EP1471493A1 - Circuit de précharge de diodes organique luminescentes pour utilisation en tant que grand écran - Google Patents

Circuit de précharge de diodes organique luminescentes pour utilisation en tant que grand écran Download PDF

Info

Publication number
EP1471493A1
EP1471493A1 EP20030076206 EP03076206A EP1471493A1 EP 1471493 A1 EP1471493 A1 EP 1471493A1 EP 20030076206 EP20030076206 EP 20030076206 EP 03076206 A EP03076206 A EP 03076206A EP 1471493 A1 EP1471493 A1 EP 1471493A1
Authority
EP
European Patent Office
Prior art keywords
oled
current
drive circuitry
voltage
charge
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP20030076206
Other languages
German (de)
English (en)
Inventor
Gino Thanghe
Robbie Thielemans
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Barco NV
Original Assignee
Barco NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Barco NV filed Critical Barco NV
Priority to EP20030076206 priority Critical patent/EP1471493A1/fr
Priority to JP2004128524A priority patent/JP2004341516A/ja
Priority to KR1020040028496A priority patent/KR20040096422A/ko
Publication of EP1471493A1 publication Critical patent/EP1471493A1/fr
Withdrawn legal-status Critical Current

Links

Images

Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3216—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using a passive matrix
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3275—Details of drivers for data electrodes
    • G09G3/3283—Details of drivers for data electrodes in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00—Aspects of the constitution of display devices
    • G09G2300/02—Composition of display devices
    • G09G2300/026—Video wall, i.e. juxtaposition of a plurality of screens to create a display screen of bigger dimensions
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
    • G09G2310/0243—Details of the generation of driving signals
    • G09G2310/0251—Precharge or discharge of pixel before applying new pixel voltage
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/06—Details of flat display driving waveforms
    • G09G2310/066—Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007—Display of intermediate tones
    • G09G3/2014—Display of intermediate tones by modulation of the duration of a single pulse during which the logic level remains constant

