KR101201331B1 - Liquid Crystal Display Device and Driving Method the Same - Google Patents

Abstract

The present invention provides a liquid crystal display panel for driving a liquid crystal according to a potential difference between a data voltage and a common voltage to display an image according to a light transmittance of the liquid crystal; A temperature detector for detecting a temperature of the liquid crystal display panel; A common voltage setting signal generator configured to generate a common voltage setting signal using a reference value for setting the reference common voltage and a compensation value for compensating the reference common voltage according to the temperature of the panel; And a common voltage generator for generating a common voltage corresponding to the common voltage setting signal and supplying the common voltage to the liquid crystal display panel.

According to the present invention, since the optimum common voltage is automatically set and supplied to the liquid crystal display panel according to the temperature change, there is no need to manually adjust the common voltage, so that the common voltage adjusting operation can be eliminated, and the image quality by the common voltage can be eliminated. The display quality of an image can be improved by preventing a fall.

Temperature detector, reference value, compensation value

Description

Liquid Crystal Display Device and Driving Method the Same

1 is a view showing an equivalent circuit for a pixel in a liquid crystal display according to the prior art.

2 is a circuit diagram schematically illustrating a common voltage generator according to the related art.

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

4 is a block diagram schematically illustrating a common voltage generator according to an exemplary embodiment of the present invention.

5 is a block diagram schematically illustrating a second memory according to an embodiment of the present invention.

6 is a block diagram schematically illustrating a common voltage generator according to an exemplary embodiment of the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS OF THE DRAWINGS FIG.

200: first memory 300: temperature detector

400: second memory 420: storage

440: comparator 500: common voltage setting signal generator

600: common voltage generator 610: resistor

620: decoder 630: switching element

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a driving method thereof for improving image quality by adjusting a common voltage according to temperature.

Ultra-thin flat panel displays with a thickness of only a few centimeters (cm). Among them, liquid crystal displays have low operating voltages, which consume less power and can be used as portable devices. Applications range from ships to spacecraft to aircraft.

The LCD displays a desired image by applying an electric field to a liquid crystal material having an anisotropic dielectric constant formed between two substrates, and adjusting the intensity of the electric field to adjust the amount of light transmitted through the substrate.

A plurality of gate wires and a plurality of data wires insulated from and intersecting the gate wires are formed on the substrate of the liquid crystal display device, and an area surrounded by the gate wires and the data wires defines one pixel. A thin film transistor is formed at a portion where the gate wiring and the data wiring of each pixel cross each other.

1 is a view showing an equivalent circuit for a pixel in a liquid crystal display according to the prior art.

As shown in FIG. 1, a pixel includes a thin film transistor TFT connected to an n-th gate line GLn and an m-th data line DLm, and a pixel electrode P connected to a thin film transistor TFT. Is done.

The gate electrode g of the thin film transistor is connected to the n-th gate line GLn, the source electrode s is connected to the m-th data line DLm, and the drain electrode d is connected to the pixel electrode P. do.

The pixel electrode P is formed to face the common electrode Vcom (not shown). The liquid crystal material is formed between the pixel electrode P and the common electrode Vcom to equivalently form the liquid crystal capacitor Clc. In addition, the storage capacitor Cst is formed in an overlapping region of the pixel electrode P and the n-th gate line GLn-1.

A parasitic capacitance Cgd is formed between the gate electrode g and the drain electrode d of the thin film transistor due to misalignment.

The operation of the liquid crystal display including the pixel will be described below.

First, a thin film transistor is conducted by applying a gate pulse to a gate electrode connected to the gate line GLn to be displayed, and then a data voltage is applied to the source electrode s to be applied to the drain electrode d.

Accordingly, the data voltage is applied to the liquid crystal capacitor Clc and the storage capacitor Cst through the pixel electrode P, respectively, and an electric field is formed by the potential difference between the pixel electrode P and the common electrode Vcom.

In this case, if an electric field in the same direction is continuously applied to the liquid crystal material, the liquid crystal is deteriorated, thereby inverting the polarity of the data voltage based on the common voltage Vcom to prevent deterioration of the liquid crystal.

