EP2277164B1 - Improved display device based on pixels with variable chromatic coordinates - Google Patents

Improved display device based on pixels with variable chromatic coordinates Download PDF

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Publication number
EP2277164B1
EP2277164B1 EP09750011.0A EP09750011A EP2277164B1 EP 2277164 B1 EP2277164 B1 EP 2277164B1 EP 09750011 A EP09750011 A EP 09750011A EP 2277164 B1 EP2277164 B1 EP 2277164B1
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European Patent Office
Prior art keywords
sub
pixel
transistor
color
diode
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EP09750011.0A
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German (de)
French (fr)
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EP2277164A1 (en
Inventor
Gunther Haas
David Vaufrey
Olivier Billoint
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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    • G09G3/20Control 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
    • G09G3/22Control 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
    • G09G3/30Control 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
    • G09G3/32Control 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]
    • G09G3/3208Control 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]
    • G09G3/3225Control 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 an active matrix
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    • G09G3/3241Control 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 an active matrix with pixel circuitry controlling the current through the light-emitting element the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
    • G09G3/325Control 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 an active matrix with pixel circuitry controlling the current through the light-emitting element the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror the data current flowing through the driving transistor during a setting phase, e.g. by using a switch for connecting the driving transistor to the data driver
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    • G09G3/22Control 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
    • G09G3/30Control 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
    • G09G3/32Control 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]
    • G09G3/3208Control 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]
    • G09G3/3225Control 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 an active matrix
    • G09G3/3258Control 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 an active matrix with pixel circuitry controlling the voltage across the light-emitting element
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Definitions

