KR100560460B1 - A liquid crystal display and a driving method thereof - Google Patents

Abstract

The present invention relates to a field sequential driving liquid crystal display device and a method of driving the same, which directly measure response characteristics of liquid crystals varying with temperature using a test pattern. A liquid crystal display driving method according to the present invention includes the steps of: a) forming a test pattern and applying it to a liquid crystal; b) measuring the light transmittance of the liquid crystal and converting it into a digital signal; c) measuring a response speed of the liquid crystal according to a light transmittance corresponding to the test pattern; d) bringing from the lookup table a drive frequency and a reset time corresponding to the response speed; And e) driving the liquid crystal at a driving frequency and a reset time corresponding to the response speed, wherein step c) corresponds to a time corresponding to the time between the falling edge of the test pattern and the point where the light transmittance becomes zero. It is characterized by measuring the speed. According to the present invention, it is possible to directly measure the response characteristics of the liquid crystals varying with temperature by using a test pattern, thereby real-time changing the reset time and driving frequency to values that are optimal for the actual response characteristics of the liquid crystals. The response characteristics of the changing liquid crystal can be greatly improved.

Liquid crystal display, test pattern, response characteristics, light transmittance, temperature sensor, field sequential driving

Description

Liquid Crystal Display and Driving Method {A LIQUID CRYSTAL DISPLAY AND A DRIVING METHOD THEREOF}

1A is a diagram illustrating a pixel of a conventional liquid crystal display.

1B is a waveform diagram illustrating a driving method of a conventional analog liquid crystal display device.

1C is a waveform diagram illustrating a driving method of a conventional digital liquid crystal display device.

2 is a view showing a conventional liquid crystal display device.

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

4 is a waveform diagram of a test pattern and a light transmittance according to an exemplary embodiment of the present invention.

5 is a detailed configuration diagram of a light transmittance measuring unit and a response speed measuring unit of a liquid crystal display according to an exemplary embodiment of the present invention.

6 is a flowchart illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

The present invention relates to a liquid crystal display and a driving method thereof, and more particularly, to a liquid crystal display and a driving method of the field-sequential driving method for directly measuring the response characteristics of the liquid crystal changes with temperature using a test pattern will be.

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 (hereinafter referred to as "LCDs") instead of cathode ray tubes (CRTs) are required. Flat panel displays are being developed.

The LCD applies an electric field to a liquid crystal material having an anisotropic dielectric constant injected between two substrates, and adjusts the strength of the electric field to control the light transmitted from the external light source (back-light) to the substrate. By adjusting the amount, a desired image is obtained.

Such LCDs are typical of portable flat panel displays, and among them, TFT-LCDs using thin film transistors (hereinafter referred to as TFTs) as switching elements are mainly used.

In the TFT-LCD, each pixel can be modeled as a liquid crystal capacitor because electrodes (pixel electrodes and common electrodes) are disposed to face each other with a liquid crystal interposed therebetween. In such LCDs, each pixel is represented by an equivalent circuit as shown in FIG. 1A. Can be.

As shown in Fig. 1A, each pixel of the liquid crystal display according to the prior art includes: a TFT 10 having a source electrode connected to a data line Dm and a gate electrode connected to a scan line Sn; A liquid crystal capacitor Cl connected between the drain electrode of the TFT 10 and the common electrode Vcom; And a storage capacitor Cst connected to the drain electrode of the TFT 10.

The TFT 10 provides the pixel electrode (not shown) with the data voltage Vd supplied from the data line Dm in response to the scan signal from the scan line Sn. An electric field corresponding to the difference between the data voltage provided to the pixel electrode (that is, the pixel voltage Vp and the common voltage Vcom applied to the common electrode (not shown) is equivalent to that of the liquid crystal capacitor (FIG. 1A). The liquid crystal adjusts the transmittance of light in response to the intensity of the applied electric field, and the storage capacitor Cst converts the pixel voltage provided to the liquid crystal capacitor Cl to the next data voltage Vd. The light is transmitted for a predetermined time by maintaining it until it is supplied.

In general, the LCD may be divided into two methods, a color filter method and a field sequential driving method, according to a method of displaying a color image.

