spatial and temporal sum of these basic colors. Examples of basic colors include red, green, and blue. 2 shows that each pixel PX has a color filter 230 indicating one of the basic colors in an area of the upper panel 200 corresponding to the pixel electrode 191 as an example of space division. 2, the color filter 230 may be formed on or below the pixel electrode 191 of the lower panel 100. [

At least one polarizer (not shown) for polarizing light is attached to the outer surface of the liquid crystal panel assembly 300.

Referring again to FIG. 1, the gradation voltage generator 800 generates two sets of gradation voltages (or a set of reference gradation voltages) related to the transmittance of the pixel PX. One of the two has a positive value for the common voltage (Vcom) and the other has a negative value.

The gate driver 400 is connected to the gate lines G ₁ -G _n of the liquid crystal panel assembly 300 and supplies a gate signal composed of a combination of the gate-on voltage Von and the gate-off voltage Voff to the gate line G ₁ -G _n .

The data driver 500 includes a plurality of data driving ICs 540 connected to the data lines D ₁ -D _m of the liquid crystal panel assembly 300 and selects the gray voltages from the gray voltage generator 800 And applies it to the data lines D ₁ -D _m as data signals. However, when the gradation voltage generator 800 provides only a predetermined number of reference gradation voltages instead of providing all the voltages for all gradations, the data driver 500 divides the reference gradation voltage and supplies the gradation voltage And selects the data voltage among them.

The light source unit 900 includes a light source for providing light to the liquid crystal panel assembly 300 and a light source driving unit for driving the light source unit. In the embodiment of the present invention, a light emitting diode (LED) is used as a light source.

The signal controller 600 controls the gate driver 400, the data driver 500, the gray scale voltage generator 800, and the light source 900.

Each of the driving devices 400, 500, 600, and 800 may be directly mounted on the liquid crystal panel assembly 300 in the form of at least one integrated circuit chip, or may be a flexible printed circuit film (not shown) Or may be attached to the liquid crystal panel assembly 300 in the form of a tape carrier package (TCP), or may be mounted on a separate printed circuit board (not shown). Alternatively, these driving devices 400, 500, 600, and 800 may be integrated in the liquid crystal panel assembly 300 together with the signal lines G ₁ -G _n , D ₁ -D _m and the switching elements Q . In addition, the drivers 400, 500, 600, 800 may be integrated into a single chip, in which case at least one of them, or at least one circuit element that makes up at least one of them, may be outside of a single chip.

The operation of the liquid crystal display device will now be described in detail.

The signal controller 600 receives an input control signal for controlling the display of the input image signals R, G, and B from an external graphic controller (not shown). The input image signals R, G and B contain luminance information of each pixel PX and the luminance has a predetermined number, for example, 1024 (= 2 ¹⁰ ), 256 (= 2 ⁸ ) 2 ⁶ ) gray levels. Examples of the input control signal include a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a main clock MCLK, and a data enable signal DE.

The signal controller 600 controls the input image signals R, G and B based on the input image signals R, G and B and the input control signals to the operation conditions of the liquid crystal panel assembly 300 and the data driver 500 The gate control signal CONT1 and the data control signal CONT2 are generated and then the gate control signal CONT1 is sent to the gate driver 400 and the video signal DAT To the data driver 500. The output video signal DAT has a predetermined number of values (or gradations) as a digital signal.

The gate control signal CONT1 includes a scan start signal STV indicating the start of scanning, at least one gate clock signal CPV controlling the output timing of the gate-on voltage Von, At least one output enable signal (OE) defining the output enable signal (OE).

The data control signal CONT2 includes a horizontal synchronization start signal STH for notifying the start of transmission of the output image signal DAT of one pixel row and a load signal TP for applying a data signal to the liquid crystal panel assembly 300 And a data clock signal HCLK. The data control signal CONT2 is also a polarity signal for inverting the voltage polarity of the data signal with respect to the common voltage Vcom (hereinafter referred to as "voltage polarity of the data signal with respect to the common voltage" POL).

The data driver 500 receives the digital video signal DAT for one row of the pixels PX in accordance with the data control signal CONT2 from the signal controller 600 and outputs the digital video signal DAT corresponding to each digital video signal DAT And converts the digital video signal DAT into an analog data signal and applies it to the corresponding data line D ₁ -D _m .