  • the invention relates to a pixel-based variable color coordinate display device comprising a plurality of color sub-pixels, each comprising a light emitter, formed by an organic electroluminescent diode and a color filter, the color coordinates of the pixel being determined periodically and the light emitters being identical.
  • the color of each pixel is made from three primary colors.
  • the CIE 1931 standard can, for example, be used to define from three primary standard colors, consisting of a precise shade of blue (B), red (R) and green (G), any visible color. at the eye. With this standard, all the color shades accessible to the human eye are defined by precise chromatic coordinates, each of which corresponds to a particular distribution of the primary standard colors.
  • a pixel is defined by its color and its luminance, that is to say by its visible light intensity.
  • luminance and the chromatic coordinates of a pixel with variable chromaticity coordinates are redefined periodically according to the image to be displayed.
  • a high definition display system is obtained by means of a very high density of sub-pixels, each pixel comprising a sub-pixel of each primary color.
  • the transmitters are chosen to use a continuous white light emitting layer, ie an emitting layer which is common to all the sub-pixels.
  • the continuous white light emitting layer is associated, for each sub-pixel, with a specific color filter, which is a function of the color that is desired for the sub-pixel considered.
  • a pixel 1 with variable chromaticity coordinates consists of three color sub pixels 2, each of which emits a primary color.
  • Each sub-pixel 2 comprises a light emitting diode 3 formed in the white light emitting layer and driven by two specific electrodes (not shown) which are arranged on either side of the emitter layer.
  • Each subpixel is associated with a colored filter 4, which allows only the desired primary color to pass through.
  • the white light emitting layer is formed continuously on a first set of electrodes. The second set of electrodes is then made on this emitting layer.
  • the light-emitting diodes 3 of the different sub-pixels are identical.
  • the variation of the chromatic coordinates of the pixel is carried out, periodically, by modulating its distribution in primary colors.
  • This modulation of the distribution in primary colors is practically translated by a modulation of the light energy released, that is to say by a modulation of the luminance of each of the sub-pixels.
  • This modulation of the luminance is conventionally performed by varying the intensity of the supply current of the sub-pixel concerned.
  • the luminance of the pixel is determined by the sum of the currents flowing through the light emitters, while the color of the pixel is a function of the luminance of its sub-pixels and therefore of the distribution of the current between the different sub-pixels. It is therefore known to modulate the current between the sub-pixels to modulate the color and the luminance of the pixel.
  • PWM Pulse Width Modulation
  • the document WO 98169382 describes a device for controlling the color of an OLED.
  • the device has OLEDs whose color of the light emitted varies according to the applied voltage (page 7, last paragraph).
  • Document D1 specifies that voltage control allows the manufacture of a color screen from a single monochrome panel in which it is possible to choose the color and brightness of each pixel (page 8, paragraph 2).
  • a color filter can be associated with each pixel to control the wavelength of the transmitted light (page 3, lines 4-5).
  • This colored filter 14, preferably tri-band, can be applied to the upper part of the OLED (the second conductive layer 13) in order to let only a particular wavelength close to the emitted light (page 8, last paragraph, page 9 first paragraph).
  • the gray level control for each color can be achieved by means of pulse width modulation (page 8, lines 9-12).
  • the document WO 20051069266 discloses an active matrix of electroluminescent devices.
  • the electroluminescent elements are associated with switching means located at the intersections of the column and line conductive lines of the matrix.
  • the pixels are thus addressed by the associated column 4 and line 6 conductors by means of the control circuits 8 and 9.
  • the pixels of the same column are subjected to the same supply conditions via the power line 26 (page 6, line 28).
  • an isolation transistor 30 isolates the conduction transistor 22 from the light emitting element 2.
  • the conduction signal applied to the isolation transistor 30 is imposed on all the pixels of the array in a sequence line by line (page 7, lines 11-18).
  • the document WO 20051106835 describes a device that allows, for OLEDs, to define the emitted color while allowing the conservation of a constant luminance.
  • the document describes a plurality of OLEDs that can emit a white color, but whose emitted color and brightness vary according to the power supply current, (0027, 0031).
  • the brightness is then modulated by means of current pulses which adjust the duration to the high state for a predefined time unit.
  • the subject of the invention is a control circuit of a pixel which is easy to implement, making it possible to limit the consumption of the pixel, to increase its lifetime and / or its luminance and to obtain a compact display system. .
  • the pixel 1 with variable chromaticity coordinates comprises a plurality of sub-pixels 2 of color, for example three sub-pixels of color, made from a continuous layer in which is formed the diode 3 emitting white light.
  • the light emitters of the sub-pixels, organic electroluminescent diodes, are identical.
  • Each color sub-pixel 2 is associated with a color filter 4 which only allows one of the primary colors to pass outwards.
  • the sub-pixels 2 of colors used are, for example, sub-pixels having specific shades of blue, green and red.
  • the pixel 1 may comprise an additional sub-pixel, without a colored filter, which emits a white light to facilitate the production and luminance of the white.
  • the pixel 1 is associated with a control circuit which notably makes it possible to fix the supply conditions (voltage, current and application time) of each of the sub-pixels independently via two sets of electrodes arranged on either side of the emitting layer.
  • the control circuit thus makes it possible to periodically determine the luminance and the chromatic coordinate of the pixel 1.
  • the emission spectrum of the emitting layer 3, that is to say the color emitted by this layer, may vary with the supply conditions (voltage, current) to a greater or lesser extent depending on the composition of the this layer. In general, this phenomenon must be limited. On the contrary, according to the invention, it is advantageous to choose a composition which generates a significant variation of the emission spectrum with the polarization.
  • the color emitted by an organic light-emitting diode 3 varies from red (R) to blue (B) via green (G) and white (W), when the supply current increases.
  • the diode 3 may conventionally comprise additional layers, in particular associated with the transport and / or confinement of the charge carriers in the structure, such as hole and / or electron blocking layers, buffer layers as well as transport layers. holes and / or electrons, necessary for its proper functioning. These layers are not explained for the sake of clarity.
  • the additional sub-pixel is powered under so-called nominal operating conditions, to emit white light.
  • Each organic light emitting diode 3 of the pixel 1 is supplied independently (current and / or voltage) of the others by the control circuit so that each emits in the color corresponding to its own color filter 4.
  • the voltage and / or the current applied to each sub-pixel, therefore to each light emitter, is determined according to the color of the sub-pixel. It is, for example, to emit in the red the organic light emitting diode 3 associated with the red color filter, in blue the diode 3 associated with the blue filter and in the green diode 3 associated with the green filter.
  • the emission spectrum of each light-emitting diode 3 is thus close to the transmission spectrum of its color filter.
  • the control circuit thus separately controls the emitters 3 of light, which have a transmission spectrum that can be modulated according to their voltage and / or their supply current.
  • the voltage and / or the supply current applied to each sub-pixel is then determined according to its color so that its emission spectrum is close to the transmission spectrum of the color filter 4 associated therewith.
  • the organic light-emitting diodes described above are particularly suitable insofar as their color varies greatly with the voltage and / or the supply current.
  • the luminance of each pixel is then modulated by varying the duration of application of this current and / or this voltage.
  • the organic light-emitting diode 3 associated with the red color filter 4 is advantageously supplied by a current I R lower than the diodes associated with the blue and green filters, which allows to obtain a deep red.
  • the organic light-emitting diode 3 associated with the blue color filter 4 is advantageously supplied by a higher current I B than the diodes associated with the red and green filters, which makes it possible to obtain a deep blue.
  • an emitter layer made from the following blue / green / red emission sublayers: SEB010 doped SEB020 (about 10nm thick) / TMM004 doped TEG341 (about 7nm thick) / TMM004 doped TER040 (thickness about 20nm), all these materials being marketed at Merck.
  • the figure 3 details, for three sub-pixels of different colors, the luminance as a function of the current density.
  • the curves G, R and B represent the evolution of the luminance as a function of the current density for a diode associated respectively with a green, red and blue filter.
  • the luminance obtained for a frame time of 20 ms is 100 Cd / m 2 .
  • the luminance being proportional to the duration of application of the current, it is sufficient to reduce the luminance to 100Cd / m 2 to apply the current only during a fraction of the frame time t namely: tx 100/250.
  • the figure 4 represents the emission spectra of a diode which is fed at two current densities: 50 and 20 mA / cm 2 .
  • the curves C and D represent the evolution of the luminance as a function of the wavelength of the emission spectrum respectively for current densities of 20 mA / cm 2 and 50 mA / cm 2 . If we compare the two emission spectra of the diode, we see that the proportion of energy emitted in the blue band, that is, between 450 and 495nm, relative to the total energy increases as the current density increases. The losses at the blue filter are therefore less important when the diode is polarized at 50 mA / cm 2 , curve D.
  • the luminance of the blue sub-pixel is then greatly increased when its polarization density is increased.
  • the selection criteria of the currents to be used are dictated by the chromatic coordinates that one wishes to obtain for the sub-pixel in question and by the luminance obtained after filtering.
  • the following table gives, as a function of the polarization (the voltage / current pair), for the same diode, the luminance (in Cd / m 2 ) obtained after filtering as well as the chromatic coordinates (X, Y) in a diagram of CIE1931 chromacity, for a frame time t of 20ms.
  • each diode is powered under conditions that favor obtaining a transmission spectrum that is close to the transmission spectrum of the associated color filter.
  • the differences in light intensity of the diode that result from these polarization differences are modulated by the specific power times for each sub-pixel.
  • each of the sub-pixels has the same luminance, here for example 100Cd / m 2 .
  • the figure 5 illustrates an addressing circuit of a sub-pixel.
  • a first transistor T1 operating as a switch, is connected by its control electrode (gate) to a selection line (SL), to select the diode, that is to say the sub-pixel, to activate.
  • the first transistor T1 is connected between a data line (DL) and the control electrode of a second transistor T2.
  • the transistor T1 When the transistor T1 is on (the subpixel is selected), the available voltage on the data line DL is available at the gate of the transistor T2.
  • the transistor T2 and the diode 3 are connected in series and supplied between the supply voltage V dd and a predefined voltage V cathode .
  • the transistor T2 is connected to the potential V dd while the diode is connected to the potential V cathode .
  • the level of current flowing in the transistor and in the diode is set by the voltage level applied to the gate of transistor T2.
  • this voltage is kept constant by a capacitor C which is arranged between the supply V dd and the gate of the transistor T2.
  • the capacitor C is charged when the transistor T1 is in the on state.
  • the pixel electrode that is to say the electrode which is controlled by the second transistor T2 corresponds to the anode of the light emitting diode.
  • the cathode is in general common to all the pixels and the potential V cathode is fixed and constant.
  • cathodes per color (a cathode for each color and for the entire display device). These cathodes are independent and it is possible to modulate the current or voltage across the various diodes driving these different cathodes.
  • the anode of each sub-pixel then remains driven at a potential / current, for example constant, as in the prior art.
  • This solution has the advantage of being able to maintain for the control circuit of the anode, at each sub-pixel, a circuit identical to the device of the prior art.
  • control circuit sets, for each organic light emitting diode 3 of the pixel 1, the supply conditions (current and / or voltage) that allow optimal light output with the corresponding color filter 4.
  • the fixed control circuit for example for each organic light emitting diode 3 of the pixel 1, a current which defines the color emitted by the diode and also its instantaneous luminance.
  • the polarization of the diode Since the polarization of the diode has been chosen to optimize the emitted color, the luminance obtained is brought back to the required luminance by varying the application time of this polarization: the diode is no longer supplied during the entire frame time t.
  • the addressing circuit of the diode 3 comprises means for controlling the duration of application of the supply voltage and / or the supply current depending on the color of the sub-pixel.
  • the addressing circuit of the diode comprises a control transistor T3, operating as a switch, connected between the control electrode (gate) of the second transistor T2 and the terminal of the power source connected to the diode, preferably, the mass.
  • the control electrode (gate) of the control transistor T3 is connected to a reset line (RL) which constitutes with the control transistor T2 means for controlling the duration of application of the current through the diode 3.
  • the transistor T3 When the transistor T3 is off, the voltage on the gate of the transistor T2 is maintained thanks to the capacitor C and the desired current flows in the diode 3.
  • the capacitor C discharges and the potential of the terminal the power source connected to the diode (preferably the ground) is returned to the gate of the transistor T2, blocking the transistor T2: no current then flows in the diode.
  • the reset line (RL) and the control transistor T3 thus make it possible to set, during each frame period ⁇ t, a maximum duration during which the diode is energized.
  • the control means of the duration of application of the supply conditions makes it possible to modulate, on the frame time, the average luminance of each sub-pixel, that is to say that they make it possible to obtain an average luminance predetermined for a predetermined period.
  • the control circuit periodically sets, for a frame period ⁇ t, for example 20 ms, the chromatic coordinates of the pixel 1 and its luminance by modulating the luminances of the sub-pixels.
  • ⁇ t for example 20 ms
  • the control circuit selects the sub-pixels 2 necessary to obtain the chromatic coordinates of the pixel and controls the luminance of each of these sub-pixels 2.
  • the control transistors T3 associated with sub-pixels of different colors are conductive for durations t on which depend on this color (t on ⁇ ⁇ t) during each period ⁇ t.
  • the duration takes into account the differences in instantaneous luminance existing between the different sub-pixels of the same pixel because of the differences in their voltage and / or supply current.
  • the control circuit controls the period t power on each of the sub-pixels 2.
  • the application time t on of the supply voltage or the supply current can be adjusted by the anode or the cathode.
  • the addressing circuit illustrated in FIG. figure 5 and which cooperates with the control circuit has been realized using n-type transistors, but similarly, a circuit could be made from a p-type transistor as shown in FIG. figure 6 .
  • the transistor T3 may be arranged in series with the diode for, in the off state, to block the current flowing in the diode. It could also be mounted in parallel with the capacity.
  • the diode 3 associated with the red filter is polarized with a lower current than the other sub-pixels to obtain the maximum emission efficiency in the red band.
  • a luminance of the red sub-pixel which is comparable to that of the other sub-pixels, it is chosen to polarize the diode for a longer time, for example, during the entire frame period ⁇ t.
  • the diode 3 associated with the blue filter is biased with a current stronger than the other sub-pixels to obtain the maximum emission efficiency in the blue band, it can be polarized for a shorter time.
  • the product of the instantaneous luminance L of the diode by its duration of supply (Lxt on ) corresponds to the average luminance of the sub-pixel over the period ⁇ t.
  • the overall luminance of pixel 1 then depends on the average luminance of the different selected subpixels.
  • the voltage or the supply current of each of the organic electroluminescent diodes 3 being fixed as a function of the color of the corresponding sub-pixel (V R , V G , V B or I R , I B , I G ), the the color of the pixel 1 and its luminance are determined by the control circuit by selection of the appropriate sub-pixels (SL command of the figure 3 ) and modulation of the supply duration t on each of the sub-pixels 2 of color.
  • each color sub-pixel 2 may be constituted by a single pulse whose duration (t on ) in the high state is set by the signals RL of the control circuit.
  • the invention is not limited to the embodiments described above.
  • the addressing circuit of the Figures 5 to 8 can be replaced by any circuit for adapting the voltage and / or the supply current of a color sub-pixel so that its emission spectrum is close to the transmission spectrum of the color filter of the sub-pixel, and to adapt the diode supply time t on the color of the sub-pixel, to obtain a predetermined average luminance for a predetermined period ⁇ t.
  • the display device also comprises an addressing circuit specific to each sub-pixel 2 in order to select the desired sub-pixel 2 and to control its duration of supply and its supply conditions.
  • This specific addressing circuit may be that represented, for example, Figures 5 to 8 .
  • the display device comprises, as before, a control circuit which cooperates with the different addressing circuits of the pixel array 1 to obtain the desired image, both in terms of colors and gray levels.
  • the control circuit manages all the sub-pixels 2 of the matrix in order to emit the desired image.
  • Each sub-pixel addressing circuit 2 has a reset terminal which controls the sub-pixel 2 power-up time, i.e. the power-on time of the light-emitting element. 3.
  • Each addressing circuit also includes a selection terminal which makes it possible to define whether the light emitter 3 of the sub-pixel 2 must be powered or not. current.
  • Each addressing circuit further comprises a power control terminal which makes it possible to modulate the supply conditions of the sub-pixel 2.
  • the cathode may be common to sub-pixels of a given color, therefore to a group of sub-pixels 2, or the cathode may be specific to each sub-pixel 2.
  • the selection input of the sub-pixel 2 may be constituted by the control terminal of a first transistor T1.
  • the first transistor T1 is in an on or off state which has the effect of allowing or not the passage of a current in the light emitter 3 of the sub-pixel 2 .
  • the control input of the supply conditions of the sub-pixel 2 may be constituted by an input terminal of the first transistor T1 whose output terminal is connected to the control terminal of the second transistor T2.
  • the second transistor T2 modulates the amount of current that can be applied to the light emitter 3.
  • the modulation of the current in the transmitter of light 3 is effective only if the first transistor T1 is in an on state.
  • the reset input of the sub-pixel 2 may be constituted by the control terminal of the third transistor T3 which is connected between the control terminal of the second transistor T2 and the ground or the supply voltage V dd . In this way, depending on the voltage applied to the control terminal of the third transistor T3, the second transistor T2 is in a blocked or on state.
  • the different addressing circuits associated with a sub-pixel color 2, that is to say to a colored filter color 4 are connected to the same reset line RL.
  • the control circuit is connected to all the sub-pixels 2 via their respective addressing circuit.
  • the control circuit is connected independently to each sub-pixel 2 by a specific selection line SL and by a control line of the specific supply conditions DL.
  • the control circuit is also connected to the different sub-pixels 2 by reset lines RL which set the duration of power supply t on the sub-pixel 2.
  • reset lines are specific to a color of sub-pixel 2.
  • the control circuit has as many RL reset lines as there are sub-pixels 2 of different colors in a pixel 1.
  • the control circuit has as many selection lines SL and control lines of the power conditions DL as subpixels 2 in the matrix. In this way, it is possible to reduce the amount of independent lines in the display device, while ensuring independence of use of different sub-pixels 2 and an increase in energy performance.
  • the reset line RL can be physically common to all sub pixels of the same color. This may be the case for example, when the reset line is connected to the anode or the cathode of a diode.
  • the first transistor T1 is connected between the control line of the supply conditions DL and the control electrode of the second transistor T2.
  • the diode 3 of the sub-pixel 2 in question is connected in series with the second transistor T2 between the supply voltage V dd and the predefined potential of the cathode V cathode .
  • the capacitor C and the third transistor T3 are connected in series between the supply voltage V dd and the ground.
  • the common terminal of the capacitor C and the third transistor T3 is connected to the control terminal of the second transistor T2 and to the first transistor T1.
  • the reset line RL is connected to an electrode of control of the third transistor T3.
  • the control terminal of the first transistor T1 is connected to the selection line SL.
  • the first transistor T1 is connected between the control line of the supply conditions DL and the control electrode of the second transistor T2.
  • the diode 3 of the sub-pixel 2 in question is connected in series with the second T2 and third T3 transistors between the supply voltage V dd and the predefined potential applied to the cathode V cathode .
  • the capacitor C is connected between the supply voltage V dd and the control terminal of the second transistor T2 or between the ground and the control terminal of the second transistor T2.
  • the reset line RL is connected to the control electrode of the third transistor T3.
  • the control terminal of the first transistor T1 is connected to the selection line SL. In this case, the relative position of the second T2 and third T3 transistors between the diode and the supply voltage Vdd is not important.
  • the matrix of pixels 1 comprises four pixels 1 1 , 1 2 , 1 3 and 1 4 which each consist of three sub-pixels 2 called blue "B", green "G” and red “R".
  • the control circuit comprises a single reset line RL R associated with the red subpixels, a single reset line RL G associated with the green subpixels and a single reset line RL B associated with the sub-pixels. blue pixels.
  • the control circuit also has as many selection lines as subpixels (here twelve selection lines SL 1 -SL 12 ) and as many control lines as subpixels (here twelve control lines DL 1 -DL 12 )
  • the reset line RL controlling the duration of supply of the sub-pixels 2 of the same color, all the red sub-pixels are fed during a first predetermined duration t on (R) , all the green sub-pixels are fed for a predetermined second time t on (G) and all Blue sub-pixels are fed for a third predetermined duration t on (B) .
  • the different sub-pixels 2 are fed with the proviso that the first transistor T1 is in an on state, that is, they have been selected to emit light. In this way, a sub-pixel 2 is fed if the information on its selection line SL authorizes it and the sub-pixel 2 is then fed only for the duration which is defined by the reset line RL .
  • the modulation of the luminance of each sub-pixel 2 and thus of the pixel 1 is carried out by modulating the supply voltage at the terminals of each sub-pixel 2. Indeed, as has been previously stated according to the supply conditions of each diode 3, there is modulation of the emitted color, but also of the instantaneous luminance. There is therefore for a given supply condition, a color and a luminance instant predefined. As a result, the modulation of the luminance for a given color is achieved by modulating for each of the sub-pixels 2 the supply conditions.
  • Each sub-pixel 2 naturally remains fed in a range such that the emitted color is close to that of the associated colored filter 4 so as to maintain an energetic interest in this architecture.
  • the color emitted by the sub-pixel 2 is defined by the intersection between the transmission spectrum of the color filter and the emission spectrum of the light-emitting element 3.
  • a display device comprising this control circuit associated with a plurality of identical pixels 1 with variable chromaticity coordinates with sub-pixels 2 and their associated addressing circuit, the operating conditions are fixed in the following manner.
  • each sub-pixel 2 (each light emitter 3) is supplied under different conditions in order to determine the most favorable energy supply conditions with the color filter 4 In this way, the light emitter 3 of each sub-pixel 2 has a transmission spectrum that is as close as possible to the transmission spectrum of the transmission spectrum of the associated color filter.
  • each sub-pixel 2 According to the power conditions selected for each sub-pixel 2, the latter present between them different instantaneous luminances.
  • Each sub-pixel 2 is then supplied with a specific predetermined duration so that the corresponding pixel 1 emits a predetermined color and luminance.
  • the feed times of each of the sub-pixels are chosen so that the pixel emits a white color under the most favorable supply conditions between each light emitter 3 and the color filter 4 associated with it. .
  • each sub-pixel is powered under different conditions (voltage and / or current).
  • the modulation of the characteristics of the radiation emitted by the pixel is achieved by modulating the power conditions of the sub-pixels that compose it.
  • the cathode is common to all the sub-pixels of the same color, it is then possible to realize control of the feeding time by means of the cathode.
  • the reset line is made by the cathode common to all the sub-pixels of the same color. This discount zero results in the appearance of a potential difference lower than a threshold voltage at the terminals of the diode 3. Indeed, it must be considered that the control voltage of the anode can vary depending on the level displayed, it is not necessary to can not guarantee a constant voltage across the diode. The use of a threshold voltage is then very advantageous.
  • the second transistor T2 it is possible to independently control the supply conditions of each of the diodes by means of the second transistor T2.
  • the pixel electrode represents the cathode of the light-emitting diode
  • the third transistor T3 can be eliminated.

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Description

Domaine technique de l'inventionTechnical field of the invention

L'invention est relative à un dispositif d'affichage à base de pixels à coordonnées chromatiques variables comportant une pluralité de sous-pixels de couleur, comprenant chacun un émetteur de lumière, formé par une diode organique électroluminescente et un filtre coloré, les coordonnées chromatiques du pixel étant déterminées périodiquement et les émetteurs de lumière étant identiques.The invention relates to a pixel-based variable color coordinate display device comprising a plurality of color sub-pixels, each comprising a light emitter, formed by an organic electroluminescent diode and a color filter, the color coordinates of the pixel being determined periodically and the light emitters being identical.

