KR20070064101A - Electron emission display device and driving method thereof - Google Patents

Abstract

An electron emission display device and a driving method thereof are provided to reduce the luminance difference between gray scales by performing gamma compensation corresponding to the sum of image signals. An electron emission display device includes a pixel unit(100), an image signal summation unit(400), a gamma level selection unit(500), a data driver(200), and a scan driver(300). Luminance of the pixel unit is adjusted corresponding to the voltage, which is applied to first and second electrodes, and a luminescence time. The image signal summation unit perceives the sum of image signals by summing the image signals, which are inputted during a frame. The gamma level selection unit selects a gamma compensation value corresponding to the summation. The data driver delivers a data signal, which is converted from the image signals, to the first electrode and adjusts the pulse width of the data signal corresponding to the gamma compensation value. The scan driver delivers a scan signal to the second electrode.

Description

Electron emission display device and driving method thereof

1 is a structural diagram showing an electron emission display device according to the prior art.

2 is a structural diagram showing a structure of an electron emission display device according to the present invention.

3 is a characteristic curve showing the relationship between gray scale and luminance.

FIG. 4 is a structural diagram showing a structure of a data driver employed in the electron emission display device shown in FIG. 2.

5 is a flowchart illustrating a step of performing gamma correction of the electron emission display device according to the present invention.

*** Explanation of symbols on main parts of drawings ***

100: pixel portion 101: pixel

200: data driver 210: shift register

220: latch 230: counter

240: comparator 250: level shifter

260: buffer 300: scanning driver

400: video signal adding unit 500: gamma level selecting unit

600: timing control unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron emission display device and a driving method thereof, and more particularly, to an electron emission display device and a driving method thereof for reducing power consumption and improving image quality.

BACKGROUND ART A thin, lightweight flat panel display is used as a display device of a portable information terminal such as a personal computer, a cellular phone, a PDA, or a monitor of various information devices. Such flat panel displays include LCDs using liquid crystal panels, organic light emitting displays using organic light emitting diodes, PDPs using plasma panels, electron emitting display devices using electron emitting devices, and the like.

The flat panel display can be classified into a memory driving method and a non-memory driving method in terms of structurally divided into an active matrix and a passive matrix, and a light emission principle. In general, the active matrix method has meaning with the memory driving method, and the passive matrix method has meaning with the non-memory driving method. The active matrix method and the memory driving method emit light at a period of a frame unit. The passive matrix method and the non-memory driving method emit a light at a period of a line unit.

As for the medium- and large-sized flat panel displays that are currently commercialized, TFT-LCD (Thin Film Transistor Liquid Crystal Display) is an active matrix method, and OLED, which is being developed as a new display device, is also an active method. On the other hand, as a new display device, an electron emission display device is a passive matrix method, and unlike other flat panel devices, a non-memory driving method selects horizontal lines sequentially and emits light only when a selected one of the horizontal lines is selected. Apply the scan method. That is, the driving method has a constant duty ratio.

In general, an electron emission device has a method using a hot cathode and a cold cathode as an electron source. The electron-emitting devices using the cold cathode are Field Emitter Array (FEA), Surface Conduction Emitter (SCE), Metal-Insulator-Metal (MIM), Metal-Insulator-Semiconductor (MIS), and BSE (Ballistic). electron surface emitting) and the like are known.

The FEA type electron emitting device uses a low work function or high β function as an electron emission source, and uses electrons to emit electrons by electric field in vacuum. In addition, devices using electron emission sources for nanomaterials have been developed.

The SCE type electron emission device is a device in which an electron emission part is formed by providing a conductive thin film between two electrodes disposed to face each other on a substrate and providing a micro crack in the conductive thin film. The device utilizes a principle that electrons are emitted from the electron emission portion, which is the fine gap, by applying a voltage to an electrode to flow a current to the surface of the conductive thin film.

The MIM type and MIS type electron emission devices each form an electron emission portion composed of a metal-dielectric layer-metal (MIM) and a metal-dielectric layer-semiconductor structure, and apply a voltage between two metals or a metal and a semiconductor disposed between dielectric layers. It is a device using the principle that electrons are released as they move and accelerate from a metal having a high electron potential or from a semiconductor to a metal having a low electron potential when applied.