Definitions

  • the present invention relates to the drive circuitry of a common anode, passive matrix large-screen organic light-emitting diode (OLED) display. More particularly, this invention relates to a pre-charge circuit for optimizing performance.
  • OLED organic light-emitting diode
  • OLED Organic light-emitting diode
  • OLED Organic light-emitting diode
  • OLEDs are also useful in a variety of applications as discrete light-emitting devices or as the active element of light-emitting arrays or displays, such as flat-panel displays in watches, telephones, laptop computers, pagers, cellular phones, calculators, and the like.
  • the use of light-emitting arrays or displays has been largely limited to small-screen applications such as those mentioned above.
  • LCDs fail to provide the bright, high light output, larger viewing angles, and high resolution and speed requirements that the large-screen display market demands.
  • OLED technology promises bright, vivid colors in high resolution and at wider viewing angles.
  • OLED technology is still in the development stage.
  • OLED displays are expected to offer a wide dynamic range of colors, contrast, and light intensity depending on various external environmental factors including ambient light, humidity, and temperature. For example, outdoor displays are required to produce more white color contrast during the day and more black color contrast at night. Additionally, light output must be greater in bright sunlight and lower during darker, inclement weather conditions.
  • the intensity of the light emission produced by an OLED device is directly proportional to the amount of current driving the device. Therefore, the more light output needed, the more current is fed to the pixel. Accordingly, less light emission is achieved by limiting the current to the OLED device.
  • a pixel by definition, is a single point or unit of programmable color in a graphic image.
  • a pixel may include an arrangement of sub-pixels, for example, red, green, and blue sub-pixels.
  • There are two basic circuit configurations for driving these sub-pixels namely, a common cathode configuration and a common anode configuration. These configurations differ as to whether the three sub-pixels are addressed via a common cathode line or addressed via a common anode line, respectively. Accordingly, in the common cathode configuration, the cathodes of the three sub-pixels are electrically connected and addressed in common; in the common anode configuration, the anodes of the three sub-pixels are electrically connected and addressed in common.
  • a current source is arranged between each individual cathode and ground, while the anodes are electrically connected in common to the positive power supply.
  • the current and voltage are completely independent of one another, and small voltage variations do not result in current variations, thereby eliminating the further consequence of light output variations.
  • the constant current source is referenced to ground, which does not vary, thereby eliminating any current variations due to its reference. For these reasons, the common anode configuration lends itself to the precise control of light emission needed in a large-screen display application.
  • the physical size of the pixel is typically 0.3 mm or less and the pixel area is, for example, only 0.1 mm 2 .
  • the pixel pitch may be 1.0 mm or greater, thereby allowing the pixel area to be as large as 0.3 to 50 mm 2 (pitch varies up to 10 mm or more with fill factors of 50%).
  • C OLED inherent capacitance
  • OLED pre-charge circuits have been developed and integrated into the existing drive circuitry to help overcome the capacitance characteristic of OLEDs within a graphics display device.
  • U.S. Patent No. 6,323,631 entitled, "Constant current driver with auto-clamped pre-charge function” describes a constant current driver with auto-clamped pre-charge function that includes a reference bias generator and a plurality of constant current driver cells, each being connected to the reference bias generator to form a respective current mirror.
  • Each constant current driver cell has a switch transistor, a current output transistor, and a pre-charge transistor.
  • the pre-charge transistor When a constant current is output from the current output transistor for driving an OLED, the pre-charge transistor is turned on to provide a drain to source current as an additional large current for rapidly pre-charging the OLED until the gate to source voltage of the pre-charge transistor is smaller than the threshold voltage.
  • the pre-charge function of the '631 patent suitably serves to rapidly pre-charge the OLED devices and thereby optimize performance, the pre-charge function of the '631 patent is designed for use in a common cathode drive circuit and is therefore not suitable for use in the common anode drive circuit of a large-screen OLED display device.
  • a further drawback of the pre-charge function of the '631 patent is that it is designed to handle the C OLED value associated with a small pixel area, such as 0.1 mm 2 , and is therefore not able to overcome the larger C OLED value associated with a large pixel area.
  • the present invention provides a drive circuitry for a common anode, passive matrix, organic light-emitting diode (OLED) display comprising at least one OLED having an anode and a cathode, the cathode of the OLED being coupled in series to a first current source and a first switching means.
  • the drive circuitry comprises means for pre-charging the at least one OLED before closing the switching means.
  • the means for pre-charging the at least one OLED may comprise a second switching means.
  • the second switching means may comprise an active switch device, which may comprise a MOSFET.
  • the MOSFET may be an NMOS transistor device having suitable voltage and current ratings for pre-charging the at least one OLED.
  • the second switching means may be coupled in a branch in parallel over the first current source. If the second switching means comprises a MOSFET, the MOSFET having a gate, the source may be electrically connected to a pre-charge voltage.