A color filter type LCD forms a color filter layer consisting of three primary colors of red (R), green (G), and blue (B) on an upper substrate of a panel, and adjusts the amount of light transmitted through the color filter layer to achieve a desired image. Is displayed. However, a color filter LCD requires unit pixels corresponding to each of red (R), green (G), and blue (B) regions, and thus requires three times as many pixels as those for displaying black and white. Therefore, in order to obtain high resolution images, sophisticated manufacturing technology of LCD panels is required. In addition, in the color filter type LCD, red (R), green (G), and blue (B) color filters must be formed on the upper substrate, which is cumbersome in manufacturing, and the light transmittance of the color filter itself must be improved. There is a problem.

Field-sequential driving LCDs periodically turn on independent light sources of red (R), green (G), and blue (B) colors sequentially, and supply a pixel voltage (Vp) to each pixel at each lighting cycle. Is displayed. That is, the field-sequential driving LCD does not divide one pixel into unit pixels of red (R), green (G), and blue (B), and red (R), green (G), and blue colors in one pixel. (B) By time-divisionally displaying the light of three primary colors supplied from each backlight, a color image is displayed using the afterimage effect of an eye.

The field sequential driving method can be classified into an analog driving method and a digital driving method.

The analog driving method sets a plurality of gray voltages corresponding to the number of gray levels to be displayed, selects one gray voltage corresponding to gray data among the gray voltages, and drives the liquid crystal panel with the selected gray voltage, thereby applying the applied gray voltage. Gradation display is performed with the amount of transmitted light corresponding to.

In addition, the digital driving method makes the driving voltage applied to the liquid crystal constant and controls the voltage application time to perform gradation display. According to such a digital driving method, gray scales are displayed by adjusting a cumulative amount of light transmitted through a liquid crystal by maintaining a constant driving voltage and controlling a voltage application state and a voltage non-application state in a timing manner.

FIG. 1B is a diagram illustrating a driving voltage and a transmitted light amount according to a conventional LCD driving apparatus.

In FIG. 1B, the driving voltage means a voltage applied to the liquid crystal, and the optical transmittance means a transmission ratio with respect to the applied light when light is applied to the liquid crystal. That is, the light transmittance refers to the degree of twist that the liquid crystal can transmit light.

Referring to FIG. 1B, in the R field section Tr for displaying the R color, a driving voltage of the V11 level is applied to the liquid crystal so that light corresponding to the driving voltage of the V11 level passes through the liquid crystal. In the G field section Tg for displaying the G color, a driving voltage of the V12 level is applied so that light corresponding to the driving voltage of the V12 level passes through the liquid crystal. Then, in the B field section Tb for displaying the B color, a driving voltage of the V13 level is applied to obtain a light transmittance corresponding to the driving voltage of the V13 level. Thus, the desired color image is displayed by the sum of the R, G, and B light transmitted through the Tr, Tg, and Tb field sections, respectively.

On the other hand, the digital driving method makes the driving voltage applied to the liquid crystal constant and controls the voltage application time to perform gradation display. According to such a digital driving method, gray scales are displayed by adjusting a cumulative amount of light transmitted through a liquid crystal by maintaining a constant driving voltage and controlling a voltage application state and a voltage non-application state in a timing manner.

FIG. 1C is a waveform diagram illustrating a conventional method of driving a liquid crystal display device of a digital driving method. The waveform diagram of the driving voltage according to the driving data of a predetermined bit and the light transmittance of the liquid crystal is accordingly shown.

Referring to FIG. 1C, grayscale waveform data corresponding to each grayscale is provided as a digital signal of a predetermined bit, for example, 7bit, and a grayscale waveform corresponding to the 7bit data is applied to the liquid crystal. Then, the light transmittance of the liquid crystal is determined according to the applied gradation waveform to perform gradation display.

On the other hand, since the above-described field sequential driving LCD (FS-LCD) is driven by dividing one frame into an R field, a G field, and a B field, the liquid crystal should have a higher response speed than the color filter type LCD. However, the lower the temperature, the lower the response speed of the liquid crystal. Therefore, when a field sequential driving LCD is used in a portable device (for example, a mobile phone) frequently exposed to a low temperature environment, the response speed of the liquid crystal is remarkably lowered. There was a problem that the recall is low. Therefore, the temperature was measured to compensate for the response characteristics that change with temperature in the conventional FS-LCD.