2 is a circuit diagram schematically illustrating a common voltage generator according to the related art.

As can be seen in FIG. 2, the common voltage generator according to the related art includes a first resistor R1, a variable resistor VR and a second resistor connected in series between a power supply voltage terminal VDD and a ground voltage terminal VSS. R2), and an output terminal No is connected between the variable resistor VR and the second resistor R2.

Each of the first and second resistors R1 and R2 has a fixed resistance value, and the variable resistor VR has a variable resistance value according to a user's adjustment.

The conventional common voltage generator outputs the voltage divided by the resistors R1, VR, and R2 to the common voltage Vcom of the DC level. At this time, the common voltage Vcom is adjusted according to the resistance value of the variable resistor VR. That is, when the resistance value of the variable resistor VR is the smallest, the lowest common voltage Vcom is output, and when the resistance value of the variable resistor VR increases, the common voltage also increases.

Such a liquid crystal display including a common voltage generator includes a flicker phenomenon in which the screen flickers when the data voltage is inverted when the common voltage Vcom is not constant. The resistance value of VR) is adjusted manually to reduce the flicker phenomenon.

As described above, although the circuit configuration of the common voltage generator is simple, manual adjustment of human beings is inevitable in delivering accurate common voltage to the panel.

Such a method of manually adjusting the variable resistor is not very reasonable to apply the optimum common voltage Vcom on the panel.

If the common voltage is not constant, since the voltage is not maintained as the center value of the data voltage, the value of the voltage charged to the pixel electrode in the frame unit is changed to cause the flicker phenomenon. This phenomenon becomes a bigger problem as the screen of the liquid crystal display becomes larger.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems,

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device and a driving method thereof, by which a common voltage is automatically adjusted according to temperature to improve image quality.

In order to achieve the above object, the present invention provides a liquid crystal display panel which displays an image according to the light transmittance of the liquid crystal by driving the liquid crystal according to a potential difference between a data voltage and a common voltage; A temperature detector for detecting a temperature of the liquid crystal display panel; A common voltage setting signal generator configured to generate a common voltage setting signal using a reference value for setting the reference common voltage and a compensation value for compensating the reference common voltage according to the temperature of the panel; And a common voltage generator for generating a common voltage corresponding to the common voltage setting signal and supplying the common voltage to the liquid crystal display panel.

The liquid crystal display may further include a first memory in which a reference value for setting the reference common voltage is stored and a second memory in which an actual value of an optimum common voltage according to temperature is stored.

The second memory may include a storage unit in which measured values of an optimum common voltage according to temperature are stored; And a comparing unit comparing the measured value from the storage unit with a reference value for setting a reference common voltage and outputting a compensation value.

The common voltage generator may include a plurality of resistors connected in series between a first voltage and a second voltage; A decoder configured to decode the common voltage setting signal to generate a switching signal; And a plurality of switching elements connected to each node between the resistors and outputting the divided voltages of the resistors as the common voltage according to the switching signal.

In addition, the present invention comprises the steps of inputting the control signal to the first memory as a synchronization signal and an address to achieve the above object; Outputting a reference value from the first memory; Using the control signal as a synchronization signal and inputting temperature data from a temperature sensor as an address to a second memory; Outputting a compensation value from the second memory; Inputting a reference value from the first memory and a compensation value from the second memory into a common voltage setting signal generator; Outputting a common voltage setting signal from the common voltage setting signal generator; A method of driving a liquid crystal display device comprising supplying a common voltage compensated according to the common voltage setting signal to a liquid crystal display panel is provided.

The outputting of the compensation value from the second memory may include: outputting an actual measurement value according to the temperature data from a storage unit; And outputting a compensation value by comparing the measured value with a reference value from the first memory.

The supplying the common voltage compensated according to the common voltage setting signal to the liquid crystal display panel may include: decoding the common voltage setting signal to generate a switching signal; Activating one of a plurality of switching elements according to the switching signal; And supplying a voltage corresponding to the activated switching element to the liquid crystal display panel.

