Description

APPARATUS AND METHOD FOR CORRECTING IMAGE DEVIATION IN PASSIVE MATRIX ORGANIC LIGHT- EMITTING DIODE DISPLAY DEVICE

Technical Field

[1] The present invention relates to an apparatus and method for correcting an image deviation in an organic light-emitting diode (OLED) display device, and more particularly, to an apparatus and method for correcting image deviation in a passive matrix OLED display device by modeling resistance elements in an OLED panel based on its properties, computing a resistance value of each pixel, on which image information is displayed, and adjusting gradation values of odd-numbered and even-numbered lines based on the resistance values. Background Art

[2] An organic light-emitting diode (OLED) display device is recently highlighted as a display device capable of providing fast response, high luminance, and a smaller thickness than that of a liquid crystal display (LCD) because it uses a self emission type organic material and does not require a backlight unit. In such an OLED display device, electrons injected from an electrode and holes injected from the other electrode are combined in a light-emitting layer interposed between both electrodes to generate exitons emitting light as well as energy.

[3] As a voltage between both electrodes of the OLED increases over a threshold voltage, the amount of electric current flowing through the OLED increases, and the amount of light emanated from the OLED also increases in proportion to the amount of electric current.

[4] The OLED can be classified into an active matrix OLED (AMOLED) and a passive matrix OLED (PMOLED). In the AMOLED, each pixel has a thin-film transistor (TFT) for controlling it. In the PMOLED, each pixel of intersection is turned on and off by controlling voltages applied to each row and column.

[5] A conventional PMOLED includes: an OLED panel having a plurality of pixels arranged in a matrix structure; a scan driver for supplying a scan voltage by sequentially selecting a common line to which a gradation current corresponding to image information will be applied; and a data driver for supplying the pixel connected to the common line selected by the scan driver with the amount of electric current corresponding to a gradation value through a source line. In this case, the luminance level of the light output from each pixel is proportional to the amount of electric current supplied to the pixel through the source line for a time period during the common line

is selected.

[6] Referring to FIG. 6, the conventional PMOLED is constructed such that image information stored in a frame memory 200 to be displayed is converted into panel data by control signals READ and ADDR in the display controller, and the amount of gradation current corresponding to the luminance level of each pixel is supplied to each pixel. However, the conventional PMOLED has significant image deviation between adjacent common lines.

[7] Specifically, referring to FIG. 7, the even-numbered lines of the conventional

PMOLED are displayed clearly in the left-hand side and dimly in the right-hand side, while the odd-numbered lines are displayed clearly in the right-hand side and dimly in the left-hand side. Therefore, image deviation is generated between pixels of the same common line and between adjacent common lines, so that it is difficult to display a high quality image.

[8] The scan voltage supplied through the common line and the gradation current supplied through the source line are different from the values supplied from the scan driver and the data driver in each pixel depending on its location on the OLED panel. The image deviation between adjacent common lines can be obviously recognized by a resistance model of the PMOLED consisting of resistors and LEDs as shown in FIG. 3.

[9] According to the resistance model of the PMOLED, an amount of electric current V/

3DR flows through the source line S<0> of the common line G<0>, and a smaller amount of electric current V/((col_max*SR)+3DR) flows through the source line S<max> of the common line G<0>. In this case, G<0>, G<1>,..., G<max> denote common lines to which the scan voltages are supplied, and S<0>, S<1>,..., S<max> denote source lines to which the gradation current corresponding to the image information is supplied. The pixels are located in each intersection between the source line and the common line in a matrix array.

[10] In addition, a reference symbol DR denotes a resistance value of the source line modeled by properties of the panel and the wires through which the gradation current is supplied from the data driver to the source line. A reference symbol SR denotes a resistance value of the common line modeled by properties of the panel and the wires through which the scan voltage is supplied from the scan driver to the common line. The resistance values of the source line and the common line linearly increase depending on the distance from the input locations of the gradation current and the scan voltage. A reference symbol col_max denotes a maximum number of columns in an OLED panel having a matrix array. In this context, a reference symbol col_max * SR denotes a maximum resistance value in a horizontal line direction when the scan voltage is supplied through the common line.

[11] While the amount of electric current flowing through the pixel located in an in-

tersection between the common line G<0> and the source line S<0> becomes V/3DR according to the Ohm s law, the amount of electric current flowing through the pixel located in the other end S<max> of the common line G<0> becomes V/ ((col_max*SR)+3DR). Therefore, even when the same amount of gradation current is supplied to both of the aforementioned pixels in order to exhibit the same gradation level, the amount of electric current actually delivered to each pixel becomes different, so that the luminance deviation occurs. For this reason, while the pixel corresponding to the common line G<0> and the source line <0> exhibits a clear image, the pixel corresponding to the common line G<0> and the source line S<max> may exhibit a dim image. Similarly, since the amount of electric current supplied to the pixel corresponding to the common line G<1> and the source line S<max> becomes V/2DR, and the amount of electric current supplied to the pixel corresponding to the common line G<1> and the source line S<0> becomes V/((col_max*SR)+2DR), the former exhibits a clearer image. Accordingly, even on the same common or source line, the same image information may be differently displayed depending on the location of the pixel. This may cause image deviation between adjacent lines.

