Pixel Circuit With Sub-Transistors and Hold Capacitors for Flicker Reduction
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Solution Overview
Problem
Flicker and deterioration of display quality due to changes in driving current magnitude, leading to undesirable luminance changes and leakage currents in display devices.
Innovation Solution
A pixel circuit design incorporating multiple transistors and capacitors, including hold capacitors and storage capacitors, to stabilize gate electrode voltage and minimize leakage currents through voltage boosting and compensation mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit with a single transistor is used, then the device complexity is low, but leakage current occurs causing non-uniform luminance and flicker
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a driving transistor for current generation, multiple sub-transistors (first through fourth sub-transistors) for threshold voltage compensation, and multiple capacitors (storage capacitor and hold capacitors) for voltage stabilization. This segmentation allows each component to perform its specific function independently, reducing leakage current effects while maintaining overall circuit functionality
Solution Approach 2:
The circuit performs preliminary threshold voltage compensation by using sub-transistors to pre-adjust the gate voltages of the driving transistor before actual operation. The hold capacitors pre-stabilize the gate electrode voltages during non-light-emitting periods, ensuring the driving transistor operates at the optimal point and minimizing leakage current before it can cause luminance non-uniformity
2Illumination intensity
If the driving current magnitude changes to adjust luminance, then the luminance control range is improved, but flicker occurs due to leakage current
Solution Approach 1:
The circuit implements feedback mechanisms where the hold capacitors continuously monitor and stabilize the gate electrode voltages of the driving transistor. During non-light-emitting periods, the hold capacitors maintain the gate voltages at stable levels, preventing leakage current-induced voltage drift that would otherwise cause flicker during luminance transitions
Solution Approach 2:
The circuit changes the operating parameters of the driving transistor by using multiple sub-transistors to adjust the gate-source and gate-drain voltages independently. This allows precise control of the driving current magnitude for luminance adjustment while maintaining stable operation points that minimize leakage current effects
3Reliability
If multiple transistors and capacitors are added to reduce leakage current, then luminance uniformity is improved, but the manufacturing process becomes more complex
Solution Approach 1:
Multiple capacitive elements (storage capacitor and multiple hold capacitors) are merged into a compact arrangement within the pixel circuit. The hold capacitors are integrated alongside the driving transistor and sub-transistors, sharing common electrode structures and interconnects, which reduces the overall area and simplifies the fabrication process despite the increased component count
Data Source
AI summary
A pixel circuit is disclosed that includes a first hold capacitor or a second hold capacitor or both the first and second hold capacitors. The first hold capacitor is connected to a first gate electrode of a first transistor and an intermediate node of a first sub-transistor and a second sub-transistor. The second hold capacitor is connected to the first gate electrode of the first transistor and an intermediate node of a third sub-transistor and a fourth sub-transistor.