EP1383103A1 - Automatische Anpassung der Versorgungsspannung eines Elektrolumineszenz-Anzeigeschirmes in Abhängigkeit der gewünschten Luminanz - Google Patents

Automatische Anpassung der Versorgungsspannung eines Elektrolumineszenz-Anzeigeschirmes in Abhängigkeit der gewünschten Luminanz Download PDF

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Publication number
EP1383103A1
EP1383103A1 EP03300065A EP03300065A EP1383103A1 EP 1383103 A1 EP1383103 A1 EP 1383103A1 EP 03300065 A EP03300065 A EP 03300065A EP 03300065 A EP03300065 A EP 03300065A EP 1383103 A1 EP1383103 A1 EP 1383103A1
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Prior art keywords
voltage
signal
current
bias voltage
pol
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EP03300065A
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English (en)
French (fr)
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EP1383103B1 (de
Inventor
Celine Mas
Eric Benoit
Olivier Scouarnec
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STMicroelectronics SA
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STMicroelectronics SA
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    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3216—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using a passive matrix
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
    • G09G3/3275—Details of drivers for data electrodes
    • G09G3/3283—Details of drivers for data electrodes in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • 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
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
    • G09G2330/02—Details of power systems and of start or stop of display operation
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
    • G09G2330/02—Details of power systems and of start or stop of display operation
    • G09G2330/021—Power management, e.g. power saving
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
    • G09G2330/08—Fault-tolerant or redundant circuits, or circuits in which repair of defects is prepared
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
    • G09G2330/12—Test circuits or failure detection circuits included in a display system, as permanent part thereof
    • 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]

Definitions

  • the present invention relates to matrix screens with electroluminescent display composed of a set of diodes emitting. These are for example screens composed of organic light emitting diodes (“OLED”) Display) or polymer (“PLED” from English Polymer Light Emitting Display).
  • OLED organic light emitting diodes
  • PLED polymer
  • the present invention relates more particularly regulating the supply voltage of the controls the light emitting diodes of such screens.
  • FIG. 1 represents a matrix screen comprising n columns C 1 to C n and k lines L 1 to L k making it possible to address n * k light-emitting diodes d whose anodes are connected to a column and the cathodes to a line.
  • Line control circuits CL 1 to CL k make it possible to respectively polarize the lines L 1 to L k . Only one line is activated at a time, and is polarized to ground. The non-activated lines are biased at a voltage Vline.
  • Column control circuits CC 1 to CC n make it possible to respectively polarize the columns C 1 to C n .
  • the columns addressing the light-emitting diodes which it is desired to activate are polarized by a current at a voltage V col greater than the threshold voltage of the light-emitting diodes of the screen.
  • the columns that you do not want to activate are grounded.
  • a light-emitting diode connected to the activated line and to a V col polarized column is then on and emits light.
  • the line voltage V is provided high enough so that the light-emitting diodes connected to the non-activated lines and to the columns at the voltage V col are not conductive and do not emit light.
  • FIG. 2 represents a column control circuit CC and a line control circuit CL addressing respectively a column C and a line L connected to a light-emitting diode d of the screen.
  • the line control circuit CL comprises a power inverter 1 controlled by a line control signal ⁇ L.
  • the power inverter 1 comprises an NMOS transistor 2 making it possible to discharge the line L when ⁇ L is at the high level and a PMOS transistor 3 making it possible to charge the line L at the bias voltage V line when ⁇ L is at the low level.
  • the CC column control circuit comprises a current mirror produced in the present example with two PMOS type transistors 4, 5.
  • the transistor 4 constitutes the reference branch of the mirror and the transistor 5 constitutes the duplicating branch.
  • the sources of transistors 4 and 5 are connected to a bias voltage V pol of the order of 15 V for OLED screens.
  • the gates of the transistors 4 and 5 are connected to each other.
  • the drain and the gate of transistor 4 are connected to each other.