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

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

As can be seen in FIG. 3, in the liquid crystal display according to the exemplary embodiment of the present invention, a thin film for driving the liquid crystal cell Clc at the intersection of the data lines DL1 to DLm and the gate lines GL1 to GLn is crossed. The liquid crystal display panel 110 having the transistor TFT, the data driver 120 for supplying data to the data lines DL1 to DLm of the liquid crystal display panel 110, and the gate of the liquid crystal display panel 110. A gate driver 130 for supplying scan pulses to the wirings GL1 to GLn, a gamma reference voltage generator 140 for generating a gamma reference voltage and supplying it to the data driver 120, and a liquid crystal display panel ( The backlight assembly 150 for irradiating light to the 110, the inverter 160 for applying an alternating voltage and current to the backlight assembly 160, for controlling the data driver 120 and the gate driver 130 Generates the timing controller 190 and the common voltage Vcom. The common voltage generator 180 is provided to supply the common electrode of the liquid crystal cell Clc of the liquid crystal display panel 110.

In the liquid crystal display panel 110, liquid crystal is injected between two glass substrates. The data lines DL1 to DLm and the gate lines GL1 to GLn are orthogonal to each other on the lower glass substrate of the liquid crystal display panel 110.

The thin film transistor is formed at the intersection of the data lines DL1 to DLm and the gate lines GL1 to GLn. The thin film transistor supplies data to the liquid crystal cell Clc on the data lines DL1 to DLm in response to the scan pulse.

The gate electrode of the thin film transistor is connected to the gate lines GL1 to GLn, and the source electrode of the thin film transistor is connected to the data lines DL1 to DLm. The drain electrode of the thin film transistor is connected to the pixel electrode of the liquid crystal cell Clc and the storage capacitor Cst.

The thin film transistor is turned on in response to a scan pulse supplied to the gate terminal via the gate lines GL1 to GLn. At turn-on of the thin film transistor, video data on the data lines DL1 to DLm is supplied to the pixel electrode of the liquid crystal cell Clc.

The data driver 120 supplies data to the data lines DL1 to DLm in response to the data driving control signal DDC supplied from the timing controller 190, and supplies the digital video data (eg, the digital video data supplied from the timing controller 190). RGB is sampled and latched, and then converted into an analog data voltage capable of expressing gray scale in the liquid crystal cell Clc of the liquid crystal display panel 110 based on the gamma reference voltage supplied from the gamma reference voltage generator 140. Supply to wirings DL1 to DLm.

The gate driver 130 sequentially generates scan pulses in response to the gate driving control signal GDC and the gate shift clock GSC supplied from the timing controller 190 and supplies them to the gate lines GL1 to GLn. In this case, the gate driver 130 determines the high level voltage and the low level voltage of the scan pulse according to the gate high voltage VGH and the gate low voltage VGL supplied from the gate driving voltage generator 180.

The gamma reference voltage generator 140 receives a high potential power supply voltage VDD to generate a positive gamma reference voltage and a negative gamma reference voltage and output the same to the data driver 120.

The backlight assembly 150 is disposed on the rear surface of the liquid crystal display panel 110 and emits light by an AC voltage and a current supplied from the inverter 160 to irradiate light to each pixel of the liquid crystal display panel 110.

The inverter 160 converts the square wave signal generated therein into a triangular wave signal and compares the triangular wave signal with a DC power supply voltage VCC supplied from the system to generate a burst dimming signal proportional to the comparison result. . When the burst dimming signal determined according to the square wave signal is generated inside, the driving integrated circuit (not shown) for controlling the generation of the AC voltage and the current in the inverter 160 is not shown in the backlight assembly 150 according to the burst dimming signal. Control the generation of alternating voltage and current supplied to the

The gate driving voltage generator 180 receives the high potential power voltage VDD to generate the gate high voltage VGH and the gate low voltage VGL to supply the gate driver 130 to the gate driver 130. Here, the gate driving voltage generator 180 generates a gate high voltage VHG that is equal to or greater than the threshold voltage of the thin film transistors provided in each pixel of the liquid crystal display panel 110 and becomes a gate low that is less than the threshold voltage of the thin film transistor. Generate the voltage VGL.