  • the MOSFET may also have a drain which is electrically connected to the cathode of the OLED.
  • the second switching means may comprise a first switch device suitable for coupling the cathode of the OLED to the ground, and a second switch device suitable for coupling the anode of the OLED to a voltage supply substantially corresponding to the normal operating voltage of the OLED.
  • the first switch device and the second switch device may be active switch devices.
  • the active switch devices may be MOSFET transistors having suitable voltage and current ratings for pre-charging the at least one OLED.
  • the means for pre-charging the at least one OLED may furthermore comprise a second current source coupled in parallel over the first current source.
  • the second current source may be suitable for supplying a current between 50 and 800 mA, preferably between 100 and 600 mA.
  • the second current source may be substantially identical to the first current source, or it may be different, for example the second current source may be suitable for supplying a current between 2 and 4 times the current supplied by the first current source.
  • the first current source may be a current source device capable of modifying its output current by selecting either one of a first or a second current reference.
  • the present invention also provides an arrangement comprising an array of OLEDs, each OLED having an anode common with other OLED's of the array and a cathode, and drive circuitry according to the present invention.
  • the present invention furthermore provides a common anode, passive matrix, organic light-emitting diode (OLED) display comprising an array of OLEDs, each OLED having an anode and a cathode, the display comprising drive circuitry according to the present invention.
  • OLED organic light-emitting diode
  • the present invention also provides a method for pre-charging an organic light-emitting diode (OLED) of a common anode, passive matrix OLED display prior to a desired ON-time of the OLED, the method comprising charging the OLED immediately prior to the desired ON-time.
  • the charging may be done by applying a pre-charge voltage to the cathode of the OLED prior to the desired ON-time.
  • it may be done by applying a first voltage level to the anode of the OLED while pulling the cathode of the OLED to a second voltage level, the difference between the first and the second voltage being equal to a desired pre-charge voltage.
  • the first voltage level may be equal to the desired pre-charge voltage
  • the second voltage level may be the ground level.
  • the charging may be done by supplying additional current to the OLED prior to the desired ON-time.
  • the pre-charge voltage may be substantially equal to a normal operating voltage of the OLED during ON-time. At low light output extra gray scales may be obtained by selectively switching two current sources.
  • the present invention will mainly be described with reference to a single display but the present invention is not limited thereto.
  • the display may be extendable, e.g. via tiling, to form larger arrays.
  • the present invention may also include assemblies of pixel arrays, e.g. they may be tiled displays and may comprise modules made up of tiled arrays which are themselves tiled into supermodules.
  • the word display relates to a set of addressable pixels in an array or in groups of arrays.
  • Several display units or "tiles" may be located adjacent to each other to form a larger display, i.e. multiple display element arrays are physically arranged side-by-side so that they can be viewed as a single image.
  • a pre-charge circuit which may be integrated within the drive circuitry of a common anode, passive matrix, OLED display device in order to overcome the inherent capacitance characteristic, C OLED , of the OLED devices therein.
  • the display may be a large-screen display.
  • a first pre-charge circuit of the present invention applies a pre-charge voltage to the cathode of a given OLED device just prior to the desired "on" time, thereby charging the OLED device rapidly.
  • a second pre-charge circuit of the present invention applies a pre-charge voltage to the anode of a given OLED device while concurrently pulling the cathode to ground just prior to the desired on time, thereby charging the OLED device rapidly.
  • a third pre-charge circuit of the present invention simply supplies additional current to the OLED device just prior to the desired on time, thereby charging the OLED device rapidly.
  • a fourth pre-charge circuit of the present invention comprises a single current source device that is capable of modifying its output current rapidly by selecting either a low or high current reference, thus being able to rapidly charge the OLED device.
  • FIG. 1 illustrates a schematic diagram of an OLED array circuit 100, which is representative of a portion of a typical common anode, passive matrix, large-screen OLED array and associated drive circuit.
  • OLED array circuit 100 includes an OLED array 110 formed of a plurality of OLEDs 112 (each having an anode and cathode, as is well known) arranged in a matrix of rows and columns.
  • OLED array 110 is formed of OLEDs 112a, 112b, 112c, 112d, 112e, 112f, 112g, 112h, and 112j arranged in a 3x3 array, where the anodes of OLEDs 112a, 112b, and 112c are electrically connected to a ROW LINE 1, the anodes of OLEDs 112d, 112e, and 112f are electrically connected to a ROW LINE 2, and the anodes of OLEDs 112g, 112h, and 112j are electrically connected to a ROW LINE 3.
  • OLEDs 112a, 112d, and 112g are electrically connected to a COLUMN LINE A
  • the cathodes of OLEDs 112b, 112e, and 112h are electrically connected to a COLUMN LINE B
  • the cathodes of OLEDs 112c, 112f, and 112j are electrically connected to a COLUMN LINE C.
  • Each OLED 112 represents a pixel in monochrome displays or a sub-pixel in a color display (typically red, green, or blue, however, any color variants are acceptable.
  • Sub-pixels are geometrically grouped together to form single addressable full color pixels, for instance 112a-c may be respectively red, green and blue).
