OLED Display Device 3T1C Driving Circuit Saturation Region Operation
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Solution Overview
Problem
Conventional OLED pixel driving circuits face issues with non-uniform threshold voltages due to TFT fabrication inconsistencies and aging, leading to display unevenness and grayscale discontinuity, as they typically operate in the linear region rather than the saturation region, affecting the aperture ratio and current flow.
Innovation Solution
An OLED display device with a 3T1C driving structure, incorporating a switch, DAC, ADC, and a reference voltage driving module, where the source of the first TFT is connected to a reference voltage metal layer covering all sub-pixels, allowing the driving TFT to operate in the saturation region during normal display, ensuring continuous grayscale and minimizing the impact of threshold voltage drift and reference voltage routing on pixel aperture ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the conventional 2T1C pixel driving circuit is used, then the structure is simple, but the driving TFT operates in the linear region causing grayscale discontinuity and display unevenness
Solution Approach 1:
The patent changes the operating parameters of the driving TFT by introducing a reference voltage module and configuring the circuit to operate in saturation region instead of linear region. This parameter change ensures continuous grayscale control while maintaining a relatively simple 3T1C circuit structure, resolving the contradiction between device simplicity and grayscale precision.
2Reliability
If the threshold voltage compensation function is added to compensate for TFT aging, then the display evenness is improved, but the device complexity increases
Solution Approach 1:
The patent merges the threshold voltage compensation function with the existing pixel driving circuit by integrating compensation TFTs and capacitors into the same 3T1C structure. This combination achieves reliable display evenness compensation while minimizing additional circuit complexity, as the compensation elements share the same pixel area and timing sequences with the driving function.
3Area of stationary object
If the reference voltage routing is minimized to improve aperture ratio, then the pixel area is increased, but the voltage distribution uniformity across sub-pixels may be affected
Solution Approach 1:
The patent implements equipotentiality by connecting all sub-pixels to a common reference voltage node through the reference voltage module. This ensures that all pixels receive the same reference voltage potential, maintaining voltage distribution uniformity across the display while minimizing routing overhead and preserving pixel aperture ratio.
4Manufacturing precision
If the driving TFT is made to operate in saturation region, then the grayscale continuity is improved, but the aperture ratio may be affected
Solution Approach 1:
The patent changes the operating region parameter of the driving TFT from linear to saturation region by adjusting the gate-source voltage relationship through the reference voltage module. This parameter change achieves continuous grayscale control while the compact 3T1C layout minimizes the area occupied by driving circuit elements, thereby preserving the pixel aperture ratio.
Data Source
AI summary
The invention provides an OLED display device, using a 3T1C driving structure, and having the source of the first TFT to the reference voltage to ensure the second TFT to operate in saturation region in normal display state through controlling the reference voltage, to ensure the grayscale continuity. By using a reference voltage metal layer to cover all sub-pixels to replace reference voltage routing to provide reference voltage to the source of the first TFT, the invention eliminates the impact of reference voltage routing on pixel aperture ration.