The BSE type electron emitting device forms an electron supply layer made of a metal or a semiconductor on an ohmic electrode by using the principle that electrons travel without scattering when the size of the semiconductor is reduced to a dimension area smaller than the average free stroke of electrons in the semiconductor. And an insulating layer and a metal thin film formed on the electron supply layer to emit electrons by applying power to the ohmic electrode and the metal thin film.

Like the CRT (Cathode-Ray Tube), the electron-emitting device operates by cathode electrode ray emission (self-light source, high efficiency, high luminance and wide luminance region, natural color and high color purity, wide viewing angle), operating speed, Due to the advantage of lighting that the operating temperature range is wide, it can be used in various fields, and active research has been made until recently.

1 is a structural diagram showing an electron emission display device according to the prior art. Referring to FIG. 1, the electron emission display device includes a pixel unit 10, a data driver 20, a scan driver 30, and a timing controller 40.

In the pixel portion 10, the pixel 10 is formed at a portion where the cathode electrodes C1, C2... Cn and the gate electrodes G1, G2 .. Gn intersect, and the pixel 10 includes an electron emitting portion. As a result, electrons emitted from the cathode at the electron emission part collide with the anode, and the phosphor emits light, thereby displaying gray levels. The gray level of the displayed image is changed according to the value of the input digital image signal. In order to adjust the gray level represented according to the value of the digital image signal, a pulse width modulation method or a pulse amplitude modulation method may be generally used.

The data driver 20 generates a data signal using an image signal and is connected to the cathode electrodes C1, C2 ... Cn so that the data signal is transferred to the pixel portion 10 so that the pixel portion 10 receives the data signal. In response to the light emission.

The scan driver 30 is connected to the gate electrodes G1, G2... Gn, generates a scan signal, and transmits the scan signal to the pixel unit 10 so that the pixel unit 10 is line-scanned in a horizontal line unit. By sequentially emitting light, the entire screen can be displayed while being driven while reducing circuit cost and power consumption.

The timing controller 40 controls the data driver 20 and the scan driver 30 to generate data signals and scan signals.

The gamma correction unit 50 can easily distinguish the difference in luminance on a dark screen even though the same luminance difference is established, but sets a gamma correction value in consideration of the visual characteristics of the person who cannot easily distinguish the difference in luminance on a bright screen. By adjusting the ratio of gradation to luminance, the difference of luminance is easily recognized in a dark screen and a bright screen.

However, according to the conventional electron emission display device, in the case of a dark screen, the bright part of the screen is recognized as bright compared to the gray scale, and in the case of the bright screen, the bright part of the screen is perceived as dark compared to the gray scale and in the case of the dark screen and the bright screen. Correcting gamma by one gamma correction value has a limit in improving visibility.

Therefore, the present invention was created to solve the problems of the prior art, an object of the present invention is to select a gamma correction value by the sum of the video signals and to adjust the pulse width of the data signal corresponding to the selected gamma correction value The present invention provides an electron-emitting display device and a driving method thereof which perform gamma correction to increase visibility.

In order to achieve the above object, the first aspect of the present invention includes a pixel unit whose luminance is adjusted in response to a voltage applied to a first electrode and a second electrode, and a light emission time, and a summing signal input in one frame section adds an image. An image signal summing unit for determining a sum of signals, a gamma level selecting unit for selecting a gamma correction value corresponding to the sum of the image signals, and converting an image signal to generate a data signal and transmit the data signal to the first electrode. The pulse width of the signal is to provide an electron emission display device including a data driver and a scan driver for generating a scan signal and transmitting the scan signal to the second electrode in response to the gamma correction value.

According to a second aspect of the present invention, there is provided a method of driving an electron emission display device for displaying an image by transmitting a data signal and a scan signal to a first electrode and a second electrode. Determining a sum of video signals, selecting a gamma correction value corresponding to the sum of the video signals, and adjusting a ratio of luminance to grayscale by adjusting a pulse width of a data signal corresponding to the gamma correction value. It is to provide a method of driving an electron-emitting display device comprising.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

2 is a structural diagram showing a structure of an electron emission display device according to the present invention. Referring to FIG. 2, the electron emission display device includes a pixel unit 100, a data driver 200, a scan driver 300, an image signal adder 400, a gamma level selector 500, and a timing controller ( 600).

