EP1697920A1 - Device for displaying images on an active matrix - Google Patents

Device for displaying images on an active matrix

Info

Publication number
EP1697920A1
EP1697920A1 EP04816458A EP04816458A EP1697920A1 EP 1697920 A1 EP1697920 A1 EP 1697920A1 EP 04816458 A EP04816458 A EP 04816458A EP 04816458 A EP04816458 A EP 04816458A EP 1697920 A1 EP1697920 A1 EP 1697920A1
Authority
EP
European Patent Office
Prior art keywords
modulator
transmitters
current
voltage
column
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP04816458A
Other languages
German (de)
French (fr)
Other versions
EP1697920B1 (en
Inventor
Philippe Le Roy
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
THOMSON LICENSING
Original Assignee
Thomson Licensing SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomson Licensing SAS filed Critical Thomson Licensing SAS
Publication of EP1697920A1 publication Critical patent/EP1697920A1/en
Application granted granted Critical
Publication of EP1697920B1 publication Critical patent/EP1697920B1/en
Not-in-force legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3225—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix
    • G09G3/3233—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix with pixel circuitry controlling the current through the light-emitting element
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3275—Details of drivers for data electrodes
    • G09G3/3283—Details of drivers for data electrodes in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3275—Details of drivers for data electrodes
    • G09G3/3291—Details of drivers for data electrodes in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00—Aspects of the constitution of display devices
    • G09G2300/04—Structural and physical details of display devices
    • G09G2300/0404—Matrix technologies
    • G09G2300/0417—Special arrangements specific to the use of low carrier mobility technology
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00—Aspects of the constitution of display devices
    • G09G2300/08—Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
    • G09G2300/0809—Several active elements per pixel in active matrix panels
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2300/00—Aspects of the constitution of display devices
    • G09G2300/08—Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
    • G09G2300/088—Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements using a non-linear two-terminal element
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
    • G09G2310/0243—Details of the generation of driving signals
    • G09G2310/0248—Precharge or discharge of column electrodes before or after applying exact column voltages
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
    • G09G2310/0243—Details of the generation of driving signals
    • G09G2310/0251—Precharge or discharge of pixel before applying new pixel voltage
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/06—Details of flat display driving waveforms
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/029—Improving the quality of display appearance by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/04—Maintaining the quality of display appearance
    • G09G2320/043—Preventing or counteracting the effects of ageing

Definitions

  • the present invention relates to an active matrix image display device.
  • Flat screens are increasingly used in all kinds of applications such as in motor vehicle display devices, digital cameras or mobile phones.
  • Displays are known in which light emitters are formed from organic electroluminescent cells such as OLED (Organic Light Emitting Diodes) displays.
  • OLED Organic Light Emitting Diodes
  • passive matrix OLED type displays are already widely marketed. However, they consume a lot of electrical energy and have a reduced lifespan.
  • Active matrix OLED displays have integrated electronics, and have many advantages such as reduced consumption, high resolution, compatibility with video rates and a longer lifespan than passive matrix OLED displays.
  • the display devices comprise a display panel formed in particular by a network of light emitters.
  • Each light emitter is linked to a pixel or a sub-pixel of an image to be displayed and is addressed by a network of column electrodes and row electrodes via an addressing circuit.
  • the addressing circuits notably include current modulators able to control the current passing through the emitters and therefore the luminance of each sub-pixel of the display panel.
  • these modulators are thin-film transistors, called TFT (Thin Film Transistor) transistors, made of crystalline poly-silicon using low-temperature poly crystalline silicon (LTPS) technology.
  • TFT Thin Film Transistor
  • the TFT transistors composing the same display panel have different trigger threshold voltages. Consequently, the TFT transistors supplied by the same supply voltage and controlled by identical voltages or data currents generate currents of different intensity.
  • the heterogeneity of the trigger thresholds of the crystalline poly-Silicon transistors leads to a non-uniformity of brightness of a screen formed by a matrix of such transistors. This results in differences between the luminance levels and obvious visual discomfort for the user.
  • a control circuit of an emitter comprising a comparison unit capable of comparing the drain current l d through the modulator at a reference current during a programming step of the control circuit.
  • this circuit requires the installation of a transmitter switching unit to switch the power source of the transmitter between the programming step and a step of transmitting end frame of the transmitter.
  • This switching unit includes two thin film transistors and an inverting amplifier. This circuit is difficult to manufacture and not very economical. It is known in particular from document EP 1 381 019 active matrix display devices comprising OLED transmitters, means for supplying the transmitters, modulators and means for compensating for the trigger threshold voltages of the modulators.
  • the compensation means comprise means for comparing the drain current passing through a selected transmitter with a display setpoint.
  • the transmitters are not supplied by the same supply means both during the programming phases and the successive transmission phases for displaying the images, which requires a specific electrode network for each supply mode.
  • a display device comprising OLED transmitters, means for supplying the transmitters, modulators and means for compensating the voltages of modulator trigger threshold.
  • the transmitters are supplied by the same supply means both during the programming phases and the successive transmission phases for displaying the images, but the compensation of the threshold voltages is carried out during a phase of calibration before displaying images.
  • the compensation means comprise means for measuring the drain current passing through a selected transmitter and means for comparing this drain current with a calibration instruction for this transmitter. These compensation means therefore do not make it possible to compensate for variations in trigger threshold voltages which would appear during the display phase of the images. It is known in particular from the document JP-2002/091377, US-2003/001832 and W0-2004 / 034364, active matrix display devices comprising OLED transmitters, modulators and means for compensating threshold voltage of triggering of the modulators.
  • the compensation means include means for measuring the drain current passing through a selected transmitter and means for comparing this drain current with a display setpoint. However, the means for measuring the drain current are specific to each emitter of a column.
  • the present invention relates to an active matrix image display device comprising: - several light emitters forming a network of emitters distributed in rows and columns; - Power supply means capable of simultaneously supplying current to all of the transmitters of a column, during an emission step and a step of programming the emitters; means for controlling the emission of the transmitters comprising: for each transmitter of the network, a current modulator comprising a source electrode, a drain electrode, a gate electrode, said modulator being capable of being traversed by a current of drain for supplying said transmitter, for a voltage between the drain or the source and the gate greater than or equal to a trigger threshold voltage; for each column of transmitters, column addressing means capable of successively addressing each transmitter of said column of transmitters by applying a value representative of a data setpoint to the gate electrode of the modulator associated with this transmitter, for controlling it, during a programming step, - for each line of transmitters, line selection means capable of successively selecting the transmitters of each line of transmitters, during the programming step,
  • the display device includes one or more of the following characteristics: - the power supply means of the transmitters are directly connected to each modulator of the control means; the power supply means of the transmitters are directly connected to each transmitter of a column; the power supply means of the transmitters comprise a voltage supply generator capable of supplying all the transmitters of a column, and the compensation means are capable of successively compensating the trigger threshold voltage of each modulator of all the transmitters in a column; - the compensation means further comprise: - a control generator capable of generating a control signal applied to the gate of said modulator; means for modulating the duration of said control signal as a function of the value of the data setpoint and the value of the triggering threshold voltage; the data setpoint is a data voltage and the comparison means are capable of emitting a warning signal when the voltage representative of the intensity of the drain current is equal to a number of times said data voltage; the means for modulating the duration of the piloting signal comprise: a switch connected in series with the piloting generator; - A control unit
  • FIG. 1 is a block diagram of a control and supply circuit of a transmitter according to the invention
  • - Figure 2 is a block diagram of an exemplary embodiment of a current measurement unit according to the invention
  • - Figures 3A to 3D are graphs representing the evolution over time of different voltages and currents during the process performed by the device according to the invention; in particular - FIG.
  • FIG. 1 represents an active matrix display device according to the invention. Such a device comprises a plurality of light emitters 2 forming an array of rows and columns, power supply means V dd of the emitters 2 and control means 3 for emitting the emitters. However, for the sake of simplification, a single emitter and a single supply means have been shown in FIG. 1.
  • the emitters 2 of the display panel are organic light emitting diodes. They include an anode and a cathode. They are each associated with a pixel when the panel is monochrome or with a sub-pixel when the display panel is polychrome. They emit a light intensity directly proportional to the current flowing through them.
  • the power supply means V dd of the emitters 2 comprise a DC voltage generator per column of emitters 2. This generator V dd supplies a line 4, to which all of the emitters 2 of this column are connected.
  • the control means 3 of the display device comprise an addressing circuit 6 for each transmitter, a network of selection electrodes 8 for row and addressing 10 for column and means for compensating 12 for the threshold for triggering the modulators.
  • An addressing circuit 6 is connected to each transmitter 2 of the display panel.
  • the addressing circuit shown in Figure 1 is a conventional structure circuit.
  • the anode of the transmitter forms the interface with the active matrix and the cathode of the transmitter is connected to a ground electrode or to a negative voltage.
  • the addressing circuit 6 comprises a current modulator 14, a switch 16 and a storage capacity 18.
  • the current modulator 14 is a transistor based on a technology using polycrystalline silicon (Poly-Si) or amorphous silicon (a-Si) deposited in thin layers on a glass substrate.
  • Such components include three electrodes: a drain electrode and a source electrode between which the modulated current flows, and a gate electrode to which an Idata data driving current is applied.
  • Thin Film Transistor English are of type n or p.
  • the modulator 14 shown in FIG. 1 is of the p type. Its source is connected directly to the supply electrode V dd and its drain is connected directly to the anode of the transmitter 2 so that in operation the modulated electric current flows between the source and the drain. Alternatively, when the modulator 14 is of type n, the drain is connected to the supply electrode V d and the modulated electric current then flows between the drain and the source.
  • the power supply generator V dd is directly connected to all of the modulators 14 for controlling the transmitters of a column, so that it is always capable of supplying a transmitter 2 selected and addressed whatever the stage of the process of transmitting an image frame.
  • Vdd- Switch 16 is also a transistor based on technology using polycrystalline silicon (Poly-Si) or amorphous silicon (a-Si) deposited in thin layers.
  • One of its electrodes (drain or source) is connected to the addressing electrode 10 and the other electrode (drain or source) is connected to the grid of the modulator 14. Its grid is connected to the line selection electrode 8.
  • the storage capacity 18 is arranged between the grid and the source of the modulator 14 to maintain the brightness of the transmitter 2 for an image frame duration. This capacity is adapted to substantially maintain the constant voltage on the grid of the modulator 14 during a time interval corresponding to the frame duration.
  • the array of selection 8 and addressing 10 electrodes makes it possible to select and address a specific transmitter from all of the transmitters of the display panel.
  • Each selection electrode 8 is connected to the gate of the switches 16 of one line and is adapted to transmit a selection voltage V IECT to all the emitters 2 from this line.
  • the selection voltage V se ie c t is a logic datum for selecting the transmitters.
  • Each addressing electrode 10 is connected to the source or to the drain of the switches 16 of a column and is capable of addressing a data driving current I da ta to the gate of the modulator 14 of all the addressing circuits 6 of this column as a function of a data setpoint U c . In the embodiment of the invention shown in FIG.
  • the intensity of current flowing through the transmitter is proportional to the amplitude of the current I d ata which is applied to the electrode 10.
  • the selection electrodes 8 and addressing 10 are each controlled by a corresponding control pilot 20, 22 to apply selection voltages V se ie c t and data set points U c to the transmitters.
