OLED luminance degradation compensation

• US 9,530,352 B2
• Filed: 07/30/2015
• Issued: 12/27/2016
• Est. Priority Date: 08/15/2006
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovations Inc.
• Inventors: Nathan, Arokia, Chaji, Gholamreza
• Primary Examiner(s): MARINELLI, PATRICK
• Application Number:
  US14/813,904
• Publication Number:
  US 20150339978A1
• Time in Patent Office: 516 Days
• Field of Search: 345 76- 83, 345204-215, 345690-699, 3151691-1694
• US Class Current: 1/1
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
• CPC Class Codes: G09G 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements
• 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]

Abstract

A system and method are disclosed for determining a pixel capacitance. The pixel capacitance is correlated to a pixel age to determine a current correction factor used for compensating the pixel drive current to account for luminance degradation of the pixel that results from the pixel aging.

Claims

1. A display for driving an array of a plurality of pixel circuits with a current compensated for luminance degradation, each of said pixel circuits having an electroluminescent device, the display comprising:

a display panel comprising the array of pixel circuits, the pixel circuits arranged in at least one row and a plurality of columns;

a column driver for driving the electroluminescent devices in the pixel circuits with a driving current;

a base pixel including an electroluminescent device not driven by display currents;

a read block for determining a capacitance of an electroluminescent device of a pixel circuit and for determining a capacitance of an electroluminescent device of the base pixel; and

a control block for correlating a difference between the determined capacitances of the electroluminescent devices in the pixel circuit and the base pixel to a current correction factor for the electroluminescent device of the pixel circuit, and for controlling the operation of the column driver and the read block, the control block being operable to adjust the driving current based on the current correction factor, and to drive the electroluminescent device with the compensated drive current.

2. The display as claimed in claim 1, wherein the array of pixel circuits includes at least two rows of pixel circuits;

and the display further comprising;

a row driver for selecting the row of pixel circuits to be driven by the column driver.

3. The display as claimed in claim 2, wherein each pixel circuit comprises:

a driving transistor for driving the electroluminescent device to emit light based on the driving current; and

a switching transistor, controlled by the row driver, to selectively connect the driving transistor to the column driver.

4. The display as claimed in claim 3, wherein the electroluminescent device is an organic light emitting diode.

5. The display as claimed in claim 3, wherein the read block comprises:

a plurality of read block elements, each read block element comprising;

a switch for electrically connecting and disconnecting the read block element to a pixel circuit of the plurality of pixel circuits;

an operational amplifier electrically connected to the switch; and

a read capacitor connected in parallel with the operational amplifier.

6. The display as claimed in claim 1, wherein each pixel circuit comprises:

a transistor for controlling the driving current from the column driver such that the electroluminescent device emits light based on the driving current.

7. The display as claimed in claim 6, wherein the electroluminescent device is an organic light emitting diode.

8. The display as claimed in claim 6, wherein the read block comprises:

a plurality of read block elements, each read block element comprising;

a switch for electrically connecting and disconnecting the read block element to a pixel circuit of the plurality of pixel circuits and electrically connecting and disconnecting the read block element to the base pixel;

an operational amplifier electrically connected to the switch; and

a read capacitor connected in parallel with the operational amplifier.

9. The display as claimed in claim 1, wherein the control block operates the display in one of at least two modes:

a display mode wherein the control block controls the current driver for driving the plurality of pixel circuits with a current based on a display signal and the current correction factor, to emit light; and

a read mode wherein the control block controls the read block to determine the capacitance of the electroluminescent device of a pixel circuit of the plurality of pixel circuits and to determine the capacitance of the electroluminescent device of the base pixel, the control block determining the current correction factor based on the difference between and the determined capacitance of the electroluminescent device of the pixel circuit and the determined capacitance of the electroluminescent device of the base pixel.

10. The display as claimed in claim 1, wherein the electroluminescent devices in the array of pixel circuits and in the base pixel are organic light emitting diodes.