Current-Driven OLED Pixel Structure with Current Mirror Circuit
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Solution Overview
Problem
Conventional voltage-driven OLED display apparatuses face inaccuracies in TFT manufacturing, leading to inconsistent current levels and luminance across pixels due to inaccuracies in doping concentration and gate-substrate distance, resulting in varying luminance values for the same voltage information.
Innovation Solution
A current-driven OLED display apparatus with a pixel structure that includes a light-emitting device, a first scan line, a data line, a first transistor, a current mirror, and a capacitor, where the current mirror is formed by second and third transistors, and the capacitor is connected to the gate and light-emitting device, allowing for stable current delivery and improved display stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If voltage-driven approach is used with conventional TFT structure, then device complexity is reduced, but manufacturing precision deteriorates leading to inconsistent current levels and luminance across pixels
Solution Approach 1:
The patent introduces a current mirror circuit as an intermediary between the voltage-driven TFT and the OLED. The current mirror (comprising second and third transistors) converts the voltage signal into a stable current signal that drives the OLED, isolating the OLED from voltage variations caused by TFT manufacturing inaccuracies.
Solution Approach 2:
The patent changes the driving parameter from voltage to current. By using a current-driven approach with a current mirror circuit, the system maintains stable current levels despite variations in TFT threshold voltage and mobility caused by manufacturing process variations, thereby improving luminance consistency across pixels.
2Ease of operation
If voltage information is used to control TFT gate voltage, then ease of operation is improved, but reliability deteriorates due to sensitivity to manufacturing inaccuracies
Solution Approach 1:
The current mirror circuit serves as an intermediary that translates simple voltage control into reliable current delivery. The first transistor receives voltage control signals, while the current mirror converts these to stable currents for the OLED, maintaining ease of operation while improving reliability.
Solution Approach 2:
The current mirror creates a copy of the control signal in current form. The second and third transistors form a current mirror that replicates the voltage-controlled signal as a stable current, ensuring consistent OLED driving current across different pixels despite manufacturing variations.
3Device complexity
If capacitor is connected through third transistor to light-emitting device, then device complexity is reduced, but noise from data line affects the light-emitting device
Solution Approach 1:
The third transistor acts as an intermediary that isolates the capacitor from direct connection to the data line and OLED. By controlling the charging/discharging of the capacitor through the third transistor rather than direct connection, noise from the data line is blocked while still allowing voltage storage functionality.
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 current-driven approach ensures better display stability and consistent gray-value luminance by utilizing the current-driven theorem, maintaining voltage levels and current ratios through the current mirror, reducing the impact of manufacturing inaccuracies and noise from data lines.
Implementation Method 1
the luminance of the organic light emitting diode (OLED) is directly proportional to the current I, the organic light emitting diode (OLED) generates a corresponding amount of light according to the current I
Data Source
AI summary
A pixel structure is disclosed. The pixel structure has a light-emitting device; a first scan line for transferring a first signal; a data line for transferring a data current signal; a first transistor having a gate coupled to the first scan line; a current mirror electrically connected to the light-emitting device; and a capacitor. The current mirror includes a second transistor having a gate connected to the data line and one of the source and the drain of the first transistor; and a third transistor having a gate coupled to the other of the source and the drain of the first transistor. The capacitor has two ends coupled to the gate of the third transistor and the light-emitting device respectively, where the capacitor is not coupled to the light-emitting device through the third transistor.