[12] In the conventional PMOLED display device, power consumption in the resistors generating the image deviation unnecessarily increases, and a total amount of power consumption also increases. Disclosure of Invention

Technical Problem

[13] The present invention provides an apparatus and method for correcting image deviation in a passive matrix OLED display device, by correcting an image in a chip level to remove image deviation between adjacent lines using a value obtained by differently computing a gradation value of image information supplied to a source line between even-numbered and odd-numbered lines in consideration of resistance of each pixel. Technical Solution

[14] According to an aspect of the present invention, there is provided an apparatus for correcting image deviation in a passive matrix OLED (organic light-emitting diode) display device, the apparatus comprising: a panel property modeling unit which stores properties of an OLED panel; an offset computing unit which computes an offset resistance value of each line, on which image information is displayed, based on the properties of the OLED panel; a pixel resistance computing unit which computes a resistance value of a pixel, on which image information is displayed, based on the offset resistance value; and an image conversion unit which computes a gradation value with the resistance value of the pixel to correct image deviation, and transmits

new gradation current obtained by correcting the image deviation to the OLED panel.

[15] According to the present invention, the panel property modeling unit may be constructed to model the OLED panel into resistance values of a plurality of light-emitting diodes and wires for supplying electric current to each light-emitting diode. The properties of the OLED panel stored in the panel property modeling unit may include: an intrinsic constant for resistance of the OLED panel; a resistance value for a vertical interval of a common line for supplying the OLED panel with a scan voltage; a resistance value for a horizontal line of the common line; a resistance value for a vertical interval of a source line for supplying the OLED panel with gradation current; and a resistance value between adjacent pixels on the source line.

[16] The offset computing unit may be constructed to compute an offset resistance value for the vertical interval of the common line; an offset resistance value for the horizontal interval of the common line; an offset resistance value for a vertical interval of the source line; and an offset resistance value between adjacent pixels on the source line. The pixel resistance computing unit may be constructed to differently compute the resistance value of the pixel between even-numbered and odd-numbered common lines.

[17] The image conversion unit may be constructed to select, using a conditional operator, the resistance value of the pixel for the even-numbered line, obtained from the pixel resistance computing unit, when the common line is the even-numbered line, or the resistance value of the pixel for the odd-numbered line, obtained from the pixel resistance computing unit, when common line is the odd-numbered line, so that the selected resistance value of each pixel is computed with a gradation current value to generate a new gradation current value for correcting image deviation.

[18] According to another aspect of the present invention, there is provided a method of correcting image deviation in a passive matrix OLED display device, the method comprising: storing, in a panel property modeling unit, OLED panel properties such as resistance values for vertical and horizontal intervals of a common line, resistance values for vertical and horizontal intervals of a source line, and an intrinsic constant for resistance in order to provide a resistance model of the OLED panel; computing, in an offset computing unit, offset resistance values for vertical and horizontal intervals of the common line, an offset resistance value for a vertical interval of the source line, and an offset resistance value between adjacent pixels on the source line based on the OLED panel properties; differently computing, in a pixel resistance computing unit, pixel resistance values between even-numbered and odd-numbered lines of the OLED panel based on the offset resistance values; and converting an image by selecting, in an image conversion unit, the pixel resistance value for the even-numbered line when the common line is the even-numbered line, or selecting a pixel resistance value for the

odd-numbered line when the common line is the odd-numbered line, so that a gradation current value is converted to correct image deviation based on the selected pixel resistance value and transmitted to the source line.

Advantageous Effects

[19] According to the present invention, the gradation current value of the image information to be displayed is differently corrected between even-numbered and odd- numbered lines in consideration of pixel resistance values modeled based on specific properties of the OLED panel. As a result, it is possible to remove image deviation between adjacent lines, reduce power consumption, overcome structural limitation of the passive matrix OLED, and significantly improve applicability of a display device. Brief Description of the Drawings

[20] The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

[21] FIG. 1 is a block diagram illustrating an apparatus for correcting image deviation in an passive matrix OLED (organic light-emitting diode) display device according to the present invention;

[22] FIG. 2 is a schematic diagram for describing gamma correction and image deviation correction of image information according to the present invention;

[23] FIG. 3 is a schematic diagram illustrating a resistance model of a passive matrix

OLED display device according to the present invention;

[24] FIG. 4 illustrating an example of program for a computation process in a method of correcting image deviation in a passive matrix OLED display device according to the present invention;

[25] FIG. 5 is flowchart illustrating a method of correcting image deviation in a passive matrix OLED display device according to the present invention;

[26] FIG. 6 is a schematic diagram illustrating a conventional process of outputting image information; and

[27] FIG. 7 illustrates an example of image deviation generated in a conventional OLED display device. Best Mode for Carrying Out the Invention

[28] Hereinafter, exemplary embodiments of present invention will be described in detail with reference to the attached drawings.

