Light Emitting Unit Driving Circuit Compensation for Brightness Uniformity
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Solution Overview
Problem
In large-sized display panels, the uneven brightness across pixels is caused by variations in supply voltage and transistor threshold voltages, leading to inconsistent image quality due to the 2T1C driving circuit structure.
Innovation Solution
A driving device for a light emitting unit comprising a driving circuit, a switch, a capacitor, and a compensation circuit that stabilizes the voltage between the control and driving terminals, making the current generated independent of transistor threshold voltage and supply voltage, ensuring uniform brightness across pixels under the same data voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 2T1C driving circuit structure is used, then the device complexity is reduced, but the brightness uniformity deteriorates due to supply voltage drop and transistor threshold voltage variations
Solution Approach 1:
The compensation circuit pre-charges the capacitor to a voltage that includes the transistor threshold voltage before the switching transistor turns on. This preliminary action ensures that when the switching transistor conducts, the threshold voltage is already compensated for in the capacitor voltage, eliminating its effect on the driving current and achieving uniform brightness across pixels with different transistor characteristics.
Solution Approach 2:
A compensation circuit is introduced as an intermediary component between the power supply and the driving transistor. This compensation circuit generates a threshold voltage compensation signal that adjusts the capacitor charging voltage, thereby mediating the effect of transistor threshold voltage variations and supply voltage drops on the driving current, achieving uniform brightness without increasing the basic 2T1C structure complexity.
2Area of stationary object
If the display panel size is increased, then the area is improved, but the brightness uniformity deteriorates due to prolonged power supply circuits and increased equivalent impedance
Solution Approach 1:
The compensation circuit performs preliminary voltage compensation by pre-charging the capacitor with a voltage that accounts for the transistor threshold voltage. This ensures that even in large-sized panels where supply voltage varies across different regions, each pixel's driving current is determined by the compensated capacitor voltage rather than the varying supply voltage, maintaining brightness uniformity across the entire large panel.
3Area of stationary object
If different supply voltages are received by pixel circuits, then the area coverage is improved, but the driving current consistency deteriorates
Solution Approach 1:
The compensation circuit acts as an intermediary that decouples the driving current from the supply voltage variations. By pre-charging the capacitor to include threshold voltage compensation, the circuit ensures that the driving current is determined by the compensated voltage rather than the varying supply voltage, maintaining current consistency across pixels receiving different supply voltages in large-area panels.
Data Source
AI summary
A driving device of a light emitting unit is provided. The driving device includes a driving circuit, a switch, a capacitor, and a compensation circuit. The driving circuit has a control terminal and a driving terminal connected to the light emitting unit. The driving circuit determines a driving current according to the voltage on the control terminal. The switch has a first end for receiving a data voltage, a second end connected to the light emitting unit, and a control end for receiving a scan voltage. The capacitor has a first end connected to the control terminal of the driving circuit and a second end connected to the second end of the switch. The compensation circuit has an output terminal connected to the first end of the capacitor. The compensation circuit supplies a reset voltage to the first end of the capacitor when the switch is turned on.