État de la techniqueState of the art

Dans les systèmes d'affichages en couleur, la couleur de chaque pixel est réalisée à partir de trois couleurs primaires. La norme CIE 1931 peut, par exemple, être utilisée pour définir à partir de trois couleurs primaires étalons, constituées par une nuance précise de bleu (B), de rouge (R) et de vert (G), n'importe quelle couleur visible à l'oeil. Avec cette norme, toutes les nuances de couleur accessibles à l'oeil humain sont définies par des coordonnées chromatiques précises, qui correspondent chacune à une répartition particulière des couleurs primaires étalons.In color display systems, the color of each pixel is made from three primary colors. The CIE 1931 standard can, for example, be used to define from three primary standard colors, consisting of a precise shade of blue (B), red (R) and green (G), any visible color. at the eye. With this standard, all the color shades accessible to the human eye are defined by precise chromatic coordinates, each of which corresponds to a particular distribution of the primary standard colors.

De manière classique, un pixel est défini par sa couleur et par sa luminance, c'est-à-dire par son intensité lumineuse visible. Ainsi, la luminance et les coordonnées chromatiques d'un pixel à coordonnées chromatiques variables sont redéfinies périodiquement en fonction de l'image à afficher.Conventionally, a pixel is defined by its color and its luminance, that is to say by its visible light intensity. Thus, the luminance and the chromatic coordinates of a pixel with variable chromaticity coordinates are redefined periodically according to the image to be displayed.

De manière classique, un système d'affichage à définition élevée est obtenu au moyen d'une très forte densité de sous-pixels, chaque pixel comportant un sous-pixel de chaque couleur primaire.Conventionally, a high definition display system is obtained by means of a very high density of sub-pixels, each pixel comprising a sub-pixel of each primary color.

Or, les matériaux émetteurs de lumière, et notamment les matériaux organiques, sont difficiles à structurer. On choisit donc, en général, d'utiliser pour les émetteurs, une couche émettrice de lumière blanche continue, c'est-à-dire une couche émettrice qui est commune à tous les sous-pixels. La couche émettrice de lumière blanche continue est associée, pour chaque sous-pixel, à un filtre de couleur spécifique, qui est fonction de la couleur que l'on souhaite obtenir pour le sous-pixel considéré.However, light-emitting materials, and in particular organic materials, are difficult to structure. Therefore, in general, the transmitters are chosen to use a continuous white light emitting layer, ie an emitting layer which is common to all the sub-pixels. The continuous white light emitting layer is associated, for each sub-pixel, with a specific color filter, which is a function of the color that is desired for the sub-pixel considered.

Comme illustré à la figure 1, de manière conventionnelle, un pixel 1 à coordonnées chromatiques variables est constitué de trois sous-pixels 2 de couleur qui émettent chacun une couleur primaire. Chaque sous-pixel 2 comporte une diode électroluminescente 3 formée dans la couche émettrice de lumière blanche et pilotée par deux électrodes spécifiques (non représentées) qui sont disposées de part et d'autre de la couche émettrice. A chaque sous-pixel est associé un filtre coloré 4, qui ne laisse passer que la couleur primaire désirée. Classiquement, la couche émettrice de lumière blanche est formée de manière continue sur un premier jeu d'électrodes. Le second jeu d'électrodes est ensuite réalisé sur cette couche émettrice. Ainsi, les diodes électroluminescentes 3 des différents sous-pixels sont identiques.As illustrated in figure 1 conventionally, a pixel 1 with variable chromaticity coordinates consists of three color sub pixels 2, each of which emits a primary color. Each sub-pixel 2 comprises a light emitting diode 3 formed in the white light emitting layer and driven by two specific electrodes (not shown) which are arranged on either side of the emitter layer. Each subpixel is associated with a colored filter 4, which allows only the desired primary color to pass through. Conventionally, the white light emitting layer is formed continuously on a first set of electrodes. The second set of electrodes is then made on this emitting layer. Thus, the light-emitting diodes 3 of the different sub-pixels are identical.

De manière classique, la variation des coordonnées chromatiques du pixel est réalisée, périodiquement, en modulant sa répartition en couleurs primaires. Cette modulation de la répartition en couleurs primaires se traduit pratiquement par une modulation de l'énergie lumineuse dégagée, c'est-à-dire par une modulation de la luminance de chacun des sous-pixels. Cette modulation de la luminance est classiquement réalisée en faisant varier l'intensité du courant d'alimentation du sous-pixel concerné. De cette manière, la luminance du pixel est déterminée par la somme des courants qui parcourent les émetteurs de lumière, tandis que la couleur du pixel est fonction de la luminance de ses sous-pixels et donc de la répartition du courant entre les différents sous-pixels. Il est donc connu de moduler le courant entre les sous-pixels pour moduler la couleur et la luminance du pixel.Conventionally, the variation of the chromatic coordinates of the pixel is carried out, periodically, by modulating its distribution in primary colors. This modulation of the distribution in primary colors is practically translated by a modulation of the light energy released, that is to say by a modulation of the luminance of each of the sub-pixels. This modulation of the luminance is conventionally performed by varying the intensity of the supply current of the sub-pixel concerned. Of this In this way, the luminance of the pixel is determined by the sum of the currents flowing through the light emitters, while the color of the pixel is a function of the luminance of its sub-pixels and therefore of the distribution of the current between the different sub-pixels. It is therefore known to modulate the current between the sub-pixels to modulate the color and the luminance of the pixel.

Une autre technique de pilotage existe : par modulation de la durée de polarisation (PWM pour Pulse Width Modulation). Cette technique consiste à maintenir le courant constant pour chaque sous-pixel. La modulation de couleur et de luminance du pixel est alors obtenue par modulation du temps d'application du courant de chaque sous-pixel.Another technique of control exists: by modulation of the duration of polarization (PWM for Pulse Width Modulation). This technique consists in keeping the current constant for each sub-pixel. The color and luminance modulation of the pixel is then obtained by modulating the application time of the current of each sub-pixel.

Ces deux techniques engendrent des pertes énergétiques importantes car la lumière blanche émise par chaque émetteur de lumière passe au travers du filtre de couleur correspondant. Si la lumière blanche a une répartition homogène dans chacune des couleurs primaires, lors du passage dans le filtre coloré, les deux tiers de l'énergie lumineuse est absorbée par le filtre pour ne laisser passer que la couleur correspondant au filtre. Ainsi, le fonctionnement du pixel avec une luminance acceptable se traduit par l'utilisation d'émetteurs de lumière à très forte luminance. Pratiquement, une forte luminance est obtenue en utilisant un courant élevé, ce qui se traduit par une forte consommation énergétique et par une réduction de la durée de vie des émetteurs de lumière.These two techniques generate significant energy losses because the white light emitted by each light emitter passes through the corresponding color filter. If the white light has a homogeneous distribution in each of the primary colors, when passing through the color filter, two-thirds of the light energy is absorbed by the filter to let only the color corresponding to the filter. Thus, the operation of the pixel with acceptable luminance results in the use of very high luminance light emitters. Practically, a high luminance is obtained by using a high current, which results in a high energy consumption and a reduction in the life of the light emitters.

Le document WO 98169382 décrit un dispositif de contrôle de la couleur d'une OLED. Le dispositif comporte des OLED dont la couleur de la lumière émise varie en fonction de la tension appliquée (page 7, dernier paragraphe). Le document D1 précise que le contrôle de la tension permet la fabrication d'un écran couleur à partir d'un simple panneau monochrome dans lequel il est possible do choisir la couleur et la luminosité de chaque pixel (page 8, paragraphe 2). Un filtre coloré peut être associé à chaque pixel pour contrôler la longueur d'onde de la lumière transmise (page 3, lignes 4-5). Ce filtre coloré 14, de préférence tribande, peut étre appliqué sur la partie supérieure de l'OLED (la seconde couche conductrice 13) afin de ne laisser passer qu'une longueur d'onde particulière proche de la lumière émise (page 8, dernier paragraphe, page 9 premier paragraphe). Le contrôle de luminance ("gray levels") pour chaque couleur peut être réalisé au moyen d'une modulation de la largeur des impulsions (page 8, lignes 9-12).The document WO 98169382 describes a device for controlling the color of an OLED. The device has OLEDs whose color of the light emitted varies according to the applied voltage (page 7, last paragraph). Document D1 specifies that voltage control allows the manufacture of a color screen from a single monochrome panel in which it is possible to choose the color and brightness of each pixel (page 8, paragraph 2). A color filter can be associated with each pixel to control the wavelength of the transmitted light (page 3, lines 4-5). This colored filter 14, preferably tri-band, can be applied to the upper part of the OLED (the second conductive layer 13) in order to let only a particular wavelength close to the emitted light (page 8, last paragraph, page 9 first paragraph). The gray level control for each color can be achieved by means of pulse width modulation (page 8, lines 9-12).

Le document WO 20051069266 décrit une matrice active de dispositifs électroluminescents. Les éléments électroluminescents sont associés à des moyens de commutations localisés aux intersections des lignes conductrices de colonne et de ligne de la matrice. Les pixels sont ainsi adressés par les conducteurs de colonne 4 et de ligne 6 associés au moyen des circuits de contrôle 8 et 9.
Les pixels d'une même colonne sont soumis aux mêmes conditions d'alimentation par la ligne 26 d'alimentation (page 6, ligne 28). Pour chaque pixel, un transistor d'isolation 30 isole le transistor de conduction 22 de l'élément émetteur de lumière 2. Le signal de conduction appliqué au transistor d'isolation 30 est imposé à tous les pixels du tableau dans une séquence ligne par ligne (page 7, lignes 11-18).
The document WO 20051069266 discloses an active matrix of electroluminescent devices. The electroluminescent elements are associated with switching means located at the intersections of the column and line conductive lines of the matrix. The pixels are thus addressed by the associated column 4 and line 6 conductors by means of the control circuits 8 and 9.
The pixels of the same column are subjected to the same supply conditions via the power line 26 (page 6, line 28). For each pixel, an isolation transistor 30 isolates the conduction transistor 22 from the light emitting element 2. The conduction signal applied to the isolation transistor 30 is imposed on all the pixels of the array in a sequence line by line (page 7, lines 11-18).

Le document WO 20051106835 décrit un dispositif qui permet, pour des OLED, de définir la couleur émise tout en autorisant la conservation d'une luminance constante. Le document décrit une pluralité d'OLED pouvant émettre une couleur blanche, mais dont la couleur émise et la luminosité varient en fonction du courant d'alimentation, (0027, 0031). La modulation de la luminosité est alors réalisée aux moyens d'impulsions de courant qui ajustent la durée à l'état haut pour une unité de temps prédéfinie.The document WO 20051106835 describes a device that allows, for OLEDs, to define the emitted color while allowing the conservation of a constant luminance. The document describes a plurality of OLEDs that can emit a white color, but whose emitted color and brightness vary according to the power supply current, (0027, 0031). The brightness is then modulated by means of current pulses which adjust the duration to the high state for a predefined time unit.

Objet de l'inventionObject of the invention

L'invention a pour objet un circuit de contrôle d'un pixel facile à mettre en oeuvre, permettant de limiter la consommation du pixel, d'augmenter sa durée de vie et/ou sa luminance et d'obtenir un système d'affichage compact.The subject of the invention is a control circuit of a pixel which is easy to implement, making it possible to limit the consumption of the pixel, to increase its lifetime and / or its luminance and to obtain a compact display system. .