[29] Referring to FIG. 1, an apparatus for correcting image deviation in a passive matrix organic light-emitting diode (OLED) display device according to an embodiment of the present invention includes: a panel property modeling unit 110 which stores properties of an OLED panel; an offset computing unit 120 which computes an offset

resistance value of each line on the OLED panel; a pixel resistance computing unit 130 which calculates a resistance value of each pixel affected by the offset resistance value; and an image conversion unit 140 which adjusts gradation current based on the resistance value of each pixel and transmits the gradation current.

[30] In this case, the OLED display device includes: an OLED panel having a plurality of pixels arranged in a matrix array; a scan driver which sequentially supplies scan voltages through common lines to the OLED panel; a data driver which supplies gradation current through source lines; a frame memory 200 which stores image information to be displayed; and a display controller 300 which converts the image information into panel data supplied to the panel and supplies gradation current appropriate to luminance to each pixel through the source line.

[31] The panel property modeling unit 110 stores properties of the OLED panel received from a panel manufacturer or the like. The properties of the panel are read and used as basic values of computation during the resistance computation for the resistance modeling of the OLED panel in order to correct image deviation. In this case, the properties of the panel stored in the panel property modeling unit 110 preferably include various intrinsic constants that can affect the current flow.

[32] Referring to FIG. 4, according to the embodiment, the properties of the OLED panel include an intrinsic constant G_base for resistance of the panel, a resistance value Gh for a vertical interval of the common line, a resistance value Gw for a horizontal interval of the common line, a resistance value Dh for a vertical interval of the source line, and a resistance value Dw between adjacent pixels on a single source line. In addition, the number of lines GATE_CNT displayed in a single screen, and the number of pixels PIXEL_CNT displayed in a single line are supplied from the display controller 300 and stored together.

[33] The offset computing unit 120 is constructed to compute the offset resistance values of each line, on which the image information is displayed, based on the aforementioned properties of the OLED panel. Preferably, in this case, the offset resistance value GH_offset for the vertical interval of the common line is computed based on a formula (R0W_MAX - G<n>)/Gh, the offset resistance value GW_offset for the horizontal interval of the common line is computed based on a formula (R0W_MAX - G<n>)/Gw, the offset resistance value DH_offset for the vertical interval of the source line is computed based on a formula (R0W_MAX - G<n>)/Dh, and the offset resistance value DW_offset between adjacent pixels on a single source line is computed based on a formula (C0L_MAX)/Dw.

[34] The pixel resistance computing unit 130 is constructed to compute the pixel resistance of each pixel, on which the image information is displayed, based on the offset resistance values of each line obtained from the offset computing unit 120.

Preferably, the pixel resistance value is differently computed between the even- numbered and odd-numbered lines.

[35] First, a specific resistance value SCAN_METAL of a wire included in the OLED panel is obtained by adding an intrinsic constant G_base for resistance of the panel, the offset resistance value GH_offset for the vertical interval of the common line, the offset resistance value GW_offset for the horizontal interval of the common line, and the offset resistance value DH_offset for the vertical interval of the source line. Also, a value PixelNum is computed based on a formula PixelCount/DW_offset. Then, a pixel resistance value EVEN for the even-numbered line is computed based on a formula SCAN_METAL + PixelNum, and a pixel resistance value ODD for the odd-numbered line is computed based on a formula SCAN_METAL + DW_offset - PixelNum.

[36] The image conversion unit 140 is constructed to compute the gradation current supplied to the source line with the pixel resistance value obtained from the pixel resistance computing unit 130 to provide a conversion value capable of correcting image deviation. In this case, when the common line is an even-numbered line, the image conversion unit 140 executes image conversion using a conditional operator (EVEN_G)?EVEN:ODD by selecting the pixel resistance value EVEN for the even- numbered line as a result value RESULT among the pixel resistance values obtained from the pixel resistance computing unit 130. Otherwise, the image conversion unit 140 executes image conversion by selecting the pixel resistance value ODD for the odd-numbered line as a result value RESULT. The result value RESULT selected using the conditional operator provides an image conversion value IMG based on a formula (PWM*RESULT)/100.

