Active-matrix display, the emitters of which are supplied by voltage-controlled current generators

• US 20060232522A1
• Filed: 04/13/2006
• Published: 10/19/2006
• Est. Priority Date: 04/14/2005
• Status: Active Grant

• Current Assignee: InterDigital CE Patent Holdings SAS (InterDigital, Inc.)
• Original Assignee: Thomson Licensing (Vantiva SA)
• Inventors: Prat, Christophe, Roy, Philippe Le, Martin, Pierrick
• Granted Patent: US 7,548,222 B2
• Time in Patent Office: Days
• US Class Current: 345/76
• CPC Class Codes: G09G 2300/043 Compensation electrodes or other additional electrodes in matrix displays related to distortions or compensation signals, e.g. for modifying TFT threshold voltage in column driver
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 3/30 using electroluminescent panels
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

The display comprises an array of pixel circuits each comprising an emitter 1 in series with a current modulation transistor, and at least one address circuit, which integrates, for each column, a differential amplifier and a passive element preferably a resistive element, which cooperate with the current modulation transistors so as to form, during address phases in which the emitters are switched “out of the circuit”, a voltage-programmable current generator. After the address phases, thanks to a suitable switch, the emitters are switched “into the circuit” and supplied with the preprogrammed current. Such a display allows the image display quality to be inexpensively improved.

Claims

1. Active-matrix display comprising an array of light emitters of the current-controllable type and an array of pixel circuits, each comprising at least one of said emitters that are distributed in rows and columns, at least one generator for supplying said emitters having first and second supply output terminals, at least one circuit capable of selecting pixel circuits for any one row and at least one circuit capable of simultaneously addressing a voltage representative of an image datum to be displayed at each of the pixel circuits of any one row selected, where each pixel circuit comprises, in addition to at least one emitter:

a voltage-controlled current modulation transistor, comprising a voltage drive electrode and two current electrodes, namely what is called a source electrode and what is called a drain electrode which is connected to said first supply output terminal of the at least one generator;

a first switch and a second switch, each provided with a drive electrode; and

a memory element capable of charging and maintaining, over the duration of display of an image, a drive voltage on said drive electrode of the modulation transistor,

in which the at least one data address circuit comprises, for each column of pixels, first and second column electrodes, a differential amplifier having an output connected to said first column electrode, an inverting input connected to said second column electrode, and a non-inverting input for addressing said voltage representative of an image datum,

said first column electrode being able to be connected to the drive electrode of the modulation transistor of each of the pixel circuits of said column by means of said first switch of this circuit,

said second column electrode being able to be connected to said source electrode of the current modulation transistor of each of the same pixel circuits by means of said second switch of this circuit and

in which the at least one row select circuit comprises, for each row of pixels, at least one row electrode that is connected to the drive electrode of the first and second switches of each of the pixel circuits of this row,

wherein;

the at least one data address circuit comprises, for each column of pixels, a passive element having two terminals, one being connected to said second column electrode of said column, the other being connected to the second supply output terminal of the at least one generator; and

said display includes at least a third switch able to connect, through the at least one emitter of each of the pixel circuits, said source electrode of the current modulation transistor of said pixel circuit to the second supply output terminal of the at least one generator.

2. Display according to claim 1, wherein said passive element is a resistor.

3. Display according to claim 2, wherein each current modulation transistor is an n-type transistor.

4. Display according to claim 3, wherein said emitters are organic light-emitting diodes.

5. Display according to claim 4, wherein said diodes each comprise an organic electroluminescent layer inserted between an anode formed by a lower conducting layer in contact with said active matrix and a cathode formed by an upper conducting layer.

6. Display according to claim 5, wherein the cathodes of the various diodes form one and the same conducting layer common to all the diodes.

7. Display according to claim 1, wherein, each emitter having two supply input terminals, namely an anode and a cathode:

in each pixel circuit, the anode of the at least one emitter is connected to the source electrode of the modulation transistor of this circuit; and

the at least one third switch is able to connect to the cathode of the at least one emitter of each of the pixel circuits to the second supply output terminal of the at least one generator.

8. Method of driving a display according to claim 1 for displaying a succession of image frames, each image being made up of a set of image data, each datum being associated with a pixel of this image and with a representative voltage to be addressed to the circuit of this pixel, wherein it comprises, for displaying each image, a suitable programming phase for programming at least one set of pixel circuits in order to charge, in the memory element of each of the circuits of this set, a drive voltage capable of generating, via the modulation transistor of said circuit and the passive element of the address circuit for this circuit, a current proportional to the representative voltage addressed to this circuit, and an emission phase in which the emitters of the circuits of this set emit in which, for each of the circuits of this set, the same drive voltage is maintained by the memory element on the drive electrode of the modulation transistor of this circuit so as to generate, via the modulation transistor of said circuit and the at least one emitter of this pixel circuit, the same current I_d as during the programming phase.

9. Drive method according to claim 8, wherein, during each address phase, the at least one third switch, which is able to connect, via the at least one emitter of each of the pixel circuits of said set, the source electrode of the current modulation transistor of said pixel circuit, to the second supply output terminal of the at least one generator, is open and in that, during each emission phase, the at least one third switch is closed.

10. Drive method according to claim 9, wherein, during each address phase for a set of pixel circuits belonging to different rows, each of said different rows of pixel circuits is selected, by means of the at least one selection circuit, by applying, to the electrode of each row selected in succession, a logic signal capable of closing the first and second switches of each pixel circuit of said row belonging to said set.

11. Drive method according to claim 10, wherein, during said selection of each row of pixel circuits of said set, the voltage representative of the image datum that corresponds to said pixel is applied, by means of the at least one address circuit, to the non-inverting input of the operational amplifier of each pixel circuit of said row belonging to said set.