  • V se ie c t selection voltages
  • U c data set points
  • the means for compensating for the trigger thresholds 12 are capable of compensating for the trigger threshold voltages Vt n of all of the modulators 14 addressed by the addressing electrode 10 of this column. They include an external controller 24 per column of transmitters. This controller comprises a measurement unit 26, a comparison unit 28, a pilot generator 30, a switch 32, a control unit 34 and means 36 for initializing the addressing circuits 6 of this column.
  • the measurement unit 26 is connected to the power supply electrode 4 of all the transmitters of a column.
  • the measurement unit 26 is able to measure a value representative of the drain current I d of a modulator 14 selected by the selection electrode 8 and to the grid of which a pilot current Idata is applied.
  • the comparison unit 28 comprises two input terminals suitable for receiving the data setpoint U c addressed by the control pilot 22 and a value representative of the drain current I d measured by the measurement unit 26.
  • the data setpoint U c is a data voltage.
  • the unit of comparison 28 is suitable for comparing the amplitude of the voltage representative of the drain current I d and the amplitude of the data voltage U c during a so-called programming step C of the addressing circuit 6.
  • the unit of comparison 28 includes an output terminal capable of emitting a warning signal S when the amplitude of the voltage representative of the intensity of the drain current I d and the amplitude of the data voltage U c are linked by a coefficient k of predetermined proportionality.
  • the warning signal S is a logic signal sent to the control unit 34.
  • the data setpoint is a digital data or a data intensity.
  • the pilot generator 30 is a direct current generator capable of supplying a pilot current I d at a which is a function of the data set point Uc applied to this generator.
  • the switch 32 is connected in series at the output of the pilot generator 30. It is able to switch between a closed position in which the pilot current l da ta supplies the addressing electrode 10 of all the circuits addressing 6 of the column and an open position in which the addressing circuits 6 are not addressed.
  • the control unit 34 is connected to the pilot 22, to the output of the comparison module 28 and to the switch 32 to receive the data voltage U c and the warning signal S and to control the switching of the switch 32.
  • the control unit 34 is able to command the closing of the switch 32 on reception of the data voltage U c and the opening of the latter on reception of the warning signal S.
  • the duration of the control current I d ata generated is modulated as a function of the triggering threshold voltage V tr ⁇ specific to each modulator 14 as will be explained below.
  • the initialization means 36 of the addressing circuits 6 are connected in parallel to the generator 30 so that the image of a frame is not influenced by the image of the previous frame. They are capable of emitting a square voltage to discharge the storage capacity 18 and a parasitic capacity induced by the display panel. They include a generator 38 of DC voltage and a switch 40. The switch 40 is connected to the control unit 34.
  • FIG. 2 represents an exemplary embodiment of a unit 26 for measuring a representative value of the drain current I d passing through the modulator 14 of the control circuit for which the programming step begins.
  • a measurement unit 26 is connected to the supply line 4 of the transmitters 2 of a column. It comprises a block 41 for determining the drain current I d , a low-pass filter 42, a differential block 43 and an amplifier 44.
  • the determination block 41 comprises a resistor 45, for example from 1 to 10 kilos Ohms, connected in series at line 4 supplying transmitters and an operational amplifier 46 of precision whose terminals are connected to the supply line 4 on either side of the resistor 45.
  • the output of the amplifier 46 is connected on the one hand to the low-pass filter 42 , itself connected to a negative terminal of an amplifier 47 of the differential block 43 and on the other hand to a positive terminal of this amplifier 47.
  • the differential block 43 comprises an amplifier 47 in a differential circuit and a network of four resistors of the same value.
  • a first resistor R1 is connected between the positive input of the amplifier 47 and a ground electrode.
  • a second resistor R2 is connected between the positive input of the amplifier 47 and the output of the amplifier 46.
  • a third resistor is connected between the negative input of the amplifier 47 and the output of the low-pass filter 42.
  • a fourth resistor R4 is connected between the negative input of the amplifier 47 and its output terminal.
  • the output of the differential block 43 is connected to an amplifier 44 having a high gain.
  • the determination block 41 is capable of measuring the total current supplying all of the emitters of a column, including the drain current passing through the modulator 14 during the programming of the latter. This drain current then appears at the terminals of the resistor 45 in the form of a current pulse.
  • the output voltage of the determination block 41 is proportional to the total current passing through the line 4. This voltage is applied to the terminals of the low-pass filter 42 which eliminates the high frequency component therefrom.
  • This high frequency component corresponds to the current pulse generated by the modulator 14 supplied by the line 4 and which is during a programming step.
  • the amplifier 47 of the differential unit receives at its negative input a voltage proportional to the total supply current of line 4, except the component corresponding to the drain current passing through the modulator 14 and, on its positive input a voltage proportional to the total current on line 4.
  • the output voltage V d it f of the differential block 43 is equal to the resistor 45 multiplied by the drain current of the modulator 14 which is at during a programming stage.
  • This voltage is amplified by amplifier 44 then is compared with the data voltage U c in the comparison block 28 as explained above.
  • the image display device is a voltage control circuit of the modulators.
  • the DC generator 30 is then replaced by a voltage supply generator and preferably by a ramp voltage generator.
  • the amplitude of the ramp voltage is modulated as a function of the value of the amplitude of the data setpoint, emitted by the column control pilot 22.
  • the duration of the ramp voltage addressed to the addressing circuits 6 is also modulated as a function of the triggering threshold voltage Vt n , by the comparison means 28 and the control unit 34.
  • the four graphs of FIGS. 3A to 3D represent the steps of addressing a transmitter when it is produced by the display device according to the invention.
  • stages include a stage A of initialization of an addressing circuit 6, an intermediate stage B, a stage C of programming of this one and a stage D of emission of light proportional to the pilot current I d ata previously program.
  • the line control pilot 20 applies a voltage V se i e c t to the electrode 8 of the selected line. This voltage is applied to the grid of the switches 16, connected to the line electrode 8.
  • the control unit 34 of the external controller 24 of a column controls the closing of the switch 40 and a voltage Vj n jt generated by the generator 38, is applied to the addressing electrode 10 of this column.
  • the voltage Vjni t is applied to a terminal of the storage capacity 18 to discharge it, the switch 16 being closed.
  • Step B is short-lived and has the sole function of creating a dead time to separate the initialization and programming steps in order to avoid short circuits.
  • the column control pilot 22 transmits a data voltage U c
  • the control unit 34 commands the closing of the switch 32 and the pilot generator 30 generates a pilot current I d at a -
  • the current I data generates a potential difference between the gate and the source of the modulator 14
  • Vt h of the modulator 14 When this potential difference is greater than the triggering threshold voltage Vt h of the modulator 14, a drain current I d is established between the drain and the source of the modulator.
  • the intensity of this drain current I which corresponds to part of the current flowing in line 4, is measured by the measurement unit 26 and a voltage representative of this drain current is compared to the data voltage U c addressed by the pilot 22.
  • the amplitude of the intensity of this current is compared to the intensity of the drain current.
  • the drain current generated passes through the emitter 2 which lights up.
  • the generator V dd supplies power to the transmitter 2.
  • the comparison unit 28 compares the data voltage U c to the voltage representative of the amplitude of the drain current I d .
  • the amplitude of the drain current increases quadratic as a function of the voltage between the gate and the source of the modulator.
  • the driving current I da t generated by the generator 30 causes an accumulation of charges in the storage capacitor 18 connected to the gate of the modulator 14. This accumulation of charges causes increased voltage V gs between the gate and the source of the modulator 14 and consequently, the progressive increase of the drain current Id.
  • the comparison unit 28 sends a warning signal S to the control unit 34 which in turn commands the closing of the switch 32.
  • the programming step is finished. The duration of the programming step is variable and depends on the triggering threshold of each current modulator in the column.
  • the addressing signal of each transmitter is therefore modulated in duration as a function of the triggering threshold voltages.
  • the current I data is of the order of a few microamps so that the storage capacity 18 and the parasitic capacities generated by the structure of the display panel are quickly charged.
  • the programming time is short, approximately of the order of a few microseconds ( ⁇ s).
  • Step C the storage capacity 18 has been sufficiently charged so that the transmitter 2 continues to transmit after its addressing for the duration of the image frame, while always being supplied from the generator V d d-
  • the means for compensating the trigger threshold 12 are able to modulate the duration of the control signal I d ata in turn for each modulator of the column of transmitters.
  • Step D begins at the end of the programming step and ends at the end of the selection of line 8.
  • step D the transmitter 2 is still selected but its programming is finished; it continues to transmit as a function of this programming thanks to the voltage stored across the terminals of the capacitor 28.
  • the drain current I d continues to cross the modulator 14 and the transmitter 2 until the voltage across the storage capacity 18 is discharged during a new step A of initialization of this addressing circuit.
  • step C of programming an addressing circuit 6 associated with a first transmitter 2 the control pilots 20, 22 and the compensation means 12 are used for the programming of another circuit of addressing associated with a second transmitter in the same column.
  • the first transmitter 2 continues to transmit.
  • FIG. 4 represents an alternative embodiment of the invention in which the control means 3 are identical to those shown in FIG. 1.
  • the addressing circuit 6 driving a light emitter 2 with conventional structure is replaced by a addressing circuit 66 driving a light emitter with a so-called inverted structure.
  • the cathode of the emitters 52 forms the interface with the active matrix and the anode of the emitters 52 is connected to the power supply generator V dd -
  • the source of the modulator 54 is connected to a ground or to a negative voltage generator.
  • the cathode of the emitter 52 is connected to the drain of the modulator 54.
  • the storage capacity 58 is connected between the grid and the source of the modulator 54.
  • a switch 56 is addressed in current I da t a by an addressing electrode 60 and is selected by a selection electrode 68.
  • the power supply generator V dd is directly connected to all the transmitters 52 of all the columns without the interposition of a switching unit. Consequently, this generator V dd supplies power to all the transmitters 52 during the programming step C and during the step D throughout the duration of the image frame. Consequently, it is the power supply means V ss which are connected separately to the compensation means 12.
  • each power supply generator V ss is capable of supplying all of the emitters 2 of a column and since each addressing electrode 60 is also capable of addressing all of the emitters 2 of a column, the means compensation 12 are able to successively compensate the trigger threshold voltage V th of all the modulators 14 of a column. Furthermore, as the compensation means 12 determine the duration of the signal before each frame, the variations in the triggering threshold linked to the aging of the modulators are automatically compensated.
  • no switching unit is interposed between the generator V d or V ss and the modulator 14 or the transmitter 52 to switch between two power sources of the transmitter during the programming and transmission process of this one.
  • the useful light-emitting area of the pixels is increased.
  • the control means are simplified and their implementation is facilitated.
  • the means for compensating all the columns compensate for the dispersions of the triggering threshold voltages of the modulators of control circuits of an active matrix screen.
  • the unit 26 for measuring the current passing through a modulator during a programming step C makes it possible to dispense with a switching unit associated with each transmitter.
  • the intensity of the driving current I ata is high, the stray capacitances generated by the addressing column of the display panel are quickly loaded. As a result, the display device is addressed instantly.

Abstract

The invention relates to an active-matrix display device which comprises: an array of light emitters, each emitter being supplied by power supply means; a current modulator having a trip-threshold voltage, said modulator being able to be addressed by applying a data setpoint to one of its terminals and a drain current being able to flow through said modulator in order to control said emitter; and trip-threshold voltage compensation means comprising a comparator for comparing the value of the drain current with the value of the data setpoint during a programming step. The power supply means for the emitters are capable of supplying the emitters during the programming step.

