Method and system for programming, calibrating and driving a light emitting device display

• US 8,994,625 B2
• Filed: 01/16/2014
• Issued: 03/31/2015
• Est. Priority Date: 12/15/2004
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Nathan, Arokia, Chaji, Gholamreza, Servati, Peyman
• Primary Examiner(s): ABDULSELAM, ABBAS I
• Application Number:
  US14/157,031
• Publication Number:
  US 20140159996A1
• Time in Patent Office: 439 Days
• Field of Search: 345/76, 345/77, 345/82, 315/169.3
• US Class Current: 345/77
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• 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 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 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• 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 2320/043 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 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/3208 organic, e.g. using organic light-emitting diodes [OLED]
• 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 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• 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: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

A method and system for programming, calibrating and driving a light emitting device display is provided. The system may include extracting a time dependent parameter of a pixel for calibration.

Claims

1. A method of controlling light emission from a pixel circuit including a light emitting device (LED), a drive transistor to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming value from said programming input, the method comprising:

determining at least one time-dependent parameter of the pixel circuit,

detecting a change in said determined time-dependent parameter,

determining calibration data for the pixel circuit based on the detected change in the determined time-dependent parameter;

storing said calibration data in a calibration memory; and

adjusting the programming value to the pixel circuit based on the stored calibration data to at least partially compensate for said detected change in the time-dependent parameter.

2. The method of claim 1 in which the determined time-dependent parameter is one of a threshold voltage of the drive transistor, the LED voltage or the LED current.

3. The method of claim 1 in which the adjusting the programming value maintains a stable brightness of the LED.

4. The method of claim 3 in which the stable LED brightness is substantially independent of aging of the pixel circuit over prolonged operation.

5. A method of adjusting a programming value for a pixel circuit in an OLED display to compensate for non-uniformity or aging of the display, said method comprising:

measuring at least a time-dependent parameter of a driving transistor, an OLED, or both a driving transistor and an OLED in the pixel circuit,

converting the measured time-dependent parameter to calibration data representing the degradation of the pixel circuit, and

during normal operation of the OLED display, adjusting the programming value to the pixel circuit based on said calibration data to compensate for said degradation of the pixel circuit.

6. The method of claim 5 in which the time-dependent parameter of at least one of the driving transistor or the OLED is measured separately.

7. The method of claim 5 in which the time-dependent parameter of the OLED is the brightness loss of the OLED.

8. The method of claim 5 in which the time-dependent parameter of the OLED is a change in the OLED voltage over a predetermined time interval.

9. The method of claim 5 in which the time-dependent parameter of the drive transistor is a change in a threshold voltage of the drive transistor over a predetermined time interval.

10. The method of claim 5 in which the time-dependent parameter degradation of the drive transistor is a threshold voltage of the drive transistor.

11. The method of claim 5 in which the time-dependent parameter of the drive transistor is a mobility of the drive transistor.

12. The method of claim 5 in which the time-dependent parameter is an inter-pixel non-uniformity.

13. The method of claim 5 in which said compensation value increases a programming voltage of the pixels to maintain a substantially constant luminance from said pixels.

14. The method of claim 5 in which said compensation value reduces luminance of said pixels at substantially the same rate as other pixels in the same OLED display.

15. The method of claim 5 in which said compensation value increases the programming value of the pixel circuit and reduces the luminance of other pixel circuits relative to other pixels in the same display to maintain display uniformity.

16. A method of extracting a circuit parameter from a pixel circuit including a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal, the method comprising:

providing a predetermined program voltage to the programming input;

charging a capacitance of the pixel circuit to a charge level or providing a current from the pixel circuit;

providing an output signal proportional to said charge level or said current;

determining calibration data for the pixel circuit based on the output signal;

storing the calibration data in a calibration memory;

updating at least one time-dependent pixel circuit parameter based on said stored calibration data; and

adjusting the predetermined program voltage during normal operation of the pixel circuit based on at least the updated time-dependent circuit parameter.

17. The method of claim 16 wherein the determining at least one time-dependent pixel circuit parameter includes extracting a threshold voltage or a shift in the threshold voltage of a drive transistor in the pixel circuit.

18. The method of claim 16, wherein the determining at least one time-dependent pixel circuit parameter includes measuring a voltage remaining on a data node of the pixel circuit during a threshold voltage acquisition.

19. The method of claim 18 wherein the voltage remaining on the data node corresponds to a threshold voltage or a shift in the threshold voltage of the drive device in the pixel circuit.

20. The method of claim 16 wherein the determining at least one time-dependent pixel circuit parameter includes measuring a rate of discharge of a voltage on a data node of the pixel circuit.

21. The method of claim 16 wherein the determining at least one time-dependent pixel circuit parameter includes:

digitizing the at least one time-dependent pixel circuit parameter to produce corresponding digital data;

storing the digital data in a memory;

adding the digital data to the predetermined program voltage to produce a resulting voltage; and

converting the resulting voltage to a corresponding analog voltage to be applied as the video input signal during a programming phase.

22. The method of claim 16 wherein the digital data is applied to the pixel circuit during programming as a current or a voltage.

23. The method of claim 16 further comprising:

generating a voltage versus current relationship for the pixel circuit based on current values applied to a data node of the pixel circuit and based on voltages sampled at the data node; and

extracting, based on the generated voltage versus current relationship, a voltage corresponding to a selected current level,

wherein the predetermined program voltage is further adjusted based on the extracted voltage.

24. A method of adjusting a programming value for a pixel circuit in an OLED display to compensate for degradation of the display, the method comprising:

applying a current to a data node of a pixel circuit;

responsive to the applying, acquiring a voltage from the data node;

creating, from the acquired voltage, calibration data indicative of a degradation of the pixel circuit;

storing the calibration data in a memory device; and

correcting the programming value a video input signal applied to the pixel circuit as a corresponding video input signal based on the stored calibration data.