  • the transistor 4 is therefore mounted as a diode, the source-gate voltage (Vsg 4 ) being equal to the source-drain voltage (Vsd 4 ).
  • the current passing through the transistor 4 is fixed by a current source 6 connected to the drain of the transistor 4.
  • the current source 6 provides a current I l called "luminance".
  • the drain of transistor 5 is connected to column C via a column selection circuit composed of a PMOS transistor 7 and an NMOS transistor 8.
  • the source of PMOS transistor 7 is connected to the drain of transistor 5 and the drain of transistor 7 is connected to column C.
  • the source of transistor 8 is grounded and its drain is connected to column C.
  • a column control signal ⁇ C is connected to the gate of PMOS transistor 7 and at the gate of the NMOS transistor 8.
  • the column control signal ⁇ C When the column control signal ⁇ C is at the high level, the transistor 8 discharges the column C.
  • the transistor 7 is on and the column C loads up 'to reach the voltage V col .
  • line L and column C are activated, the control signals for line ⁇ L and column ⁇ C are respectively high and low, the light-emitting diode d is conducting and the current passing through the diode is equal to the luminance current I l .
  • the bias voltage V pol is equal to the sum of the source-drain voltage Vsd 2 of the transistor 2, of the voltage V d at the terminals of the light-emitting diode d, of the source-drain voltage Vsd 7 of the transistor 7 and of the source-drain voltage Vsd 5 of transistor 5.
  • the transistor 5 When the copying of the current I l is correct, the transistor 5 is in saturation mode and the voltage Vsd 5 is at least equal to the source-drain voltage Vsd 4 of the transistor 4.
  • a correct copying therefore requires that the bias voltage V pol is at least equal to the sum previously mentioned when the current flowing through it is equal to the luminance current I l . If the bias voltage V pol is too low, the current passing through the light-emitting diode d is less than the current I l and the luminance of the diodes is insufficient.
  • the luminance current I l supplied by the current source 6 can generally vary as a function of the desired luminance for the screen.
  • the source-drain voltage Vsd 4 of the diode-mounted transistor 4 increases and the voltage V d of the light-emitting diode d also increases. It follows that the bias voltage V pol must be large enough for the transistor 5 to be in saturation whatever the luminance current.
  • An object of the present invention is to provide a column control circuit whose polarization voltage V pol is as low as possible regardless of the aging of the light-emitting diodes of the screen.
  • Another object of the present invention is to provide a control circuit of simple design.
  • the present invention provides a device for regulating the bias voltage of control circuits for columns of a matrix screen composed of light-emitting diodes each connected to one of the lines and to one of the columns of the screen, the circuits of column control comprising a compound current mirror a reference branch and several branches of duplication related to the bias voltage, each branch of duplication being connected to a column of the screen, the branch being connected at a reference point to a reference current source providing a current of desired luminance, the device comprising: first measuring means providing a first signal representative of the tension of at least one of the columns; second means of measurement providing a second signal representative of the voltage at the reference point; and an adjustment circuit receiving the first and second signals and adapted to increase the voltage of polarization when the first signal is greater than the second signal and vice versa.
  • each branch of the current mirror has a PMOS type field effect transistor whose source is connected to the bias voltage, the gates of each branch being connected together, the drain and the grid of the transistor of the reference branch being connected to the source reference current, the branch transistor drains duplicates being connected to the columns.
  • the first measuring means include for each column a diode whose anode is connected to the column and whose cathode is connected on the one hand to a first source of observation current and on the other hand connected to a first input of the adjustment circuit, and in which the second measurement means include a diode whose anode is connected to the reference point and whose cathode is connected to a second source of observation current and to a second input of the adjustment circuit.
  • the cathodes of each of the diodes are connected to the first input of the adjustment circuit via a switch, a capacitor being placed between the first input of the adjustment circuit and a fixed potential point.
  • the adjustment circuit includes an amplifier receiving the first signal on its positive input and receiving the second signal on its negative input, the output of the error amplifier being connected to a converter DC-DC voltage supplying the output voltage polarization and adapted to increase the polarization voltage when the first signal is greater than the second signal and Conversely.