The gate high voltage VGH and the gate low voltage VGL generated as described above are used to determine the high level voltage and the low level voltage of the gate pulse generated by the gate driver 130, respectively.

The timing controller 190 supplies digital video data RGB, which is supplied from a digital video card (not shown), to the data driver 120, and also the horizontal / vertical synchronization signals H and V according to the clock signal CLK. The data driving control signal DDC and the gate driving control signal GDC may be generated and supplied to the data driver 120 and the gate driver 130, respectively. The data driving control signal DDC includes a source shift clock SSC, a source start pulse SSP, a polarity control signal POL, a source output enable signal SOE, and a gate driving control signal GDC. ) Includes a gate start pulse (GSP) and a gate output enable (GOE).

The common voltage generator 170 receives a control signal for a reference common voltage from the outside, and compensates the reference common voltage according to a temperature to compensate the common common voltage for each pixel of the liquid crystal display panel 110. It is supplied to the common electrode of (Clc).

4 is a block diagram schematically illustrating a common voltage generator according to an exemplary embodiment of the present invention.

As can be seen in Figure 4, the common voltage generator 170 according to an embodiment of the present invention is the first memory 200, the temperature detector 300, the second memory 400, the common voltage setting signal generator 500 ) And the common voltage generator 600, and have a single chip shape.

The first memory 200 is formed to output a reference value. The first memory 200 receives a control signal CS applied by an I2C method from the outside as a synchronization signal In and an address to set a reference common voltage. The reference value is output to the common voltage setting signal generator 500 and the second memory 400. The first memory 200 initially stores a reference value for setting a reference common voltage, and outputs a reference value corresponding to the control signal CS when input from the outside as an address.

That is, when the control signal CS corresponding to the optimum common voltage at room temperature is input to the first memory 200 by the I2C method, which is a chip-to-chip communication method, the first memory 200 is one of the stored reference values. A value corresponding to the control signal CS is found and output.

As the first memory 200, it is preferable to use EEPROM (Electrically Erasable and Programmable Read Only Memory).

The temperature detector 300 is formed to detect the temperature of the panel. After detecting the temperature of the panel using a temperature sensor, the temperature detector 300 converts the temperature into a temperature data TD to address the second memory 400. Enter The temperature sensor is preferably embedded in a chip constituting the common voltage generator 170.

The second memory 400 is formed to output a compensation value. The second memory 400 receives the control signal CS applied by the I2C method from the outside as the synchronization signal In and receives the temperature data TD from the temperature detector 300. Is input as an address, and the compensation value is output to the common voltage setting signal generator 500.

5 is a block diagram schematically illustrating a second memory according to an embodiment of the present invention.

As can be seen in Figure 5, the second memory 400 according to an embodiment of the present invention and the storage unit 420 and the measured value from the storage unit 420, the actual value stored for the optimum common voltage according to the temperature and Comparing unit 440 for comparing the reference value for setting the reference common voltage and outputs a compensation value.

The storage unit 420 initially stores the measured value of the optimum common voltage according to the temperature, and outputs the measured value corresponding to the temperature data TD from the temperature detector 300 as an address.

That is, when the temperature of the panel is changed and the temperature data TD according to the temperature is input from the temperature detector 300 to the storage unit 420 through the address terminal of the second memory 400, the storage unit ( 420 finds a value corresponding to the temperature data TD among the stored measured values and outputs the value to the comparator 440.

The comparator 440 outputs a value obtained by subtracting the reference value from the first memory 200 from the measured value from the storage 420 as a compensation value.

As the second memory 400, it is preferable to use an EEPROM (Electrically Erasable and Programmable Read Only Memory).

The common voltage setting signal generator 500 generates a setting signal for supplying the common voltage generator 600, and the reference value from the first memory 200 and the compensation value from the second memory 400. Add to generate a common voltage setting signal.

