Pixel circuits including feedback capacitors and reset capacitors, and display systems therefore

• US 9,747,834 B2
• Filed: 05/11/2012
• Issued: 08/29/2017
• Est. Priority Date: 05/11/2012
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Chaji, Gholamreza
• Primary Examiner(s): EURICE, MICHAEL
• Application Number:
  US13/470,059
• Publication Number:
  US 20130300724A1
• Time in Patent Office: 1,936 Days
• Field of Search: 345 76, 345 78, 345 82, 345205
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than 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 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2310/066 Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
• 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 3/325 the data current flowing through the driving transistor during a setting phase, e.g. by using a switch for connecting the driving transistor to the data driver
• 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 display with a pixel circuit for driving a current-driven emissive element includes a feedback capacitor in series between the emissive element and a programming node of the pixel circuit. During driving, variations in the operating voltage of the emissive element due to variations in the current conveyed through the emissive element by a driving transistor are accounted for. The feedback capacitor generates voltage adjustments at the programming node that correspond to the variations at the emissive element, and thus reduces variations in light emission. A reset capacitor connected to a select line is selectively connected to the gate terminal of the driving transistor and resets the driving transistor prior to programming. The select line adjusts the voltage on the gate terminal to reset the driving transistor by the capacitive coupling of the select line to the gate terminal created by the reset capacitor.

Claims

1. A method of operating a pixel circuit including:

a drive transistor including a gate terminal and arranged to convey a drive current through a light emitting device, the drive current being conveyed according to a voltage on the gate terminal;

a capacitor connected to the gate terminal of the drive transistor for applying a voltage to the gate terminal according to programming information;

a first switch transistor connected between the gate terminal of the drive transistor and a node of the pixel circuit, wherein the node is between the output of the drive transistor and the light emitting device; and

a reset capacitor connected between the node and a reset line such that the reset line is capacitively coupled to the gate terminal of the drive transistor while the first switch transistor is turned on;

the method comprising;

turning on the first switch transistor to capacitively couple the reset line to the gate terminal of the drive transistor only while the first switch transistor is turned on;

adjusting the voltage on the reset line to generate a change in voltage at the gate terminal of the drive transistor via the capacitive coupling of the reset capacitor;

programming the pixel circuit according to programming information; and

driving the pixel circuit to emit light according to the programming information.

2. The method of operating the pixel circuit according to claim 1, wherein the first switch transistor is operated by the reset line and the adjusting the voltage on the reset line includes changing the voltage on the reset line from an off voltage to an on voltage for the first switch transistor such that the adjusting the voltage on the reset line simultaneously turns on the first switch transistor.

3. The method of operating the pixel circuit according to claim 1, wherein the first switch transistor is operated by a select line and the adjusting the voltage on the reset line is carried out following the turning on the first switch transistor.

4. The method of operating the pixel circuit according to claim 1, further comprising, preventing the pixel circuit from emitting light by turning off an emission control transistor connected in series between the drive transistor and the light emitting device.