Description

Dispositif d'affichage d'images à matrice active. La présente invention concerne un dispositif d'affichage d'images à matrice active. Les écrans plats sont de plus en plus utilisés dans toutes sortes d'applications telles que dans des dispositifs d'affichage de véhicule automobile, dans des appareils photos numériques ou dans des téléphones portables. Il est connu des afficheurs dans lesquels les émetteurs de lumière sont formés à partir de cellules organiques électroluminescentes tels que les afficheurs OLED (Organic Light Emitting Diodes). En particulier, les afficheurs de type OLED à matrice passive sont déjà largement commercialisés. Cependant, ils consomment beaucoup d'énergie électrique et ont une durée de vie réduite. Les afficheurs OLED à matrice active comportent une électronique intégrée, et présentent de nombreux avantages tels qu'une consommation réduite, une haute résolution, une compatibilité avec les cadences vidéo et une durée de vie plus longue que les afficheurs OLED à matrice passive. Classiquement, les dispositifs d'affichage comprennent un panneau de visualisation formé notamment par un réseau d'émetteurs de lumière. Active matrix image display device. The present invention relates to an active matrix image display device. Flat screens are increasingly used in all kinds of applications such as in motor vehicle display devices, digital cameras or mobile phones. Displays are known in which light emitters are formed from organic electroluminescent cells such as OLED (Organic Light Emitting Diodes) displays. In particular, passive matrix OLED type displays are already widely marketed. However, they consume a lot of electrical energy and have a reduced lifespan. Active matrix OLED displays have integrated electronics, and have many advantages such as reduced consumption, high resolution, compatibility with video rates and a longer lifespan than passive matrix OLED displays. Conventionally, the display devices comprise a display panel formed in particular by a network of light emitters.
Chaque émetteur de lumière est lié à un pixel ou à un sous-pixel d'une, image à visualiser et est adressé par un réseau d'électrodes de colonne et d'électrodes de ligne via un circuit d'adressage. Les circuits d'adressage comprennent notamment des modulateurs de courant aptes à piloter le courant traversant les émetteurs et donc la luminance de chaque sous-pixel du panneau d'affichage. Dans une matrice active, ces modulateurs sont des transistors à couches minces, appelés transistors TFT (Thin Film Transistor), fabriqués en poly-Silicium cristallin selon la technologie du silicium poly cristallin basse température (LTPS). Cependant, cette technique introduit des variations spatiales locales de la tension de seuil de déclenchement des transistors à couches minces. Ces variations sont dues au fait que les joints et les dimensions des grains du poly-Silicium ne sont pas suffisamment maîtrisables pendant la phase de cristallisation du Silicium amorphe en Silicium poly-cristallin. Ainsi, les transistors TFT composant un même panneau d'affichage, présentent des tensions de seuil de déclenchement différentes. En conséquence, les transistors TFT alimentés par la même tension d'alimentation et commandés par des tensions ou des courants de données identiques génèrent des courants d'intensité différente. Or, comme un émetteur émet généralement une intensité lumineuse directement proportionnelle au courant qui le traverse, l'hétérogénéité des seuils de déclenchement des transistors en poly-Silicium cristallin entraîne une non uniformité de brillance d'un écran constitué par une matrice de tels transistors. Il en résulte des différences entre les niveaux de luminance et un inconfort visuel manifeste pour l'utilisateur. Pour compenser les tensions de seuil de déclenchement des transistors TFT d'une matrice active, il est connu notamment par le document US 6,433,488, un circuit de commande d'un émetteur comprenant une unité de comparaison apte à comparer le courant de drain ld traversant le modulateur à un courant de référence pendant une étape de programmation du circuit de commande. Cependant, ce circuit nécessite l'implantation d'une unité de commutation par émetteur pour commuter la source d'alimentation de l'émetteur entre l'étape de programmation et une étape de fin trame d'émission de l'émetteur. Cette unité de commutation comprend deux transistors à couches minces et un amplificateur inverseur. Ce circuit est difficile à fabriquer et peu économique. Il est connu notamment par le document EP 1 381 019 des dispositifs d'affichage à matrice active comprenant des émetteurs OLED, des moyens d'alimentation des émetteurs, des modulateurs et des moyens de compensation des tensions de seuil de déclenchement des modulateurs. Les moyens de compensation comprennent des moyens de comparaison du courant de drain traversant un émetteur sélectionné à une consigne d'affichage. Toutefois, dans ces dispositifs d'affichage, les émetteurs ne sont pas alimentés par les mêmes moyens d'alimentation à la fois pendant les phases de programmation et les phases d'émission qui se succèdent pour l'affichage des images, ce qui nécessite un réseau d'électrodes spécifique pour chaque mode d'alimentation. Il est connu notamment par le document JP-2002/278513 un dispositif d'affichage comprenant des émetteurs OLED, des moyens d'alimentation des émetteurs, des modulateurs et des moyens de compensation des tensions de seuil de déclenchement des modulateurs. Les émetteurs sont alimentés par les mêmes moyens d'alimentation à la fois pendant les phases de programmation et les phases d'émission qui se succèdent pour l'affichage des images, mais la compensation des tensions de seuil est effectuée lors d'une phase de calibration préalable à l'affichage des images. Les moyens de compensation comprennent des moyens de mesure du courant de drain traversant un émetteur sélectionné et des moyens de comparaison de ce courant de drain à une consigne de calibrage de cet émetteur. Ces moyens de compensation ne permettent donc pas d'assurer la compensation de variations de tensions de seuil de déclenchement qui apparaîtraient en cours de phase d'affichage des images. Il est connu notamment par le document JP-2002/091377, US- 2003/001832 et W0-2004/034364, des dispositifs d'affichage à matrice active comprenant des émetteurs OLED, des modulateurs et des moyens de compensation des tensions de seuil de déclenchement des modulateurs. Les moyens de compensation comprennent des moyens de mesure du courant de drain traversant un émetteur sélectionné et des moyens de comparaison de ce courant de drain à une consigne d'affichage. Toutefois, les moyens de mesure du courant de drain sont propres à chaque émetteur d'une colonne. Par exemple dans le document WO-2004/034364, ils comprennent une résistance, deux électrodes et deux interrupteurs pour chaque émetteur d'une colonne. Cette architecture est par conséquent complexe et coûteuse. Un but de la présente invention est la mise en œuvre d'un circuit de commande moins complexe et donc moins onéreux. A cet effet, la présente invention a pour objet un dispositif d'affichage d'images à matrice active comprenant : - plusieurs émetteurs de lumière formant un réseau d'émetteurs répartis en lignes et en colonnes ; - des moyens d'alimentation en puissance aptes à alimenter en courant simultanément l'ensemble des émetteurs d'une colonne, pendant une étape d'émission et une étape de programmation des émetteurs ; - des moyens de commande de l'émission des émetteurs comprenant : - pour chaque émetteur du réseau, un modulateur de courant comportant une électrode de source, une électrode de drain, une électrode de grille, ledit modulateur étant apte à être traversé par un courant de drain pour alimenter ledit émetteur, pour une tension entre le drain ou la source et la grille supérieure ou égale à une tension de seuil de déclenchement ; - pour chaque colonne d'émetteurs, des moyens d'adressage de colonne aptes à adresser successivement chaque émetteur de ladite colonne d'émetteurs par application d'une valeur représentative d'une consigne de données à l'électrode de grille du modulateur associé à cet émetteur, pour le commander, au cours d'une étape de programmation, - pour chaque ligne d'émetteurs, des moyens de sélection de ligne aptes à sélectionner successivement les émetteurs de chaque ligne d'émetteurs, pendant l'étape de programmation, - pour chaque modulateur, des moyens de stockage aptes à stocker des charges électriques à l'électrode de grille du modulateur, et - des moyens de compensation des tensions de seuil de déclenchement comprenant des moyens de comparaison, les moyens de comparaison étant aptes à comparer, pendant l'étape de programmation d'un émetteur sélectionné, une valeur représentative du courant de drain alimentant l'émetteur sélectionné à la valeur représentative de la consigne de données, pour commander la quantité de charges stockées sur les moyens de stockage, caractérisé en ce que les moyens de compensation comprennent pour chaque colonne d'émetteurs une unique unité de détermination d'une valeur représentative du courant de drain alimentant l'émetteur sélectionné à partir d'une mesure d'une valeur représentative du courant d'alimentation de l'ensemble des émetteurs de la colonne. Suivant des modes particuliers de réalisation, le dispositif d'affichage comporte une ou plusieurs des caractéristiques suivantes : - les moyens d'alimentation en puissance des émetteurs sont directement connectés à chaque modulateur des moyens de commande ; - les moyens d'alimentation en puissance des émetteurs sont directement connectés à chaque émetteur d'une colonne ; - les moyens d'alimentation en puissance des émetteurs comprennent un générateur d'alimentation en tension apte à alimenter l'ensemble des émetteurs d'une colonne, et les moyens de compensation sont aptes à compenser successivement la tension de seuil de déclenchement de chaque modulateur de l'ensemble des émetteurs d'une colonne ; - les moyens de compensation comprennent en outre : - un générateur de pilotage apte à générer un signal de pilotage appliqué à la grille dudit modulateur ; - des moyens de modulation de la durée dudit signal de pilotage en fonction de la valeur de la consigne de données et de la valeur de la tension de seuil de déclenchement ; - la consigne de données est une tension de données et les moyens de comparaison sont aptes à émettre un signal d'avertissement lorsque la tension représentative de l'intensité du courant de drain est égale à un nombre de fois ladite tension de données ; - les moyens de modulation de la durée du signal de pilotage comprennent : - un interrupteur connecté en série au générateur de pilotage ; - une unité de contrôle apte à la commuter ledit interrupteur d'une part lors de la réception de la consigne de données et, d'autre part lors de la réception du signal d'avertissement ; - le signal de pilotage généré par le générateur de pilotage est modulé en amplitude en fonction de la valeur de la consigne de données ; - le générateur de pilotage est un générateur de courant et le modulateur est apte à être piloté en courant ; - le générateur de pilotage est un générateur de tension en rampe et le modulateur est apte à être piloté en tension ; - les moyens de compensation comprennent en outre une unité de mesure de l'intensité d'un courant apte à mesurer l'intensité du courant de drain traversant un émetteur sélectionné au cours de l'étape de programmation ; - les moyens d'alimentation comprennent une ligne à laquelle l'unité de mesure est directement raccordée ; et - les moyens de stockage comprennent au moins une capacité de stockage reliée à la grille et à la source du modulateur, et les moyens de compensation comprennent en outre des moyens d'initialisation aptes à appliquer une impulsion de tension à ladite capacité pour la décharger. L'invention sera mieux comprise à la lecture de la description qui va suivre, donnée à titre d'exemple non limitatif et, faite en référence aux figures annexées sur lesquelles : - la figure 1 est un schéma synoptique d'un circuit de commande et d'alimentation d'un émetteur selon l'invention ; - la figure 2 est un schéma synoptique d'un exemple de réalisation d'une unité de mesure de courant selon l'invention ; - les figures 3A à 3D sont des graphes représentant l'évolution au cours du temps de différents tensions et courants au cours du processus réalisé par le dispositif selon l'invention ; en particulier - la figure 3A est un graphe représentant la tension de sélection appliquée à l'électrode de sélection ; - la figure 3B est un graphe représentant la tension appliquée à l'électrode d'adressage par les moyens d'initialisation ; - la figure 3C est un graphe représentant le signal d'avertissement généré par l'unité de comparaison ; - la figure 3D est un graphe représentant l'évolution du courant de drain et du courant de pilotage ; et - la figure 4 est un schéma synoptique d'un circuit d'adressage selon une variante de réalisation de l'invention. La figure 1 représente un dispositif d'affichage à matrice active selon l'invention. Un tel dispositif comprend une pluralité d'émetteurs 2 de lumière formant un réseau de lignes et de colonnes, des moyens d'alimentation en puissance Vdd des émetteurs 2 et des moyens de commande 3 d'émission des émetteurs. Cependant, par souci de simplification, un seul émetteur et un seul moyen d'alimentation ont été représentés sur la figure 1. Les émetteurs 2 du panneau de