By adding a reference value corresponding to an optimum common voltage at room temperature and a compensation value obtained by subtracting the reference value from an actual value corresponding to an optimum common voltage according to temperature, a common voltage setting signal corresponding to an optimum common voltage according to a change in temperature. May be supplied to the common voltage generator 600.

The common voltage generator 600 generates a common voltage Vcom and supplies the common voltage Vcom to the liquid crystal display panel 110 of FIG. 3. After receiving the set signal from the common voltage set signal generator 500, the set signal is generated. The common voltage Vcom is generated and applied to the liquid crystal display panel 110.

6 is a block diagram schematically illustrating a common voltage generator according to an exemplary embodiment of the present invention.

As can be seen in FIG. 6, the common voltage generator 600 according to an exemplary embodiment of the present invention includes a plurality of resistors 610 and the common voltage connected in series between a first voltage VCH and a second voltage VCL. A decoder 620 which decodes a setting signal to generate a switching signal is connected to each node between the resistors 610 and the divided voltages of the resistors 610 to the common voltage Vcom according to the switching signal. It comprises a plurality of switching elements 630 for outputting.

When the common voltage setting signal is input to the decoder 620 of the common voltage generating unit 600, the decoder 620 decodes the setting signal to generate a switching signal, and then, to any one of the plurality of switching elements 630. Is applied to activate the switching element 630.

The switching element 630 is connected to each node of the plurality of resistors 610 connected in series between the first voltage VCH, which is a common high voltage, and the second voltage VCL, which is a common low and low voltage. When the switching signal is applied and activated at 630, the divided voltage of the corresponding node is applied to the liquid crystal display panel 110 as the common voltage Vcom.

Hereinafter, an operation of the common voltage generator including the configuration will be described with reference to FIGS. 4 to 6.

First, when the panel temperature is room temperature, the control signal CS for the optimum common voltage at room temperature is input to the first memory 200 as the synchronization signal In and the address, and the second memory ( 400 is input as a synchronization signal In. In addition, the temperature data TD detected by the temperature detector 300 is input to the second memory 400 as an address.

The first memory 200 is synchronized with the control signal CS and outputs a reference value corresponding to the control signal CS among the stored reference values to the second memory 400 and the common voltage setting signal generator 500. .

The second memory 400 is synchronized with the control signal CS to output the measured value corresponding to the temperature data TD of the room temperature among the stored measured values from the storage unit 420, and then the temperature of the room temperature. The compensation value is output by subtracting the reference value from the first memory 200 from the measured value corresponding to the data TD.

The measured value corresponding to the temperature data TD at room temperature has the same value as the reference value corresponding to the optimum common voltage at room temperature, and the compensation value output from the second memory 400 becomes zero.

The reference value from the first memory 200 and the compensation value from the second memory 400 are input to the common voltage setting signal generator 500 and summed. At this time, since the compensation value is zero, the setting signal generated by the common voltage setting signal generator 500 corresponds to a common voltage of room temperature.

The setting signal from the common voltage setting signal generating unit 500 is input to the decoder 620 of the common voltage generating unit 600 and converted into a switching signal.

The switching signal activates any one of the plurality of switching elements 630, preferably the 63rd switching element 630. The node voltage between the resistors connected in series between the first voltage VCH and the second voltage VCL through the activated switching element 630 is set to the common voltage Vcom (110 of FIG. 3). To supply.

Thereafter, when the panel temperature is changed, the current temperature data TD detected by the temperature detector 300 is input to the second memory 400 as an address.

The second memory 400 synchronizes with the control signal CS to output the measured value corresponding to the current temperature data TD among the stored measured values from the storage unit 420, and then corresponds to the current temperature data TD. The compensation value is output by subtracting the reference value from the first memory 200 from the measured value.

Since the measured value corresponding to the current temperature data TD has a value different from the reference value corresponding to the optimum common voltage at room temperature, the compensation value output from the second memory 400 is not zero but any value. Will have

The reference value from the first memory 200 and the compensation value from the second memory 400 are input to the common voltage setting signal generation unit 500 and summed, whereupon the common voltage setting signal generation unit 500 is added. The set signal generated at is a value corresponding to the optimum common voltage according to the current temperature.