Ce but est atteint par les revendications annexées et plus particulièrement par le fait que le dispositif comporte :

  • une matrice de pixels identiques à coordonnées chromatiques et luminances variables déterminées périodiquement pendant une période de rafraîchissement prédéterminée, chaque pixel comportant une pluralité de sous-pixels de couleur,
  • chaque sous-pixel de couleur comprenant un émetteur de lumière formé par une diode organique électroluminescente et un filtre coloré, les émetteurs de lumière de tous les sous-pixels étant identiques et ayant un spectre d'émission variable en fonction de leur tension et/ou de leur courant d'alimentation,
  • un circuit d'adressage associé à chaque sous-pixel et comportant au moins une entrée de sélection, une entrée de contrôle de la durée d'alimentation et une entrée de contrôle des conditions d'alimentation du sous-pixel,
  • un circuit de contrôle du dispositif d'affichage connecté à la pluralité de circuits d'adressage,
chaque sous-pixel de chaque pixel étant alimenté par une tension et/ou un courant d'alimentation spécifique fonction de la couleur du sous-pixel pour que le spectre d'émission de l'émetteur de lumière dudit sous-pixel se rapproche du spectre de transmission du filtre coloré associé et fonction de la coordonnée chromatique et de la luminance désirée pour le pixel associé, le circuit de contrôle étant connecté à l'entrée de sélection de chaque circuit d'adressage par une ligne spécifique de sélection, à l'entrée de contrôle des conditions d'alimentation par une ligne spécifique de contrôle d'alimentation et aux entrées de contrôle de la durée d'alimentation de tous les circuits d'adressage associés à chaque couleur de sous-pixel par une ligne de remise à zéro spécifique de ladite couleur de sous-pixel.This object is achieved by the appended claims and more particularly by the fact that the device comprises:
  • an array of identical pixels with chromatic coordinates and variable luminances determined periodically during a predetermined refresh period, each pixel comprising a plurality of color subpixels,
  • each color sub-pixel comprising a light emitter formed by an organic electroluminescent diode and a color filter, the light emitters of all the sub-pixels being identical and having a variable emission spectrum depending on their voltage and / or of their power supply,
  • an addressing circuit associated with each sub-pixel and comprising at least one selection input, a control input of the supply duration and a control input of the sub-pixel supply conditions,
  • a control circuit of the display device connected to the plurality of addressing circuits,
each sub-pixel of each pixel being powered by a voltage and / or a specific supply current depending on the color of the sub-pixel so that the emission spectrum of the light emitter of said sub-pixel approaches the spectrum transmission of the associated color filter and function of the chromatic coordinate and the desired luminance for the associated pixel, the control circuit being connected to the selection input of each addressing circuit by a specific selection line, at the control input of the supply conditions by a specific power control line and power supply control inputs of all addressing circuits associated with each subpixel color by a reset line specific to said subpixel color.

Description sommaire des dessinsBrief description of the drawings

D'autres avantages et caractéristiques ressortiront plus clairement de la description qui va suivre de modes particuliers de réalisation de l'invention donnés à titre d'exemples non limitatifs et représentés aux dessins annexés, dans lesquels :

  • la figure 1 représente, de manière schématique, en coupe, un pixel selon l'art antérieur,
  • la figure 2 représente, de manière schématique, sur un diagramme de chromaticité CIE1931, le déplacement des coordonnées chromatiques d'une diode organique électroluminescente en fonction de sa tension d'alimentation,
  • la figure 3 représente, de manière schématique, pour trois filtres colorés différents, l'évolution de la luminance en fonction de la densité de courant qui traverse un sous-pixel,
  • la figure 4 représente, de manière schématique, l'évolution de la luminance en fonction de la longueur d'onde pour deux densités de courants,
  • les figures 5 à 8 représentent, de manière schématique, différentes variantes de réalisation d'un circuit d'adressage d'un pixel selon l'invention,
  • la figure 9 représente, de manière schématique, une répartition temporelle du courant d'alimentation des sous-pixels d'un pixel avec un circuit de contrôle selon l'invention,
  • la figure 10 représente, de manière schématique, un mode de réalisation particulier d'un dispositif d'affichage selon l'invention.
Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given by way of non-limiting example and represented in the accompanying drawings, in which:
  • the figure 1 represents, schematically, in section, a pixel according to the prior art,
  • the figure 2 represents, schematically, on a chromaticity diagram CIE1931, the displacement of the chromatic coordinates of an organic electroluminescent diode according to its supply voltage,
  • the figure 3 represents schematically, for three different color filters, the evolution of the luminance as a function of the current density which passes through a sub-pixel,
  • the figure 4 represents, in a schematic way, the evolution of the luminance as a function of the wavelength for two densities of currents,
  • the Figures 5 to 8 show, schematically, different variants of an addressing circuit of a pixel according to the invention,
  • the figure 9 represents, schematically, a temporal distribution of the supply current of the sub-pixels of a pixel with a control circuit according to the invention,
  • the figure 10 represents, schematically, a particular embodiment of a display device according to the invention.

Description de modes de réalisation préférentiels de l'inventionDESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

De manière classique, le pixel 1 à coordonnées chromatiques variables comporte une pluralité de sous-pixels 2 de couleur, par exemple trois sous-pixels de couleur, réalisés à partir d'une couche continue dans laquelle est formée la diode 3 émettrice de lumière blanche. Ainsi, les émetteurs de lumière des sous-pixels, des diodes organiques électroluminescentes, sont identiques. Chaque sous-pixel 2 de couleur est associé à un filtre coloré 4 qui ne laisse passer vers l'extérieur qu'une des couleurs primaires. Les sous-pixels 2 de couleurs utilisés sont, par exemple, des sous-pixels ayant des nuances précises de bleu, de vert et de rouge. Avantageusement, le pixel 1 peut comporter un sous-pixel supplémentaire, sans filtre coloré, qui émet une lumière blanche pour faciliter la réalisation et la luminance du blanc.Conventionally, the pixel 1 with variable chromaticity coordinates comprises a plurality of sub-pixels 2 of color, for example three sub-pixels of color, made from a continuous layer in which is formed the diode 3 emitting white light. Thus, the light emitters of the sub-pixels, organic electroluminescent diodes, are identical. Each color sub-pixel 2 is associated with a color filter 4 which only allows one of the primary colors to pass outwards. The sub-pixels 2 of colors used are, for example, sub-pixels having specific shades of blue, green and red. Advantageously, the pixel 1 may comprise an additional sub-pixel, without a colored filter, which emits a white light to facilitate the production and luminance of the white.

Le pixel 1 est associé à un circuit de contrôle qui permet notamment de fixer les conditions d'alimentation (tension, courant et temps d'application) de chacun des sous-pixels indépendamment via deux jeux d'électrodes disposés de part et d'autres de la couche émettrice. Le circuit de contrôle permet ainsi de déterminer périodiquement la luminance et la coordonnée chromatique du pixel 1.The pixel 1 is associated with a control circuit which notably makes it possible to fix the supply conditions (voltage, current and application time) of each of the sub-pixels independently via two sets of electrodes arranged on either side of the emitting layer. The control circuit thus makes it possible to periodically determine the luminance and the chromatic coordinate of the pixel 1.

Le spectre d'émission de la couche émettrice 3, c'est-à-dire la couleur émise par cette couche, peut varier avec les conditions d'alimentation (tension, courant) de façon plus ou moins importante en fonction de la composition de cette couche. De manière générale, ce phénomène doit être limité. Au contraire, selon l'invention, il est avantageux de choisir une composition qui engendre une variation significative du spectre d'émission avec la polarisation.The emission spectrum of the emitting layer 3, that is to say the color emitted by this layer, may vary with the supply conditions (voltage, current) to a greater or lesser extent depending on the composition of the this layer. In general, this phenomenon must be limited. On the contrary, according to the invention, it is advantageous to choose a composition which generates a significant variation of the emission spectrum with the polarization.

Ainsi, comme illustré à la figure 2 par la courbe A, sur un diagramme de chromaticité CIE1931, la couleur émise par une diode électroluminescente organique 3 varie du rouge (R) vers le bleu (B) en passant par le vert (G) et le blanc (W), lorsque le courant d'alimentation augmente.Thus, as illustrated in figure 2 by the curve A, on a chromaticity diagram CIE1931, the color emitted by an organic light-emitting diode 3 varies from red (R) to blue (B) via green (G) and white (W), when the supply current increases.

Une diode électroluminescente organique 3 comporte, de manière connue, une couche électroluminescente pouvant elle-même comporter au moins deux sous-couches en matériaux émetteurs de teintes différentes. Avantageusement, la couche électroluminescente présente une des structures schématiques suivantes :

  • Anode / sous-couche d'émission Bleue / sous-couche d'émission Rouge / sous-couche d'émission Verte / Cathode.
  • Anode / sous-couche d'émission Bleue / sous-couche d'émission Verte / sous-couche d'émission Rouge / Cathode.
Cette dernière structure procure, en général, le maximum de variation de son spectre d'émission avec la polarisation et sera donc préférée pour la mise en oeuvre de l'invention.An organic light-emitting diode 3 comprises, in a known manner, a light-emitting layer which can itself comprise at least two sublayers of emitting materials of different hues. Advantageously, the electroluminescent layer has one of the following schematic structures:
  • Blue Emission Anode / Emission Underlayer / Red Emission Underlayment / Green / Cathode Emission Underlayment.
  • Anode / Blue Emission Underlayment / Green Emission Underlayment / Red / Cathode Emission Underlayment.
This latter structure generally provides the maximum variation of its emission spectrum with the polarization and will therefore be preferred for the implementation of the invention.

L'émission peut être intrinsèque aux matériaux choisis pour réaliser les sous-couches ou être obtenue par dopage. D'autres empilements sont possibles à base de couches multidopées, c'est-à-dire des couches comportant au moins deux dopants qui permettent une émission de la sous-couche considérée dans au moins deux couleurs. On peut citer notamment les empilements suivants :

  • Anode/ sous-couche d'émission Bleue / sous-couche multidopée d'émission Rouge et Vert ou Rouge et Jaune / Cathode
  • Anode/ sous-couche multidopée d'émission Rouge, Vert et Bleue / Cathode
The emission may be intrinsic to the materials chosen for producing the sublayers or may be obtained by doping. Other stacks are possible based on multidoped layers, that is to say layers comprising at least two dopants that allow emission of the underlayer considered in at least two colors. These include the following stacks:
  • Anode / Blue Emission / Emission Underlayment Red / Green or Red and Yellow / Cathode
  • Red, Green, and Blue / Cathode Multidrop Emission Anode / Underlayment

La diode 3 peut comporter classiquement des couches additionnelles, notamment associées au transport et/ou confinement des porteurs de charge dans la structure, comme des couches de blocage de trous et/ou d'électrons, des couches tampon ainsi que des couches de transport de trous et/ou d'électrons, nécessaires à son bon fonctionnement. Ces couches ne sont pas explicitées dans un souci de clarté.The diode 3 may conventionally comprise additional layers, in particular associated with the transport and / or confinement of the charge carriers in the structure, such as hole and / or electron blocking layers, buffer layers as well as transport layers. holes and / or electrons, necessary for its proper functioning. These layers are not explained for the sake of clarity.

Par ailleurs, le sous-pixel supplémentaire, dépourvu de filtre, est alimenté dans des conditions de fonctionnement dites nominales, pour émettre une lumière blanche.Furthermore, the additional sub-pixel, without filter, is powered under so-called nominal operating conditions, to emit white light.

Chaque diode électroluminescente organique 3 du pixel 1 est alimentée indépendamment (courant et/ou tension) des autres par le circuit de contrôle pour que chacune émette dans la couleur correspondant à son propre filtre coloré 4. La tension et/ou le courant appliqué à chaque sous-pixel, donc à chaque émetteur de lumière, est déterminé en fonction de la couleur du sous-pixel. Il s'agit, par exemple, de faire émettre dans le rouge la diode électroluminescente organique 3 associée au filtre coloré rouge, dans le bleu la diode 3 associée au filtre bleu et dans le vert la diode 3 associée au filtre vert. Le spectre d'émission de chaque diode électroluminescente 3 se rapproche ainsi du spectre de transmission de son filtre coloré. Ainsi, la majeure partie de l'énergie lumineuse émise par une diode électroluminescente organique 3 passe au travers du filtre coloré 4 correspondant, ce qui se traduit par une augmentation importante du rendement lumineux du pixel 1. Le circuit de contrôle contrôle donc séparément des émetteurs 3 de lumière, qui ont un spectre d'émission modulable en fonction de leur tension et/ou de leur courant d'alimentation. La tension et/ou le courant d'alimentation appliqué à chaque sous-pixel est alors déterminé en fonction de sa couleur pour que son spectre d'émission se rapproche du spectre de transmission du filtre coloré 4 qui lui est associé. Les diodes électroluminescentes organiques décrites ci-dessus sont particulièrement adaptées dans la mesure où leur couleur varie fortement avec la tension et/ou le courant d'alimentation. On module alors la luminance de chaque pixel en jouant sur la durée d'application de ce courant et/ou de cette tension.Each organic light emitting diode 3 of the pixel 1 is supplied independently (current and / or voltage) of the others by the control circuit so that each emits in the color corresponding to its own color filter 4. The voltage and / or the current applied to each sub-pixel, therefore to each light emitter, is determined according to the color of the sub-pixel. It is, for example, to emit in the red the organic light emitting diode 3 associated with the red color filter, in blue the diode 3 associated with the blue filter and in the green diode 3 associated with the green filter. The emission spectrum of each light-emitting diode 3 is thus close to the transmission spectrum of its color filter. Thus, most of the light energy emitted by an organic light-emitting diode 3 passes through the corresponding color filter 4, which results in a significant increase in the luminous efficiency of the pixel 1. The control circuit thus separately controls the emitters 3 of light, which have a transmission spectrum that can be modulated according to their voltage and / or their supply current. The voltage and / or the supply current applied to each sub-pixel is then determined according to its color so that its emission spectrum is close to the transmission spectrum of the color filter 4 associated therewith. The organic light-emitting diodes described above are particularly suitable insofar as their color varies greatly with the voltage and / or the supply current. The luminance of each pixel is then modulated by varying the duration of application of this current and / or this voltage.

