Pixel circuits for AMOLED displays

• US 9,659,527 B2
• Filed: 04/20/2016
• Issued: 05/23/2017
• Est. Priority Date: 03/08/2013
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Azizi, Yaser, Chaji, Gholamreza
• Primary Examiner(s): XAVIER, ANTONIO J
• Application Number:
  US15/133,318
• Publication Number:
  US 20160232845A1
• Time in Patent Office: 398 Days
• Field of Search: None
• 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 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2320/048 using evaluation of the usage time
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 2320/10 Special adaptations of display systems for operation with variable images
• 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
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules

Abstract

The OLED voltage of a selected pixel is extracted from the pixel produced when the pixel is programmed so that the pixel current is a function of the OLED voltage. One method for extracting the OLED voltage is to first program the pixel in a way that the current is not a function of OLED voltage, and then in a way that the current is a function of OLED voltage. During the latter stage, the programming voltage is changed so that the pixel current is the same as the pixel current when the pixel was programmed in a way that the current was not a function of OLED voltage. The difference in the two programming voltages is then used to extract the OLED voltage.

Claims

1. A method of determining a change, between a first time and a second time, in the current effective voltage V_OLED of a light-emitting device in a selected pixel in an array of pixels in a display in which each pixel includes a drive transistor for supplying current to said light-emitting device, the second time after the first time following substantial usage of said display, said method comprising

supplying a first programming voltage to said drive transistor in said selected pixel to supply a first current to said light-emitting device in said selected pixel at the first time, said first current being a function of the effective voltage V_OLED of said light-emitting device;

measuring said first current;

supplying a second programming voltage to said drive transistor in said selected pixel to supply a second current to said light-emitting device in said selected pixel at the second time;

measuring said second current and comparing said first and second current measurements,

adjusting said second programming voltage to make said second current substantially the same as said first current, and

extracting the value of the change, between the first time and the second time, in the current effective voltage V_OLED of said light-emitting device from the difference between said first and second programming voltages.

2. A method of determining the current effective voltage V_OLED of a light-emitting device in a selected pixel in an array of pixels in a display in which each pixel includes a drive transistor for supplying current to said light-emitting device, said method comprising

at a first time, extracting a first value of the current effective voltage V_OLED of said light-emitting device,

supplying a first programming voltage to said drive transistor in said selected pixel to supply a first current to said light-emitting device in said selected pixel at the first time, said first current being a function of the effective voltage V_OLED of said light-emitting device;

measuring said first current;

supplying a second programming voltage to said drive transistor in said selected pixel to supply a second current to said light-emitting device in said selected pixel at a second time after the first time following substantial usage of said display;

measuring said second current and comparing said first and second current measurements,

adjusting said second programming voltage to make said second current substantially the same as said first current,

determining a value of the change in the current effective voltage V_OLED of said light-emitting device from the difference between said first and second programming voltages, and

extracting the value of the current effective voltage V_OLED of said light-emitting device from the first value of the current effective voltage V_OLED of said light-emitting device and the change in the value of the current effective voltage V_OLED of said light-emitting device.

3. A method of determining the current effective voltage V_OLED of a light-emitting device in a selected pixel in an array of pixels in a display in which each pixel includes a drive transistor for supplying current to said light-emitting device, said method comprising

at a first time,

supplying a programming voltage to said drive transistor in said selected pixel to supply a first current to said light-emitting device in said selected pixel, said first current being independent of the effective voltage V_OLED of said light-emitting device,

measuring said first current,

supplying a second programming voltage to said drive transistor in said selected pixel to supply a second current to said light-emitting device in said selected pixel, said second current being a function of the current effective voltage V_OLED of said light-emitting device,

measuring said second current and comparing said first and second current measurements,

adjusting said second programming voltage to make said second current substantially the same as said first current, and

extracting a first value of the current effective voltage V_OLED of said light-emitting device from the difference between said first and second programming voltages, at a second time after the first time following substantial usage of said display,

supplying a third programming voltage to said drive transistor in said selected pixel to supply a third current to said light-emitting device in said selected pixel, said third current being a function of the current effective voltage V_OLED of said light-emitting device,

measuring said third current and comparing said second and third current measurements,

adjusting said second programming voltage to make said third current substantially the same as said second current, and

determining a change in the value of the current effective voltage V_OLED of said light-emitting device from the difference between said second and third programming voltages, and

extracting the value of the current effective voltage V_OLED of said light-emitting device from the first value of the current effective voltage V_OLED of said light-emitting device and the change in the value of the current effective voltage V_OLED of said light-emitting device.