  • An OLED emits light when forward biased in conjunction with an adequate current supply, as is well known.
  • Switches 114a, 114b, 114c are conventional active switch devices, such as MOSFET switches or transistors having suitable voltage and current ratings. More specifically, a positive voltage +V LED is electrically connected to ROW LINE 1 via switch 114a, to ROW LINE 2 via switch 114b, and to ROW LINE 3 via switch 114c.
  • Switched in series between current source I SOURCE 116c and ground is a switch 118c.
  • Current sources I SOURCE 116a, 116b, 116c are conventional current sources capable of supplying a constant current typically in the range of 5 to 50 mA.
  • Examples of constant current devices include a Toshiba TB62705 (8-bit constant current LED driver with shift register and latch functions) and a Silicon Touch ST2226A (PWM-controlled constant current driver for LED displays).
  • Switches 118a, 118b, 118c are normally included in the current source integrated circuit and consist of a conventional active switch device, such as MOSFET switches or transistors having suitable voltage and current ratings.
  • the matrix of OLEDs 112a-112j within OLED array circuit 100 are arranged in the common anode configuration. For each colour pixel for instance on ROW LINE 2, the anodes of each sub-pixel 112d-112f are all connected to the same row line. In this way the current source is referenced to the ground and the current and voltage are independent of one another providing better control of the light emission.
  • any given OLED 112a-112j its associated row line ROW LINE 1, ROW LINE 2, ROW LINE 3 and column line COLUMN LINE A, COLUMN LINE B, COLUMN LINE C are activated by simultaneously closing their associated switches 114a, 114b, 114c and 118a, 118b, 118c.
  • a positive voltage +V LED is applied to ROW LINE 1 by closing switch 114a and, simultaneously, a constant current is supplied to COLUMN LINE B via current source I SOURCE 116b by closing switch 118b. In this way, OLED 112b is forward biased and current flows through OLED 112b.
  • OLED 112b starts emitting light. OLED 112b remains lit up as long as switch 114a and switch 118b remain closed. To deactivate OLED 112b, switch 118b is opened.
  • a positive voltage +V LED is applied to ROW LINE 3 by closing switch 114c and, simultaneously, a constant current is supplied to COLUMN LINE A via current source I SOURCE 116a by closing switch 118a. In this way, OLED 112g is forward biased and current flows through OLED 112g.
  • OLED 112g starts emitting light. OLED 112g remains lit up as long as switch 114c and switch 118a remain closed. To deactivate OLED 112g , switch 118a is opened.
  • any one or more OLEDs 112a-112j may be activated at any given time.
  • ROW LINE A, ROW LINE B, ROW LINE C only one OLED 112 may be activated at any given time.
  • a complete image is built from sequentially or randomly selecting each row of OLED array 110, by closing its corresponding switch 114a-114c.
  • a current with a certain intensity and a certain duration is sent through the diodes 112a-112c, 112d-112f, 112g-112j on that row by current sources 116a, 116b, 116c by closing and opening switches 118a, 118b, 118c, such as to display the correct intensity in each pixel or sub-pixel.
  • a switch 114a, 114b, 114c remains closed as long as its row is selected and opens when the next row is selected. All switches 118a, 118b, 118c open before the next row is selected. Further details of the operation of any given OLED 112a-112j is found in reference to Figures 2A and 2B below.
  • FIG. 2A illustrates a schematic diagram of an OLED drive circuit 200, which is representative of a typical drive circuit of a single OLED 112 within OLED array circuit 100 of Figure 1.
  • OLED drive circuit 200 includes switch 114, OLED 112 , current source I SOURCE 116, and switch 118 all arranged in series between positive voltage +V LED and ground as shown in Figure 2A.
  • OLED drive circuit 200 further includes a capacitor 210 arranged in parallel with OLED 112. Capacitor 210 is representative of the device capacitance (C OLED ) of OLED 112.
  • a typical value of C OLED can be more than 500 pF, which is relatively high compared with a usual C OLED value of 5 pF for a small OLED structure used in a small-screen OLED display application.
  • the value of C OLED along with any additional line capacitance of the physical package, which for the purpose of this description are assumed to be negligible, must be overcome in order to achieve satisfactory display performance.
  • a voltage V OLED represents the voltage potential across OLED 112 and a voltage V ISOURCE represents the voltage potential across the series-connected current source I SOURCE 116 and switch 118.
  • FIG. 2B shows a plot 250 of the voltage potential V ISOURCE across the series-connected current source 116 and switch 118, from a time t0, when switches 114 and 118 are closed, to a time t2, when switch 118 is opened, thereby illustrating the operation of OLED drive circuit 200.
  • V ISOURCE is equal to positive voltage +V LED and begins to fall slowly towards the working voltage (V WORKING ) of OLED 112 due to the relatively high capacitance value C OLED of the OLED 112.
  • the OLED starts lighting up a little bit as soon as the threshold level or threshold voltage is reached (the threshold voltage of an OLED is the voltage across the OLED just enough to let it light up; the normal operating voltage or working voltage across the OLED is higher than this threshold voltage).
  • V ISOURCE reaches the working voltage of OLED 112 at a time t1.
  • the period between t0 and t1 represents the charge time T CHARGE of capacitor 210 of OLED 112.
  • the voltage transition from t0 to t1 is linear because the current output of current source I SOURCE 116 is constant.
  • OLED 112 begins to emit its full light and continues to emit light for a predetermined period of time which is the OLED emission time T ON as long as switches 114 and 118 remain closed.