In the pixel unit 100, a pixel 101 is formed at a portion where the cathode electrodes C1, C2... Cn and the gate electrodes G1, G2 .. Gn intersect, and the pixel 101 includes an electron emission unit. As a result, electrons emitted from the cathode at the electron emission part collide with the anode, and the phosphor emits light, thereby displaying gray levels. The gray level of the displayed image is changed according to the value of the input digital image signal. In order to adjust the gray level represented according to the value of the digital image signal, a pulse width modulation method or a pulse amplitude modulation method may be generally used.

The data driver 200 generates a data signal using an image signal and is connected to the cathode electrodes C1, C2... Cn so that the data signal is transmitted to the pixel unit 100 so that the pixel unit 10 receives the data signal. In response to the light emission.

The scan driver 300 is connected to the gate electrodes G1, G2 ... Gn, generates a scan signal, and transmits the scan signal to the pixel unit 101 so that the pixel unit 101 is line-scanned for a predetermined time in a horizontal line unit. By sequentially emitting light, the entire screen can be displayed while being driven while reducing circuit cost and power consumption.

The image signal adding unit 400 receives the image signal and sums the image signals in units of one frame section to determine the sum of the image signals corresponding to one frame section. A frame with a large sum of video signals is judged to represent a bright screen by judging that there are many video signals expressing high gradation, and a frame with a small sum of video signals contains many video signals expressing low gradation. It judges that it is present and expresses a dark screen.

The gamma level selection unit 500 selects one gamma correction value from among the plurality of gamma correction values, selects a gamma correction value through the sum of the image signals summed by the image signal adding unit 400, and applies the gamma correction value to the gamma correction value. Correspondingly, data corresponding to the pulse width of the clock pulse is stored, and the timing controller 600 generates a clock pulse using data corresponding to the pulse width of the clock pulse and transmits the clock pulse to the data driver 200.

In addition, the gamma level selector 500 stores the data corresponding to the pulse width of the clock pulse through the lookup table and specifies the pulse width of the clock pulse corresponding to the gamma correction value. When the pulse width of the clock pulse is short in the same gradation, light is emitted at high luminance. If the width of the clock pulse is long, the light is emitted at low luminance. If the selected gamma correction value is small, the gamma level selection unit 500 reduces the pulse width of the clock pulse. If it is short and the selected gamma correction value is large, increase the pulse width of the clock pulse to adjust the ratio of brightness and gradation.

The timing controller 600 transmits an image signal and a data driver control signal to the data driver 200, and transmits a scan driver control signal to the scan driver 300 to operate the data driver 200 and the scan driver 300. Do it. In addition, the timing controller 600 adjusts the pulse width of the clock pulse in response to the gamma correction value selected by the gamma level selector 500 and transmits the pulse width to the data driver 200 to transmit the pulse width of the clock pulse from the data driver 200. In response to this, the pulse width of the data signal is adjusted.

3 is a characteristic curve showing the relationship between gray scale and luminance. Referring to FIG. 3, the horizontal axis represents gray scale and the vertical axis represents luminance, and the relationship between the gray scale and the luminance is expressed by Equation 1 below.

는 휘도를 나타내고

는 계조를 나타낸다. 또한,

는 감마보정값을 나타낸다. here,

Indicates luminance

Indicates gradation. Also,

Represents a gamma correction value.

In addition, the ratio of the gray scale and the luminance is different according to the gamma correction value, and the case where the gamma correction value is small shows a brighter brightness at the same gray level than when the gamma correction value is large. That is, when the gamma correction value is 1.5 at the same gray level, the luminance is brighter than when the gamma correction value is 2.2.

FIG. 4 is a structural diagram showing a structure of a data driver employed in the electron emission display device shown in FIG. 2. Referring to FIG. 4, the data driver 200 includes a shift register 210, a latch 220, a counter 230, a comparator 240, a level shifter 250, and a buffer 260.

The shift register 210 receives an image signal in series and transmits the image signal to the latch 220. The latch 220 outputs the image signal input in series and transmits the image signal in parallel to the comparator 240. The counter 230 counts the clock pulse when the input gray level of the video signal represents 8 bits, and counts the number from 255 to 0 using the clock. At this time, the pulse width of the clock pulse is stored in the lookup table, and the clock pulse width is determined according to the data for the pulse width stored in the lookup table.