FIG. 2 is a diagram illustrating a conventional liquid crystal display device. The temperature of the FS-LCD panel 100 is measured using a temperature sensor 900, and thus response characteristics are measured. Each component of the liquid crystal display will be described in detail later in the present invention.

However, in the conventional method for measuring the response characteristic according to the temperature measurement, the FS-LCD has a problem that it is difficult to measure the accurate response characteristic by measuring the temperature because the change of the response characteristic with temperature is very nonlinear.

An object of the present invention for solving the above problems is to calculate the response characteristics by applying a test pattern, and by changing the drive frequency and reset time according to the response characteristics of the field sequential driving method that can operate stably at low temperatures An object of the present invention is to provide a liquid crystal display and a driving method thereof.

As a means for achieving the above object, the liquid crystal display driving method according to the present invention,

a) forming a test pattern and applying it to the liquid crystal;

b) measuring the light transmittance of the liquid crystal and converting it into a digital signal;

c) measuring a response speed of the liquid crystal according to a light transmittance corresponding to the test pattern;

d) obtaining a drive frequency and a reset time corresponding to the response speed from a lookup table; And

e) driving the liquid crystal at a driving frequency and a reset time corresponding to the response speed

There is a feature that includes.

Here, the step c) is characterized in that for measuring the response speed corresponding to the time between the falling edge of the test pattern and the point where the light transmittance becomes zero.

In addition, as another means for achieving the above object, the liquid crystal display device according to the present invention,

A liquid crystal panel having a liquid crystal and having an upper substrate and a lower substrate;

At least three light sources sequentially outputting red (R), green (G), and blue (B) light to each pixel disposed in the liquid crystal panel;

A light source controller for controlling light emission of the light source;

A response speed measuring unit measuring a response speed of the liquid crystal by applying a test pattern to the liquid crystal; And

A light transmittance measuring unit which transmits a digital signal to the response speed measuring unit by measuring the light transmittance of the liquid crystal to which the test pattern is applied

There is a feature that includes.

According to the present invention, in order to solve the problem that the conventional temperature measurement does not exhibit accurate response characteristics, the response characteristics of the liquid crystals varying with temperature using a test pattern are directly measured, and thus optimal for the actual response characteristics of the liquid crystals. By changing the reset time and the driving frequency in real time with the phosphorus value, it is possible to greatly improve the response characteristic of the liquid crystal which varies with temperature.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

The term "reset" described below means applying a voltage (or waveform) to make the liquid crystal material in the LCD black, which cannot transmit light. In addition, "light transmittance" refers to a ratio of transmitted light to applied light when a certain light is applied to the liquid crystal, and 'light transmittance' is the amount of light transmitted through the liquid crystal by the actual light is applied to the liquid crystal. Means.

3 is a diagram illustrating a liquid crystal display (LCD) according to an embodiment of the present invention.

Referring to FIG. 3, a liquid crystal display according to an exemplary embodiment of the present invention may include a liquid crystal panel 100, a scan driver 300, a data driver 400, a gray voltage generator 500, a timing controller 600, and at least Three or more light sources 800R, 800G, and 800B, a light source controller 700, a light transmittance measuring unit 1100, and a response characteristic measuring unit 1000 are provided. Here, the light sources 800R, 800G, and 800B use a light emitting diode (LED) for backlight of the liquid crystal panel 100.

The liquid crystal panel 100 includes a plurality of pixels 120 arranged in a matrix at the intersection of the scan line S and the data line D. FIG.

The timing controller 600 receives the gray level data signals R, G, and B data, the horizontal synchronization signal Hsync, and the vertical synchronization signal Vsync from an external or graphic controller (not shown), and scan scan unit 300. ), A scan control signal Sg for controlling the control panel, a data control signal Sd for controlling the data driver 400, and a light source control signal Sb for controlling the light source controller 700. The timing controller 600 supplies the gray data signals R, G, and B data to the gray voltage generator 500.