  • OLED 112 is deactivated by opening switch 118, and subsequently V ISOURCE returns sharply to the +V LED value. OLED 112 remains off for a period from t2 to the next t0, i.e., OLED off time or period T OFF . Therefore, a cycle time T CYCLE is represented by T CHARGE + T ON + T OFF . As shown in plot 250, T CHARGE represents time wasted when switches 114 and 118 are closed and capacitor 210 is charging but OLED 112 is not yet emitting light at the desired emission level. This results in an extended T CYCLE , thereby decreasing the achievable T ON /T OFF rate and limiting the achievable performance of OLED drive circuit 200.
  • Figures 3A, 3B, 4, 5, and 6 that follow illustrate ways to minimize or eliminate the T CHARGE time by performing a pre-charge operation on capacitor 210, thereby minimizing T CYCLE .
  • FIG 3A illustrates a schematic diagram of an OLED pre-charge circuit 300 in accordance with a first and preferred embodiment of the invention.
  • OLED pre-charge circuit 300 is identical to OLED drive circuit 200 of Figure 2A except for the addition of a MOSFET 310 arranged in parallel with current source I SOURCE 116. More specifically, the drain of MOSFET 310 is electrically connected directly to the cathode of OLED 112, the source of MOSFET 310 is connected to a pre-charge voltage +V PRE-CHARGE, and the gate of MOSFET 310 is electrically connected to a precharge control voltage V PRECHARGE-CONTROL ⁇ MOSFET 310 may be any conventional NMOS transistor device having suitable voltage and current ratings for this application. However, MOSFET 310 is representative of any suitable active switch device.
  • Figure 3B shows a plot 350 of V ISOURCE vs. +V PRE-CHARGE from a time t0, when the pre-charge operation begins, to a time t2, when switch 118 is opened, thereby illustrating the operation of OLED pre-charge circuit 300.
  • the plot of V ISOURCE vs. +V PRE-CHARGE is not drawn to scale in relation to one another along the voltage axis.
  • Plot 350 is intended to illustrate only general voltage transitions and timing.
  • MOSFET 310 connects a source that is able to sink typically 100 to 600 ma of current.
  • switch 114 is closed, while switch 118 remains open. As a result, current begins to flow through OLED 112 for a short period of time via the electrical path created by MOSFET 310 .
  • This time period must be long enough to build up a voltage across capacitor 210 of OLED 112 that approaches the working voltage of OLED 112. Once this voltage has built up across capacitor 210 of OLED 112, MOSFET 310 is switched off, i.e., the +V PRE-CHARGE voltage at the cathode of the OLED is removed, and switch 118 is simultaneously closed, thereby allowing the normal operating current from current source I SOURCE 116 to flow through OLED 112, causing light to be emitted.
  • V ISOURCE is equal to +V LED at t0 when V PRECHARGE-CONTROL is applied (MOSFET 310 on), switch 114 is closed, and switch 118 is open. Subsequently, V ISOURCE falls sharply toward the working voltage of OLED 112 due to +V PRE-CHARGE rapidly charging capacitor 210. At t1, V PRECHARGE-CONTROL is removed and switch 118 is closed. The period between t0 and t1 represents the charge time T CHARGE of capacitor 210 of OLED 112. At time t1, OLED 112 begins normal light emission and continues to emit light for a predetermined period of time T ON as long as switches 114 and 118 remain closed.
  • switch 114 is closed for a period of time equal to at least charge time T CHARGE + OLED emission time T ON
  • switch 118 is closed for a period of time equal to the OLED emission time T ON
  • OLED 112 is deactivated by opening switch 118, and subsequently V ISOURCE returns sharply to the +V LED value.
  • OLED 112 remains off for a period from t2 to the next t0, i.e., OLED off time T OFF . Therefore, a cycle time T CYCLE is represented by T CHARGE + T ON + T OFF .
  • charge time T CHARGE of OLED pre-charge circuit 300 which is typically in the range of 12 ns to 50 ns, is significantly minimized compared with the charge time T CHARGE of OLED drive circuit 200, which is typically in the range of 25 ns to 65 s.
  • T CYCLE of OLED pre-charge circuit 300 is allowed to be significantly shorter than T CYCLE of OLED drive circuit 200 while achieving equivalent T ON time. Consequently, the achievable T ON /T OFF rate of OLED 112 within OLED pre-charge circuit 300 is increased compared with the achievable on/off rate of OLED 112 within OLED drive circuit 200 , thereby enhancing overall performance.
  • a pre-charge voltage (+V PRE-CHARGE ) from a source that is able to sink a suitable amount of current is applied to the OLED cathode via MOSFET 310.
  • capacitor 210 is charged rapidly, not via the normal current source (I SOURCE 116 ), but instead via a high current through MOSFET 310.
  • FIG. 4 illustrates a schematic diagram of an OLED pre-charge circuit 400 in accordance with a second embodiment of the invention.
  • OLED pre-charge circuit 400 is identical to OLED drive circuit 200 of Figure 2 except that a voltage +V OLED may be electrically connected to the anode of OLED 112 via a switch 410, and the cathode of OLED 112 may be electrically connected to ground via a switch 412 .
  • Switches 410 and 412 are conventional active switch devices, such as MOSFET switches or transistors having suitable voltage and current ratings.
  • T CHARGE of OLED pre-charge circuit 400 which is typically in the range of 12 ns to 50 ns, is significantly minimized compared with charge time T CHARGE of OLED drive circuit 200, which is typically in the range of 25 ns to 65 s.
  • T CYCLE of OLED pre-charge circuit 400 is allowed to be significantly shorter than T CYCLE of OLED drive circuit 200 while achieving equivalent OLED emission time T ON . Consequently, the achievable T ON /T OFF rate of OLED 112 within OLED pre-charge circuit 400 is increased compared with the achievable on/off rate of OLED 112 within OLED drive circuit 200, thereby enhancing overall performance.
  • a pre-charge voltage (+V OLED ) is applied to the anode of OLED 112 while, concurrently, the cathode of OLED 112 is pulled to ground; thus, capacitor 210 is charged rapidly, not via the normal current source (I SOURCE 116), but instead via +V OLED and the straight connection of the cathode to the ground.
