Driver for Controlling a Light Emitting Element, in Particular an Organic Light Emitting Diode

• US 20090206764A1
• Filed: 05/11/2007
• Published: 08/20/2009
• Est. Priority Date: 05/18/2006
• Status: Active Grant

• Current Assignee: Magnolia Licensing LLC (IP Edge LLC)
• Original Assignee: Thomson Licensing (Vantiva SA)
• Inventors: Haas, Gunther, Le Roy, Philippe, Schemmann, Heinrich
• Granted Patent: US 8,836,615 B2
• Time in Patent Office: Days
• US Class Current: 315/241.R
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than one capacitor
• CPC Class Codes: G09G 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G11C 27/024 using a capacitive memory element G11C27/04 takes precedence
• CPC Class Codes: H02H 9/001 limiting speed of change of electric quantities, e.g. soft switching on or off progressive control of electronic switches for eliminating interferences H03K17/16
• CPC Class Codes: H05B 45/60 Circuit arrangements for operating LEDs comprising organic material, e.g. for operating organic light-emitting diodes [OLED] or polymer light-emitting diodes [PLED]
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

The present invention relates to a circuit for controlling a light emitting element, in particular an organic light emitting diode. The circuit comprises a capacitor connectable with the light emitting element, charging means for charging the capacitor and a switching means. The switching means is adapted to alternately disconnect the capacitor from the light emitting element and connect the capacitor to the light emitting element. The capacitor is alternately charged and discharged. A charging current or a discharge current from the capacitor drives the current of the light emitting element. Said charging means comprises at least one charging transistor for charging the capacitor.

Claims

1-10. -10. (canceled)

11. A circuit for controlling a light emitting element, in particular an organic light emitting diode, comprising:

a first capacitor connectable with the light emitting element,

charging means for charging the capacitor, wherein said charging means comprises a current control means for controllably charging the first capacitor,

the current control means having a control electrode responsive to a control voltage,

switching means adapted to alternately connect and disconnect the first capacitor from the charging means and for correspondingly connecting the capacitor to the light emitting element, wherein the switching means are arranged in such a way that the first capacitor can alternately be charged and discharged, and wherein a charging current or a discharge current from the first capacitor substantially corresponds to the current of the light emitting element,

wherein the circuit further comprises a diode or transistor adapted to operate as a diode, the diode or diode transistor being connected to the anode or cathode of the light emitting element for controlling the potential of the anode or cathode of the light emitting element.

12. The circuit of claim 11, wherein the current control means of the charging means include at least one charging transistor operating as a controllable current source or controllable resistor.

13. The circuit according to claim 12, wherein said charging means include a storage capacitor connected to the control electrode for storing the control voltage.

14. The circuit of claim 13, wherein said charging means is adapted to controllably receive a predetermined programming voltage to the storage capacitor.

15. The circuit of claim 11, wherein said first capacitor is connectable with the anode or cathode of the light emitting element.

16. The circuit of claim 11, wherein the drain or source electrode of the charging transistor is connected to the first capacitor and the said charging means is adapted to continuously increase or decrease a gate voltage of the charging transistor for providing an essentially constant drain or source current.

17. The circuit of claim 11, comprising discharging means for discharging the first capacitor, said discharging means comprising a switching transistor, which is adapted to selectively either connect the first capacitor to a predetermined potential, in particular ground potential, short-circuit both electrodes of the first capacitor, or connect the first capacitor in a reversed manner between a reference potential and the light emitting element.

18. An active matrix display comprising a plurality of light emitting elements and a plurality of circuits according to claim 11, wherein an individual circuit is provided for each light emitting element.

19. A method for controlling an electronic circuit comprising:

a capacitor connectable with a light emitting element,

charging means including a current control means for charging the capacitor,

the current control means having a transistor with a control electrode responsive to a control voltage and a storage capacitor connected to the control electrode with a first electrode for storing the control voltage,

switching means arranged for selectively connecting the capacitor to the charging means and to the light emitting element,

a diode or transistor adapted to operate as a diode, the diode or diode transistor being connected to the anode or cathode of the light emitting element;

the method comprising the steps of;

applying a control voltage to the control electrode for controlling the current control means in the charging means so as to set a predetermined current for charging the capacitor;

alternately connecting and disconnecting the capacitor and the charging means and correspondingly connecting the capacitor to the light emitting element by correspondingly controlling the switching means, thereby charging and discharging the capacitor, wherein the charging current or the discharge current of the capacitor substantially corresponds to the current through the light emitting element;

wherein the method, for compensating for the threshold voltage of the transistor of the current control means, further comprises the steps of;

connecting the diode or diode transistor so as to short circuit the light emitting element;

changing the potential of a second electrode of the storage capacitor by an amount sufficient for the transistor of the current control means to begin to conduct.