KR100696684B1 - LCD and its driving method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a field sequential driving method for directly measuring a response characteristic of a liquid crystal by disposing a light receiving element for measuring the light transmittance of the liquid crystal and a driving method thereof. A method of driving a liquid crystal display according to the present invention includes the steps of: a) directly measuring a light transmittance of a liquid crystal being driven by using a light receiving element; b) converting the light transmittance measured using the light receiving element into a digital signal; c) calculating a response speed of the liquid crystal corresponding to the digital signal; d) setting a driving condition corresponding to the response speed; And e) driving the liquid crystal according to a driving condition corresponding to the response speed, wherein the driving condition may be a driving frequency or a reset time, and a value preset in the lookup table for each response characteristic of the liquid crystal. This is changed according to the response characteristic of the liquid crystal. According to the present invention, by placing a light-receiving element for measuring the light transmittance of the liquid crystal to directly measure the response characteristics according to the temperature change, and by setting the driving conditions such as reset time and driving frequency optimally according to the response characteristics of the panel, It is possible to greatly improve the low temperature characteristics.

Liquid crystal display, light receiving element, response characteristics, light transmittance, 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 detailed configuration diagram of a light transmittance measuring unit of a liquid crystal display according to an exemplary embodiment of the present invention.

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

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly, to a field sequential driving method for directly measuring a response characteristic of a liquid crystal by disposing a light receiving element for measuring the light transmittance of the liquid crystal and a driving method thereof. It is about a method.

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, a driving voltage means a voltage applied to a liquid crystal and an 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, in order to compensate the response characteristics (transmission characteristics) that change with temperature in the conventional FS-LCD, the response characteristics of the liquid crystals were indirectly measured by measuring the temperature or the ambient temperature of the liquid crystal panel.

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. That is, in the conventional FS-LCD panel 100 to measure the temperature using the temperature sensor 900 to compensate for the change in the response speed of the panel according to the temperature, the FS-LCD panel 100 by using the temperature ) Was estimated indirectly. 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 speed using a temperature sensor, there is no clear relationship between the response speed of the panel and the temperature, and in particular, in the FS-LCD, since the change of the response characteristic with temperature is very nonlinear, the temperature is measured. There is a problem that it is difficult to measure the accurate response characteristics. In addition, since there is an error between the temperature measured by using the temperature sensor and the actual temperature of the liquid crystal panel, there is a problem that there is a limit in estimating the response speed of the liquid crystal panel and compensating for it when using the existing temperature sensor. .

An object of the present invention for solving the above problems is to arrange a light receiving element for measuring the light transmittance of the liquid crystal to directly measure the response characteristics according to the temperature change, by changing the driving frequency and reset time according to the response characteristics, To provide a liquid crystal display and a driving method of the field-sequential driving method that can operate stably in the.

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

a) directly measuring the amount of light passing through the liquid crystal being driven from the light source using a light receiving element;

b) converting the light transmittance measured using the light receiving element into a digital signal;

c) calculating a response speed of the liquid crystal corresponding to the digital signal;

d) setting a driving condition corresponding to the response speed; And

e) driving the liquid crystal according to a driving condition corresponding to the response speed

There is a feature that includes.

Here, the driving condition is a driving frequency or a reset time, and the driving frequency or reset time is a value preset in the lookup table for each response characteristic of the liquid crystal, and is changed according to the response characteristic of the liquid crystal. .

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; And

The light transmittance measuring unit which directly measures the light transmittance passing through the liquid crystal from the light source, obtains the response speed of the liquid crystal, and sets the driving conditions corresponding to the response speed.

There is a feature that includes.

According to the present invention, rather than measuring the indirect response characteristics through the temperature, by placing a light receiving element for measuring the light transmittance of the liquid crystal to directly measure the response characteristics according to the temperature change, reset time and drive frequency (frame frequency) By optimally setting the driving conditions such as the response characteristics of the panel, the low temperature characteristics of the FS-LCD can be greatly improved.

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, and a light transmittance 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 scale 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 light transmittance measuring unit 1000 directly measures the light transmittance of the liquid crystal or the liquid crystal panel 100 to obtain a response speed of the liquid crystal 100, and sets driving conditions corresponding to the response speed.

Here, the driving condition is a driving frequency (frame frequency) or a reset time, and the driving frequency or reset time is a value preset in the lookup table (LUT) for each response characteristic of the liquid crystal 100. It is changed according to the response characteristic of 100). Here, the response speed of the liquid crystal 100 is a value linearly proportional to the digital signal, but is not limited thereto.

