Stable driving scheme for active matrix displays

• US 8,743,096 B2
• Filed: 06/04/2013
• Issued: 06/03/2014
• Est. Priority Date: 04/19/2006
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Nathan, Arokia, Chaji, Gholamreza
• Primary Examiner(s): Pervan, Michael
• Application Number:
  US13/909,177
• Publication Number:
  US 20130293602A1
• Time in Patent Office: 364 Days
• Field of Search: 345 76- 84, 345 87-104, 345/204, 345208-210, 3151691-1694
• US Class Current: 345/204
• 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 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2310/0254 Control of polarity reversal in general, other than for liquid crystal displays
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• 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 3/3258 with pixel circuitry controlling the voltage across the light-emitting element

Abstract

A method and system for operating a pixel array having at least one pixel circuit is provided. The method includes repeating an operation cycle defining a frame period for a pixel circuit, including at each frame period, programming the pixel circuit, driving the pixel circuit, and relaxing a stress effect on the pixel circuit, prior to a next frame period. The system includes a pixel array including a plurality of pixel circuits and a plurality of lines for operation of the plurality of pixel circuits. Each of the pixel circuits includes a light emitting device, a storage capacitor, and a drive circuit connected to the light emitting device and the storage capacitor. The system includes a drive for operating the plurality of lines to repeat an operation cycle having a frame period so that each of the operation cycle comprises a programming cycle, a driving cycle and a relaxing cycle for relaxing a stress on a pixel circuit, prior to a next frame period.

Claims

1. A method of operating a pixel array having pixel circuits arranged in rows and columns, each of the pixel circuits including a switch, a select line connected to the switch, a drive transistor coupled to a data line via the switch and to a controllable power supply line, a light emitting device coupled to the drive transistor, and a storage capacitor coupled to the drive transistor, the method comprising:

programming a first of the pixel circuits responsive to driving the select line for the first pixel circuit from a first state to a second state to select the first pixel circuit for programming, the programming including;

during a first operating cycle, adjusting the controllable power supply line for the first pixel circuit to a first voltage while applying on the data line for the first pixel circuit a second voltage of opposite polarity to that of the first voltage;

responsive to the first operating cycle, during a second operating cycle, changing the controllable power supply line to a driving voltage corresponding to a voltage used to drive the light emitting device of the first pixel circuit, the driving voltage being different from the first voltage; and

responsive to the second operating cycle, during a programming cycle, changing the controllable power supply line for the first pixel circuit to a third voltage different from the first voltage and the driving voltage while applying at least a programming voltage on the data line for the first pixel circuit.

2. The method of claim 1, wherein the switch and the drive transistor are n-type thin-film transistors, and the first voltage is negative, and the second and third voltages are positive.

3. The method of claim 1, wherein the first voltage is negative to develop a negative voltage at a second node between a source terminal of the drive transistor and a first terminal of the light emitting device, and wherein the second voltage is positive to charge a first node between a gate of the drive transistor and a first terminal of the storage capacitor to the second voltage during the first operating cycle.

4. The method of claim 3, wherein during the second operating cycle the second node is charged until the drive transistor turns off, thereby causing a threshold voltage of the drive transistor to be stored in the storage capacitor.

5. The method of claim 4, wherein during the programming cycle, a voltage stored in the storage capacitor includes a threshold voltage of the drive transistor and the programming voltage provided from the data line.

6. The method of claim 1, wherein the second voltage is smaller than a threshold voltage of the drive transistor in an unstressed state and an ON voltage of the light emitting device in an unstressed state.

7. The method of claim 1, further comprising:

programming a second of the pixel circuits responsive to driving the select line for the second pixel circuit from a first state to a second state to select the second pixel circuit for programming, the programming including;

during a first operating cycle, adjusting the controllable power supply line for the second pixel circuit to a first voltage while applying on the data line for the second pixel circuit a second voltage of opposite polarity to that of the first voltage;

responsive to the first operating cycle, during a second operating cycle, changing the controllable power supply line to a driving voltage corresponding to a voltage used to drive the light emitting device of the second pixel circuit, the driving voltage being different from the first voltage; and

responsive to the second operating cycle, during a programming cycle, changing the controllable power supply line for the second pixel circuit to a third voltage different from the first voltage and the driving voltage while applying at least a programming voltage on the data line for the second pixel circuit.

8. The method of claim 7, wherein the first pixel circuit and the second pixel circuits are in different rows of the pixel array.

9. The method of claim 7, wherein each of the controllable power supply lines for the first and second pixel circuits intersects both of the data lines for the first and second pixel circuits.