visualisation sont des diodes électroluminescentes organiques. Ils comprennent une anode et une cathode. Ils sont chacun associés à un pixel lorsque le panneau est monochrome ou à un sous pixel lorsque le panneau de visualisation est polychrome. Ils émettent une intensité lumineuse directement proportionnelle au courant qui les traverse. Les moyens d'alimentation en puissance Vdd des émetteurs 2 comprennent un générateur de tension continue par colonne d'émetteurs 2. Ce générateur Vdd alimente une ligne 4, à laquelle est connecté l'ensemble des émetteurs 2 de cette colonne. Les moyens de commande 3 du dispositif d'affichage comprennent un circuit d'adressage 6 pour chaque émetteur, un réseau d'électrodes de sélection 8 de ligne et d'adressage 10 de colonne et des moyens de compensation 12 du seuil du déclenchement des modulateurs. Un circuit d'adressage 6 est connecté à chaque émetteur 2 du panneau de visualisation. Le circuit d'adressage représenté sur la figure 1 est un circuit de structure classique. Dans ce type de circuit, l'anode de l'émetteur forme l'interface avec la matrice active et la cathode de l'émetteur est connectée à une électrode de masse ou à une tension négative. Le circuit d'adressage 6 comprend un modulateur de courant 14, un interrupteur 16 et une capacité de stockage 18. Le modulateur de courant 14 est un transistor basé sur une technologie utilisant du Silicium poly-cristallin (Poly-Si) ou du Silicium amorphe (a-Si) déposé en couches minces sur un substrat de verre. De tels composants comprennent trois électrodes: une électrode de drain et une électrode de source entre lesquelles circule le courant modulé, et une électrode de grille à laquelle est appliqué un courant de pilotage de données Idata- Les transistors en couches minces (Thin Film Transistor en anglais) sont de type n ou p. Le modulateur 14 représenté sur la figure 1 est de type p. Sa source est connectée directement à l'électrode d'alimentation Vdd et son drain est relié directement à l'anode de l'émetteur 2 de sorte que en fonctionnement le courant électrique modulé circule entre la source et le drain. Alternativement, lorsque le modulateur 14 est de type n, le drain est connecté à l'électrode d'alimentation Vd et le courant électrique modulé circule alors entre le drain et la source. Le générateur d'alimentation en puissance Vdd est directement connecté à l'ensemble des modulateurs 14 de commande des émetteurs d'une colonne, de sorte qu'il est toujours apte à alimenter un émetteur 2 sélectionné et adressé quelque soit l'étape du processus d'émission d'une trame d'image. Ainsi, dès qu'un modulateur 14 de la colonne est débloqué par application d'une tension d'adressage et de sélection, l'émetteur correspondant est alimenté par le seul générateur Vdd- L'interrupteur 16 est également un transistor basé sur la technologie utilisant du Silicium poly-cristallin (Poly-Si) ou du Silicium amorphe (a-Si) déposé en couches minces. L'une de ses électrodes (drain ou source) est reliée à l'électrode d'adressage 10 et l'autre électrode (drain ou source) est reliée à la grille du modulateur 14. Sa grille est connectée à l'électrode 8 de sélection de ligne. La capacité de stockage 18 est disposée entre la grille et la source du modulateur 14 pour maintenir la brillance de l'émetteur 2 pendant une durée de trame d'image. Cette capacité est adaptée pour maintenir sensiblement la tension constante sur la grille du modulateur 14 pendant un intervalle de temps correspondant à la durée de trame. Le réseau d'électrodes de sélection 8 et d'adressage 10 permet de sélectionner et d'adresser un émetteur spécifique parmi l'ensemble des émetteurs du panneau de visualisation. Chaque électrode 8 de sélection est reliée à la grille des interrupteurs 16 d'une ligne et est apte à transmettre une tension de sélection Vseiect à l'ensemble des émetteurs 2 de cette ligne. La tension de sélection Vseiect est une donnée logique de sélection des émetteurs. Chaque électrode 10 d'adressage est reliée à la source ou au drain des interrupteurs 16 d'une colonne et est apte à adresser un courant de pilotage de données Idata à la grille du modulateur 14 de l'ensemble des circuits d'adressage 6 de cette colonne en fonction d'une consigne de données Uc. Dans l'exemple de réalisation de l'invention représenté sur la figure 1 , l'intensité de courant passant dans l'émetteur est proportionnelle à l'amplitude du courant Idata qui est appliqué sur l'électrode 10. Les électrodes de sélection 8 et d'adressage 10 sont chacune commandée par un pilote de commande correspondant 20, 22 pour appliquer des tensions de sélection Vseiect et des consignes de données Uc aux émetteurs. Ainsi, en sélectionnant une seule électrode 8 de ligne du panneau et en activant uniquement le pilote 20 correspondant à cette ligne et en appliquant une consigne de données Uc à une électrode de colonne 10 de ce panneau, propre à appliquer un courant de pilotage Idata sur le modulateur 14, un unique émetteur au croisement de l'électrode de cette ligne 8 et de l'électrode 10 de cette colonne est apte à émettre de la lumière. Les moyens de compensation 12 des seuils de déclenchement sont aptes à compenser les tensions de seuil de déclenchement Vtn de l'ensemble des modulateurs 14 adressés par l'électrode 10 d'adressage de cette colonne. Ils comprennent un contrôleur externe 24 par colonne d'émetteurs. Ce contrôleur comprend une unité de mesure 26, une unité de comparaison 28, un générateur de pilotage 30, un interrupteur 32, une unité de contrôle 34 et des moyens d'initialisation 36 des circuits d'adressage 6 de cette colonne. L'unité de mesure 26 est connectée à l'électrode 4 d'alimentation en puissance de tous les émetteurs d'une colonne. L'unité de mesure 26 est apte à mesurer une valeur représentative du courant de drain Id d'un modulateur 14 sélectionné par l'électrode 8 de sélection et à la grille duquel un courant de pilotage Idata est appliqué. Plus précisément, le rôle de l'unité 26 est d'extraire de la somme des courants mesurés dans la ligne 4, uniquement le courant du modulateur 14 en cours de programmation. Un exemple de réalisation de l'unité de mesure 26 sera décrit ci-après en liaison avec la figure 2. L'unité de comparaison 28 comprend deux bornes d'entrée propres à recevoir la consigne de données Uc adressée par le pilote de commande 22 et une valeur représentative du courant de drain Id mesuré par l'unité de mesure 26. Dans l'exemple de réalisation de l'invention représenté sur la figure 1 , la consigne de données Uc est une tension de données. L'unité de comparaisonEach light emitter is linked to a pixel or a sub-pixel of an image to be displayed and is addressed by a network of column electrodes and row electrodes via an addressing circuit. The addressing circuits notably include current modulators able to control the current passing through the emitters and therefore the luminance of each sub-pixel of the display panel. In an active matrix, these modulators are thin-film transistors, called TFT (Thin Film Transistor) transistors, made of crystalline poly-silicon using low-temperature poly crystalline silicon (LTPS) technology. However, this technique introduces local spatial variations in the trigger threshold voltage of thin film transistors. These variations are due to the fact that the grain boundaries and dimensions of the poly-silicon are not sufficiently controllable during the crystallization phase from amorphous silicon to poly-crystalline silicon. Thus, the TFT transistors composing the same display panel have different trigger threshold voltages. Consequently, the TFT transistors supplied by the same supply voltage and controlled by identical voltages or data currents generate currents of different intensity. However, as an emitter generally emits a light intensity directly proportional to the current flowing through it, the heterogeneity of the trigger thresholds of the crystalline poly-Silicon transistors leads to a non-uniformity of brightness of a screen formed by a matrix of such transistors. This results in differences between the luminance levels and obvious visual discomfort for the user. To compensate for the triggering threshold voltages of the TFT transistors of an active matrix, it is known in particular from document US 6,433,488, a control circuit of an emitter comprising a comparison unit capable of comparing the drain current l d through the modulator at a reference current during a programming step of the control circuit. However, this circuit requires the installation of a transmitter switching unit to switch the power source of the transmitter between the programming step and a step of transmitting end frame of the transmitter. This switching unit includes two thin film transistors and an inverting amplifier. This circuit is difficult to manufacture and not very economical. It is known in particular from document EP 1 381 019 active matrix display devices comprising OLED transmitters, means for supplying the transmitters, modulators and means for compensating for the trigger threshold voltages of the modulators. The compensation means comprise means for comparing the drain current passing through a selected transmitter with a display setpoint. However, in these display devices, the transmitters are not supplied by the same supply means both during the programming phases and the successive transmission phases for displaying the images, which requires a specific electrode network for each supply mode. It is known in particular from document JP-2002/278513 a display device comprising OLED transmitters, means for supplying the transmitters, modulators and means for compensating the voltages of modulator trigger threshold. The transmitters are supplied by the same supply means both during the programming phases and the successive transmission phases for displaying the images, but the compensation of the threshold voltages is carried out during a phase of calibration before displaying images. The compensation means comprise means for measuring the drain current passing through a selected transmitter and means for comparing this drain current with a calibration instruction for this transmitter. These compensation means therefore do not make it possible to compensate for variations in trigger threshold voltages which would appear during the display phase of the images. It is known in particular from the document JP-2002/091377, US-2003/001832 and W0-2004 / 034364, active matrix display devices comprising OLED transmitters, modulators and means for compensating threshold voltage of triggering of the modulators. The compensation means include means for measuring the drain current passing through a selected transmitter and means for comparing this drain current with a display setpoint. However, the means for measuring the drain current are specific to each emitter of a column. For example in document WO-2004/034364, they include a resistor, two electrodes and two switches for each emitter of a column. This architecture is therefore complex and expensive. An object of the present invention is the implementation of a less complex and therefore less expensive control circuit. To this end, the present invention relates to an active matrix image display device comprising: - several light emitters forming a network of emitters distributed in rows and columns; - Power supply means capable of simultaneously supplying current to all of the transmitters of a column, during an emission step and a step of programming the emitters; means for controlling the emission of the transmitters comprising: for each transmitter of the network, a current modulator comprising a source electrode, a drain electrode, a gate electrode, said modulator being capable of being traversed by a current of drain for supplying said transmitter, for a voltage between the drain or the source and the gate greater than or equal to a trigger threshold voltage; for each column of transmitters, column addressing means capable of successively addressing each transmitter of said column of transmitters by applying a value representative of a data setpoint to the gate electrode of the modulator associated with this transmitter, for controlling it, during a programming step, - for each line of transmitters, line selection means capable of successively selecting the transmitters of each line of transmitters, during the programming step, - For each modulator, storage means capable of storing electrical charges at the gate electrode of the modulator, and - means for compensating the trigger threshold voltages comprising comparison means, the comparison means being able to compare , during the programming step of a selected transmitter, a value representative of the drain current supplying the selected transmitter to the value represented of the data setpoint, for controlling the quantity of charges stored on the storage means, characterized in that the compensation means comprise for each column of transmitters a single unit for determining a value representative of the drain current supplying the transmitter selected from a measurement of a value representative of the supply current of all the transmitters in the column. According to particular embodiments, the display device includes one or more of the following characteristics: - the power supply means of the transmitters are directly connected to each modulator of the control means; the power supply means of the transmitters are directly connected to each transmitter of a column; the power supply