Pixel Driving Circuit for Low-Gray Micro LED Brightness Control
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Solution Overview
Problem
Micro LED and Mini LED display devices experience low luminous efficiency and poor display effects during low gray scale due to low current density, leading to high energy consumption and color coordinate offsets.
Innovation Solution
A pixel driving circuit with a data writing sub-circuit, driving sub-circuit, and control sub-circuit that compensates for the threshold voltage of the driving transistor, allowing for variable operating durations based on data signals to maintain high current density and adjust brightness, thereby improving luminous efficiency and display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a conventional pixel circuit with one transistor and one capacitor is used, then the circuit area is minimized, but the display uniformity deteriorates due to voltage threshold shifts and leakage currents
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: first and second switching sub-circuits for controlled charging, a holding sub-circuit for voltage storage, and a compensation sub-circuit for threshold shift correction. This segmentation allows each sub-circuit to perform its function optimally while maintaining overall compactness.
Solution Approach 2:
The compensation sub-circuit performs preliminary compensation for transistor threshold voltage shifts before the display operation. By pre-compensating for expected threshold variations, the circuit ensures more uniform display performance without requiring larger circuit area.
2Duration of action of moving object
If the holding period is extended to maintain gray levels, then the gray level maintenance is improved, but the leakage current effects worsen causing gray level shifts
Solution Approach 1:
The compensation sub-circuit implements a feedback mechanism that detects voltage changes caused by leakage currents during the holding period and applies corrective adjustments. This feedback loop maintains accurate gray levels despite extended holding times and leakage effects.
Solution Approach 2:
The circuit dynamically adjusts operating parameters such as charging voltage levels and timing durations based on detected leakage characteristics. By changing these parameters adaptively, the circuit maintains gray level accuracy throughout the extended holding period.
3Speed
If switching transistors with high on-state current are used, then the switching speed is improved, but the leakage current increases causing gray level shifts
Solution Approach 1:
Different regions of the pixel circuit use transistors with optimized characteristics for their specific functions. Switching transistors are designed for high on-state current to ensure fast switching, while storage and compensation transistors are optimized for low leakage current to maintain gray level accuracy during holding periods.
Solution Approach 2:
The circuit employs dynamic control strategies where switching transistor operating points are adjusted based on operational phase. During switching operations, transistors operate in high-current mode for speed, while during holding phases, bias conditions are modified to minimize leakage current.
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 solution ensures high luminous efficiency, reduces energy consumption, and enhances display brightness and color accuracy by maintaining high current density across all gray scales, resulting in a superior display effect.
Implementation Method 1
Each pixel in the array of pixels has a corresponding pixel circuit comprising a switching circuit and a capacitor. The capacitor holds the voltage for a period, which corresponds to a gray level of a pixel
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 2D~3
AI summary
A pixel driving circuit (1) comprises a data writing sub-circuit (10), a driving sub-circuit (11), and a control sub-circuit (12). The data writing sub-circuit (10) is configured to: write a first data signal provided by a first data signal end (Data1) into the driving sub-circuit (11) in response to a received first scanning signal from a first scanning signal end (G1) and a received third scanning signal from a third scanning signal end (G3); and write a second data signal provided by a second data signal end (Data2) into the driving sub-circuit (11) in response to a received second scanning signal from a second scanning signal end (G2) and the received third scanning signal from the third scanning signal end (G3). The control sub-circuit (12) is configured to enable, in response to a received enable signal from an enable signal end (EM), a driving transistor (T1) to be connected to a first power supply voltage signal end (VDD) and an element to be driven (D). The driving sub-circuit (11) is configured to: output a driving signal according to the first data signal and a first power supply voltage signal; and control a working state of said element (D) according to the second data signal and the first power supply voltage signal.