OLED Drive Circuit Feedback Loop for Brightness Uniformity
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Solution Overview
Problem
The current drive circuit for Organic Light-Emitting Diodes (OLEDs) is affected by unstable threshold voltages of the drive transistor, leading to uneven brightness across the screen due to inaccurate current flow through the OLED devices.
Innovation Solution
An actively driven organic light-emitting display apparatus is designed with a feedback loop comprising a resistor and an operational amplifier, which controls the current flowing through the light emitting device, making it independent of the drive transistor's threshold voltage and dependent only on the resistor, input data signal voltage, and supply voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a TFT transistor is directly driven by a grayscale voltage VDATA to generate current for the OLED, then the circuit structure is simple, but the threshold voltage variation of the TFT causes inaccurate current flow and uneven brightness
Solution Approach 1:
The patent introduces a feedback loop comprising an operational amplifier and a resistor that monitors the actual current flowing through the OLED and adjusts the drive signal accordingly. This feedback mechanism compensates for threshold voltage variations in the TFT, ensuring accurate current flow and uniform brightness across the display while maintaining a relatively simple circuit structure.
2Ease of manufacture
If the drive transistor threshold voltage is unstable due to process offset, then the circuit can be manufactured with standard processes, but the current flowing through the OLED becomes inaccurate causing brightness non-uniformity
Solution Approach 1:
The feedback loop using an operational amplifier continuously monitors and compensates for threshold voltage variations caused by process offset. This allows the use of standard manufacturing processes while maintaining accurate current control and uniform brightness across all pixels in the display.
Solution Approach 2:
The operational amplifier acts as an intermediary element that decouples the OLED current from the TFT threshold voltage. By introducing this intermediate control stage, the system can use standard manufacturing processes with inherent threshold variations while still achieving precise current control and uniform brightness.
3Manufacturing precision
If a feedback loop with operational amplifier and resistor is introduced to control OLED current, then the current accuracy and brightness uniformity are improved, but the circuit complexity increases
Solution Approach 1:
The feedback loop provides precise current control by monitoring and adjusting for TFT threshold voltage variations. While it does increase circuit complexity, the design uses a minimal number of additional components (one operational amplifier and one resistor per pixel) to achieve significant improvements in current accuracy and brightness uniformity.
Solution Approach 2:
The patent changes the control parameter from direct voltage control to current control through the feedback loop. This parameter transformation allows the system to compensate for threshold voltage variations and achieve accurate current flow, justifying the increased circuit complexity.
Data Source
AI summary
An embodiment of the present disclosure provides an actively driven organic light-emitting display apparatus to eliminate a defect in which the current flowing through the lighting device in the actively driven organic light-emitting display apparatus is affected by the instable current caused by the instable threshold voltage of the drive transistor, so that the current flowing through the lighting device is accurate and make the brightness of the whole actively driven organic light-emitting display apparatus be even. The display apparatus comprises a light emitting device, a light emitting device drive unit, a first switch unit, a second switch unit, a current control unit and a resistor which constitute a feedback loop. An input terminal of the current control unit is input a data signal to control that the current of the light emitting device is only associated with the resistor, voltage of the input data signal and the supply voltage.