  • FIG. 5 illustrates a schematic diagram of an OLED pre-charge circuit 500 in accordance with a third embodiment of the invention.
  • OLED pre-charge circuit 500 is identical to OLED drive circuit 200 of Figure 2, except that an additional current source (i.e., a current source I SOURCE 510 with an associated series-connected switch 512 ) is connected in parallel with current source I SOURCE 116, as shown in Figure 5.
  • Current source I SOURCE 510 is a conventional current source capable of supplying a constant current typically in the range of 100 to 600 mA.
  • Switch 512 is a conventional active switch device, such as a MOSFET switch or transistor having suitable voltage and current ratings.
  • charge time T CHARGE of OLED pre-charge circuit 500 is significantly minimized compared with charge time T CHARGE of OLED drive circuit 200, which is typically in the range of 25 ns to 65 s.
  • T CYCLE of OLED pre-charge circuit 400 is allowed to be significantly shorter than T CYCLE of OLED drive circuit 200 while achieving equivalent OLED emission time T ON . Consequently, the achievable T ON /T OFF rate of OLED 112 within OLED pre-charge circuit 500 is increased compared with the achievable on/off rate of OLED 112 within OLED drive circuit 200, thereby enhancing overall performance.
  • capacitor 210 is charged rapidly, not via the normal current source (I SOURCE 116) only, but with the additional current available to OLED 112 via current source I SOURCE 510.
  • the charge time T CHARGE used for pre-charge greatly influences the performance of a display. Longer pre-charge times T CHARGE , limit the maximum light output while compensating by increasing the current level increases the lowest light output and thus eliminates gray scales. High quality displays need a large number of gray scales, thus requiring a high digital resolution or number of possible output values or current sources operating at high clock speeds.
  • a single current pulse (one clock cycle) will only generate light if the threshold is reached within that pulse, for instance in half the time of a clock cycle. If f c is the clock frequency, then the shortest t2-t0 is 1/ f c . For example a 40 MHz clock, the pre-charge time T CHARGE would then have to be as short as 12 ns.
  • a pre-charge current of at least 375 mA (C OLED *dV/dt) is required, which is quite high.
  • the requirement of reaching the pre-charge state within a clock pulse period may be overcome by using two current sources 116, 510 as in Figure 5 .
  • FIG. 5A demonstrates the possible result of using two current sources 116 and 510 as in Figure 5.
  • Current source 510 is for instance capable of delivering twice the current of current source 116. That means that V ISOURCE of current source 510 reaches the threshold voltage in half the time of V ISOURCE of current source 116. Consequently, when both current sources 510, 116 operate simultaneously, V ISOURCE will reach the threshold in a third of the time.
  • corresponding currents I OLED through the OLED 112 are shown for a t 2 -t 0 equal to the time required for the two current sources 510, 116 to together reach the threshold.
  • the surface under the current curve is a measure for the emitted light.
  • V ISOURCE for each current source 510, 116 separately does not necessarily reach the threshold within the on time
  • three possible light output values are generated as long as the reached V OLED (not drawn in Figure 5A ) is high enough for the diode 112 to start emitting light. Expanding on this principle, at low light output values highly precise gray scales can be obtained by varying the on time of one or two current sources 510 , 116 . Additionally, high current can be obtained at high light output by switching on both current sources 510, 116 .
  • FIG. 6 illustrates a schematic diagram of an OLED pre-charge circuit 600 in accordance with a fourth embodiment of the invention.
  • OLED pre-charge circuit 600 is identical to OLED drive circuit 200 of Figure 2, except that current source I SOURCE 116 is replaced with a current source I SOURCE 610, which is a single current source device that is capable of modifying its output current rapidly by selecting either a low or high current reference via a switch 612 and a switch 614 , respectively.
  • Switches 612 and 614 are conventional active switch devices, such as MOSFET switches or transistors having suitable voltage and current ratings.
  • switches 114, 118 and 612 are closed and switch 614 is open, thereby supplying the high current reference to current source I SOURCE 610 and thus charging capacitor 210 rapidly.
  • switch 612 is opened and switch 614 is closed, thereby supplying the low current reference to current source I SOURCE 610.
  • current source I SOURCE 610 rapidly drops to the normal constant operating current.
  • Switches 114, 118, and 614 remain closed for the duration of OLED emission time T ON and normal operation occurs. At time t2 switch 118 is opened, thus ending OLED emission time T ON .
  • the pre-charge circuits of the present invention overcome the adverse performance effects due to C OLED , any process variations affecting C OLED do not factor into the OLED overall display performance.
  • the pre-charge circuits of the present invention eliminate the effects of varying OLED device characteristics, such as capacitance, due to manufacturing process variations.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
  • Electroluminescent Light Sources (AREA)
EP20030076206 2003-04-25 2003-04-25 Circuit de précharge de diodes organique luminescentes pour utilisation en tant que grand écran Withdrawn EP1471493A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP20030076206 EP1471493A1 (fr) 2003-04-25 2003-04-25 Circuit de précharge de diodes organique luminescentes pour utilisation en tant que grand écran
JP2004128524A JP2004341516A (ja) 2003-04-25 2004-04-23 共通アノード受動マトリクス有機発光ダイオード（ｏｌｅｄ）ディスプレイ、そのための駆動回路、その有機発光ダイオードをプリチャージするための方法、および配置
KR1020040028496A KR20040096422A (ko) 2003-04-25 2004-04-24 공통 양극 대형화면 디스플레이에서 사용되는 유기발광다이오드(ｏｌｅｄ) 프리차지 회로