La diode électroluminescente organique 3 associée au filtre coloré 4 rouge, est avantageusement alimentée par un courant IR plus bas que les diodes associées aux filtres bleu et vert, ce qui permet l'obtention d'un rouge profond. De manière analogue, la diode électroluminescente organique 3 associée au filtre coloré 4 bleu, est avantageusement alimentée par un courant IB plus élevé que les diodes associées aux filtres rouge et vert, ce qui permet l'obtention d'un bleu profond.The organic light-emitting diode 3 associated with the red color filter 4 is advantageously supplied by a current I R lower than the diodes associated with the blue and green filters, which allows to obtain a deep red. Similarly, the organic light-emitting diode 3 associated with the blue color filter 4 is advantageously supplied by a higher current I B than the diodes associated with the red and green filters, which makes it possible to obtain a deep blue.

A titre d'exemple, on considère une couche émettrice réalisée à partir des sous-couches d'émission Bleue/Verte/Rouge suivantes : SEB010 dopé SEB020 (d'épaisseur environ 10nm) / TMM004 dopé TEG341 (d'épaisseur environ 7nm) / TMM004 dopé TER040 (d'épaisseur environ 20nm), tous ces matériaux étant commercialisés chez Merck.By way of example, consider an emitter layer made from the following blue / green / red emission sublayers: SEB010 doped SEB020 (about 10nm thick) / TMM004 doped TEG341 (about 7nm thick) / TMM004 doped TER040 (thickness about 20nm), all these materials being marketed at Merck.

La figure 3 détaille, pour trois sous-pixels de différentes couleurs, la luminance en fonction de la densité de courant. Les courbes G, R et B représentent l'évolution de la luminance en fonction de la densité de courant pour une diode associée respectivement à un filtre vert, rouge et bleu. A titre d'exemple, pour une diode associée à un filtre bleu, lorsque la diode est alimentée avec une densité de courant de 20mA/cm2, la luminance obtenue pour un temps trame de 20ms est de 100Cd/m2. Elle est de 250Cd/m2 pour le même sous-pixel, c'est-à-dire le même couple diode/filtre coloré, alimenté avec une densité de courant de 50mA/cm2. La luminance étant proportionnelle à la durée d'application du courant, il suffit pour ramener la luminance à 100Cd/m2 de n'appliquer le courant que pendant une fraction du temps trame t à savoir : t x 100/250.The figure 3 details, for three sub-pixels of different colors, the luminance as a function of the current density. The curves G, R and B represent the evolution of the luminance as a function of the current density for a diode associated respectively with a green, red and blue filter. By way of example, for a diode associated with a blue filter, when the diode is supplied with a current density of 20 mA / cm 2 , the luminance obtained for a frame time of 20 ms is 100 Cd / m 2 . It is 250 Cd / m 2 for the same sub-pixel, that is to say the same diode / color filter pair, supplied with a current density of 50 mA / cm 2 . The luminance being proportional to the duration of application of the current, it is sufficient to reduce the luminance to 100Cd / m 2 to apply the current only during a fraction of the frame time t namely: tx 100/250.

La figure 4 représente les spectres d'émission d'une diode qui est alimentée suivant deux densités de courant : 50 et 20mA/cm2. Les courbes C et D représentent l'évolution de la luminance en fonction de la longueur d'onde du spectre d'émission respectivement pour des densités de courant de 20mA/cm2 et 50mA/cm2. Si on compare les deux spectres d'émission de la diode, on constate que la proportion d'énergie émise dans la bande bleue, c'est-à-dire entre 450 et 495nm, par rapport à l'énergie totale augmente quand la densité de courant augmente. Les pertes au niveau du filtre bleu sont donc moins importantes lorsque l'on polarise la diode à 50mA/cm2, courbe D. La luminance du sous-pixel bleu est alors fortement augmentée quand on augmente sa densité de polarisation. Ainsi comme précédemment, pour obtenir une luminance identique, à la même diode polarisée à 20mA/cm2 pendant tout le temps trame t, il suffit alors d'alimenter la diode pendant une durée plus courte.The figure 4 represents the emission spectra of a diode which is fed at two current densities: 50 and 20 mA / cm 2 . The curves C and D represent the evolution of the luminance as a function of the wavelength of the emission spectrum respectively for current densities of 20 mA / cm 2 and 50 mA / cm 2 . If we compare the two emission spectra of the diode, we see that the proportion of energy emitted in the blue band, that is, between 450 and 495nm, relative to the total energy increases as the current density increases. The losses at the blue filter are therefore less important when the diode is polarized at 50 mA / cm 2 , curve D. The luminance of the blue sub-pixel is then greatly increased when its polarization density is increased. Thus, as before, in order to obtain the same luminance, at the same diode polarized at 20 mA / cm 2 during the entire frame time t, it is then sufficient to supply the diode for a shorter period of time.

Pour chaque sous-pixel, les critères de sélection des courants à utiliser sont dictés par les coordonnées chromatiques que l'on souhaite obtenir pour le sous-pixel en question et par la luminance obtenue après filtrage. Le tableau ci-dessous donne en fonction de la polarisation (le couple tension/courant), pour une même diode, la luminance (en Cd/m2) obtenue après filtrage ainsi que les coordonnées (X, Y) chromatiques dans un diagramme de chromacité CIE1931, pour un temps trame t de 20ms. V I Luminance (Vert) Luminance (Rouge) Luminance (Bleu) X Y 2,975 0,659 12,6175687 21,2840743 1,85441232 3,075 1,21 23,4090786 35,0653817 3,87144001 3,175 2,07 39,2788901 53,1572501 7,2437429 3,275 3,30 61,4091397 75,9675504 12,4416941 3,375 4,99 90,7088203 103,613592 19,9391214 0,66 0,33 3,475 7,13 126,969486 135,475569 29,8250871 3,575 9,78 170,623653 171,628165 42,4023372 0,28 0,6 3,675 13,1 223,836446 212,973066 58,4723248 0,28 0,599 3,775 16,9 286,26392 259,014261 78,023142 0,27 0,598 3,875 21,6 359,343857 310,43009 101,711398 0,266 0,596 3,975 27,1 445,507072 368,509646 130,565117 0,26 0,59 4,075 33,6 554,08549 432,988299 164,62027 0,25 0,59 4,275 50,0 796,948856 587,292835 254,149127 4,675 95,1 1446,65256 944,827876 496,6258 5,075 166 2410,45222 1422,65922 876,830878 0,08 0,39 For each sub-pixel, the selection criteria of the currents to be used are dictated by the chromatic coordinates that one wishes to obtain for the sub-pixel in question and by the luminance obtained after filtering. The following table gives, as a function of the polarization (the voltage / current pair), for the same diode, the luminance (in Cd / m 2 ) obtained after filtering as well as the chromatic coordinates (X, Y) in a diagram of CIE1931 chromacity, for a frame time t of 20ms. V I Luminance (Green) Luminance (Red) Luminance (Blue) X Y 2,975 0.659 12.6175687 21.2840743 1.85441232 3,075 1.21 23.4090786 35.0653817 3.87144001 3,175 2.07 39.2788901 53.1572501 7.2437429 3,275 3.30 61.4091397 75.9675504 12.4416941 3,375 4,99 90.7088203 103.613592 19.9391214 0.66 0.33 3,475 7.13 126.969486 135.475569 29.8250871 3,575 9.78 170.623653 171.628165 42.4023372 0.28 0.6 3,675 13.1 223.836446 212.973066 58.4723248 0.28 0.599 3,775 16.9 286.26392 259.014261 78.023142 0.27 0.598 3.875 21.6 359.343857 310.43009 101.711398 0.266 0.596 3,975 27.1 445.507072 368.509646 130.565117 0.26 0.59 4,075 33.6 554.08549 432.988299 164.62027 0.25 0.59 4.275 50.0 796.948856 587.292835 254.149127 4,675 95.1 1446.65256 944.827876 496.6258 5,075 166 2410.45222 1422.65922 876.830878 0.08 0.39

D'après ce tableau, si on souhaite pour le pixel, et donc pour chaque sous-pixel, une luminance égale à 100Cd/m2, les caractéristiques suivantes sont privilégiées:

  • Le sous-pixel rouge est alimenté avec une densité de courant égale à 4,99mA/cm2 pendant un temps d'application correspondant au temps trame t, par exemple 20ms, une luminance de 100Cd/m2 est alors obtenue après filtrage.
  • Le sous-pixel bleu est alimenté avec une densité de courant égale à 166mA/cm2 pendant un temps d'application égale à t x100/876 soit 2,3ms. En effet avec cette densité de courant, les coordonnés chromatique du rayonnement lumineux émis sont les plus proches du bleu le plus profond, dans la représentation CIE.
  • Le sous-pixel vert est alimenté avec une densité de courant égale à 13,1mA/cm2 pendant un temps d'application égale à t x100/223 soit 9ms. Avec cette densité de courant, les coordonnés chromatique du rayonnement lumineux émis sont les plus proches du vert désiré, dans la représentation CIE.
According to this table, if one wishes for the pixel, and therefore for each sub-pixel, a luminance equal to 100Cd / m2, the following characteristics are preferred:
  • The red sub-pixel is supplied with a current density equal to 4.99 mA / cm 2 for an application time corresponding to the frame time t, for example 20 ms, a luminance of 100 cd / m 2 is then obtained after filtering.
  • The blue subpixel is fed with a current density equal to 166 mA / cm 2 for an application time equal to t x100 / 876, ie 2.3 ms. Indeed, with this current density, the chromatic coordinates of the emitted light radiation are closest to the deepest blue in the CIE representation.
  • The green sub-pixel is fed with a current density equal to 13.1 mA / cm 2 for an application time equal to t x100 / 223 is 9 ms. With this current density, the chromatic coordinates of the emitted light radiation are closest to the desired green in the CIE representation.

De cette manière, chaque diode est alimentée dans des conditions qui favorisent l'obtention d'un spectre d'émission qui se rapproche du spectre de transmission du filtre coloré associé. Les différences d'intensité lumineuse de la diode qui résultent de ces différences de polarisation sont modulées par les durées spécifiques d'alimentation pour chaque sous pixel. Ainsi chacun des sous-pixels présente la même luminance, ici par exemple 100Cd/m2.In this way, each diode is powered under conditions that favor obtaining a transmission spectrum that is close to the transmission spectrum of the associated color filter. The differences in light intensity of the diode that result from these polarization differences are modulated by the specific power times for each sub-pixel. Thus each of the sub-pixels has the same luminance, here for example 100Cd / m 2 .

