OLED display with aging and efficiency compensation

• US 7,355,574 B1
• Filed: 01/24/2007
• Issued: 04/08/2008
• Est. Priority Date: 01/24/2007
• Status: Active Grant

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Eastman Kodak Company
• Inventors: Leon, Felipe A., White, Christopher J., Parrett, Gary
• Primary Examiner(s): VO, TUYET THI
• Application Number:
  US11/626,563
• Time in Patent Office: 440 Days
• Field of Search: 345/82, 345 76- 78, 345 90- 92, 345/101, 345/102, 345/204, 345/207, 345/211, 345/212, 345/214, 345/55, 345/63, 315/169.3, 315/169.4
• US Class Current: 345/82
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• 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

Abstract

Compensated drive circuit adjusting for changes in the threshold voltage of a drive transistor and for aging of an OLED device, comprising: a data line carrying analog data representative of the brightness level, and a select line; the drive transistor connected to a power supply and to the OLED device such that when the select line is activated and a voltage from the data line is applied to the gate electrode of such transistor and current proportional to the applied voltage will flow through the drain and source electrodes through the OLED device; circuitry for measuring first and second parameters associated with the drive circuitry and responsive to the measured first and second parameters for computing offset voltages to adjust for changes in the threshold voltage of the drive transistors and for aging of the OLED device.

Claims

1. A compensated drive circuit adjusting for changes in the threshold voltage of a drive transistor and for aging of an OLED device, comprising:

a. a data line carrying analog data representative of the brightness level desired from the OLED device, and a select line;

b. the drive transistor connected to a power supply and to the OLED device such that when the select line is activated and a voltage from the data line is applied to the gate electrode of such transistor, current proportional to the applied voltage will flow through the drain and source electrodes through the OLED device;

c. means for measuring first and second parameters associated with the drive circuitry, the first parameter being a function of the voltage across the OLED device, and the second parameter being a function of the current passing through the OLED device; and

d. means responsive to the measured first and second parameters for computing offset voltages to be applied to the data line analog voltages to adjust for changes in the threshold voltage of the drive transistors and for aging of the OLED device.

2. The drive circuit of claim 1 wherein the drive transistor is an amorphous silicon transistor.

3. The OLED device of claim 1, wherein the responsive means further includes a lookup table having an offset voltage for each of the OLED devices.

4. The OLED device of claim 1, wherein the responsive means sequentially activates individual OLED devices to measure the first and second parameters associated with each OLED device.

5. The OLED device of claim 1, wherein the responsive means activates one or more OLED devices at a plurality of different brightness levels to compute the offset voltage.

6. A method of adjusting for changes in the threshold voltage of the drive transistor and aging of an OLED device, comprising:

a. providing a data line carrying analog data representative of the brightness level desired from the OLED device, and a select line;

b. providing a drive transistor connected to a power supply and to the OLED device such that when the select line is activated and a voltage from the data line is applied to the gate electrode of such transistor, current proportional to the applied voltage will flow through the drain and source electrodes through the OLED device;

c. measuring first and second parameters associated with the drive transistor and the OLED device, wherein the first parameter is a function of the voltage across the OLED device, and the second parameter is a function of the current passing through the drive transistor and the OLED device; and

d. computing offset voltages applied to the data line analog voltages for adjusting for changes in the threshold voltage of the drive transistors and aging of the OLED device.