OLED Pixel Feedback Circuit for Brightness Uniformity
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Solution Overview
Problem
Organic electroluminescent devices suffer from non-uniform brightness between pixels, which decays over long-term use, affecting the performance and lifespan of OLED displays.
Innovation Solution
An organic electroluminescent device is designed with a pixel element comprising a substrate, a switch device, a driving device, a photo diode acting as a sensor, and a capacitor, where the photo current generated by the photo diode adjusts the voltage to control the current through the driving device, maintaining uniform brightness by compensating for changes in illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If organic electroluminescent devices are operated with simple driving circuits, then device complexity is reduced, but brightness uniformity deteriorates over time due to decay
Solution Approach 1:
The patent implements a feedback mechanism where a photodiode detects the actual brightness output of the OLED element and generates a photocurrent that adjusts the capacitor voltage. This closed-loop feedback system automatically compensates for brightness decay and non-uniformity, maintaining reliable display performance without requiring complex external driving circuits.
Solution Approach 2:
The pixel element performs self-compensation for brightness decay through its internal photodiode and capacitor circuitry. The photodiode continuously monitors the OLED's own output and automatically adjusts the driving current via the capacitor, enabling the device to maintain brightness uniformity autonomously without external intervention or complex control systems.
2Device complexity
If no brightness compensation mechanism is used, then device complexity is minimized, but brightness decay occurs over long term use
Solution Approach 1:
The photodiode-capacitor feedback circuit continuously monitors OLED brightness output and automatically adjusts the driving current to compensate for decay. This real-time feedback mechanism extends device lifespan by maintaining acceptable brightness levels throughout the operational period, preventing the brightness decay that would otherwise limit device longevity.
Solution Approach 2:
The capacitor stores compensatory voltage that is gradually applied to counteract brightness decay before it becomes visually significant. By preparing compensation in advance through the capacitor's voltage storage capability, the system proactively maintains brightness uniformity throughout the device's operational life, effectively extending usable lifespan.
3Measurement precision
If photodiode area is increased to improve detection accuracy, then measurement precision is improved, but pixel area available for light emission is reduced
Solution Approach 1:
The patent divides the pixel into distinct functional zones: the photodiode occupies the control area for detection, while the sensitive area is dedicated to light emission. This spatial separation allows the photodiode to have sufficient area for accurate brightness detection without compromising the emission area, as each zone is optimized for its specific function rather than competing for the same space.
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
This solution ensures consistent brightness and extends the lifespan of OLED devices by dynamically adjusting the illumination based on detected brightness levels, preventing non-uniformity and degradation over time.
Implementation Method 1
a photo current corresponding to a brightness of the OLED element is generated by the photo diode responsive to the OLED element illuminating the photo diode
Implementation Method 2
a voltage of the capacitor is adjusted by the photo current to control the current passing through the driving device
Data Source
AI summary
The invention discloses an organic electroluminescent device comprising a pixel element. The pixel element comprises a substrate comprising a control area and a sensitive area, a switch device and a driving device overlying the control area, a photo diode serving as a photo sensor overlying the sensitive area, an OLED element disposed in the sensitive area and illuminating to the photo sensor, and a capacitor coupled to the photo sensor and the driving device. Specifically, a photo current corresponding to a brightness of the OLED element is generated by the photo diode responsive to the OLED element illuminating the photo diode such that a voltage of the capacitor is adjusted by the photo current to control the current passing through the driving device, thus changing the illumination of the OLED element. A method for fabricating the OLED is also provided.