A titre d'exemple, la figure 5 illustre un circuit d'adressage d'un sous-pixel. De manière classique, un premier transistor T1, fonctionnant en interrupteur, est connecté par son électrode de commande (grille) à une ligne de sélection (SL), permettant de sélectionner la diode, c'est-à-dire le sous-pixel, à activer. Le premier transistor T1 est connecté entre une ligne de donnée (DL) et l'électrode de commande d'un deuxième transistor T2. Lorsque le transistor T1 est passant (le sous-pixel est sélectionné), la tension disponible sur la ligne de donnée DL est disponible au niveau de la grille du transistor T2. Le transistor T2 et la diode 3 sont connectés en série et alimentés entre la tension d'alimentation Vdd et un potentiel prédéfini Vcathode. Le transistor T2 est relié au potentiel Vdd tandis que la diode est reliée au potentiel Vcathode. Le niveau de courant circulant dans le transistor et dans la diode est fixé par le niveau de tension appliqué sur la grille du transistor T2. Lorsque le transistor T1 est à l'état bloqué, cette tension est maintenue constante par un condensateur C qui est disposé entre l'alimentation Vdd et la grille du transistor T2. Le condensateur C est chargé lorsque le transistor T1 est à l'état passant. En général, l'électrode pixel, c'est-à-dire l'éléctrode qui est commandée par le deuxième transistor T2 correspond à l'anode de la diode électroluminescente. Dans ce cas, la cathode est en général commune à tous les pixels et le potentiel Vcathode est fixe et constant. Cependant, on peut également prévoir des cathodes spécifiques par couleur (une cathode pour chaque couleur et pour tout le dispositif d'affichage). Ces cathodes sont indépendantes et il est possible de moduler le courant ou la tension aux bornes des différentes diodes en pilotant ces différentes cathodes. L'anode de chaque sous-pixel reste alors pilotée à un potentiel/courant, par exemple constant, comme dans l'art antérieur. Cette solution présente l'avantage de pouvoir conserver pour le circuit de commande de l'anode, au niveau de chaque sous-pixel, un circuit identique au dispositif de l'art antérieur.For example, the figure 5 illustrates an addressing circuit of a sub-pixel. In a conventional manner, a first transistor T1, operating as a switch, is connected by its control electrode (gate) to a selection line (SL), to select the diode, that is to say the sub-pixel, to activate. The first transistor T1 is connected between a data line (DL) and the control electrode of a second transistor T2. When the transistor T1 is on (the subpixel is selected), the available voltage on the data line DL is available at the gate of the transistor T2. The transistor T2 and the diode 3 are connected in series and supplied between the supply voltage V dd and a predefined voltage V cathode . The transistor T2 is connected to the potential V dd while the diode is connected to the potential V cathode . The level of current flowing in the transistor and in the diode is set by the voltage level applied to the gate of transistor T2. When the transistor T1 is in the off state, this voltage is kept constant by a capacitor C which is arranged between the supply V dd and the gate of the transistor T2. The capacitor C is charged when the transistor T1 is in the on state. In general, the pixel electrode, that is to say the electrode which is controlled by the second transistor T2 corresponds to the anode of the light emitting diode. In this case, the cathode is in general common to all the pixels and the potential V cathode is fixed and constant. However, it is also possible to provide specific cathodes per color (a cathode for each color and for the entire display device). These cathodes are independent and it is possible to modulate the current or voltage across the various diodes driving these different cathodes. The anode of each sub-pixel then remains driven at a potential / current, for example constant, as in the prior art. This solution has the advantage of being able to maintain for the control circuit of the anode, at each sub-pixel, a circuit identical to the device of the prior art.

Pratiquement, le circuit de contrôle fixe, pour chaque diode électroluminescente organique 3 du pixel 1, les conditions d'alimentation (courant et/ou tension) qui autorisent un rendement lumineux optimal avec le filtre coloré 4 correspondant. Le circuit de contrôle fixe par exemple pour chaque diode électroluminescente organique 3 du pixel 1, un courant qui définit la couleur émise par la diode et aussi sa luminance instantanée.Practically, the control circuit sets, for each organic light emitting diode 3 of the pixel 1, the supply conditions (current and / or voltage) that allow optimal light output with the corresponding color filter 4. The fixed control circuit for example for each organic light emitting diode 3 of the pixel 1, a current which defines the color emitted by the diode and also its instantaneous luminance.

La polarisation de la diode ayant été choisie pour optimiser la couleur émise on ramène la luminance obtenue à la luminance requise en jouant sur le temps d'application de cette polarisation : la diode n'est plus alimentée pendant tout le temps trame t.Since the polarization of the diode has been chosen to optimize the emitted color, the luminance obtained is brought back to the required luminance by varying the application time of this polarization: the diode is no longer supplied during the entire frame time t.

Pour cela, le circuit d'adressage de la diode 3 comporte des moyens de contrôle de la durée d'application de la tension d'alimentation et/ou du courant d'alimentation en fonction de la couleur du sous-pixel.For this, the addressing circuit of the diode 3 comprises means for controlling the duration of application of the supply voltage and / or the supply current depending on the color of the sub-pixel.

A titre d'exemple, le circuit d'adressage de la diode comporte un transistor de contrôle T3, fonctionnant en interrupteur, connecté entre l'électrode de commande (grille) du deuxième transistor T2 et la borne de la source d'alimentation connectée à la diode, de préférence, la masse. L'électrode de commande (grille) du transistor de contrôle T3 est connectée à une ligne de remise à zéro (RL) qui constitue avec le transistor de contrôle T2 des moyens de contrôle de la durée d'application du courant au travers de la diode 3.For example, the addressing circuit of the diode comprises a control transistor T3, operating as a switch, connected between the control electrode (gate) of the second transistor T2 and the terminal of the power source connected to the diode, preferably, the mass. The control electrode (gate) of the control transistor T3 is connected to a reset line (RL) which constitutes with the control transistor T2 means for controlling the duration of application of the current through the diode 3.

Lorsque le transistor T3 est bloqué, la tension sur la grille du transistor T2 est maintenue grâce à la capacité C et le courant désiré circule dans la diode 3. Lorsque le transistor T3 est passant, la capacité C se décharge et le potentiel de la borne de la source d'alimentation connectée à la diode (de préférence, la masse) est ramené sur la grille du transistor T2, bloquant le transistor T2 : plus aucun courant ne circule alors dans la diode.When the transistor T3 is off, the voltage on the gate of the transistor T2 is maintained thanks to the capacitor C and the desired current flows in the diode 3. When the transistor T3 is on, the capacitor C discharges and the potential of the terminal the power source connected to the diode (preferably the ground) is returned to the gate of the transistor T2, blocking the transistor T2: no current then flows in the diode.

La ligne de remise à zéro (RL) et le transistor de contrôle T3 permettent ainsi de fixer, pendant chaque période trame Δt, une durée maximale pendant laquelle la diode est alimentée. De cette manière, les moyens de contrôle de la durée d'application des conditions d'alimentation (tension/courant) permettent de moduler, sur le temps trame, la luminance moyenne de chaque sous-pixel, c'est-à-dire qu'ils permettent d'obtenir une luminance moyenne prédéterminée pendant une période prédéterminée.The reset line (RL) and the control transistor T3 thus make it possible to set, during each frame period Δt, a maximum duration during which the diode is energized. In this way, the control means of the duration of application of the supply conditions (voltage / current) makes it possible to modulate, on the frame time, the average luminance of each sub-pixel, that is to say that they make it possible to obtain an average luminance predetermined for a predetermined period.

De manière classique, le circuit de contrôle fixe périodiquement, pour une période trame Δt, par exemple de 20ms, les coordonnées chromatiques du pixel 1 et sa luminance en modulant les luminances des sous-pixels. Ainsi, à chaque début de période Δt, le circuit de contrôle sélectionne les sous-pixels 2 nécessaires pour obtenir les coordonnées chromatiques du pixel et contrôle la luminance de chacun de ces sous-pixels 2.In a conventional manner, the control circuit periodically sets, for a frame period Δt, for example 20 ms, the chromatic coordinates of the pixel 1 and its luminance by modulating the luminances of the sub-pixels. Thus, at each beginning of period Δt, the control circuit selects the sub-pixels 2 necessary to obtain the chromatic coordinates of the pixel and controls the luminance of each of these sub-pixels 2.

Pour une luminance donnée, les transistors de contrôle T3 associés à des sous-pixels de couleurs différentes sont conducteurs pendant des durées ton qui dépendent de cette couleur (ton ≤ Δt) pendant chaque période Δt. La durée tient compte des différences de luminance instantanée existant entre les différents sous-pixels d'un même pixel en raison des différences de leur tension et/ou courant d'alimentation. Pour obtenir une luminance moyenne donnée sur une période Δt, le circuit de contrôle contrôle la durée ton d'alimentation de chacun des sous-pixels 2. La durée d'application ton de la tension d'alimentation ou du courant d'alimentation peut être réglée par l'anode ou par la cathode.For a given luminance, the control transistors T3 associated with sub-pixels of different colors are conductive for durations t on which depend on this color (t on ≤ Δt) during each period Δt. The duration takes into account the differences in instantaneous luminance existing between the different sub-pixels of the same pixel because of the differences in their voltage and / or supply current. To obtain an average luminance data on a period .DELTA.t, the control circuit controls the period t power on each of the sub-pixels 2. The application time t on of the supply voltage or the supply current can be adjusted by the anode or the cathode.

A titre d'exemple, le circuit d'adressage illustré à la figure 5 et qui coopère avec le circuit de contrôle a été réalisé à l'aide de transistors de type n, mais de manière analogue, un circuit pourrait être réalisé à partir d'un transistor de type p comme illustré à la figure 6.For example, the addressing circuit illustrated in FIG. figure 5 and which cooperates with the control circuit has been realized using n-type transistors, but similarly, a circuit could be made from a p-type transistor as shown in FIG. figure 6 .

Dans des variantes de réalisation illustrées aux figures 7 et 8, le transistor T3 peut être disposé en série avec la diode pour, à l'état bloqué, bloquer le courant circulant dans la diode. Il pourrait être également monté en parallèle de la capacité.In variant embodiments illustrated at Figures 7 and 8 , the transistor T3 may be arranged in series with the diode for, in the off state, to block the current flowing in the diode. It could also be mounted in parallel with the capacity.

Ainsi, comme illustré sur la figure 9, la diode 3 associée au filtre rouge est polarisée avec un courant plus faible que les autres sous-pixels pour obtenir le maximum d'efficacité d'émission dans la bande rouge. Pour obtenir une luminance du sous-pixel rouge qui est comparable à celle des autres sous-pixels, on choisit de polariser la diode pendant un temps plus long, par exemple, pendant tout la période trame Δt. Inversement, la diode 3 associée au filtre bleu est polarisée avec un courant plus fort que les autres sous-pixels pour obtenir le maximum d'efficacité d'émission dans la bande bleue, elle peut donc être polarisée pendant un temps plus court. Pour obtenir une luminance comparable à celle des autres sous-pixels, on choisira de polariser pendant une durée ton(B) inférieure à la durée d'alimentation ton(G) du sous-pixel vert, elle-même inférieure à la durée d'alimentation ton(R) du sous-pixel rouge.So, as illustrated on the figure 9 , the diode 3 associated with the red filter is polarized with a lower current than the other sub-pixels to obtain the maximum emission efficiency in the red band. To obtain a luminance of the red sub-pixel which is comparable to that of the other sub-pixels, it is chosen to polarize the diode for a longer time, for example, during the entire frame period Δt. Conversely, the diode 3 associated with the blue filter is biased with a current stronger than the other sub-pixels to obtain the maximum emission efficiency in the blue band, it can be polarized for a shorter time. To obtain a luminance comparable to that of the other sub-pixels, it will be chosen to polarize for a duration t on (B) less than the supply duration t on (G) of the green sub-pixel, itself less than the duration power supply on (R) of the red subpixel.

Pratiquement, le produit de la luminance instantanée L de la diode par sa durée d'alimentation (Lxton) correspond à la luminance moyenne du sous-pixel sur la période Δt. La luminance globale du pixel 1 dépend alors de la luminance moyenne des différents sous-pixels sélectionnés.Practically, the product of the instantaneous luminance L of the diode by its duration of supply (Lxt on ) corresponds to the average luminance of the sub-pixel over the period Δt. The overall luminance of pixel 1 then depends on the average luminance of the different selected subpixels.

Ainsi, la tension ou le courant d'alimentation de chacune des diodes organiques électroluminescentes 3 étant fixé en fonction de la couleur du sous-pixel correspondant (VR, VG, VB ou IR, IB, IG), la couleur du pixel 1 et sa luminance sont déterminées par le circuit de contrôle par sélection des sous-pixels appropriés (commande SL de la figure 3) et modulation de la durée d'alimentation ton de chacun des sous-pixels 2 de couleur.Thus, the voltage or the supply current of each of the organic electroluminescent diodes 3 being fixed as a function of the color of the corresponding sub-pixel (V R , V G , V B or I R , I B , I G ), the the color of the pixel 1 and its luminance are determined by the control circuit by selection of the appropriate sub-pixels (SL command of the figure 3 ) and modulation of the supply duration t on each of the sub-pixels 2 of color.

Comme illustré à la figure 9, les durées d'alimentation des diodes bleue, verte et rouge sont croissantes (ton(B)<ton(G)<ton(R)) pendant la période Δt, l'alimentation de chaque sous-pixel 2 de couleur peut être constituée par une impulsion unique dont la durée (ton) à l'état haut est fixée par les signaux RL du circuit de contrôle.As illustrated in figure 9 the feeding times of the blue, green and red diodes are increasing (t on (B) <t on (G) <t on (R)) during the period Δt, the supply of each color sub-pixel 2 may be constituted by a single pulse whose duration (t on ) in the high state is set by the signals RL of the control circuit.