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP20030076206 EP1471493A1 (fr) 2003-04-25 2003-04-25 Circuit de précharge de diodes organique luminescentes pour utilisation en tant que grand écran

Publications (1)

Publication Number Publication Date
EP1471493A1 true EP1471493A1 (fr) 2004-10-27

Family

ID=32946906

Family Applications (1)

Application Number Title Priority Date Filing Date
EP20030076206 Withdrawn EP1471493A1 (fr) 2003-04-25 2003-04-25 Circuit de précharge de diodes organique luminescentes pour utilisation en tant que grand écran

Country Status (1)

Country Link
EP (1) EP1471493A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102006032071A1 (de) * 2006-07-11 2008-01-17 Austriamicrosystems Ag Steuerschaltung und Verfahren zum Steuern von Leuchtdioden
DE102010018865A1 (de) * 2010-04-30 2011-11-03 Austriamicrosystems Ag Treiberschaltung für Leuchtdioden und Verfahren
EP3029661A1 (fr) * 2014-12-03 2016-06-08 Revolution Display, LLC Modules d'affichage oled pour des affichages oled grand format
WO2021063884A1 (fr) * 2019-10-01 2021-04-08 Signify Holding B.V. Multiplexage de luminaire à del avec circuit d'attaque à courant constant

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6177767B1 (en) * 1995-10-13 2001-01-23 Sony Corporation Luminescent device having drive-current controlled pixels and method therefor
WO2001054107A1 (fr) * 2000-01-21 2001-07-26 Emagin Corporation Circuit d'excitation de pixels a echelle de gris pour affichage electronique et son procede d'exploitation
US6310589B1 (en) * 1997-05-29 2001-10-30 Nec Corporation Driving circuit for organic thin film EL elements
US6366116B1 (en) * 2001-01-18 2002-04-02 Sunplus Technology Co., Ltd. Programmable driving circuit
US6369786B1 (en) * 1998-04-30 2002-04-09 Sony Corporation Matrix driving method and apparatus for current-driven display elements
US6473064B1 (en) * 1998-02-13 2002-10-29 Pioneer Corporation Light emitting display device and driving method therefor
US6486607B1 (en) * 2001-07-19 2002-11-26 Jian-Jong Yeuan Circuit and system for driving organic thin-film EL elements
EP1274065A2 (fr) * 2001-07-06 2003-01-08 Lg Electronics Inc. Circuit et méthode d'attaque d'un dispositif d'affichage commandé par courant

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6177767B1 (en) * 1995-10-13 2001-01-23 Sony Corporation Luminescent device having drive-current controlled pixels and method therefor
US6310589B1 (en) * 1997-05-29 2001-10-30 Nec Corporation Driving circuit for organic thin film EL elements
US6473064B1 (en) * 1998-02-13 2002-10-29 Pioneer Corporation Light emitting display device and driving method therefor
US6369786B1 (en) * 1998-04-30 2002-04-09 Sony Corporation Matrix driving method and apparatus for current-driven display elements
WO2001054107A1 (fr) * 2000-01-21 2001-07-26 Emagin Corporation Circuit d'excitation de pixels a echelle de gris pour affichage electronique et son procede d'exploitation
US6366116B1 (en) * 2001-01-18 2002-04-02 Sunplus Technology Co., Ltd. Programmable driving circuit
EP1274065A2 (fr) * 2001-07-06 2003-01-08 Lg Electronics Inc. Circuit et méthode d'attaque d'un dispositif d'affichage commandé par courant
US6486607B1 (en) * 2001-07-19 2002-11-26 Jian-Jong Yeuan Circuit and system for driving organic thin-film EL elements