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

Referring to FIG. 4, the light transmittance measuring unit 1000 is measured by the light receiving element 1100 and the light receiving element 1100 for measuring the light transmittance passing through the FS-LCD 100 through the light source. An analog / digital converter 1200 for converting light transmission amount into a digital signal, and a controller for obtaining a response speed of the FS-LCD 100 according to the digitally converted light transmission amount, and setting a driving condition corresponding to the response speed. 1300.

Therefore, the controller 1300 directly measures the light transmittance of the FS-LCD using the light-receiving element 1100, calculates the response speed accordingly, and then measures the accurate response speed of the FS-LCD 100, By setting a driving condition corresponding to the response speed and applying the driving condition, for example, a driving frequency or a reset time to the LCD driver 400a, the FS-LCD 100 is in a state where the low temperature characteristic is improved. Can be restarted.

According to an exemplary embodiment of the present invention, an accurate response speed of the liquid crystal is calculated using the light receiving element 1100, and a driving frequency and reset time applied to the FS-LCD liquid crystal panel 100 are measured using the measured response speed. By setting it optimally, the response characteristic of liquid crystal is improved. 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.

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

Referring to FIG. 5, in the driving method of the liquid crystal display according to the exemplary embodiment of the present invention, first, when the FS-LCD 100 is driven 501, the light receiving element 1100 in the light transmittance measuring unit 1000 is used. Using directly measure the light transmittance of the FS-LCD (100) (S502).

Next, the A / D converter 1200 in the light transmittance measuring unit 1000 converts the light transmittance, which is an analog signal, into a digital signal (S503).

Next, the control unit 1300 in the light transmittance measuring unit 1000 calculates a response speed of the FS-LCD 100 corresponding to the converted digital signal (S504).

Thereafter, a driving condition corresponding to the response characteristic of the FS-LCD 100 is set, for example, a driving frequency and a reset time (S505). In this case, the driving frequency and the reset time are taken from a preset lookup table. 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.

Next, the FS-LCD 100 is driven again according to the driving frequency and the reset time. That is, the FS-LCD 100 is driven again according to the changed driving frequency and reset time taken from the lookup table LUT.

Thereafter, it is checked whether the preset setting condition is satisfied (S507). If the setting condition is not satisfied, the above-described steps S501 to S506 are repeated. Here, the setting condition may be the number of times that the light receiving element 1100 measures the light transmission amount, and by repeating steps S501 to S506, a more accurate response characteristic of the liquid crystal may be obtained. Accordingly, the FS-LCD ( 100) can be restarted.

As a result, the embodiment of the present invention can directly measure the response characteristics of the liquid crystals varying with temperature by using the light receiving element, and accordingly, by setting the reset time and the driving frequency to the optimum values for the actual response characteristics of the liquid crystals, The response characteristic of the liquid crystal which changes with temperature can be improved significantly.

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, by placing a light-receiving element for measuring the light transmittance of the liquid crystal to directly measure the response characteristics according to the temperature change, and by setting the driving conditions such as reset time and driving frequency optimally according to the response characteristics of the panel, It is possible to greatly improve the low temperature characteristics.

Claims (10)

In the driving method of a liquid crystal display device, a) directly measuring the amount of light passing through the liquid crystal being driven from the light source using a light receiving element; b) converting the light transmittance measured using the light receiving element into a digital signal; c) calculating a response speed of the liquid crystal corresponding to the digital signal; d) setting a driving condition corresponding to the response speed; And e) driving the liquid crystal according to a driving condition corresponding to the response speed Liquid crystal display driving method comprising a. The method of claim 1, And the driving condition is a driving frequency or a reset time. The method of claim 2, The driving frequency or the reset time is a value preset in the lookup table for each response characteristic of the liquid crystal and is changed according to the response characteristic of the liquid crystal. The method of claim 1, And repeating steps a) to e) to accurately measure the light transmittance. The method of claim 1, The response speed of the liquid crystal of step c) is linearly proportional to the digital signal. 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; And The light transmittance measuring unit which directly measures the light transmittance passing through the liquid crystal from the light source to obtain a response speed of the liquid crystal, and sets a driving condition corresponding to the response speed. Liquid crystal display comprising a. According to claim 6, The light transmittance measuring unit, A light receiving element for measuring a light transmission amount passing through the liquid crystal through the light source; An analog / digital converter for converting the light transmittance measured by the light receiving element into a digital signal; And A control unit for obtaining a response speed of the liquid crystal according to the digitally converted light transmission amount and setting a driving condition corresponding to the response speed Liquid crystal display comprising a. The method according to claim 6 or 7, And the driving condition is a driving frequency or a reset time. The method of claim 8, The driving frequency or the reset time is a value preset in the lookup table for each response characteristic of the liquid crystal, and is changed according to the response characteristic of the liquid crystal. The method of claim 6, The response speed of the liquid crystal is linearly proportional to the digital signal.

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