L'invention n'est pas limitée aux modes de réalisation décrits ci-dessus. En particulier, le circuit d'adressage des figures 5 à 8 peut être remplacé par tout circuit permettant d'adapter la tension et/ou le courant d'alimentation d'un sous-pixel de couleur pour que son spectre d'émission se rapproche du spectre de transmission du filtre coloré du sous-pixel, et d'adapter la durée d'alimentation ton de la diode en fonction de la couleur du sous-pixel, pour obtenir une luminance moyenne prédéterminée pendant une période prédéterminée Δt.The invention is not limited to the embodiments described above. In particular, the addressing circuit of the Figures 5 to 8 can be replaced by any circuit for adapting the voltage and / or the supply current of a color sub-pixel so that its emission spectrum is close to the transmission spectrum of the color filter of the sub-pixel, and to adapt the diode supply time t on the color of the sub-pixel, to obtain a predetermined average luminance for a predetermined period Δt.

Dans un autre mode de réalisation particulier, le système d'affichage également appelé dispositif d'affichage comporte une matrice de pixels 1 qui est identique aux modes de réalisation précédents. Le dispositif d'affichage comporte également un circuit d'adressage spécifique à chaque sous-pixel 2 afin de sélectionner le sous-pixel 2 désiré et de contrôler sa durée d'alimentation et ses conditions d'alimentation. Ce circuit d'adressage spécifique peut être celui représenté, par exemple, aux figures 5 à 8. Le dispositif d'affichage comporte, comme précédemment, un circuit de contrôle qui coopère avec les différents circuits d'adressage de la matrice de pixels 1 pour obtenir l'image désirée, tant au niveau des couleurs que des niveaux de gris. Le circuit de contrôle gère l'ensemble des sous-pixels 2 de la matrice afin d'émettre l'image désirée.In another particular embodiment, the display system also called display device comprises a matrix of pixels 1 which is identical to the previous embodiments. The display device also comprises an addressing circuit specific to each sub-pixel 2 in order to select the desired sub-pixel 2 and to control its duration of supply and its supply conditions. This specific addressing circuit may be that represented, for example, Figures 5 to 8 . The display device comprises, as before, a control circuit which cooperates with the different addressing circuits of the pixel array 1 to obtain the desired image, both in terms of colors and gray levels. The control circuit manages all the sub-pixels 2 of the matrix in order to emit the desired image.

Chaque circuit d'adressage de sous-pixel 2, comporte une borne de remise à zéro qui contrôle la durée d'alimentation du sous-pixel 2, c'est-à-dire la durée d'alimentation de l'élément émetteur de lumière 3. Chaque circuit d'adressage comporte également une borne de sélection qui permet de définir si l'émetteur de lumière 3 du sous-pixel 2 doit être alimenté ou non en courant. Chaque circuit d'adressage comporte encore une borne de contrôle de l'alimentation qui permet de moduler les conditions d'alimentation du sous-pixel 2. Comme expliqué précédemment, la cathode peut être commune à des sous-pixels d'une couleur déterminée, donc à un groupe de sous-pixels 2, ou la cathode peut être spécifique à chaque sous-pixel 2.Each sub-pixel addressing circuit 2 has a reset terminal which controls the sub-pixel 2 power-up time, i.e. the power-on time of the light-emitting element. 3. Each addressing circuit also includes a selection terminal which makes it possible to define whether the light emitter 3 of the sub-pixel 2 must be powered or not. current. Each addressing circuit further comprises a power control terminal which makes it possible to modulate the supply conditions of the sub-pixel 2. As explained above, the cathode may be common to sub-pixels of a given color, therefore to a group of sub-pixels 2, or the cathode may be specific to each sub-pixel 2.

Comme dans les modes de réalisation précédents, illustrés aux figures 5 à 8, l'entrée de sélection du sous-pixel 2 peut être constituée par la borne de commande d'un premier transistor T1. Selon la valeur de la ligne de sélection SL associée, le premier transistor T1 est dans un état passant ou bloqué ce qui a pour effet d'autoriser ou non le passage d'un courant dans l'émetteur de lumière 3 du sous-pixel 2.As in the previous embodiments, illustrated in Figures 5 to 8 , the selection input of the sub-pixel 2 may be constituted by the control terminal of a first transistor T1. According to the value of the associated selection line SL, the first transistor T1 is in an on or off state which has the effect of allowing or not the passage of a current in the light emitter 3 of the sub-pixel 2 .

L'entrée de contrôle des conditions d'alimentation du sous-pixel 2 peut être constituée par une borne d'entrée du premier transistor T1 dont la borne de sortie est connectée à la borne de commande du second transistor T2. De cette manière suivant la valeur appliquée sur la ligne de contrôle, également appelée ligne de donnée DL, le second transistor T2 module la quantité de courant qui peut être appliquée sur l'émetteur de lumière 3. La modulation du courant dans l'émetteur de lumière 3 n'est effective que si le premier transistor T1 est dans un état passant.The control input of the supply conditions of the sub-pixel 2 may be constituted by an input terminal of the first transistor T1 whose output terminal is connected to the control terminal of the second transistor T2. In this way, following the value applied on the control line, also called DL data line, the second transistor T2 modulates the amount of current that can be applied to the light emitter 3. The modulation of the current in the transmitter of light 3 is effective only if the first transistor T1 is in an on state.

L'entrée de remise à zéro du sous-pixel 2 peut être constituée par la borne de commande du troisième transistor T3 qui est connecté entre la borne de commande du second transistor T2 et la masse ou la tension d'alimentation Vdd. De cette manière, selon la tension appliquée sur la borne de commande du troisième transistor T3, le second transistor T2 est dans un état bloqué ou passant.The reset input of the sub-pixel 2 may be constituted by the control terminal of the third transistor T3 which is connected between the control terminal of the second transistor T2 and the ground or the supply voltage V dd . In this way, depending on the voltage applied to the control terminal of the third transistor T3, the second transistor T2 is in a blocked or on state.

Dans ce mode de réalisation particulièrement avantageux car compact, les différents circuits d'adressage associés à une couleur de sous-pixel 2, c'est-à-dire à une couleur de filtre coloré 4 sont connectés à la même ligne de remise à zéro RL. Le circuit de contrôle est connecté à tous les sous-pixels 2 par l'intermédiaire de leur circuit d'adressage respectif. Le circuit de contrôle est connecté indépendamment à chaque sous-pixel 2 par une ligne de sélection SL spécifique et par une ligne de contrôle des conditions d'alimentation DL spécifique. Le circuit de contrôle est également connecté aux différents sous-pixels 2 par des lignes de remise à zéro RL qui fixent la durée d'alimentation ton du sous-pixel 2. Cependant, ces lignes de remise à zéro sont spécifiques à une couleur de sous-pixel 2. Ainsi, le circuit de contrôle comporte, autant de lignes de remise à zéro RL qu'il existe de sous-pixels 2 de couleurs différentes dans un pixel 1. Il en va de même des entrées de remise à zéro dans un pixel 1. Au contraire, le circuit de contrôle comporte autant de lignes de sélection SL et de lignes de contrôle des conditions d'alimentation DL que de sous-pixels 2 dans la matrice. De cette manière, il est possible de réduire la quantité de lignes indépendantes dans le dispositif d'affichage, tout en assurant une indépendance d'utilisation des différents sous-pixels 2 et une augmentation des performances énergétiques. La ligne de remise à zéro RL peut être physiquement commune à tous les sous pixels d'une même couleur. Ce peut être le cas par exemple, lorsque la ligne de remise à zéro est connectée à l'anode ou à la cathode d'une diode.In this particularly advantageous embodiment because compact, the different addressing circuits associated with a sub-pixel color 2, that is to say to a colored filter color 4 are connected to the same reset line RL. The control circuit is connected to all the sub-pixels 2 via their respective addressing circuit. The control circuit is connected independently to each sub-pixel 2 by a specific selection line SL and by a control line of the specific supply conditions DL. The control circuit is also connected to the different sub-pixels 2 by reset lines RL which set the duration of power supply t on the sub-pixel 2. However, these reset lines are specific to a color of sub-pixel 2. Thus, the control circuit has as many RL reset lines as there are sub-pixels 2 of different colors in a pixel 1. The same is true of the reset entries in On the contrary, the control circuit has as many selection lines SL and control lines of the power conditions DL as subpixels 2 in the matrix. In this way, it is possible to reduce the amount of independent lines in the display device, while ensuring independence of use of different sub-pixels 2 and an increase in energy performance. The reset line RL can be physically common to all sub pixels of the same color. This may be the case for example, when the reset line is connected to the anode or the cathode of a diode.

De manière générale selon les différents circuits d'adressage illustrés aux figures 5 et 6, le premier transistor T1 est connecté entre la ligne de contrôle des conditions d'alimentation DL et l'électrode de commande du second transistor T2. La diode 3 du sous-pixel 2 considéré est connectée en série avec le second transistor T2 entre la tension alimentation Vdd et le potentiel prédéfini de la cathode Vcathode. Le condensateur C et le troisième transistor T3 sont connectés en série entre la tension d'alimentation Vdd et la masse. La borne commune du condensateur C et du troisième transistor T3 est connectée à la borne de commande du second transistor T2 et au premier transistor T1. La ligne de remise à zéro RL est connectée à une électrode de commande du troisième transistor T3. La borne de commande du premier transistor T1 est pour sa part connectée à la ligne de sélection SL.In general, according to the different addressing circuits illustrated in FIGS. Figures 5 and 6 the first transistor T1 is connected between the control line of the supply conditions DL and the control electrode of the second transistor T2. The diode 3 of the sub-pixel 2 in question is connected in series with the second transistor T2 between the supply voltage V dd and the predefined potential of the cathode V cathode . The capacitor C and the third transistor T3 are connected in series between the supply voltage V dd and the ground. The common terminal of the capacitor C and the third transistor T3 is connected to the control terminal of the second transistor T2 and to the first transistor T1. The reset line RL is connected to an electrode of control of the third transistor T3. The control terminal of the first transistor T1 is connected to the selection line SL.

En ce qui concerne les circuits d'adressage illustrés aux figures 7 et 8, le premier transistor T1 est connecté entre la ligne de contrôle des conditions d'alimentation DL et l'électrode de commande du second transistor T2. La diode 3 du sous-pixel 2 considéré est connectée en série avec les second T2 et troisième T3 transistors entre la tension alimentation Vdd et le potentiel prédéfini appliqué à la cathode Vcathode. Le condensateur C est connecté entre la tension d'alimentation Vdd et la borne de commande du second transistor T2 ou entre la masse et la borne de commande du second transistor T2. La ligne de remise à zéro RL est connectée à l'électrode de commande du troisième transistor T3. Pour sa part la borne de commande du premier transistor T1 est connectée à la ligne de sélection SL. Dans ce cas de figure la position relative des second T2 et troisième T3 transistors entre la diode et la tension d'alimentation Vdd n'est pas importante.With regard to the addressing circuits illustrated in Figures 7 and 8 the first transistor T1 is connected between the control line of the supply conditions DL and the control electrode of the second transistor T2. The diode 3 of the sub-pixel 2 in question is connected in series with the second T2 and third T3 transistors between the supply voltage V dd and the predefined potential applied to the cathode V cathode . The capacitor C is connected between the supply voltage V dd and the control terminal of the second transistor T2 or between the ground and the control terminal of the second transistor T2. The reset line RL is connected to the control electrode of the third transistor T3. For its part, the control terminal of the first transistor T1 is connected to the selection line SL. In this case, the relative position of the second T2 and third T3 transistors between the diode and the supply voltage Vdd is not important.

A titre d'exemple, illustré à la figure 10, la matrice de pixels 1 comporte quatre pixels 11, 12, 13 et 14 qui sont constitués chacun par trois sous-pixels 2 dits bleu « B », vert « G » et rouge « R ». Le circuit de contrôle comporte une seule ligne de remise à zéro RLR associée aux sous-pixels rouge, une seule ligne de remise à zéro RLG associée aux sous-pixels vert et une seule ligne de remise à zéro RLB associée aux sous-pixels bleu. Le circuit de contrôle comporte également autant de lignes de sélection que de sous-pixels (ici douze lignes de sélection SL1-SL12) et autant de ligne de contrôle que de sous-pixels (ici douze lignes de contrôle DL1-DL12)For example, illustrated in figure 10 , the matrix of pixels 1 comprises four pixels 1 1 , 1 2 , 1 3 and 1 4 which each consist of three sub-pixels 2 called blue "B", green "G" and red "R". The control circuit comprises a single reset line RL R associated with the red subpixels, a single reset line RL G associated with the green subpixels and a single reset line RL B associated with the sub-pixels. blue pixels. The control circuit also has as many selection lines as subpixels (here twelve selection lines SL 1 -SL 12 ) and as many control lines as subpixels (here twelve control lines DL 1 -DL 12 )

La ligne de remise à zéro RL contrôlant la durée d'alimentation des sous-pixels 2 d'une même couleur, tous les sous-pixels rouge sont alimentés pendant une première durée prédéterminée ton(R), tous les sous-pixels vert sont alimentés pendant une seconde durée prédéterminée ton(G) et tous les sous-pixels bleu sont alimentés pendant une troisième durée prédéterminée ton(B). Les différents sous-pixels 2 sont alimentés sous réserve que le premier transistor T1 soit dans un état passant, c'est-à-dire qu'ils aient été sélectionnés pour émettre de la lumière. De cette manière, un sous-pixel 2 est alimenté si l'information sur sa ligne de sélection SL l'autorise et le sous-pixel 2 n'est alors alimenté que pendant la durée qui est définie par la ligne de remise à zéro RL.The reset line RL controlling the duration of supply of the sub-pixels 2 of the same color, all the red sub-pixels are fed during a first predetermined duration t on (R) , all the green sub-pixels are fed for a predetermined second time t on (G) and all Blue sub-pixels are fed for a third predetermined duration t on (B) . The different sub-pixels 2 are fed with the proviso that the first transistor T1 is in an on state, that is, they have been selected to emit light. In this way, a sub-pixel 2 is fed if the information on its selection line SL authorizes it and the sub-pixel 2 is then fed only for the duration which is defined by the reset line RL .

