Compensating for aging in OLED devices

• US 20040135749A1
• Filed: 01/14/2003
• Published: 07/15/2004
• Est. Priority Date: 01/14/2003
• Status: Active Grant

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Eastman Kodak Company
• Inventors: Kondakov, Denis Y., Young, Ralph H., Milch, James R., Sandifer, James R.
• Granted Patent: US 7,079,091 B2
• Time in Patent Office: Days
• US Class Current: 345/82
• 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 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/048 using evaluation of the usage time
• CPC Class Codes: G09G 3/3208 organic, e.g. using organic light-emitting diodes [OLED]

Abstract

A method of adjusting the voltage applied across the pixels of an OLED display to compensate for aging including measuring the accumulation of trapped positive charge to produce a signal representative of such accumulation, and responding to such signal to adjust the voltages applied across the pixels of the OLED to compensate for aging.

Claims

1. A method of adjusting the voltage applied across the pixels of an OLED display to compensate for aging, comprising the steps of:

a) measuring the accumulation of trapped positive charge to produce a signal representative of such accumulation; and

b) responding to such signal to adjust the voltages applied across the pixels of the OLED to compensate for aging.

2. A method of adjusting the voltage applied across the pixels of an OLED display to compensate for aging, comprising the steps of:

a) controlling a test voltage applied across the pixels of an OLED display to produce an output signal;

b) producing a signal representative of the degradation of the OLED pixels due to aging in response to such output signal; and

c) adjusting the input voltages applied to the OLED pixels during normal operation in response to such degradation signal to compensate for aging of the OLED device.

3. The method of claim 2 wherein sequence of steps a), b), and c) is performed during a power-up procedure.

4. The method of claim 2 wherein sequence of steps a), b), and c) is performed periodically during OLED device operation.

5. The method of claim 2 wherein step a) includes application of voltage ramp with constant dV/dt.

6. The method of claim 2 wherein step a) includes producing an AC voltage suitable for AC impedance measurement.

7. The method of claim 2 wherein step b) includes providing a current measuring circuit to produce a signal and differentiating such signal to provide a signal representative of the degradation of the OLED pixels

8. The method of claim 2 wherein step b) includes integrating circuit and measuring an output of such circuit to produce a signal representative of the degradation of the OLED pixels.

9. The method of claim 2 wherein step c) includes current calculation using the following equation:

10. The method of claim 2 wherein step c) includes current calculation using the following equation:

I_t=a(V_t−

V₀)I₀

where, I_t is a required current at this time, I₀ is a previous required current, V_t−

V₀ is a change in the extent of device degradation (difference in inflection or midpoint transition voltages from I-V or C-V traces, or integrated currents from I-V traces), and the value of coefficient a is preferably determined by the separate aging calibration performed during short initial time (pre-burn) on the same device or during suitable aging time on a comparable device.