Pixel Driving Circuit for Display Uniformity
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Solution Overview
Problem
Current self-luminous display technologies face challenges in achieving both high brightness and high contrast due to uneven display caused by different threshold voltages of light emitting elements and driving transistors, which affects gray level control.
Innovation Solution
A pixel driving circuit is designed with a current control circuit and a time control circuit, incorporating various transistors and capacitors to control the driving current and light emitting time period based on reference and data voltages, independent of threshold voltages, ensuring uniform display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If current control ability is limited in self-luminous display technology, then it is difficult to achieve high brightness and high contrast simultaneously, but increasing current control capability would require more complex circuit design
Solution Approach 1:
The pixel circuit is divided into two independent control modules: a current control circuit (including second driving transistor T4 and current control capacitor C1) and a time control circuit (including first driving transistor T8 and time control capacitor C2). This segmentation allows separate optimization of brightness control (via current) and contrast control (via time), avoiding the need for a single complex control mechanism while achieving both high brightness and high contrast simultaneously.
2Illumination intensity
If gray level is controlled by current and time simultaneously, then both brightness and contrast can be improved, but different threshold voltages of light emitting elements and driving transistors cause uneven display
Solution Approach 1:
The circuit incorporates compensation mechanisms that detect and correct for threshold voltage variations. The current control capacitor C1 and time control capacitor C2 work with their respective driving transistors to compensate for threshold voltage differences, ensuring that gray level control remains accurate despite manufacturing variations in light emitting elements and transistors, thereby maintaining display uniformity.
Solution Approach 2:
The patent changes the control parameters from direct current magnitude control to a combination of current control (via capacitor charging voltage) and time control (via capacitor charging/discharging duration). This parameter transformation makes the system less sensitive to threshold voltage variations, as the capacitors integrate the control signals over time, averaging out the effects of voltage variations and improving display uniformity.
3Device complexity
If threshold voltage variations of light emitting elements are not compensated, then circuit design is simpler, but display uniformity deteriorates
Solution Approach 1:
The pixel circuit performs self-compensation for threshold voltage variations through its inherent capacitor-transistor structure. The current control capacitor C1 and time control capacitor C2 automatically adjust their charging and discharging characteristics based on the actual threshold voltages of their respective driving transistors, enabling the circuit to compensate for manufacturing variations without requiring external calibration or complex additional compensation circuits.
Data Source
AI summary
A pixel driving circuit includes a current control circuit and a time control circuit, the current control circuit controls to generate a driving current, and outputs the driving current through a driving current output terminal, the time control circuit includes a first data writing-in circuit and a driving time control circuit. The first data writing-in circuit writes a first data voltage provided by a first data line to the driving time control circuit under the control of a first gate driving signal provided by a first gate line. The driving time control circuit is connected to a reference voltage terminal, the current control circuit, the first data writing-in circuit, and a light emitting element, and controls a light emitting time period of the light emitting element based on the reference voltage and the first data voltage, the reference voltage terminal is used to provide the reference voltage.