Dans ce mode de réalisation particulier, la modulation de la luminance de chaque sous-pixel 2 et donc du pixel 1 est réalisée en modulant la tension d'alimentation aux bornes de chaque sous-pixel 2. En effet, comme cela a été précisé précédemment, selon les conditions d'alimentation de chaque diode 3, il y a modulation de la couleur émise, mais également de la luminance instantanée. Il y a donc pour une condition d'alimentation donnée, une couleur et une luminance instantanée prédéfinies. De ce fait, la modulation de la luminance pour une couleur déterminée est réalisée en modulant pour chacun des sous-pixels 2 les conditions d'alimentation. Chaque sous-pixel 2 reste bien entendu alimenté dans une gamme telle que la couleur émise est proche de celle du filtre colorée 4 associée de manière à conserver un intérêt énergétique à cette architecture. La couleur émise par le sous-pixel 2 est définie par l'intersection entre le spectre de transmission du filtre coloré et le spectre d'émission de l'élément émetteur de lumière 3.In this particular embodiment, the modulation of the luminance of each sub-pixel 2 and thus of the pixel 1 is carried out by modulating the supply voltage at the terminals of each sub-pixel 2. Indeed, as has been previously stated according to the supply conditions of each diode 3, there is modulation of the emitted color, but also of the instantaneous luminance. There is therefore for a given supply condition, a color and a luminance instant predefined. As a result, the modulation of the luminance for a given color is achieved by modulating for each of the sub-pixels 2 the supply conditions. Each sub-pixel 2 naturally remains fed in a range such that the emitted color is close to that of the associated colored filter 4 so as to maintain an energetic interest in this architecture. The color emitted by the sub-pixel 2 is defined by the intersection between the transmission spectrum of the color filter and the emission spectrum of the light-emitting element 3.

Dans un dispositif d'affichage comportant ce circuit de contrôle associé à une pluralité de pixels 1 identiques à coordonnées chromatiques variables avec des sous-pixels 2 et leur circuit d'adressage associé, les conditions de fonctionnement sont fixées de la manière suivante.In a display device comprising this control circuit associated with a plurality of identical pixels 1 with variable chromaticity coordinates with sub-pixels 2 and their associated addressing circuit, the operating conditions are fixed in the following manner.

Dans un pixel 1, chaque sous-pixel 2 (chaque émetteur de lumière 3) est alimenté suivant des conditions différentes afin de déterminer les conditions d'alimentation les plus favorables énergétiquement avec le filtre coloré 4 associé du sous-pixel 2. De cette manière, l'émetteur de lumière 3 de chaque sous-pixel 2 présente un spectre d'émission qui est le plus proche possible du spectre de transmission du spectre de transmission du filtre coloré associé.In a pixel 1, each sub-pixel 2 (each light emitter 3) is supplied under different conditions in order to determine the most favorable energy supply conditions with the color filter 4 In this way, the light emitter 3 of each sub-pixel 2 has a transmission spectrum that is as close as possible to the transmission spectrum of the transmission spectrum of the associated color filter.

Suivant les conditions d'alimentation retenues pour chaque sous-pixel 2, ces derniers présentent entre eux des luminances instantanées différentes. Chaque sous-pixel 2 est alors alimenté selon une durée prédéterminée spécifique de manière à ce que le pixel 1 correspondant émette une couleur et une luminance prédéterminées. Typiquement, les durées d'alimentation de chacun des sous-pixels sont choisies de manière à ce que le pixel émette une couleur blanche dans les conditions d'alimentation les plus favorables entre chaque émetteur de lumière 3 et le filtre coloré 4 qui lui est associé.According to the power conditions selected for each sub-pixel 2, the latter present between them different instantaneous luminances. Each sub-pixel 2 is then supplied with a specific predetermined duration so that the corresponding pixel 1 emits a predetermined color and luminance. Typically, the feed times of each of the sub-pixels are chosen so that the pixel emits a white color under the most favorable supply conditions between each light emitter 3 and the color filter 4 associated with it. .

Les lignes de remise à zéro RL étant associées à une couleur de sous-pixel, tous les sous-pixels d'une même couleur ont normalement les mêmes durées d'alimentation. De ce fait, tous les pixels émettent une lumière blanche lorsque qu'ils sont alimentés dans leur condition d'alimentation la plus favorable avec leur filtre coloré. Afin que les différents pixels émettent des couleurs et des luminances qui leurs sont propres, chaque sous-pixel est alimenté dans des conditions différentes (tension et/ou courant). Dans ce mode de réalisation, la modulation des caractéristiques du rayonnement émis par le pixel est réalisée par la modulation des conditions d'alimentation des sous-pixels qui le composent.Since the reset lines RL are associated with a sub-pixel color, all the sub-pixels of the same color normally have the same feeding times. As a result, all pixels emit white light when they are powered in their most favorable power condition with their color filter. In order for the different pixels to emit their own colors and luminances, each sub-pixel is powered under different conditions (voltage and / or current). In this embodiment, the modulation of the characteristics of the radiation emitted by the pixel is achieved by modulating the power conditions of the sub-pixels that compose it.

Dans une variante de réalisation où l'électrode pixel (l'électrode commandée par le transistor T2) représente l'anode de la diode électroluminescente la cathode est commune à tous les sous-pixels d'une même couleur, il est alors possible de réaliser le contrôle de la durée d'alimentation au moyen de la cathode. De ce cas particulier, la ligne de remise à zéro est réalisée par la cathode commune à tous les sous-pixels de la même couleur. Cette remise à zéro se traduit par l'apparition d'une différence de potentiel inférieure à une tension seuil aux bornes de la diode 3. En effet, il faut considérer que la tension de contrôle de l'anode peut varier en fonction du niveau affiché, on ne peut donc pas garantir une tension constante aux bornes de la diode. L'utilisation d'une tension seuil est alors très avantageux. Dans ce mode de réalisation, il est possible de contrôler indépendamment les conditions d'alimentation de chacune des diodes au moyen du second transistor T2. Dans le cas où l'électrode de pixel représente la cathode de la diode électroluminescente, il est également possible de faire la même modulation au moyen de l'anode qui est alors commune à tous les sous-pixels d'une même couleur. Dans ces deux modes de réalisation particuliers, le troisième transistor T3 peut être éliminé.In an alternative embodiment in which the pixel electrode (the electrode controlled by the transistor T2) represents the anode of the light emitting diode, the cathode is common to all the sub-pixels of the same color, it is then possible to realize control of the feeding time by means of the cathode. In this particular case, the reset line is made by the cathode common to all the sub-pixels of the same color. This discount zero results in the appearance of a potential difference lower than a threshold voltage at the terminals of the diode 3. Indeed, it must be considered that the control voltage of the anode can vary depending on the level displayed, it is not necessary to can not guarantee a constant voltage across the diode. The use of a threshold voltage is then very advantageous. In this embodiment, it is possible to independently control the supply conditions of each of the diodes by means of the second transistor T2. In the case where the pixel electrode represents the cathode of the light-emitting diode, it is also possible to make the same modulation by means of the anode, which is then common to all the sub-pixels of the same color. In these two particular embodiments, the third transistor T3 can be eliminated.

Ainsi, si deux pixels émettent des couleurs et/ou des luminances différentes, la seule différence qui existe entre ces deux pixels est liée aux conditions d'alimentation de chacun des sous-pixels dans chaque pixel.Thus, if two pixels emit different colors and / or luminances, the only difference that exists between these two pixels is related to the supply conditions of each of the sub-pixels in each pixel.

Claims (8)

  1. Display device characterized in that it comprises:
    - a matrix of identical organic light-emitting diodes (3) with variable chromatic coordinates and luminances,
    - a plurality of color filters (4), a color filter (4) being associated with a diode (3) to form a color sub-pixel (2),
    - an addressing circuit associated with each sub-pixels (2), with a control input of the supply time and a control input of the supply conditions of the color sub-pixel and a selection input,
    - a display device control circuit connected:
    - to control input of the supply conditions by a supply conditions control line (DL) specific to the sub-pixel (2) to modify the supply conditions of the diode (3) so as to adjust the emission spectrum of the diode and obtain the required chromatic coordinates of the sub-pixel (2),
    - to the supply time control input of each addressing circuit by a reset line (RLG, RLB, RLR) to adjust the mean luminance of the diode (3) during a first period (Δt), the reset line (RLG, RLB, RLR) being common to all the sub-pixels (2) of the same color,
    - to the selection input of each addressing circuit by a specific selection line (SL) to define if the diode (3) of the sub-pixel (2) has to be supplied or not.
    - the control circuit comprising an many selection line (SL) and supply conditions control line (DL) as sub-pixel (2) in the matrix.
  2. Display device according to claim 1, characterized in that the specific reset line (RLG, RLB, RLR) of said color of sub-pixel (2) is connected to the cathodes of the diodes (3) of said color.
  3. Display device according to claim 1, characterized in that the specific reset line (RLG, RLB, RLR) of said color of sub-pixel (2) is formed by an anode of the diodes (3) of said color.
  4. Device according to claim 1, characterized in that a first transistor (T1) being connected between the supply conditions control line (DL) and a control electrode of a second transistor (T2), the diode (3) of a sub-pixel (2) being connected in series with the second transistor (T2) between a supply voltage (Vdd) and a predefined potential (Vcathode), a capacitor (C) and a third transistor (T3) being connected in series between said supply voltage (Vdd) and ground, said capacitor (C) and the third transistor (T3) having their common terminal connected to the control terminal of the second transistor (T2) and to the first transistor (T1), the reset line (RL) is connected to a control electrode of the third transistor (T3), a control terminal of the first transistor (T1) being connected to the selection line (SL).
  5. Device according to claim 1, characterized in that a first transistor (T1) being connected between the supply conditions control line (DL) and a control electrode of a second transistor (T2), the diode (3) of a sub-pixel (2) being connected in series with second (T2) and third (T3) transistors between a supply voltage (Vdd) and a predefined potential (Vcathode), a capacitor (C) being connected between said supply voltage (Vdd) or ground and the control terminal of the second transistor (T2), the reset line (RL) is connected to a control electrode of the third transistor (T3), a control terminal of the first transistor (T1) being connected to the selection line (SL).
  6. Device according to any one of claims 1 to 5, characterized in that the structure of the organic light-emitting diode (3) is anode/blue emission sublayer /green emission sub-layer/red emission sub-layer/cathode.
  7. Device according to any one of claims 1 to 6, characterized in that a red sub-pixel is supplied with a weaker current (IR) than a green sub-pixel, itself supplied with a weaker current (IG) than a blue sub-pixel.
  8. Device according to any one of claims 1 to 5, characterized in that the structure of the organic light-emitting diode (3) is anode/blue emission sublayer/red emission sub-layer/green emission sub-layer/cathode.
EP09750011.0A 2008-05-13 2009-05-06 Improved display device based on pixels with variable chromatic coordinates Active EP2277164B1 (en)

Applications Claiming Priority (2)

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FR0802584A FR2931296B1 (en) 2008-05-13 2008-05-13 CONTROL CIRCUIT OF A PIXEL WITH VARIABLE CHROMATIC COORDINATES
PCT/FR2009/000533 WO2009141530A1 (en) 2008-05-13 2009-05-06 Improved display device based on pixels with variable chromatic coordinates

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US20110037791A1 (en) 2011-02-17
FR2931296A1 (en) 2009-11-20
KR20110007182A (en) 2011-01-21
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KR101614174B1 (en) 2016-04-20
EP2277164A1 (en) 2011-01-26

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