means of the transmitters comprise a voltage supply generator capable of supplying all the transmitters of a column, and the compensation means are capable of successively compensating the trigger threshold voltage of each modulator of all the transmitters in a column; - the compensation means further comprise: - a control generator capable of generating a control signal applied to the gate of said modulator; means for modulating the duration of said control signal as a function of the value of the data setpoint and the value of the triggering threshold voltage; the data setpoint is a data voltage and the comparison means are capable of emitting a warning signal when the voltage representative of the intensity of the drain current is equal to a number of times said data voltage; the means for modulating the duration of the piloting signal comprise: a switch connected in series with the piloting generator; - A control unit able to switch said switch on the one hand when receiving the data setpoint and, on the other hand when receiving the warning signal; the control signal generated by the control generator is amplitude-modulated as a function of the value of the data setpoint; the pilot generator is a current generator and the modulator is able to be piloted in current; - the pilot generator is a ramp voltage generator and the modulator is able to be piloted in voltage; the compensation means further comprise a unit for measuring the intensity of a current capable of measuring the intensity of the drain current passing through a transmitter selected during the programming step; the supply means comprise a line to which the measurement unit is directly connected; and - the storage means comprise at least one storage capacity connected to the gate and to the source of the modulator, and the compensation means further comprise initialization means able to apply a voltage pulse to said capacity to discharge it . The invention will be better understood on reading the description which follows, given by way of nonlimiting example and, made with reference to the appended figures in which: - Figure 1 is a block diagram of a control and supply circuit of a transmitter according to the invention; - Figure 2 is a block diagram of an exemplary embodiment of a current measurement unit according to the invention; - Figures 3A to 3D are graphs representing the evolution over time of different voltages and currents during the process performed by the device according to the invention; in particular - FIG. 3A is a graph representing the selection voltage applied to the selection electrode; - Figure 3B is a graph showing the voltage applied to the addressing electrode by the initialization means; - Figure 3C is a graph representing the warning signal generated by the comparison unit; - Figure 3D is a graph representing the evolution of the drain current and the control current; and - Figure 4 is a block diagram of an addressing circuit according to an alternative embodiment of the invention. FIG. 1 represents an active matrix display device according to the invention. Such a device comprises a plurality of light emitters 2 forming an array of rows and columns, power supply means V dd of the emitters 2 and control means 3 for emitting the emitters. However, for the sake of simplification, a single emitter and a single supply means have been shown in FIG. 1. The emitters 2 of the display panel are organic light emitting diodes. They include an anode and a cathode. They are each associated with a pixel when the panel is monochrome or with a sub-pixel when the display panel is polychrome. They emit a light intensity directly proportional to the current flowing through them. The power supply means V dd of the emitters 2 comprise a DC voltage generator per column of emitters 2. This generator V dd supplies a line 4, to which all of the emitters 2 of this column are connected. The control means 3 of the display device comprise an addressing circuit 6 for each transmitter, a network of selection electrodes 8 for row and addressing 10 for column and means for compensating 12 for the threshold for triggering the modulators. An addressing circuit 6 is connected to each transmitter 2 of the display panel. The addressing circuit shown in Figure 1 is a conventional structure circuit. In this type of circuit, the anode of the transmitter forms the interface with the active matrix and the cathode of the transmitter is connected to a ground electrode or to a negative voltage. The addressing circuit 6 comprises a current modulator 14, a switch 16 and a storage capacity 18. The current modulator 14 is a transistor based on a technology using polycrystalline silicon (Poly-Si) or amorphous silicon (a-Si) deposited in thin layers on a glass substrate. Such components include three electrodes: a drain electrode and a source electrode between which the modulated current flows, and a gate electrode to which an Idata data driving current is applied. Thin Film Transistor English) are of type n or p. The modulator 14 shown in FIG. 1 is of the p type. Its source is connected directly to the supply electrode V dd and its drain is connected directly to the anode of the transmitter 2 so that in operation the modulated electric current flows between the source and the drain. Alternatively, when the modulator 14 is of type n, the drain is connected to the supply electrode V d and the modulated electric current then flows between the drain and the source. The power supply generator V dd is directly connected to all of the modulators 14 for controlling the transmitters of a column, so that it is always capable of supplying a transmitter 2 selected and addressed whatever the stage of the process of transmitting an image frame. Thus, as soon as a modulator 14 of the column is released by applying an addressing and selection voltage, the corresponding transmitter is supplied by the only generator Vdd- Switch 16 is also a transistor based on technology using polycrystalline silicon (Poly-Si) or amorphous silicon (a-Si) deposited in thin layers. One of its electrodes (drain or source) is connected to the addressing electrode 10 and the other electrode (drain or source) is connected to the grid of the modulator 14. Its grid is connected to the line selection electrode 8. The storage capacity 18 is arranged between the grid and the source of the modulator 14 to maintain the brightness of the transmitter 2 for an image frame duration. This capacity is adapted to substantially maintain the constant voltage on the grid of the modulator 14 during a time interval corresponding to the frame duration. The array of selection 8 and addressing 10 electrodes makes it possible to select and address a specific transmitter from all of the transmitters of the display panel. Each selection electrode 8 is connected to the gate of the switches 16 of one line and is adapted to transmit a selection voltage V IECT to all the emitters 2 from this line. The selection voltage V se ie c t is a logic datum for selecting the transmitters. Each addressing electrode 10 is connected to the source or to the drain of the switches 16 of a column and is capable of addressing a data driving current I da ta to the gate of the modulator 14 of all the addressing circuits 6 of this column as a function of a data setpoint U c . In the embodiment of the invention shown in FIG. 1, the intensity of current flowing through the transmitter is proportional to the amplitude of the current I d ata which is applied to the electrode 10. The selection electrodes 8 and addressing 10 are each controlled by a corresponding control pilot 20, 22 to apply selection voltages V se ie c t and data set points U c to the transmitters. Thus, by selecting a single line electrode 8 of the panel and by activating only the pilot 20 corresponding to this line and by applying a data setpoint U c to a column electrode 10 of this panel, suitable for applying a pilot current I da ta on the modulator 14, a single emitter at the intersection of the electrode of this line 8 and the electrode 10 of this column is capable of emitting light. The means for compensating for the trigger thresholds 12 are capable of compensating for the trigger threshold voltages Vt n of all of the modulators 14 addressed by the addressing electrode 10 of this column. They include an external controller 24 per column of transmitters. This controller comprises a measurement unit 26, a comparison unit 28, a pilot generator 30, a switch 32, a control unit 34 and means 36 for initializing the addressing circuits 6 of this column. The measurement unit 26 is connected to the power supply electrode 4 of all the transmitters of a column. The measurement unit 26 is able to measure a value representative of the drain current I d of a modulator 14 selected by the selection electrode 8 and to the grid of which a pilot current Idata is applied. More specifically, the role of the unit 26 is to extract from the sum of the currents measured in line 4, only the current of the modulator 14 during programming. An exemplary embodiment of the measurement unit 26 will be described below in conjunction with FIG. 2. The comparison unit 28 comprises two input terminals suitable for receiving the data setpoint U c addressed by the control pilot 22 and a value representative of the drain current I d measured by the measurement unit 26. In the embodiment of the invention shown in FIG. 1, the data setpoint U c is a data voltage. The comparison unit
28 est adaptée pour comparer l'amplitude de la tension représentative du courant de drain Id et l'amplitude de la tension de données Uc pendant une étape dite de programmation C du circuit d'adressage 6. De plus, l'unité de comparaison 28 comprend une borne de sortie apte à émettre un signal d'avertissement S lorsque l'amplitude de la tension représentative de l'intensité du courant de drain Id et l'amplitude de la tension de données Uc sont liées par un coefficient k de proportionnalité prédéterminé. Le signal d'avertissement S est un signal logique envoyé à l'unité de contrôle 34. En variante, la consigne de données est une donnée numérique ou une intensité de données. Le générateur de pilotage 30 est un générateur de courant continu propre à fournir un courant de pilotage Idata qui est fonction de la consigne de données Uc appliquée à ce générateur. Il est raccordé en série à l'électrode d'adressage 10. Il est apte à recevoir la tension de données Uc adressée par le pilote 22 de commande de colonne et à générer un courant de pilotage Idata dont l'amplitude est modulée en fonction de l'amplitude de la tension de données Uc. L'interrupteur 32 est raccordé en série en sortie du générateur de pilotage 30. Il est apte à commuter entre une position de fermeture dans laquelle le courant de pilotage ldata, alimente l'électrode 10 d'adressage de l'ensemble des circuits d'adressage 6 de la colonne et une position ouverte dans laquelle les circuits d'adressage 6 ne sont pas adressés. L'unité de contrôle 34 est connectée au pilote 22, à la sortie du module de comparaison 28 et à l'interrupteur 32 pour recevoir la tension de données Uc et le signal d'avertissement S et pour commander la commutation de l'interrupteur 32. L'unité de contrôle 34 est apte à commander la fermeture de l'interrupteur 32 sur réception de la tension de données Uc et l'ouverture de celui- ci sur réception du signal d'avertissement S. Ainsi, la durée du courant de pilotage Idata généré, est modulée en fonction de la tension de seuil de déclenchement Vtrι propre à chaque modulateur 14 comme cela sera expliqué dans la suite. Les moyens d'initialisation 36 des circuits d'adressage 6 sont connectés en parallèle au générateur 30 pour que l'image d'une trame ne soit pas influencée par l'image de la trame précédente. Ils sont aptes à émettre une tension carrée pour décharger la capacité de stockage 18 et une capacité parasite induite par le panneau de visualisation. Ils comprennent un générateur 38 de tension continue et un interrupteur 40. L'interrupteur 40 est relié à l'unité de contrôle 34. L'unité de contrôle 34 est connectée au pilote 20 pour commander la fermeture de l'interrupteur 40 sur réception de la tension de sélection Vseiect- Alternativement, le circuit d'adressage 6 comprend un interrupteur de shunt de la capacité de stockage 18. La figure 2 représente un exemple de réalisation d'une unité 26 de mesure d'une valeur représentative du courant de drain Id traversant le modulateur 14 du circuit de commande pour lequel l'étape de programmation débute. Une telle unité de mesure 26 est connectée à la ligne 4 d'alimentation des émetteurs 2 d'une colonne. Elle comprend un bloc 41 de détermination du courant de drain Id, un filtre passe-bas 42, un bloc différentiel 43 et un amplificateur 44. Le bloc de détermination 41 comprend une résistance 45, par exemple de 1 à 10 kilos Ohms, connectée en série à la ligne 4 d'alimentation des émetteurs et un amplificateur opérationnel 46 de précision dont les bornes sont raccordées à la ligne d'alimentation 4 de part et d'autre de la résistance 45. La sortie de l'amplificateur 46 est connectée d'une part au filtre passe -bas 42, lui- même connecté à une borne négative d'un amplificateur 47 du bloc différentiel 43 et d'autre part à une borne positive de cet amplificateur 47. Le bloc différentiel 43 comprend un amplificateur 47 dans un montage différentiel et un réseau de quatre résistances de même valeur. Une première résistance R1 est raccordée entre l'entrée positive de