Compensation technique for luminance degradation in electro-luminance devices

• US 10,019,941 B2
• Filed: 05/01/2014
• Issued: 07/10/2018
• Est. Priority Date: 09/13/2005
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Nathan, Arokia, Chaji, Gholamreza, Jafarabadiashtiani, Shahin
• Primary Examiner(s): DAVIS, TONY O
• Application Number:
  US14/266,901
• Publication Number:
  US 20140232623A1
• Time in Patent Office: 1,531 Days
• Field of Search: 345204, 345 76, 345 82
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• 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 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 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2320/0252 Improving the response speed
• 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 3/3258 with pixel circuitry controlling the voltage across the light-emitting element

Abstract

A method and system for compensation for luminance degradation in electro-luminance devices is provided. The system includes a pixel circuit having a light emitting device, a storage capacitor, a plurality of transistors, and control signal lines to operate the pixel circuit. The storage capacitor is connected or disconnected to the transistor and a signal line(s) when programming and driving the pixel circuit.

Claims

1. A pixel circuit comprising:

a light emitting device having an initial ON voltage;

a power source for supplying a driving current to said light emitting device;

a driving transistor having a first terminal coupled to said power source and a second terminal coupled to said light emitting device, for supplying a driving current to the light emitting device during a driving cycle, the driving transistor also having a gate terminal, the driving transistor having a threshold voltage less than said initial ON voltage of said light emitting device;

a source of a programming voltage;

a storage capacitor having a first terminal coupled to said gate terminal of said driving transistor, and a second terminal coupled to said source of the programming voltage and to a node between said driving transistor and said light emitting device for charging to a voltage that is a function of said programming voltage and said initial ON voltage of said light emitting device during a programming cycle, so that the voltage between said gate terminal and said second terminal of said driving transistor is a function of said programming voltage and said initial ON voltage of said light emitting device, at said node between said driving transistor and said light emitting device, during a driving cycle.

2. The pixel circuit of claim 1, further comprising:

a second transistor for providing a discharging connection between the first terminal of the storage capacitor and a drain terminal of the driving transistor during the programming cycle according to a second voltage signal supplied, via a second select line, to a gate terminal of the second transistor, the discharging connection providing a path to partially discharge the storage capacitor through the driving transistor and the light emitting device during the programming cycle.

3. The pixel circuit of claim 1, wherein the storage capacitor is configured to be charged with said initial voltage during a pre-charging cycle having a duration less than a duration of the programming cycle, said initial voltage exceeding a compensated voltage, the compensated voltage being substantially the same as the sum of a programming voltage, a threshold voltage of the driving transistor, and a voltage drop of the light emitting device.

4. The pixel circuit of claim 3, wherein the storage capacitor is configured to partially discharge during a compensation cycle having a duration less than the duration of the programming cycle, until the storage capacitor is charged with the compensated voltage and the current through the driving transistor and the light emitting device is substantially zero.

5. The pixel circuit of claim 3, wherein the compensated voltage is stored in the storage capacitor at the conclusion of the pre-charging cycle, and wherein the pre-charging cycle precedes the driving cycle of the pixel circuit.

6. The pixel circuit of claim 1, wherein the light emitting device is configured to emit light responsive to the driving current flowing through the light emitting device, and wherein the driving current flowing through the light emitting device is controlled-according to the gate-source voltage of the driving transistor during the driving cycle.

7. The pixel circuit of claim 6, wherein the pixel circuit is configured to compensate for a shift in an on voltage of the light emitting device by allowing the storage capacitor to partially discharge through the light emitting device during the programming cycle such that the gate-source voltage of the driving transistor during the driving cycle accounts for the on voltage of the light emitting device.

8. The pixel circuit of claim 6, wherein the pixel circuit is configured to compensate for a shift in the threshold voltage of the driving transistor by allowing the storage capacitor to partially discharge through the driving transistor during the programming cycle such that the gate-source voltage of the driving transistor during the driving cycle accounts for the threshold voltage of the driving transistor.

9. The pixel circuit of claim 2, wherein the light emitting device is configured to emit light responsive to the driving current flowing through the light emitting device, and wherein the driving current flowing through the light emitting device is controlled according to the gate-source voltage of the driving transistor during the driving cycle.

10. The pixel circuit of claim 9, wherein the pixel circuit is configured to compensate for a shift in an on voltage of the light emitting device by allowing the storage capacitor to partially discharge via the discharging connection during the programming cycle such that the gate-source voltage of the driving transistor during the driving cycle accounts for the on voltage of the light emitting device.

11. The pixel circuit of claim 9, wherein the pixel circuit is configured to compensate for a shift in the threshold voltage of the driving transistor by allowing the storage capacitor to partially discharge via the discharging connection during the programming cycle such that the gate-source voltage of the driving transistor during the driving cycle accounts for the threshold voltage of the driving transistor.

12. The pixel circuit of claim 1, wherein the light emitting device is an organic light emitting diode.

13. The pixel circuit of claim 1, wherein the pixel circuit is incorporated in an active matrix organic light emitting diode display.