Pixel Circuit Correcting Section for OLED Luminance Uniformity
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Solution Overview
Problem
Existing pixel circuits for organic EL display apparatuses face challenges in maintaining image uniformity due to variations in threshold voltage and carrier mobility of thin-film transistors, leading to inconsistent luminance levels across the screen.
Innovation Solution
A pixel circuit design that includes a correcting section to adjust the input voltage and account for variations in carrier mobility and threshold voltage, using additional capacitance to stabilize the operation and ensure uniformity, with a negative feedback loop to correct the output current and maintain consistent luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional pixel circuits are used without correction, then the structure is simple, but image uniformity deteriorates due to transistor parameter variations
Solution Approach 1:
The patent implements a feedback mechanism where the pixel capacitance holds the input voltage and the drive transistor's output current is fed back through the light-emitting device's capacitance. This feedback loop compensates for threshold voltage and carrier mobility variations, maintaining consistent luminance across pixels despite transistor parameter differences.
Solution Approach 2:
The patent introduces a capacitance element (pixel capacitance and light-emitting device capacitance) as an intermediary between the drive transistor and the light-emitting device. This intermediary stores electrical charge and mediates the relationship between the transistor's varying output and the required stable luminance output, effectively decoupling the variability from the final output.
2Manufacturing precision
If additional correction components are added to compensate for transistor variations, then image uniformity improves, but device complexity increases
Solution Approach 1:
The patent makes the pixel capacitance and light-emitting device capacitance serve multiple functions: they act as charge storage elements for the drive transistor, provide feedback for compensation, and utilize the light-emitting device's inherent capacitance. This multi-functionality reduces the need for separate correction components, achieving compensation while limiting complexity increase.
Solution Approach 2:
The patent utilizes the light-emitting device's own capacitance (inherent property) as part of the compensation mechanism. The light-emitting device serves itself by providing its capacitance for the feedback loop, eliminating the need for additional external correction components and reducing overall device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively stabilizes the operation of the pixel circuit, ensuring uniform image brightness across the screen by compensating for variations in transistor characteristics, thereby improving image uniformity and maintaining consistent luminance levels.
Implementation Method 1
The pixel capacitance holds an input voltage depending on the sampled video signal
Implementation Method 2
the light-emitting device emits light at a luminance level depending on the video signal in response to the output current supplied from the drive transistor
Data Source
AI summary
Disclosed herein is a pixel circuit that includes a correcting section configured to correct the input voltage sampled in the pixel capacitance in order to cancel out the dependency of the output current on the carrier mobility. In the pixel circuit, the correcting section operates depending on the control signal supplied from the scanning line to extract the output current from the drive transistor and introduce the extracted output current into a capacitance of the light-emitting device and the pixel capacitance, thereby correcting the input voltage. The pixel circuit further includes an additional capacitance added to the capacitance of the light-emitting device. In the pixel circuit, a portion of the output current extracted from the drive transistor flows into the additional capacitance to give a time margin to operation of the correcting section.