The scan driver 300 selects a horizontal line to which the data voltage Vd is supplied by sequentially supplying a scan signal to the scan line S in response to the scan control signal Sg supplied from the timing controller 600.

The gray voltage generator 500 generates a gray voltage (data voltage Vd) corresponding to the gray data signals R, G, and B DATA, and converts the generated data voltage Vd to the data driver 400. Supply. The data driver 400 supplies the data voltage Vd to the data line D while being controlled by the data control signal Sd.

The light source controller 700 may emit the light sources 800R, the green light sources 800R, the blue light sources 800G, and the blue light sources 800B in different periods of one frame in response to the light source control signal Sb. 800G, 800B). In this case, driving currents I _R , I _G , and I _B expressing color are supplied to the light sources 800R, 800G, and 800B.

The response characteristic measuring unit 1000 applies a test pattern to the liquid crystal or the liquid crystal panel 100 to measure the response speed of the liquid crystal 100. The falling edge and the light transmittance of the test pattern become zero. The response speed corresponding to the time between the points is measured. In addition, the response speed measuring unit 1000 may bring the driving frequency and reset time preset in the lookup table LUT according to the response characteristics of the liquid crystal 100 according to the measured response speed.

The light transmittance measuring unit 1100 measures a light transmittance of the liquid crystal 100 to which the test pattern is applied and transmits a digital signal to the response speed measuring unit 1000.

An embodiment of the present invention calculates an accurate response speed by applying the test pattern, and changes the driving frequency and reset time applied to the FS-LCD liquid crystal panel 100 by using the measured response speed, thereby providing response characteristics. Will improve. Therefore, since the liquid crystal contained in the liquid crystal panel 100 maintains a response speed higher than or equal to a predetermined temperature at low temperature, reliability of the LCD may be secured.

4 is a waveform diagram of a test pattern and a light transmittance according to an exemplary embodiment of the present invention. When the test pattern, which is a square wave, is applied, the light transmittance of the liquid crystal measured using the light receiving element 1110 may change with temperature. In this case, the accurate response speed of the FS-LCD can be measured by measuring the time between the falling edge of the test pattern and the point where the light transmittance becomes zero.

5 is a detailed configuration diagram of a light transmittance measuring unit and a response speed measuring unit of a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 5, the response speed measuring unit 1000 starts counting at a falling edge of a test pattern applied to the FS-LCD 100 and stops counting when the digital signal reaches zero ( 1010, and a controller 1020 that applies a test pattern to the FS-LCD 100, reads the value of the timer 1010 when the digital signal becomes 0, and resets the timer 1010. do.

In addition, the light transmittance measuring unit 1100 includes a light receiving element 1110 for measuring the light transmittance of the FS-LCD 100, and an analog-to-digital converter 1120 for converting the light transmittance into a digital signal. .

Therefore, when the control pattern 1020 is applied to the square wave test pattern, the light transmittance of the FS-LCD measured using the light receiving element 1110 is changed according to the temperature, at this time, the falling edge and the light of the test pattern By measuring the time between the points where the transmittance becomes zero, the accurate response speed of the FS-LCD 100 can be measured.

6 is a flowchart illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 6, in the method of driving the liquid crystal display according to the exemplary embodiment of the present invention, first, the control unit 1020 in the response speed measuring unit 1000 applies a square wave test pattern to the FS-LCD 100. (S601).

Thereafter, the timer 1010 in the response speed measuring unit 1000 starts counting at the falling edge of the test pattern (S602).

Thereafter, the light transmittance is measured using the light receiving element 1110 in the light transmittance measuring unit 1100 (S603), and the analog is measured using the A / D converter 1120 in the light transmittance measuring unit 1100. The light transmittance, which is a signal, is converted into a digital signal (S604).

Next, when the digital signal becomes 0, the timer 1010 stops counting (S605). Then, when the output of the A / D converter becomes 0, the timer 1010 reads out the timer value. In operation S606, the timer 1010 is reset.