l'amplificateur 47 et une électrode de masse. Une seconde résistance R2 est raccordée entre l'entrée positive de l'amplificateur 47 et la sortie de l'amplificateur 46. Une troisième résistance est raccordée entre l'entrée négative de l'amplificateur 47 et la sortie du filtre passe-bas 42. Enfin, une quatrième résistance R4 est raccordée entre l'entrée négative de l'amplificateur 47 et sa borne de sortie. De plus, la sortie du bloc différentiel 43 est branchée à un amplificateur 44 ayant un gain élevé. Le bloc de détermination 41 est apte à mesurer le courant total alimentant l'ensemble des émetteurs d'une colonne, y compris le courant de drain traversant le modulateur 14 pendant la programmation de celui-ci. Ce courant de drain apparaît alors aux bornes de la résistance 45 sous la forme d'une impulsion de courant. La tension de sortie du bloc de détermination 41 est proportionnelle au courant total traversant la ligne 4. Cette tension est appliquée aux bornes du filtre passe-bas 42 qui en élimine la composante haute fréquence. Cette composante haute fréquence correspond à l'impulsion du courant générée par le modulateur 14 alimenté par la ligne 4 et qui est au cours d'une étape de programmation. L'amplificateur 47 du bloc différentiel reçoit à son entrée négative une tension proportionnelle au courant total d'alimentation de la ligne 4, excepté la composante correspondant au courant de drain traversant le modulateur 14 et, sur son entrée positive une tension proportionnelle au courant total sur la ligne 4. Comme les résistances R1 , R2, R3 et R4 sont de même valeur, la tension en sortie Vditf du bloc différentiel 43 est égale à la résistance 45 multipliée par le courant de drain du modulateur 14 qui est au cours d'une étape de programmation. Cette tension est amplifiée par l'amplificateur 44 puis est comparée à la tension de données Uc dans le bloc de comparaison 28 comme cela a été explicité précédemment. Selon une variante de réalisation de l'invention, le dispositif d'affichage d'image est un circuit de commande en tension des modulateurs. Le générateur de courant continue 30 est alors remplacé par un générateur d'alimentation en tension et préférentiellement par un générateur de tension en rampe. Dans ce cas, tout comme dans le cas d'un circuit de commande en courant des modulateurs tel décrit précédemment, l'amplitude de la tension de rampe est modulée en fonction de la valeur de l'amplitude de la consigne de données, émise par le pilote de commande 22 de colonne. La durée de la tension de rampe adressée aux circuits d'adressage 6 est également modulée en fonction de la tension de seuil de déclenchement Vtn, par les moyens de comparaison 28 et l'unité de contrôle 34. Les quatre graphes des figures 3A à 3D représentent les étapes d'adressage d'un émetteur lorsque celui-ci est réalisé par le dispositif d'affichage selon l'invention. Ces étapes comprennent une étape A d'initialisation d'un circuit d'adressage 6, une étape B intermédiaire, une étape C de programmation de celui-ci et une étape D d'émission de lumière proportionnelle au courant de pilotage Idata précédemment programmé. Au cours de l'étape A d'initialisation, le pilote 20 de commande de ligne applique une tension Vseiect à l'électrode 8 de la ligne sélectionnée. Cette tension est appliquée à la grille des interrupteurs 16, reliée à l'électrode de ligne 8. Parallèlement, l'unité de contrôle 34 du contrôleur externe 24 d'une colonne, commande la fermeture de l'interrupteur 40 et une tension Vjnjt générée par le générateur 38, est appliquée à l'électrode d'adressage 10 de cette colonne. La tension Vjnit est appliquée à une borne de la capacité de stockage 18 pour la décharger, l'interrupteur 16 étant fermé. L'étape intermédiaire B est de courte durée et a pour unique fonction de créer un temps mort pour séparer les étapes d'initialisation et de programmation afin d'éviter les courts-circuit. Au cours d'une étape C de programmation, le pilote 22 de commande de colonne émet une tension de données Uc, l'unité de contrôle 34 commande la fermeture de l'interrupteur 32 et le générateur 30 de pilotage génère un courant de pilotage Idata- Comme l'interrupteur 16 est fermé, le courant Idata génère une différence de potentiel entre la grille et la source du modulateur 14. Lorsque cette différence de potentiel est supérieure à la tension de seuil de déclenchement Vth du modulateur 14, un courant de drain Id s'établit entre le drain et la source du modulateur. L'intensité de ce courant de drain I qui correspond à une partie du courant circulant dans la ligne 4, est mesurée par l'unité de mesure 26 et une tension représentative de ce courant de drain est comparée à la tension de données Uc adressée par le pilote 22. En variante, lorsque la consigne de données est un courant, l'amplitude de l'intensité de ce courant est comparée à l'intensité du courant de drain. Le courant de drain généré traverse l'émetteur 2 qui s'illumine. Le générateur Vdd alimente en puissance l'émetteur 2. L'unité de comparaison 28 compare la tension de données Uc à la tension représentative de l'amplitude du courant de drain Id. Comme visible sur la figure 3D, l'amplitude du courant de drain augmente quadratique en fonction de la tension entre la grille et la source du modulateur. Petit à petit, le courant de pilotage Idata généré par le générateur 30 provoque une accumulation de charges dans la capacité de stockage 18 reliée à la grille du modulateur 14. Cette accumulation de charges provoque l'augmentation de tension Vgs entre la grille et la source du modulateur 14 et en conséquence, l'augmentation progressive du courant de drain Id. Lorsque la tension représentative du courant de drain Id est proportionnel à la tension de données Uc, plus exactement lorsque Id≈&j^- avec k > 1 , l'unité de comparaison 28 envoie un signal d'avertissement S à l'unité de contrôle 34 qui en retour, commande la fermeture de l'interrupteur 32. L'étape de programmation est terminée. La durée de l'étape de programmation est variable et dépend du seuil de déclenchement de chaque modulateur de courant de la colonne. Le signal d'adressage de chaque émetteur est donc modulé en durée en fonction des tensions de seuil de déclenchement. En pratique, le courant Idata est de l'ordre de quelques microampères de sorte que la capacité de stockage 18 et les capacités parasites générées par la structure du panneau de visualisation, sont rapidement chargées. Comme le courant Idata est environ 4 fois supérieur au courant de drain Id, le temps de programmation est court, environ de l'ordre de quelques micros secondes (μs). Au cours de l'étape C de programmation, la capacité de stockage 18 a été suffisamment chargée pour que l'émetteur 2 continue d'émettre après son adressage pendant la durée de la trame d'image, en étant toujours alimenté depuis le générateur Vdd- La durée d'adressage du courant de pilotage ldata correspondant à la durée de fermeture de l'interrupteur 32, est à la fois fonction de la tension de seuil de déclenchement Vth du modulateur 14 sélectionné et de la valeur de la consigne Idata- Ainsi, les moyens de compensation 12 du seuil de déclenchement sont aptes à moduler la durée du signal de pilotage Idata à tour de rôle pour chaque modulateur de la colonne d'émetteurs. L'étape D débute à la fin de l'étape de programmation et s'achève à la fin de la sélection de la ligne 8. Pendant cette étape D, l'émetteur 2 est toujours sélectionné mais sa programmation est terminée ; il continue d'émettre en fonction de cette programmation grâce à la tension stockée aux bornes de la capacité 28. Pendant le reste de la trame d'image et avant une autre programmation correspondant à une nouvelle trame, le courant de drain Id continue à traverser le modulateur 14 et l'émetteur 2 jusqu'à ce que la tension aux bornes de la capacité de stockage 18 soit déchargée au cours d'une nouvelle étape A d'initialisation de ce circuit d'adressage. Dès la fin de l'étape C de programmation d'un circuit d'adressage 6 associé à un premier émetteur 2, les pilotes de commande 20, 22 et les moyens de compensation 12 sont utilisés pour la programmation d'un autre circuit d'adressage associé à un second émetteur de la même colonne. Pendant l'étape d'initialisation A du circuit d'adressage associé au second émetteur, le premier émetteur 2 continue à émettre. Le générateur Vdd qui a alimenté en puissance l'émetteur 2 durant l'étape de programmation C continue à l'alimenter tant que la tension de grille du modulateur 14 est supérieure à sa tension de seuil de déclenchement. La figure 4 représente une variante de réalisation de l'invention dans laquelle les moyens de commande 3 sont identiques à ceux représentés sur la figure 1. Cependant, le circuit d'adressage 6 pilotant un émetteur de lumière 2 à structure classique est remplacé par un circuit d'adressage 66 pilotant une émetteur de lumière à structure dite inversée. Dans ce type de circuit, la cathode des émetteurs 52 forme l'interface avec la matrice active et l'anode des émetteurs 52 est connectée au générateur d'alimentation en puissance Vdd- La source du modulateur 54 est connectée à une masse ou à un générateur de tension négative. La cathode de l'émetteur 52 est raccordée au drain du modulateur 54. La capacité de stockage 58 est branchée entre la grille et la source du modulateur 54. Un interrupteur 56 est adressé en courant Idata par une électrode d'adressage 60 et est sélectionné par une électrode de sélection 68. Le générateur d'alimentation en puissance Vdd est directement raccordé à tous les émetteurs 52 de toutes les colonnes sans interposition d'une unité de commutation. En conséquence, ce générateur Vdd alimente en puissance tous les émetteurs 52 pendant l'étape C de programmation et pendant l'étape D tout au long de la durée de la trame d'image. En conséquence, ce sont les moyens d'alimentation en puissance Vss qui sont connectés séparément au moyen de compensation 12. Comme les moyens d'alimentation sont directement connectés à chaque modulateur ou directement connectés à chaque émetteur d'une colonne, le schéma électrique du dispositif d'affichage est simplifié et techniquement plus facilement réalisable. Comme chaque générateur d'alimentation en puissance Vss est apte à alimenter l'ensemble des émetteurs 2 d'une colonne et que chaque électrode d'adressage 60 est également apte à adresser l'ensemble des émetteurs 2 d'une colonne, les moyens de compensation 12 sont aptes à compenser successivement la tension de seuil de déclenchement Vth de l'ensemble des modulateurs 14 d'une colonne. Par ailleurs, comme les moyens de compensation 12 déterminent la durée du signal avant chaque trame, les variations du seuil de déclenchement liées au vieillissement des modulateurs sont automatiquement compensées. Avantageusement, aucune unité de commutation n'est interposée entre le générateur V d ou Vss et le modulateur 14 ou l'émetteur 52 pour commuter entre deux sources d'alimentation de l'émetteur au cours du processus de programmation et d'émission de celui-ci. En conséquence, la surface utile d'émission de lumière des pixels est augmentée. Comme le circuit d'adressage est adressé par un courant ou une tension analogique et non numérique, les moyens de contrôle sont simplifiés et leur implémentation est facilitée. Avantageusement, les moyens de compensation de l'ensemble des colonnes compensent les dispersions des tensions de seuil de déclenchement des modulateurs de circuits de commande d'un écran à matrice active. Avantageusement, l'unité 26 de mesure du courant traversant un modulateur pendant une étape de programmation C, permet de se dispenser d'une unité de commutation associée à chaque émetteur. Avantageusement, comme l'intensité du courant de pilotage I ata est élevée, les capacités parasites générées par la colonne d'adressage du panneau de visualisation sont rapidement chargées. En conséquence, le dispositif d'affichage est adressé instantanément. 