Gate driver 400 is a signal control gate lines (G ₁ -G _n) is applied to the gate line of the gate-on voltage (Von), (G ₁ -G _n) in accordance with the gate control signal (CONT1) of from 600 The switching element Q is turned on. Then, the data signal applied to the data lines D ₁ -D _m is applied to the corresponding pixel PX through the turned-on switching element Q.

The difference between the voltage of the data signal applied to the pixel PX and the common voltage Vcom appears as the charging voltage of the liquid crystal capacitor Clc, that is, the pixel voltage. The liquid crystal molecules vary in arrangement depending on the magnitude of the pixel voltage, and thus the polarization of light passing through the liquid crystal layer 3 changes. Such a change in polarization is caused by a change in light transmittance by the polarizer attached to the liquid crystal panel assembly 300.

This process is repeated in units of one horizontal period (also referred to as "1H ", which is the same as one cycle of the horizontal synchronization signal Hsync and the data enable signal DE), so that all the gate lines G ₁ -G _n On voltage Von is sequentially applied to all the pixels PX to display an image of one frame by applying a data signal to all the pixels PX.

At the end of one frame, the next frame starts and the state of the inversion signal RVS applied to the data driver 500 is controlled such that the polarity of the data signal applied to each pixel PX is opposite to the polarity of the previous frame ( "Frame inversion"). At this time, the polarity of the data signal flowing through one data line changes (for example, row inversion and dot inversion) depending on the characteristics of the inversion signal RVS in one frame, or the polarity of the data signal applied to one pixel row is different (For example, thermal inversion, dot inversion).

3 to 6, a light source unit according to an embodiment of the present invention will be described in more detail.

3 is a circuit diagram of a light source unit according to an embodiment of the present invention.

Referring to FIG. 3, the light source unit 900 includes a plurality of light emitting diodes 950 connected in series to each other, a switching device SW having an input terminal connected to the light emitting diode 950, A PWM driving unit 910 connected to the control terminal of the switching element SW and a constant current driving unit 920 connected to the output terminal of the switching element SW.

The PWM driver 910 generates a square wave having a high level and a low level within one period and inputs it to the control terminal of the switching element SW.

The switching element SW is turned on or off according to the square wave to adjust the flow of the current flowing in the light emitting diode 950.

The constant current driving unit 920 makes the current flowing through the light emitting diode 950 constant, as is known.

One end of the light emitting diode 950 is connected to a predetermined power supply voltage Vbs and the total voltage V1 is determined according to the number of the light emitting diodes 950 connected in series.

In this case, each of the drivers 910 and 920 including the switching element SW has a so-called module, which is an exchangeable component having a unique function. For example, the PWM driver 910 may generate a PWM voltage control signal, and may be a model name dsPIC33F of Microchip. Also, the constant current driving unit 920 may be a model name MBI 816 of Macroblock.

As described above, when each driving unit for driving the light source unit 900 is implemented as a separate module, it can be applied to any display device having different design specifications. That is, the present invention is also applicable to a case where the number of display devices, for example, the light emitting diode 950 having a different number of light emitting diodes 950 is larger and exceeds the voltage current allowable value.

The switching element SW having a breakdown voltage higher than the voltage V1 applied to the light emitting diode 950 may be selected and the size of the external resistor R0 connected to the constant current driving part 920 may be set to Adjust the maximum value of the current. When a current value exceeding the allowable value of one constant current driving part is required, the constant current driving parts 921 and 922 are connected in parallel to the output terminal of the switching element SW as shown in FIG. 4 to increase the allowable value of the current . Further, the switching element SW may be a semiconductor element such as a MOSFET or a BJT.

The light source unit 900 according to an embodiment of the present invention includes a plurality of individual modules to form one light source unit.

Although the PWM driving unit 920 shown in FIG. 4 uses a module capable of generating a voltage control signal, a PWM driving unit capable of generating a current control signal can be used any number of times and will be described with reference to FIG. 5 .

5 is an example of a circuit diagram of a light source unit according to another embodiment of the present invention.

5, a light source unit 900 according to another embodiment of the present invention includes a plurality of light emitting diodes 950 connected in series with each other, a switching device SW having an input end connected to the light emitting diode 950, A PWM driver 930 connected to the control terminal of the switching element SW, a pull-up resistor Rpu whose one end is connected between the control terminals of the PWM driver 930 and the switching element SW, And a constant current driving unit 920 connected to an output terminal of the constant current driving unit 920.