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102006032071A1 (de) * 2006-07-11 2008-01-17 Austriamicrosystems Ag Steuerschaltung und Verfahren zum Steuern von Leuchtdioden
DE102006032071B4 (de) * 2006-07-11 2008-07-10 Austriamicrosystems Ag Steuerschaltung und Verfahren zum Steuern von Leuchtdioden
US8098028B2 (en) 2006-07-11 2012-01-17 Austriamicrosystems Ag Control circuit and method for controlling LEDs
DE102010018865A1 (de) * 2010-04-30 2011-11-03 Austriamicrosystems Ag Treiberschaltung für Leuchtdioden und Verfahren
US8779672B2 (en) 2010-04-30 2014-07-15 Ams Ag Driver circuit for light-emitting diodes and method
DE102010018865B4 (de) * 2010-04-30 2015-11-26 Austriamicrosystems Ag Treiberschaltung für Leuchtdioden und Verfahren
EP3029661A1 (fr) * 2014-12-03 2016-06-08 Revolution Display, LLC Modules d'affichage oled pour des affichages oled grand format
US9524666B2 (en) 2014-12-03 2016-12-20 Revolution Display, Llc OLED display modules for large-format OLED displays
US9530347B2 (en) 2014-12-03 2016-12-27 Revolution Display, Llc OLED display modules for large-format OLED displays
TWI567952B (zh) * 2014-12-03 2017-01-21 革命顯示有限公司 用於大尺寸有機發光二極體顯示器之有機發光二極體顯示模組
US9703519B2 (en) 2014-12-03 2017-07-11 Revolution Display, Llc LED display modules for large-format LED displays
WO2021063884A1 (fr) * 2019-10-01 2021-04-08 Signify Holding B.V. Multiplexage de luminaire à del avec circuit d'attaque à courant constant

Similar Documents

Publication Publication Date Title
US7079092B2 (en) Organic light-emitting diode (OLED) pre-charge circuit for use in a common anode large-screen display
US7019721B2 (en) Organic light-emitting diode drive circuit for a display application
KR100432173B1 (ko) 유기ｅｌ표시장치 및 그 구동방법
US8018401B2 (en) Organic electroluminescent display and demultiplexer
US7221343B2 (en) Image display apparatus
US7609234B2 (en) Pixel circuit and driving method for active matrix organic light-emitting diodes, and display using the same
KR101005646B1 (ko) 화상표시장치
US7285797B2 (en) Image display apparatus without occurence of nonuniform display
US7170233B2 (en) Self light emitting display panel and drive control method therefor
EP2439724B1 (fr) Dispositif d'affichage et procédé de commande pour le dispositif d'affichage
KR20040071132A (ko) 구동장치, 상기 구동장치를 이용한 디스플레이 장치, 및이를 위한 구동방법
JP2001142413A (ja) アクティブマトリクス型表示装置
JP2002202754A (ja) 有機ｅｌ駆動回路及びパッシブマトリクス有機ｅｌ表示装置並びに有機ｅｌ駆動方法
US20060232612A1 (en) Display device using self-luminous element and driving method of same
US20100295845A1 (en) Back to back pre-charge scheme
US20040108979A1 (en) Driving device of active type light emitting display panel
US20210327350A1 (en) Display device
CN101816036A (zh) 电流驱动式el显示器的电源电压的动态自适应
KR20040020799A (ko) 표시 구동 회로
US7812793B2 (en) Active matrix organic electroluminescent display device
US20060290611A1 (en) Display device using self-luminous element and driving method of same
US20060066525A1 (en) Colour control for active matrix electroluminescent display
JP2004341516A (ja) 共通アノード受動マトリクス有機発光ダイオード（ｏｌｅｄ）ディスプレイ、そのための駆動回路、その有機発光ダイオードをプリチャージするための方法、および配置
JP2003131619A (ja) 自己発光型表示装置
WO2006054189A1 (fr) Dispositifs d'affichage a matrice active

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LI LU MC NL PT RO SE SI SK TR

AX Request for extension of the european patent

Extension state: AL LT LV MK

17P Request for examination filed

Effective date: 20041209

17Q First examination report despatched

Effective date: 20050411

AKX Designation fees paid

Designated state(s): AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LI LU MC NL PT RO SE SI SK TR

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION HAS BEEN WITHDRAWN

18W Application withdrawn

Effective date: 20061130