28 is suitable for comparing the amplitude of the voltage representative of the drain current I d and the amplitude of the data voltage U c during a so-called programming step C of the addressing circuit 6. In addition, the unit of comparison 28 includes an output terminal capable of emitting a warning signal S when the amplitude of the voltage representative of the intensity of the drain current I d and the amplitude of the data voltage U c are linked by a coefficient k of predetermined proportionality. The warning signal S is a logic signal sent to the control unit 34. As a variant, the data setpoint is a digital data or a data intensity. The pilot generator 30 is a direct current generator capable of supplying a pilot current I d at a which is a function of the data set point Uc applied to this generator. It is connected in series to the addressing electrode 10. It is able to receive the data voltage U c addressed by the column control pilot 22 and to generate a pilot current I d a ta whose amplitude is modulated as a function of the amplitude of the data voltage U c . The switch 32 is connected in series at the output of the pilot generator 30. It is able to switch between a closed position in which the pilot current l da ta supplies the addressing electrode 10 of all the circuits addressing 6 of the column and an open position in which the addressing circuits 6 are not addressed. The control unit 34 is connected to the pilot 22, to the output of the comparison module 28 and to the switch 32 to receive the data voltage U c and the warning signal S and to control the switching of the switch 32. The control unit 34 is able to command the closing of the switch 32 on reception of the data voltage U c and the opening of the latter on reception of the warning signal S. Thus, the duration of the control current I d ata generated, is modulated as a function of the triggering threshold voltage V trι specific to each modulator 14 as will be explained below. The initialization means 36 of the addressing circuits 6 are connected in parallel to the generator 30 so that the image of a frame is not influenced by the image of the previous frame. They are capable of emitting a square voltage to discharge the storage capacity 18 and a parasitic capacity induced by the display panel. They include a generator 38 of DC voltage and a switch 40. The switch 40 is connected to the control unit 34. The control unit 34 is connected to the pilot 20 to control the closing of the switch 40 on receipt of the selection voltage V se i e ct- Alternatively, the addressing circuit 6 comprises a shunt switch for the storage capacity 18. FIG. 2 represents an exemplary embodiment of a unit 26 for measuring a representative value of the drain current I d passing through the modulator 14 of the control circuit for which the programming step begins. Such a measurement unit 26 is connected to the supply line 4 of the transmitters 2 of a column. It comprises a block 41 for determining the drain current I d , a low-pass filter 42, a differential block 43 and an amplifier 44. The determination block 41 comprises a resistor 45, for example from 1 to 10 kilos Ohms, connected in series at line 4 supplying transmitters and an operational amplifier 46 of precision whose terminals are connected to the supply line 4 on either side of the resistor 45. The output of the amplifier 46 is connected on the one hand to the low-pass filter 42 , itself connected to a negative terminal of an amplifier 47 of the differential block 43 and on the other hand to a positive terminal of this amplifier 47. The differential block 43 comprises an amplifier 47 in a differential circuit and a network of four resistors of the same value. A first resistor R1 is connected between the positive input of the amplifier 47 and a ground electrode. A second resistor R2 is connected between the positive input of the amplifier 47 and the output of the amplifier 46. A third resistor is connected between the negative input of the amplifier 47 and the output of the low-pass filter 42. Finally, a fourth resistor R4 is connected between the negative input of the amplifier 47 and its output terminal. In addition, the output of the differential block 43 is connected to an amplifier 44 having a high gain. The determination block 41 is capable of measuring the total current supplying all of the emitters of a column, including the drain current passing through the modulator 14 during the programming of the latter. This drain current then appears at the terminals of the resistor 45 in the form of a current pulse. The output voltage of the determination block 41 is proportional to the total current passing through the line 4. This voltage is applied to the terminals of the low-pass filter 42 which eliminates the high frequency component therefrom. This high frequency component corresponds to the current pulse generated by the modulator 14 supplied by the line 4 and which is during a programming step. The amplifier 47 of the differential unit receives at its negative input a voltage proportional to the total supply current of line 4, except the component corresponding to the drain current passing through the modulator 14 and, on its positive input a voltage proportional to the total current on line 4. As the resistors R1, R2, R3 and R4 are of the same value, the output voltage V d it f of the differential block 43 is equal to the resistor 45 multiplied by the drain current of the modulator 14 which is at during a programming stage. This voltage is amplified by amplifier 44 then is compared with the data voltage U c in the comparison block 28 as explained above. According to an alternative embodiment of the invention, the image display device is a voltage control circuit of the modulators. The DC generator 30 is then replaced by a voltage supply generator and preferably by a ramp voltage generator. In this case, as in the case of a modulator current control circuit as described above, the amplitude of the ramp voltage is modulated as a function of the value of the amplitude of the data setpoint, emitted by the column control pilot 22. The duration of the ramp voltage addressed to the addressing circuits 6 is also modulated as a function of the triggering threshold voltage Vt n , by the comparison means 28 and the control unit 34. The four graphs of FIGS. 3A to 3D represent the steps of addressing a transmitter when it is produced by the display device according to the invention. These stages include a stage A of initialization of an addressing circuit 6, an intermediate stage B, a stage C of programming of this one and a stage D of emission of light proportional to the pilot current I d ata previously program. During the initialization step A, the line control pilot 20 applies a voltage V se i e c t to the electrode 8 of the selected line. This voltage is applied to the grid of the switches 16, connected to the line electrode 8. In parallel, the control unit 34 of the external controller 24 of a column, controls the closing of the switch 40 and a voltage Vj n jt generated by the generator 38, is applied to the addressing electrode 10 of this column. The voltage Vjni t is applied to a terminal of the storage capacity 18 to discharge it, the switch 16 being closed. Intermediate step B is short-lived and has the sole function of creating a dead time to separate the initialization and programming steps in order to avoid short circuits. During a programming step C, the column control pilot 22 transmits a data voltage U c , the control unit 34 commands the closing of the switch 32 and the pilot generator 30 generates a pilot current I d at a - As the switch 16 is closed, the current I data generates a potential difference between the gate and the source of the modulator 14 When this potential difference is greater than the triggering threshold voltage Vt h of the modulator 14, a drain current I d is established between the drain and the source of the modulator. The intensity of this drain current I which corresponds to part of the current flowing in line 4, is measured by the measurement unit 26 and a voltage representative of this drain current is compared to the data voltage U c addressed by the pilot 22. As a variant, when the data setpoint is a current, the amplitude of the intensity of this current is compared to the intensity of the drain current. The drain current generated passes through the emitter 2 which lights up. The generator V dd supplies power to the transmitter 2. The comparison unit 28 compares the data voltage U c to the voltage representative of the amplitude of the drain current I d . As shown in Figure 3D, the amplitude of the drain current increases quadratic as a function of the voltage between the gate and the source of the modulator. Little by little, the driving current I da t generated by the generator 30 causes an accumulation of charges in the storage capacitor 18 connected to the gate of the modulator 14. This accumulation of charges causes increased voltage V gs between the gate and the source of the modulator 14 and consequently, the progressive increase of the drain current Id. When the voltage representative of the drain current I d is proportional to the data voltage U c , more precisely when Id≈ & j ^ - with k> 1, the comparison unit 28 sends a warning signal S to the control unit 34 which in turn commands the closing of the switch 32. The programming step is finished. The duration of the programming step is variable and depends on the triggering threshold of each current modulator in the column. The addressing signal of each transmitter is therefore modulated in duration as a function of the triggering threshold voltages. In practice, the current I data is of the order of a few microamps so that the storage capacity 18 and the parasitic capacities generated by the structure of the display panel are quickly charged. As the current I data is approximately 4 times greater than the drain current I d , the programming time is short, approximately of the order of a few microseconds (μs). During the programming step C, the storage capacity 18 has been sufficiently charged so that the transmitter 2 continues to transmit after its addressing for the duration of the image frame, while always being supplied from the generator V d d- The addressing duration of the driving current l da ta corresponding to the duration of closing of the switch 32, is both a function of the triggering threshold voltage Vt h of the selected modulator 14 and the value of the setpoint I d a t a- Thus, the means for compensating the trigger threshold 12 are able to modulate the duration of the control signal I d ata in turn for each modulator of the column of transmitters. Step D begins at the end of the programming step and ends at the end of the selection of line 8. During this step D, the transmitter 2 is still selected but its programming is finished; it continues to transmit as a function of this programming thanks to the voltage stored across the terminals of the capacitor 28. During the rest of the image frame and before another programming corresponding to a new frame, the drain current I d continues to cross the modulator 14 and the transmitter 2 until the voltage across the storage capacity 18 is discharged during a new step A of initialization of this addressing circuit. At the end of step C of programming an addressing circuit 6 associated with a first transmitter 2, the control pilots 20, 22 and the compensation means 12 are used for the programming of another circuit of addressing associated with a second transmitter in the same column. During the initialization step A of the addressing circuit associated with the second transmitter, the first transmitter 2 continues to transmit. The generator V dd which supplied power to the transmitter 2 during the programming step C continues to supply it as long as the gate voltage of the modulator 14 is greater than its trigger threshold voltage. FIG. 4 represents an alternative embodiment of the invention in which the control means 3 are identical to those shown in FIG. 1. However, the addressing circuit 6 driving a light emitter 2 with conventional structure is replaced by a addressing circuit 66 driving a light emitter with a so-called inverted structure. In this type of circuit, the cathode of the emitters 52 forms the interface with the active matrix and the anode of the emitters 52 is connected to the power supply generator V dd - The source of the modulator 54 is connected to a ground or to a negative voltage generator. The cathode of the emitter 52 is connected to the drain of the modulator 54. The storage capacity 58 is connected between the grid and the source of the modulator 54. A switch 56 is addressed in current I da t a by an addressing electrode 60 and is selected by a selection electrode 68. The power supply generator V dd is directly connected to all the transmitters 52 of all the columns without the interposition of a switching unit. Consequently, this generator V dd supplies power to all the transmitters 52 during the programming step C and during the step D throughout the duration of the image frame. Consequently, it is the power supply means V ss which are connected separately to the compensation means 12. As the supply means are directly connected to each modulator or directly connected to each emitter of a column, the electrical diagram of the display device is simplified and technically more easily achievable. As each power supply generator V ss is capable of supplying all of the emitters 2 of a column and since each addressing electrode 60 is also capable of addressing all of the emitters 2 of a column, the means compensation 12 are able to successively compensate the trigger threshold voltage V th of all the modulators 14 of a column. Furthermore, as the compensation means 12 determine the duration of the signal before each frame, the variations in the triggering threshold linked to the aging of the modulators are automatically compensated. Advantageously, no switching unit is interposed between the generator V d or V ss and the modulator 14 or the transmitter 52 to switch between two power sources of the transmitter during the programming and transmission process of this one. As a result, the useful light-emitting area of the pixels is increased. As the addressing circuit is addressed by an analog rather than digital current or voltage, the control means are simplified and their implementation is facilitated. Advantageously, the means for compensating all the columns compensate for the dispersions of the triggering threshold voltages of the modulators of control circuits of an active matrix screen. Advantageously, the unit 26 for measuring the current passing through a modulator during a programming step C makes it possible to dispense with a switching unit associated with each transmitter. Advantageously, since the intensity of the driving current I ata is high, the stray capacitances generated by the addressing column of the display panel are quickly loaded. As a result, the display device is addressed instantly.

