Pixel circuits for amoled displays

• US 9,978,310 B2
• Filed: 12/09/2013
• Issued: 05/22/2018
• Est. Priority Date: 12/11/2012
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Chaji, Gholamreza
• Primary Examiner(s): Faragalla, Michael
• Application Number:
  US14/363,379
• Publication Number:
  US 20150294622A1
• Time in Patent Office: 1,625 Days
• CPC Class Codes: G09G 2300/0408 Integration of the drivers onto the display substrate
• 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 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 2330/10 Dealing with defective pixels
• 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: 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 system for controlling a display in which each pixel circuit comprises a light-emitting device, a drive transistor, a storage capacitor, a reference voltage source, and a programming voltage source. The storage capacitor stores a voltage equal to the difference between the reference voltage and the programming voltage, and a controller supplies a programming voltage that is a calibrated voltage for a known target current, reads the actual current passing through the drive transistor to a monitor line, turns off the light emitting device while modifying the calibrated voltage to make the current supplied through the drive transistor substantially the same as the target current, modifies the calibrated voltage to make the current supplied through the drive transistor substantially the same as the target current, and determines a current corresponding to the modified calibrated voltage based on predetermined current-voltage characteristics of the drive transistor.

Claims

1. A system for controlling an array of pixels in a display in which each pixel includes a pixel circuit that comprises

a light-emitting device,

a drive transistor for driving current through the light emitting device according to a driving voltage across the drive transistor during an emission cycle, said drive transistor having a gate, a source and a drain,

a storage capacitor coupled to the gate of said drive transistor for controlling said driving voltage,

a reference voltage source coupled to a first switching transistor that controls the coupling of said reference voltage source to said storage capacitor,

a programming voltage source coupled to a second switching transistor that controls the coupling of said programming voltage to the gate of said drive transistor, so that said storage capacitor stores a voltage equal to the difference between said reference voltage and said programming voltage, and

a controller configured to

supply a programming voltage that is a calibrated voltage for a known target current,

read the actual current passing through the drive transistor to a monitor line,

turn off the light emitting device while modifying said calibrated voltage to make the current supplied through the drive transistor substantially the same as said target current,

modify said calibrated voltage to make the current supplied through the drive transistor substantially the same as said target current, and

determine a current corresponding to said modified calibrated voltage based on predetermined current-voltage characteristics of said drive transistor.

2. A system for controlling an array of pixels in a display in which each pixel includes a pixel circuit that comprises

a light-emitting device,

a drive transistor for driving current through the light emitting device according to a driving voltage across the drive transistor during an emission cycle, said drive transistor having a gate, a source and a drain,

a storage capacitor coupled to the gate of said drive transistor for controlling said driving voltage,

a reference voltage source coupled to a first switching transistor that controls the coupling of said reference voltage source to said storage capacitor,

a programming voltage source coupled to a second switching transistor that controls the coupling of said programming voltage to the gate of said drive transistor, so that said storage capacitor stores a voltage equal to the difference between said reference voltage and said programming voltage, and

a controller configured to

supply a programming voltage that is a predetermined fixed voltage,

supply a current from an external source to said light emitting device, and

read the voltage at said node between said drive transistor and said light emitting device.

3. A system for controlling an array of pixels in a display in which each pixel includes a pixel circuit that comprises

a light-emitting device,

a drive transistor for driving current through the light emitting device according to a driving voltage across the drive transistor during an emission cycle, said drive transistor having a gate, a source and a drain,

a storage capacitor coupled to the gate of said drive transistor for controlling said driving voltage,

a reference voltage source coupled to a first switching transistor that controls the coupling of said reference voltage source to said storage capacitor,

a programming voltage source coupled to a second switching transistor that controls the coupling of said programming voltage to the gate of said drive transistor, so that said storage capacitor stores a voltage equal to the difference between said reference voltage and said programming voltage, and

a controller configured to

supply a programming voltage that is an off voltage so that said drive transistor does not provide any current to said light emitting device,

supply a current from an external source to a node between said drive transistor and said light emitting device, said external source having a pre-calibrated voltage based on a known target current,

modify said pre-calibrated voltage to make said current substantially the same as said target current,

read the current corresponding to the modified calibrated voltage, and

determine a current corresponding to said modified calibrated voltage based on predetermined current-voltage characteristics of said OLED.