  • the error amplifier includes first and second PMOS transistors whose gates are connected the positive and negative inputs of the error amplifier, the source of each of the first and second transistors being connected to the bias voltage by a current source, the sources of the first and second transistors being connected by a resistor, the drains of first and second transistors being connected to a converter providing the error signal, the source and drain of a third PMOS transistor being connected to the source and drain of the first transistor, the gate of the third transistor being polarized at a fixed voltage.
  • the present invention also provides a method of regulation of the bias voltage of control circuits columns of a matrix screen composed of diodes electroluminescent connected each to one of the lines and to a screen columns, column control circuits comprising a current mirror composed of a branch of reference and several duplication branches linked to the bias voltage, each branch of duplication being connected to a column of the screen, the reference branch being connected at a reference point to a current source of reference providing a desired luminance current, characterized in that it comprises the following stages: supplying a first signal representative of the voltage of at least one of columns; provide a second signal representative of the voltage at the reference point; and increase the bias voltage when the first signal is greater than the second signal and Conversely.
  • the first signal is the image of the voltage maximum of activated light emitting diodes.
  • FIG. 3 is a diagram of an embodiment of column control circuits and of the device for regulating the bias voltage V pol according to the present invention.
  • the column control circuits include a current mirror 9 composed of a reference branch b ref and n duplication branches b 1 to b n .
  • Each branch is composed of a PMOS transistor, P ref for the reference branch and P 1 to P n for the branches b 1 to b n.
  • the sources of the transistors of each of the branches are connected to the bias voltage V pol and the gates are connected to each other.
  • the drain and the gate of the transistor P ref of the reference branch are connected to a reference current source 10 at a point C ref .
  • the reference current source 10 provides a luminance current I l .
  • each transistor P i i being between 1 and n, is connected to a column C i of the screen by means of a column selection circuit as described in relation to FIG. 2.
  • L all the column selection circuits are represented by a selection device 11 controlled by a column signal ⁇ C.
  • Each column C 1 to C n is connected to the anode of a diode respectively D 1 to D n .
  • the cathodes of diodes D 1 to D n are connected to a current source 15 at a point C o .
  • the current source 15 provides a so-called observation current I ob chosen to be low compared to the minimum luminance current.
  • the connection point C ref is connected to the anode of a diode D ref identical to the diodes D 1 to D n
  • the cathode of the diode D ref is connected at a point C oref to a current source 16 providing a current equal to the observation current I ob .
  • the points C ref and C oref are connected to two inputs of an adjustment circuit CR which supplies the bias voltage V pol .
  • the light-emitting diodes can, even when they are crossed by the same current, present at their terminals different voltage drops. In particular, this voltage drop tends to increase when the light-emitting diodes age.
  • the present invention aims to adjust the voltage V pol to take account of these voltage variations and to ensure that the luminance current I l chosen flows through all the selected columns, V pol remaining as small as possible.
  • the diodes D 1 to D n corresponding to the selected columns tend to be conductive.
  • the diode connected to the column having the highest voltage imposes the voltage V o on the cathodes of the diodes D 1 to D n .
  • the other diodes are therefore not conductive because the voltage across their terminals is lower than their threshold voltage.
  • the voltage V o is the image of the voltage on the column at the highest potential shifted by a diode threshold voltage.
  • the voltage V oref at the connection point C oref is the image of the voltage Vref shifted by a diode threshold voltage.
  • the adjustment circuit CR then increases the bias voltage V pol until the voltages V o and V oref are equal.
  • the adjustment circuit decreases the polarization voltage V pol up to the minimum voltage V pol ensuring circulation of the luminance current I l in all the selected columns.
  • FIG. 4 is a diagram of the circuit for adjusting the bias voltage V pol as a function of the difference between the voltages V o and V oref .