[37] As described above, the amount of the gradation current for the image information to be transmitted to the frame memory is controlled in response to the image conversion value IMG obtained from the image conversion unit 140, and then transmitted to even- numbered and odd-numbered lines. As a result, it is possible to correct image deviation in the image information to be displayed on the OLED panel.

[38] In addition, the apparatus 100 for correcting image deviation preferably includes a comb filter for separating the image information transmitted from the frame memory 200 or the gamma correction unit 400 into a color signal and a luminance signal.

[39] Preferably, the image conversion using the apparatus 100 for correcting image deviation is executed by receiving a basic value of the gradation current converted in the image conversion unit 140 in association with the gamma correction unit 400 in order to receive RGB signals of the image information that has been corrected in the gamma correction unit 400 which non-linearly modifies light intensity signals and execute display operation.

[40] Hereinafter, a method of correcting image deviation in an OLED display device

according to the present invention will be described.

[41] Referring to FIG. 5, the method of correcting image deviation in the OLED display device according to the present invention includes: storing properties of the OLED panel (SlO); computing an offset resistance value of each line on which image information is displayed (S20); computing a pixel resistance value of each pixel on which the image information is displayed (S30); and converting an image by differently applying a gradation current value between even-numbered and odd-numbered lines based on the pixel resistance value to correct image deviation (S40).

[42] In operation S 10 of storing properties of the OLED panel, properties of the panel, including an intrinsic constant G_base for resistance of the panel, a resistance value Gh for a vertical interval determined by the height of the common line, a resistance value Gw for a horizontal interval determined by the width of the common line, a resistance value Dh for a vertical interval determined by the height of the source line, and a resistance value Dw between adjacent pixels for a horizontal interval determined by the width of the source line are stored in the panel property modeling unit 110. In this case, the properties of the panel may be directly received from a panel manufacturer and stored.

[43] In operation S20 of computing the offset resistance value, the offset resistance value

GH_offset for a vertical interval of the nth common line (where, n denotes any natural number) is computed based on a formula (R0W_MAX - G<n>)/Gh, the offset resistance value GW_offset for a horizontal interval of the nth common line is computed based on a formula (R0W_MAX - G<n>)/Gw, the offset resistance value DH_offset for a vertical interval of the nth source line is computed based on a formula (R0W_MAX - G<n>)/Dh, and the offset resistance value DW_offset between adjacent pixels on a single source line is computed based on a formula (C0L_MAX)/Dw.

[44] In operation S30 of computing the pixel resistance value, the pixel resistance value is differently computed between the even-numbered and odd-numbered lines of the OLED panel to correct image deviation generated between the even-numbered and odd- numbered lines. In this case, the pixel resistance value EVEN for the even- numbered line is obtained by adding a specific resistance value SCAN_METAL of a wire, obtained by adding the intrinsic constant G_base of the panel, the offset resistance values GH_offset and GW_offset for vertical and horizontal intervals of the common line, and the offset resistance value DH_offset for a vertical interval of the source line, and a value PixelNum computed based on a formula PixelCount/ DW_offset. On the other hand, the pixel resistance value ODD for the odd-numbered line is computed based on a formula SCAN_METAL + DW_offset - PixelNum. As a result, the pixel resistance computing unit 130 is constructed to differently compute a resistance value of each pixel between the even-numbered and odd-numbered lines

base on the offset resistance.

[45] In operation S40 of converting an image, an image conversion value is selected as a new gradation current value and then transmitted to the data driver. The image conversion value is obtained by correcting image deviation that may be generated between the even-numbered and odd-numbered lines based on the gradation current value of the image information delivered after reading operation from the frame memory 200 and gamma correction and the pixel resistance value obtained in the operation S30. In this case, using a conditional operator (EVEN_G)?EVEN:ODD, the pixel resistance value EVEN is selected as a reference value RESULT for correcting image deviation when the common line is an even-numbered line, or the pixel resistance value ODD is selected as a reference value RESULT for correcting image deviation when the common line is an even-numbered line. Then, the gradation current value supplied to the data driver is converted by applying the selected value RESULT to a formula (PWM*RESULT)/100, so that the image deviation that may be generated between the even-numbered and odd-numbered lines can be corrected. The value PWM denotes a reference current value used in a pulse width modulation (PWM) driving technique in which different luminance levels can be obtained by controlling a time period for flowing current using a single reference current value.

[46] In this case, the gamma correction in the gamma correction unit 400 is preferably performed before the image deviation correction in the image conversion unit 140 in order to prevent non-linearity of RGB signals of the image information from being damaged in the image conversion unit 140.

[47] As a result of the aforementioned processes, it is possible to significantly alleviate image deviation between adjacent lines and display an image fully reflecting original image information by supplying a gradation current value differently converted between the even-numbered and odd-numbered lines in the matrix array of the OLED panel.

[48] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.