OLED Driving Compensation Circuit for AMOLED Luminance Uniformity
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Solution Overview
Problem
In AMOLED display devices, threshold voltage drift in driving transistors and voltage drops in power supply lines lead to non-uniform display brightness, causing 'ghost' phenomena and affecting image quality, while film thickness non-uniformity during fabrication further complicates display uniformity.
Innovation Solution
An OLED driving compensation circuit with a driving module and external compensation module, where the driving transistor and storage capacitor are reset to initial voltages, and a reference voltage is provided to compensate for threshold voltage drift and voltage drops, improving luminance uniformity and reducing pixel area by optimizing transistor ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the threshold voltage of the driving transistor is compensated by increasing the width-length ratio of the transistor in the external compensation module, then the compensation effect is improved, but the aperture ratio of pixel units is reduced and the area occupied by each pixel unit is increased
Solution Approach 1:
The patent changes the voltage parameter (applying reset voltage to the second terminal of the storage capacitor) to achieve compensation without increasing transistor dimensions. This allows maintaining small pixel area while still achieving effective threshold voltage compensation through voltage control rather than geometry control.
Solution Approach 2:
The patent applies preliminary reset action to the second terminal of the storage capacitor before the driving phase. By pre-resetting the voltage at the second terminal to a reference voltage level, the system prepares the compensation state in advance, eliminating the need for large transistor width-length ratios during operation and thus preserving pixel aperture ratio.
2Measurement precision
If the power supply voltage is increased to compensate for voltage drop (IR Drop), then the display uniformity is improved, but the power consumption and potential damage to OLED are increased
Solution Approach 1:
The patent applies local compensation by resetting the voltage at the second terminal of the storage capacitor individually for each pixel unit. This localized approach allows each pixel to compensate for its specific voltage drop without requiring global voltage increase, thus maintaining display uniformity while avoiding excessive power consumption and OLED stress.
3Illumination intensity
If the film thickness is increased to improve OLED performance, then the luminescence brightness is improved, but the manufacturing precision requirement is increased and display uniformity across different devices is worsened
Solution Approach 1:
The patent implements a feedback mechanism where the voltage at the second terminal of the storage capacitor is monitored and adjusted through the reset operation. This feedback loop compensates for variations in OLED characteristics (including film thickness differences) by adjusting the voltage state, allowing consistent display performance without requiring extremely precise film thickness control during manufacturing.
Data Source
AI summary
An OLED driving compensation circuit and a driving method thereof are provided. The circuit comprises an external compensation module and a driving module comprising a driving transistor and a storage capacitor. The driving transistor is respectively connected with a power supply voltage terminal and an OLED via a first electrode and a second electrode thereof, a first terminal of the storage capacitor is connected with a control electrode of the driving transistor, and a second terminal thereof is connected between the driving transistor and the OLED. The external compensation module is connected between the driving transistor and the OLED and provides a reference voltage to the electrode of the driving transistor connected with the second terminal of the storage capacitor, to reset the voltage on the electrode. The power supply voltage terminal as variable voltage source inputs a first voltage equal to the reference voltage when the voltage is reset.