Pixel Circuit Kickback Prevention in OLED Displays
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Solution Overview
Problem
Organic light emitting display devices experience luminance deviations and undesirable kickback phenomena due to characteristic deviations of elements in pixel circuits, leading to luminance non-uniformity when the operating period changes from threshold voltage compensating to data writing periods.
Innovation Solution
A pixel circuit design that sequentially performs on-bias, initializing, threshold voltage compensating, data writing, and light emitting operations, utilizing a configuration of transistors and a storage capacitor to manage control signals and power signals, ensuring different voltage levels and edge times for transistors in various operating periods to prevent kickback phenomena.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the operating period changes from threshold voltage compensating to data writing period, then the pixel circuit performs data writing operation, but kickback phenomenon occurs causing luminance non-uniformity
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before data writing operation. The pixel circuit sequentially executes on-bias operation, initializing operation, and threshold voltage compensating operation before the data writing period. This preliminary compensation adjusts the threshold voltage of transistors in advance, preventing kickback phenomena during the subsequent data writing operation and ensuring luminance uniformity.
Solution Approach 2:
The patent applies dynamics by implementing sequential operation modes with different control signal characteristics. The pixel circuit transitions through multiple operating periods (on-bias, initializing, threshold voltage compensating, data writing, and light emitting) with dynamically adjusted control signals. Each period has specific voltage levels and edge times for control signals to optimize performance and prevent kickback phenomena.
2Ease of manufacture
If characteristic deviations of elements occur in pixel circuit, then manufacturing variations are present, but luminance deviations occur among pixel circuits
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting control signal parameters (voltage levels and edge times) based on operating periods. The first control signal has different voltage levels and edge times in data writing period versus other periods. This parameter adjustment compensates for element characteristic deviations and ensures consistent pixel circuit performance across the display device despite manufacturing variations.
Solution Approach 2:
The patent implements feedback through threshold voltage compensation mechanisms. The pixel circuit measures and compensates for threshold voltage deviations of transistors using feedback signals during the threshold voltage compensating operation. This feedback mechanism adjusts operating parameters to counteract manufacturing variations and maintain luminance uniformity across all pixel circuits.
Data Source
AI summary
A pixel circuit includes three transistors, a capacitor, and an OLED. The first transistor includes a gate terminal for receiving a first control signal, a first terminal connected to a first node, and a second terminal connected to a second node. The second transistor includes a gate terminal for receiving a second control signal, a first terminal connected to the second node, and a second terminal connected to a third node. The third transistor includes a gate terminal connected to the first node, a first terminal for receiving a first power signal, and a second terminal connected to the third node. The capacitor may receive an initialization signal and is connected to the first node. The OLED is connected to the third node and may receive a second power signal. The control signals have same voltage levels in a data writing period and have different voltage levels in other periods.