The setting signal from the common voltage setting signal generating unit 500 is input to the decoder 620 of the common voltage generating unit 600 and converted into a switching signal.

The switching signal activates the switching element 630 corresponding to the optimum common voltage according to the current temperature, not the switching element 630 activated at room temperature.

The node voltage between the resistors connected in series between the first voltage VCH and the second voltage VCL through the activated switching element 630 is set to the common voltage Vcom (110 of FIG. 3). To supply.

According to the present invention,

Since the optimum common voltage in accordance with the change in temperature is set and supplied to the liquid crystal display panel, the display quality of the image can be improved by preventing the degradation of the image quality caused by the common voltage.

In addition, since the value corresponding to the optimal common voltage according to the temperature is stored in the memory, it is automatically output according to the change of temperature to set the common voltage. Therefore, there is no need to adjust the common voltage manually. Can be.

Claims (14)

A liquid crystal display panel which drives an liquid crystal according to a potential difference between a data voltage and a common voltage and displays an image according to the light transmittance of the liquid crystal; A temperature detector for detecting a temperature of the liquid crystal display panel; A common voltage setting signal generator configured to generate a common voltage setting signal using a reference value for setting the reference common voltage and a compensation value for compensating the reference common voltage according to the temperature of the panel; And And a common voltage generator for generating a common voltage corresponding to the common voltage setting signal and supplying the common voltage to the liquid crystal display panel. The method of claim 1, And a first memory in which a reference value for setting the reference common voltage is stored. The method of claim 2, And the first memory receives a control signal as a synchronization signal and an address and outputs a reference value. The method of claim 1, And a second memory in which measured values for optimal common voltages according to temperature are stored. 5. The method of claim 4, The second memory is And a control signal as a synchronous signal, a temperature data from the temperature detector as an address, and a compensation value to be output. 5. The method of claim 4, The second memory is A storage unit storing measured values of optimum common voltages according to temperature; And And a comparator for comparing a measured value from the storage with a reference value for setting a reference common voltage and outputting a compensation value. The method of claim 6, And the comparator outputs a value obtained by subtracting the reference value from the measured value as a compensation value. The method of claim 1, The common voltage setting signal generating unit generates a common voltage setting signal by adding a reference value for setting a reference common voltage and a compensation value for compensating the reference common voltage according to a panel temperature. The method of claim 1, The common voltage generator A plurality of resistors connected in series between the first voltage and the second voltage; A decoder configured to decode the common voltage setting signal to generate a switching signal; And And a plurality of switching elements connected to each node between the resistors and outputting the divided voltages of the resistors to the common voltage according to the switching signal. Inputting a control signal into the first memory as a synchronization signal and an address; Outputting a reference value from the first memory; Using the control signal as a synchronization signal and inputting temperature data from a temperature sensor as an address to a second memory; Outputting a compensation value from the second memory; Inputting a reference value from the first memory and a compensation value from the second memory into a common voltage setting signal generator; Outputting a common voltage setting signal from the common voltage setting signal generator; And supplying a common voltage compensated according to the common voltage setting signal to a liquid crystal display panel. 11. The method of claim 10, The step of outputting the compensation value from the second memory Outputting a measured value according to the temperature data from a storage unit; And And comparing the measured value with a reference value from the first memory to output a compensation value. The method of claim 11, And comparing the measured value with a reference value from the first memory and outputting a compensation value comprises using a value obtained by subtracting the reference value from the measured value as a compensation value. 11. The method of claim 10, And outputting the common voltage setting signal from the common voltage setting signal generation unit using a sum of a reference value and a compensation value as a common voltage setting signal. 11. The method of claim 10, The step of supplying the common voltage compensated according to the common voltage setting signal to the liquid crystal display panel Generating a switching signal by decoding the common voltage setting signal; Activating one of a plurality of switching elements according to the switching signal; And And supplying a voltage corresponding to the activated switching element to the liquid crystal display panel.

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