Claims

REVENDICATIONS 1. Dispositif d'affichage d'images à matrice active comprenant : - plusieurs émetteurs (2 ; 52) de lumière formant un réseau d'émetteurs répartis en lignes et en colonnes ; - des moyens d'alimentation en puissance (Vdd) aptes à alimenter en courant simultanément l'ensemble des émetteurs (2 ; 52) d'une colonne, pendant une étape d'émission et une étape de programmation des émetteurs (2 ; 52) ; - des moyens de commande (3) de l'émission des émetteurs (2 ; 52) comprenant : - pour chaque émetteur (2 ; 52) du réseau, un modulateur (14 ; 54) de courant comportant une électrode de source, une électrode de drain, une électrode de grille, ledit modulateur étant apte à être traversé par un courant de drain (Id) pour alimenter ledit émetteur (2 ; 52), pour une tension entre le drain ou la source et la grille supérieure ou égale à une tension de seuil de déclenchement (Vth) ; - pour chaque colonne d'émetteurs (2 ; 52), des moyens d'adressage de colonne (10 ; 60) aptes à adresser successivement chaque émetteur (2 ; 52) de ladite colonne d'émetteurs par application d'une valeur (Idata, Vdata) représentative d'une consigne de données (UG) à l'électrode de grille du modulateur (14 ; 54) associé à cet émetteur (2 ; 52), pour le commander, au cours d'une étape de programmation, - pour chaque ligne d'émetteurs (2 ; 52), des moyens de sélection de ligne (8 ; 68) aptes à sélectionner successivement les émetteurs (2 ; 52) de chaque ligne d'émetteurs, pendant l'étape de programmation, - pour chaque modulateur (14 ; 54), des moyens de stockage (18) aptes à stocker des charges électriques à l'électrode de grille du modulateur (14 ; 54), et - des moyens de compensation (12) des tensions de seuil de déclenchement comprenant des moyens de comparaison (28), les moyens de comparaison (28) étant aptes à comparer, pendant l'étape de programmation d'un émetteur (2 ; 52) sélectionné, une valeur représentative du courant de drain (Id) alimentant l'émetteur sélectionné à la valeur (ldata. Vdata) représentative de la consigne de données (Uc), pour commander la quantité de charges stockées sur les moyens de stockage (18), caractérisé en ce que les moyens de compensation (12) comprennent pour chaque colonne d'émetteurs (2 ; 52) une unique unité (26) de détermination d'une valeur représentative du courant de drain (ld) alimentant l'émetteur sélectionné (2 ; 52) à partir d'une mesure d'une valeur représentative du courant d'alimentation de l'ensemble des émetteurs (2 ; 52) de la colonne. CLAIMS 1. Device for displaying active matrix images comprising: - several light emitters (2; 52) forming a network of emitters distributed in rows and columns; - power supply means (V dd ) capable of simultaneously supplying current to all of the transmitters (2; 52) of a column, during an emission step and a step of programming the emitters (2; 52 ); - control means (3) for the emission of the transmitters (2; 52) comprising: - for each transmitter (2; 52) of the network, a current modulator (14; 54) comprising a source electrode, an electrode drain, a gate electrode, said modulator being capable of being traversed by a drain current (I d ) to supply said transmitter (2; 52), for a voltage between the drain or the source and the gate greater than or equal to a trigger threshold voltage (Vt h ); - for each column of transmitters (2; 52), column addressing means (10; 60) capable of successively addressing each transmitter (2; 52) of said column of transmitters by applying a value (Idata , V d ata) representative of a data set point (U G ) at the gate electrode of the modulator (14; 54) associated with this transmitter (2; 52), to control it, during a step of programming, - for each line of transmitters (2; 52), line selection means (8; 68) capable of successively selecting the transmitters (2; 52) of each line of transmitters, during the programming step , - for each modulator (14; 54), storage means (18) capable of storing electrical charges at the gate electrode of the modulator (14; 54), and - means for compensating (12) for the voltages of triggering threshold comprising comparison means (28), the comparison means (28) being able to compare, during the programming step of a selected transmitter (2; 52), a value representative of the drain current (Id) supplying the selected transmitter at the value (l da ta. V da ta) representative of the data setpoint (U c ), for controlling the quantity of charges stored on the storage means (18), characterized in that the compensation means (12) comprise for each column of transmitters (2; 52) a single unit (26) for determining a value representative of the drain current (l d ) supplying the selected transmitter ( 2; 52) from a measurement of a value representative of the supply current of all the transmitters (2; 52) of the column.
2. Dispositif d'affichage d'images selon la revendication 1, caractérisé en ce que les moyens d'alimentation en puissance (Vdd) des émetteurs sont directement connectés à chaque modulateur (14) des moyens de commande. 2. Image display device according to claim 1, characterized in that the power supply means (V dd ) of the transmitters are directly connected to each modulator (14) of the control means.
3. Dispositif d'affichage d'images selon la revendication 1 , caractérisé en ce que les moyens d'alimentation en puissance (Vdd) des émetteurs sont directement connectés à chaque émetteur (2) d'une colonne. 3. Image display device according to claim 1, characterized in that the power supply means (V dd ) of the transmitters are directly connected to each transmitter (2) of a column.
4. Dispositif d'affichage d'images selon l'une quelconque des revendications précédentes, caractérisé en ce que les moyens d'alimentation en puissance (Vdd) des émetteurs comprennent un générateur d'alimentation en tension apte à alimenter l'ensemble des émetteurs d'une colonne, et en ce que les moyens de compensation (12) sont aptes à compenser successivement la tension de seuil de déclenchement (Vth) de chaque modulateur (14 ; 54) de l'ensemble des émetteurs d'une colonne. 4. Image display device according to any one of the preceding claims, characterized in that the power supply means (V dd ) of the transmitters comprise a voltage supply generator capable of supplying all of the transmitters of a column, and in that the compensation means (12) are capable of successively compensating the triggering threshold voltage (V th ) of each modulator (14; 54) of all the transmitters of a column .
5. Dispositif d'affichage d'images selon l'une quelconque des revendications précédentes, caractérisé en ce que les moyens de compensation5. Image display device according to any one of the preceding claims, characterized in that the compensation means
(12) comprennent en outre : - un générateur de pilotage (30) apte à générer un signal de pilotage ('data) appliqué à la grille dudit modulateur (14 ; 54), - des moyens (28, 34) de modulation de la durée dudit signal de pilotage (Idata) en fonction de la valeur de la consigne de données (Uc) et de la valeur de la tension de seuil de déclenchement (Vth). (12) further comprise: - a control generator (30) capable of generating a control signal (' d at a ) applied to the gate of said modulator (14; 54), - means (28, 34) for modulation the duration of said control signal (I d ata) as a function of the value of the data setpoint (U c ) and of the value of the triggering threshold voltage (Vt h ).
6. Dispositif d'affichage d'images selon l'une quelconque des revendications précédentes, caractérisé en ce que la consigne de données (Uc) est une tension de données et en ce que les moyens de comparaison (28) sont aptes à émettre un signal d'avertissement (S) lorsque la tension représentative de l'intensité du courant de drain (Id) est égale à un nombre de fois ladite tension de données. 6. Image display device according to any one of the preceding claims, characterized in that the data setpoint (U c ) is a data voltage and in that the comparison means (28) are capable of transmitting a warning signal (S) when the voltage representative of the intensity of the drain current (I d ) is equal to a number of times said data voltage.
7. Dispositif d'affichage d'images selon la revendication 5 en combinaison avec la revendication 6, caractérisé en ce que les moyens de modulation de la durée du signal de pilotage (Idata) comprennent : - un interrupteur (32) connecté en série au générateur de pilotage (30), - une unité de contrôle (34) apte à la commuter ledit interrupteur (32) d'une part lors de la réception de la consigne de données (Uc) et, d'autre part lors de la réception du signal d'avertissement (S). 7. Image display device according to claim 5 in combination with claim 6, characterized in that the means for modulating the duration of the control signal (I data ) comprise: - a switch (32) connected in series to the pilot generator (30), a control unit (34) able to switch said switch (32) on the one hand when receiving the data set point (U c ) and, on the other hand when receipt of the warning signal (S).
8. Dispositif d'affichage d'images selon l'une quelconque des revendications 5 à 7, caractérisé en ce que le signal de pilotage (Idata) généré par le générateur de pilotage (30) est modulé en amplitude en fonction de la valeur de la consigne de données (Uc). 8. Image display device according to any one of claims 5 to 7, characterized in that the control signal (I da ta) generated by the control generator (30) is amplitude-modulated as a function of the data setpoint value (U c ).
9. Dispositif d'affichage d'images selon l'une quelconque des revendications 5 à 8, caractérisé en ce que le générateur de pilotage (30) est un générateur de courant et le modulateur (14 ; 54) est apte à être piloté en courant. 9. Image display device according to any one of claims 5 to 8, characterized in that the control generator (30) is a current generator and the modulator (14; 54) is able to be controlled by current.
10. Dispositif d'affichage d'images selon l'une quelconque des revendications 5 à 8, caractérisé en ce que le générateur de pilotage (30) est un générateur de tension en rampe et le modulateur (14 ; 54) est apte à être piloté en tension. 10. Image display device according to any one of claims 5 to 8, characterized in that the pilot generator (30) is a ramp voltage generator and the modulator (14; 54) is able to be piloted in tension.
11. Dispositif d'affichage d'images selon l'une quelconque des revendications précédentes, caractérisé en ce que les moyens de compensation11. Image display device according to any one of the preceding claims, characterized in that the compensation means
(12) comprennent en outre une unité de mesure (26) de l'intensité d'un courant apte à mesurer l'intensité du courant de drain (ld) traversant un émetteur sélectionné (2) au cours de l'étape de programmation (C). (12) further comprise a measurement unit (26) of the intensity of a current capable of measuring the intensity of the drain current (l d ) passing through a selected transmitter (2) during the programming step (VS).
12. Dispositif d'affichage d'image selon la revendication 11 , caractérisé en ce que les moyens d'alimentation comprennent une ligne (4) à laquelle l'unité de mesure (26) est directement raccordée. 12. Image display device according to claim 11, characterized in that the supply means comprise a line (4) to which the measurement unit (26) is directly connected.
13. Dispositif d'affichage d'images selon l'une quelconque des revendications précédentes, caractérisé en ce que les moyens de stockage comprennent au moins une capacité de stockage (18) reliée à la grille et à la source du modulateur (14), et en ce que les moyens de compensation (12) comprennent en outre des moyens d'initialisation (36) aptes à appliquer une impulsion de tension à ladite capacité pour la décharger. 13. Image display device according to any one of the preceding claims, characterized in that the storage means comprise at least one storage capacity (18) connected to the grid and to the source of the modulator (14), and in that the compensation means (12) further comprises initialization means (36) able to apply a voltage pulse to said capacitor to discharge it.
EP04816458A 2003-12-23 2004-12-21 Device for displaying images on an oled active matrix Not-in-force EP1697920B1 (en)

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