Next, the response speed of the FS-LCD 100 is measured (S607), that is, by measuring the time between the falling edge of the test pattern and the point where the light transmittance becomes zero, the response speed is measured and thus obtained. If the response speed satisfies the preset measurement conditions (S608), and if it is not satisfied, by repeating the above steps S601 to S607, the response speed of the FS-LCD 100 can be accurately measured in real time. . Here, the predetermined measurement condition is a condition for checking whether the response speed is accurately obtained in real time. For example, the predetermined measurement condition may be a repeated measurement number. This means repeating it several times for more accurate measurements.

Next, the drive frequency and reset time changed in response to the measured response speed are taken from the lookup table (LUT) (S609), and the FS-LCD 100 is driven at the changed drive frequency and reset time (S610). ). Here, it is apparent to those skilled in the art that the look-up table LUT is used as a specific method of setting the gray voltage, and thus, detailed description thereof will be omitted.

As a result, the embodiment of the present invention can directly measure the response characteristics of the liquid crystals varying with temperature using a test pattern, thereby real-time changing the reset time and the driving frequency to values that are optimal for the actual response characteristics of the liquid crystals. As a result, the response characteristics of the liquid crystals varying with temperature can be greatly improved.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

For example, in the above-described embodiment of the present invention, the LCD of the field sequential driving method has been described as an example, but may be applied to various LCDs other than the field sequential driving LCD.

According to the present invention, it is possible to directly measure the response characteristics of the liquid crystals that change with temperature using a test pattern, thereby real-time changing the reset time and the driving frequency to a value that is optimal for the actual response characteristics of the liquid crystals. The response characteristic of the liquid crystal which changes accordingly can be improved significantly.

Claims (11)

In the driving method of a liquid crystal display device, a) forming a test pattern and applying it to the liquid crystal; b) measuring the light transmittance of the liquid crystal and converting it into a digital signal; c) measuring a response speed of the liquid crystal according to a light transmittance corresponding to the test pattern; d) obtaining a drive frequency and a reset time corresponding to the response speed from a lookup table; And e) driving the liquid crystal at a driving frequency and a reset time corresponding to the response speed Liquid crystal display driving method comprising a. The method of claim 1, And c) measuring a response speed corresponding to a time between a falling edge of the test pattern and a point where the light transmittance becomes zero. The method of claim 1, wherein c) is c-1) using the timer to start counting at the falling edge of the test pattern; c-2) stopping the count when the digital signal becomes zero; And c-3) when the digital signal becomes 0, reading a value of the timer and resetting the timer Liquid crystal display driving method comprising a. The method of claim 1, And the test pattern is a square wave. The method of claim 1, B) measuring the light transmittance using a light receiving element, and converting into a digital signal using an analog / digital converter. The method of claim 1, The driving frequency and the reset time of step d) are preset in the lookup table for each response characteristic of the liquid crystal. A liquid crystal panel having a liquid crystal and having an upper substrate and a lower substrate; At least three light sources sequentially outputting red (R), green (G), and blue (B) light to each pixel disposed in the liquid crystal panel; A light source controller for controlling light emission of the light source; A response speed measuring unit measuring a response speed of the liquid crystal by applying a test pattern to the liquid crystal; And A light transmittance measuring unit which transmits a digital signal to the response speed measuring unit by measuring the light transmittance of the liquid crystal to which the test pattern is applied Liquid crystal display comprising a. The method of claim 7, wherein And the response speed measuring unit measures a response speed corresponding to a time between a falling edge of the test pattern and a point where the light transmittance becomes zero. The method of claim 8, And the response speed measuring unit obtains a driving frequency and a reset time preset in a lookup table for each response characteristic of the liquid crystal corresponding to the measured response speed. The method of claim 7, wherein the response speed measuring unit, A timer that starts counting at the falling edge of the test pattern applied to the liquid crystal and stops counting when the digital signal becomes zero; And A control unit which applies a test pattern to the liquid crystal, reads the value of the timer when the digital signal becomes 0, and resets the timer. Liquid crystal display comprising a. The method of claim 7, wherein the light transmittance measuring unit, A light receiving element for measuring the light transmittance of the liquid crystal; And Analog-to-digital converter for converting the light transmittance into a digital signal Liquid crystal display comprising a.

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