4. A system for controlling an array of pixels in a display in which each pixel includes a pixel circuit that comprises

a light-emitting device,

a drive transistor for driving current through the light emitting device according to a driving voltage across the drive transistor during an emission cycle, said drive transistor having a gate, a source and a drain,

a storage capacitor coupled to the gate of said drive transistor for controlling said driving voltage,

a reference voltage source coupled to a first switching transistor that controls the coupling of said reference voltage source to said storage capacitor,

a programming voltage source coupled to a second switching transistor that controls the coupling of said programming voltage to the gate of said drive transistor, so that said storage capacitor stores a voltage equal to the difference between said reference voltage and said programming voltage, and

a controller configured to

supply a current from an external source to said light emitting device, and

read the voltage at said node between said drive transistor and said light emitting device as the gate voltage of the drive transistor for the corresponding current.

5. A system for controlling an array of pixels in a display in which each pixel includes a pixel circuit that comprises

a light-emitting device,

a drive transistor for driving current through the light emitting device according to a driving voltage across the drive transistor during an emission cycle, said drive transistor having a gate, a source and a drain,

a storage capacitor coupled to the gate of said drive transistor for controlling said driving voltage,

a supply voltage source coupled to a first switching transistor that controls the coupling of said supply voltage source to said storage capacitor and said drive transistor,

a programming voltage source coupled to a second switching transistor that controls the coupling of said programming voltage to the gate of said drive transistor, so that said storage capacitor stores a voltage equal to the difference between said reference voltage and said programming voltage,

a monitor line coupled to a third switching transistor that controls the coupling of said monitor line to a node between said light emitting device and said drive transistor, and

a controller that

controls said programming voltage source to produce a voltage that is a calibrated voltage corresponding to a known target current through the drive transistor,

controls said monitor line to read a current through the monitor line, with a monitoring voltage low enough to prevent said light emitting device from turning on,

controls said programming voltage source to modify the calibrated voltage until the current through the drive transistor is substantially the same as said target current, and

identifies a current corresponding to the modified calibrated voltage in predetermined current-voltage characteristics of the drive transistor, said identified current corresponding to the current threshold voltage of the drive transistor.

6. A system for controlling an array of pixels in a display in which each pixel includes a pixel circuit that comprises

a light-emitting device,

a drive transistor for driving current through the light emitting device according to a driving voltage across the drive transistor during an emission cycle, said drive transistor having a gate, a source and a drain,

a storage capacitor coupled to the gate of said drive transistor for controlling said driving voltage,

a supply voltage source coupled to a first switching transistor that controls the coupling of said supply voltage source to said storage capacitor and said drive transistor,

a programming voltage source coupled to a second switching transistor that controls the coupling of said programming voltage to the gate of said drive transistor, so that said storage

capacitor stores a voltage equal to the difference between said reference voltage and said programming voltage,

a monitor line coupled to a third switching transistor that controls the coupling of said monitor line to a node between said light emitting device and said drive transistor, and

a controller that

controls said programming voltage source to produce an off voltage that prevents the drive transistor from passing current to the light emitting device,

controls said monitor line to supply a pre-calibrated voltage from the monitor line to a node between the drive transistor and the light emitting device, the pre-calibrated voltage causing current to flow through said node to said light emitting device, the pre-calibrated voltage corresponding to a predetermined target current through the drive transistor,

modifies the pre-calibrated voltage until the current flowing through said node to said light emitting device is substantially the same as said target current, and

identifies a current corresponding to the modified pre-calibrated voltage in predetermined current-voltage characteristics of the drive transistor, said identified current corresponding to the voltage of the light emitting device.