  • the adjustment circuit comprises an error amplifier 20, an operational amplifier 21 and an RS flip-flop 22 operating with a low supply voltage, for example 3.3 V.
  • the error amplifier 20 receives on a positive input , the voltage V o and on a negative input, the voltage V oref .
  • the levels of the voltages V o and V oref are very high for the error amplifier 20, provision may be made for a voltage converter supplying voltages proportional to the voltages V o and V oref , over a voltage range more low.
  • the error amplifier 20 amplifies the difference between V o and V oref and provides an error signal er which varies for example between 1 and 2 V. When the voltages V o and V oref are equal, the error signal is for example 1.5 V. The higher the voltage V o with respect to V oref , the higher the error signal er and vice versa.
  • the signal er is applied to the positive input of the differential amplifier 21.
  • the output of the differential amplifier 21 is connected to the reset terminal R (reset) of the flip-flop RS 22.
  • the output of an oscillator osc is connected to the activation terminal S (set) of the flip-flop RS 22.
  • the output Q is at the high logic level (for example 3.3 V) when the activation terminal S is at the high level and at the low logic level (for example 0V) when the reset terminal R is high.
  • output Q keeps the last level set.
  • the output of the flip-flop RS 22 is connected to the gate of an NMOS transistor Tf.
  • a resistor R is placed between the source of the transistor Tf and the ground.
  • a coil L is placed between the drain of the transistor Tf and the supply terminal at a voltage V bat , for example at 3.3 V.
  • the anode of a diode D f is connected to the drain of the transistor Tf and its cathode is connected to a first electrode of capacitor C.
  • the second electrode of capacitor C is connected to ground.
  • the first electrode of the capacitor C supplies the voltage V pol .
  • the source of the transistor Tf is connected to the negative input of the differential amplifier 21.
  • the output Q of the flip-flop RS 22 goes high.
  • the transistor Tf closes and the voltage across the coil L quickly goes from 0 to V bat .
  • the voltage V R across the resistor R and the current in the coil L are initially zero.
  • the current in the coil L gradually increases, the voltage V R therefore also increases.
  • the amplifier 21 changes state and goes high.
  • the output Q of the flip-flop RS 22 goes to the low level and the transistor Tf opens.
  • the voltage on the drain of transistor Tf increases suddenly.
  • the diode Df becomes on and the capacitor C charges.
  • the load current is higher the higher the current passing through the coil L when the transistor Tf opens.
  • the bias voltage V pol is therefore adjusted as a function of the temporal variations of the voltage across the light-emitting diodes of the screen.
  • An advantage of the regulation device according to the present invention is that the bias voltage is always minimal, which saves money energy.
  • Another advantage of such a device is that its design is very simple.
  • FIG. 5 is a diagram of column control circuits identical to those of FIG. 3 as well as a diagram of an alternative embodiment of the device for regulating the bias voltage V pol which makes it possible to alleviate the following problem.
  • a line of the screen is "black", that is to say that no light-emitting diode of the selected line is conductive
  • the voltage V o at point C o of the regulation circuit of FIG. 3 decreases because none of the diodes D 1 to D n is conducting.
  • the adjustment circuit CR decreases the bias voltage V pol .
  • the bias voltage V pol can greatly decrease.
  • the conductive light-emitting diodes of the "lit” lines may then receive a current lower than the luminance current.
  • the overall screen brightness decreases.
  • the device for regulating the bias voltage V pol is identical to that of FIG. 3 except that the point C o is connected to the adjustment circuit CR by means of a switch 31.
  • a capacitor 32 is placed between the input of the adjustment circuit CR and the ground.
  • the switch 31 is controlled so as to be non-conducting when a line of the screen is black, that is to say when no light-emitting diode of the selected line is conductive.
  • the capacitor 32 retains the value of the voltage V o corresponding to the last non-black line.
  • the switch control device not shown, analyzes the column signal ⁇ C to know if at least one column is selected and therefore that at least one diode is conductive.