The comparator 240 compares the number input from the latch 320 with the number counted by the counter 230 and outputs a signal when the value of the image signal matches the value of the counter 230.

The signal output from the comparator 240 is transferred to the buffer 260 through the level shifter 250 to output the data signal. Therefore, the larger the sum of the video signals, the higher the counting speed of the counter even when the same gray level is expressed, and the larger the pulse width of the data signal is. The smaller the sum of the video signals, the lower the counting speed of the counter, resulting in the same gray level. Even in this case, the pulse width of the data signal is made small so that the ratio of gradation to luminance can be adjusted.

5 is a flowchart illustrating a step of performing gamma correction of the electron emission display device according to the present invention. Referring to Figure 5,

First Step (ST 100): The video signal is input and the sum of the video signals input in one frame period is determined. If the sum of video signals in a frame is large, the frame contains many pixels expressing high brightness, and the whole frame is brighter. If the sum of video signals is small, the frame contains fewer pixels expressing high brightness. do.

Second Step (ST 110): One gamma correction value is selected from among the plurality of gamma correction values in response to the sum of the image signals. If a frame is expressed brightly, a small gamma correction value is selected to display a large luminance difference for each gray level. If a frame is represented dark, a large gamma correction value is selected to display a small luminance difference for each gray scale.

Third Step (ST 120): The gamma is corrected by adjusting the pulse width of the data signal in response to the selected gamma correction value. The pulse width of the clock pulse transmitted to the data driver is changed by the gamma correction value.However, in the method of counting clock pulses to express gray scales, if the pulse width of the clock pulses is short, a predetermined number can be counted in a shorter time. The longer the pulse width of the data signal is, the brighter it is. The longer the pulse width of the clock pulse is, the longer the time required for counting a predetermined number is, the shorter the pulp width of the data signal is.

According to the electron emission display device and the driving method thereof according to the present invention, gamma correction is performed corresponding to the image signal of the electron emission display device to minimize the visual difference according to the brightness difference of the image.

While preferred embodiments of the present invention have been described using specific terms, such descriptions are for illustrative purposes only and it is understood that various changes and modifications may be made without departing from the spirit and scope of the following claims. You must lose.

Claims (7)

A pixel unit whose luminance is adjusted in response to a voltage and a light emission time applied to the first electrode and the second electrode; A video signal summing unit for summing the video signals inputted in one frame section to determine the sum of the video signals; A gamma level selector which selects a gamma correction value corresponding to the sum of the video signals; A data driver converting an image signal to generate a data signal and transferring the generated data signal to the first electrode, wherein a pulse width of the data signal is adjusted to correspond to the gamma correction value; And And a scan driver for generating a scan signal and transmitting the scan signal to the second electrode. The method of claim 1, The gamma level selector includes a lookup table that stores information about a plurality of gamma correction values corresponding to the sum of the video signals and pulse widths of the data signals respectively corresponding to the plurality of gamma correction values. Electronic emission display device. The method of claim 1, And the gamma correction value has a small value when the sum of the video signals is large and a large value when the sum of the video signals is small. The method of claim 2, And the width of the clock pulse is large when the sum of the video signals is large and the width of the clock pulse is large when the sum of the video signals is small. The method of claim 1, The data driver A shift register configured to receive the video signal in series; A latch connected to the shift register and outputting the video signal in parallel; A counter for receiving and counting the clock pulses; And And a comparator for comparing the number counted by the counter with the image signal output from the latch and outputting a signal when the counted number and the image signal are equal. A method of driving an electron emission display device for displaying an image by transferring a data signal and a scanning signal to a first electrode and a second electrode, Calculating a sum of video signals by calculating a video signal input in a section of one frame; Selecting a gamma correction value corresponding to the sum of the video signals; And And adjusting a ratio of luminance to grayscale by adjusting a pulse width of a data signal corresponding to the gamma correction value. The method of claim 6, In selecting the gamma correction value, A large gamma correction value is selected if the sum of the video signals is large, and a gamma correction value is selected if the sum of the video signals is small.

Images