The light emitting diode 950, the switching element SW, and the constant current driver 920 are the same as those described with reference to FIG. 3, and a detailed description thereof will be omitted here.

As described above, the PWM driver 930 outputs a current control signal and controls the voltage applied to the control terminal of the switching element SW together with the pull-up resistor Rpu.

Here, the operation of the light source unit 900 will be described with reference to the waveform shown in FIG. 6, assuming that the current flowing to the PWM driver 930 is 'Ic' and the voltage of the node N is 'V _N '.

When the current Ic flows through the PWM driver 930, the voltage V _N of the control terminal is lowered due to the voltage drop in the pull-up resistor Rpu, so that the switching element SW is turned off, The bias voltage Vcc is directly transmitted without a voltage drop in the pull-up resistor Rpu and the switching element SW is turned on. That is, the voltage V _N input to the control terminal of the switching element SW has a waveform inverted from the waveform of the current. At this time, the voltage for turning on and off the switching element SW can be appropriately adjusted by using the magnitude of the pull-up resistor Rpu.

The PWM driver 930 may also be a single module, for example, the model name TLC5940 of Texas Instruments.

As described above, since the driving unit made up of the individual modules is provided instead of a chip that can be used only for a specific display device, the specifications suited to the display device can be suitably added, thereby facilitating the design of various display devices having different numbers of light emitting diodes (LEDs) Of course, you can save costs.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG.

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

2 is an equivalent circuit diagram of a pixel of a liquid crystal display according to an exemplary embodiment of the present invention.

3 is an example of a circuit diagram of a light source unit according to an embodiment of the present invention.

4 is another example of a circuit diagram of a light source unit according to an embodiment of the present invention.

5 is an example of a circuit diagram of a light source unit according to another embodiment of the present invention.

FIG. 6 is a voltage waveform diagram of a current flowing to the PWM driver and a control terminal of the switching element shown in FIG. 5;

Description of the Drawings:

3: liquid crystal layer 100: lower panel

191: pixel electrode 200: upper panel

230: color filter 270: common electrode

300: liquid crystal panel assembly 400: gate driver

500: Data driver

600: a signal controller 800: a gradation voltage generator

900: light source unit 910, 930: PWM driving unit

920, 921, and 922:

SW: Switching element

R, G, B: input image data DE: data enable signal

MCLK: Main clock signal Hsync: Horizontal synchronization signal

Vsync: Vertical synchronization signal CONT1: Gate control signal

CONT2: Data control signal DAT: Digital video signal

Clc: liquid crystal capacitor Cst: holding capacitor

Q: Switching element

Claims (9)

A display device comprising at least one light emitting diode, A switching element having an input terminal connected to one end of the light emitting diode, A PWM driver connected to a control terminal of the switching element for outputting a voltage control signal or a current control signal, A constant current driver connected to an output terminal of the switching element, Wherein when the PWM driving unit outputs the current control signal, a pull-up resistor having one end connected between the PWM driving unit and the control terminal of the switching device and the other end connected to the bias voltage / RTI > Wherein at least one of the switching device, the PWM driving unit, and the constant current driving unit comprises a separate module Display device. A display device comprising: a display panel assembly including a plurality of pixels arranged in a matrix; and a light source part including at least one light emitting diode and supplying light to the display panel assembly, The light source unit A switching element having an input terminal connected to one end of the light emitting diode, A PWM driver connected to a control terminal of the switching element for outputting a voltage control signal or a current control signal, A constant current driver connected to an output terminal of the switching element, Wherein when the PWM driving unit outputs the current control signal, a pull-up resistor having one end connected between the PWM driving unit and the control terminal of the switching device and the other end connected to the bias voltage / RTI > Wherein at least one of the switching device, the PWM driving unit, and the constant current driving unit comprises a separate module Display device. delete delete 3. The method according to claim 1 or 2, And the constant current driving unit controls the current flowing in the light emitting diode to flow constantly. The method of claim 5, And an external resistor connected to the outside of the constant current driving unit. The method of claim 6, Wherein the constant current driving unit is connected to an output terminal of the switching device in parallel, The magnitude of the current flowing through the light emitting diode increases in proportion to the number of the constant current driving parts Display device. The method of claim 5, Wherein a breakdown voltage of the switching device is greater than a voltage applied to the light emitting diode. 9. The method of claim 8, Wherein the switching element is a semiconductor element such as a MOSFET or a BJT.

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