  • the switch control device analyzes the control signals of the line control circuits so as to turn on the switch 31 once the voltages of the selected columns have passed from their precharge voltages to their "operating" voltages corresponding to the voltages induced by each of the conductive light-emitting diodes.
  • An advantage of such a regulation device is that it makes it possible to adjust the bias voltage V pol as a function of the characteristics of the light-emitting diodes of the screen regardless of the number of consecutive black lines on the screen.
  • FIG. 6 is a diagram of an embodiment of the error amplifier 20 of the adjustment circuit CR of FIG. 4 which makes it possible to alleviate the following problem.
  • the voltage V o can be very close of the bias voltage V pol .
  • Such a defect leads not only to a disproportionate increase in the bias voltage V pol but also to overvoltages liable inter alia to deteriorate the adjustment circuit CR.
  • the detection of a manufacturing defect makes it possible to detect faulty circuits before their marketing.
  • the error amplifier shown in FIG. 6 comprises two PMOS transistors 40 and 41, the gates of which receive the voltages V o and V oref respectively from the regulation device shown in FIG. 3.
  • Two identical current sources 42 and 43 are placed between the bias voltage V pol and the sources of the transistors 40 and 41.
  • a resistor R1 is placed between the sources of the transistors 40 and 41.
  • the drains of the transistors 40 and 41 are connected to a conversion device 44 which supplies the error signal st.
  • a PMOS transistor 45 is placed in parallel on transistor 40.
  • the source of transistor 45 is connected to the source of transistor 40 and the drain of transistor 45 is connected to the drain of transistor 40.
  • the gate of transistor 45 receives a voltage "of protection "V protect which is provided by a device not shown.
  • the protection voltage V protect corresponds to the maximum voltage V o corresponding to correct operation of the screen and of the column and line control circuits.
  • the voltage V o is lower than the protection voltage V protect .
  • the transistors 40, 41 and 45 are such that when they conduct a current equal to that supplied by the current sources 42 and 43, their gate-source voltages is substantially equal to the threshold voltage of a PMOS transistor. Thus, when the voltage V o is less than the voltage V protect , the transistor 45 is non-conductive. Similarly, when the voltages V o and V oref are different the voltages on the sources of the transistors 40 and 41 are different. The resistance R1 is then crossed by a current which is higher the higher the difference between the voltages V o and V oref .
  • the conversion device 44 analyzes the current differences in the transistors 40 and 41 and provides an error signal er the higher the current in the transistor 40 is low compared to the current in the transistor 41 and vice versa.
  • the voltage V o can be very close to the bias voltage V pol .
  • the transistor 45 becomes conductive and the transistor 40 non-conductive.
  • the polarization voltage V pol is then maximum.
  • the maximum value of the voltage V pol depends on the choice of the voltage V protect and the voltage V oref which is a function of the desired luminance current.
  • the presence of transistor 45 ensures that the bias voltage V pol does not exceed a given maximum value and also makes it possible to suppress any overvoltages liable to damage the adjustment circuit CR.
  • the present invention is susceptible to various variants and modifications which will appear to those skilled in the art.
  • other devices for evaluating the current flowing in the light-emitting diodes of the screen may be provided, as well as other devices for adjusting the bias voltage V pol as a function of the differences between the desired luminance current. and the smallest current flowing through the LEDs on the screen.
  • those skilled in the art will be able to produce a current mirror different from that described, for example by using two transistors per branch.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
  • Control Of El Displays (AREA)
EP03300065A 2002-07-19 2003-07-17 Automatische Anpassung der Versorgungsspannung eines Elektrolumineszenz-Anzeigeschirmes in Abhängigkeit der gewünschten Luminanz Expired - Lifetime EP1383103B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR0209227 2002-07-19
FR0209227 2002-07-19

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US7755580B2 (en) 2010-07-13
EP1383103B1 (de) 2012-03-21
US20050035933A1 (en) 2005-02-17
US20040017725A1 (en) 2004-01-29

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