OLED Pixel Driving Circuit Compensating Threshold Voltage Drift
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Solution Overview
Problem
Conventional OLED displays experience improper image display due to the drifting threshold voltage of driving TFTs, affecting the driving current and overall display quality.
Innovation Solution
A pixel driving circuit with a 7T1C structure is introduced, where specific TFTs are activated during different phases to maintain a constant voltage across the capacitor, isolating the driving current from the threshold voltage of the driving TFT, thereby compensating for voltage drifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional 2T1C pixel driving circuit is used, then the device complexity is low, but the threshold voltage drift of the driving TFT causes improper image display and degraded display quality
Solution Approach 1:
The pixel driving circuit is divided into multiple functional modules: a driving TFT for current control, a compensation TFT for threshold voltage compensation, and multiple capacitors for signal storage. This segmentation allows each component to perform its specific function independently, resolving the threshold voltage drift issue without requiring a complete circuit redesign.
Solution Approach 2:
The compensation capacitor is pre-charged to a reference voltage before the driving phase. During the compensation phase, the compensation TFT adjusts the capacitor's voltage to account for the driving TFT's threshold voltage drift. This preliminary compensation action ensures that the driving current remains accurate despite threshold voltage changes, improving display quality without increasing operational complexity.
2Ease of operation
If the threshold voltage of the driving TFT is allowed to drift, then the device operates simpler without compensation circuits, but the driving current changes and causes improper image display
Solution Approach 1:
The compensation TFT and compensation capacitor form a feedback mechanism that continuously monitors and corrects for threshold voltage drift. During the compensation phase, the compensation TFT adjusts the capacitor's voltage based on the actual threshold voltage of the driving TFT. This feedback loop maintains accurate driving current despite threshold voltage changes, ensuring image display accuracy while keeping the circuit operationally simple through automated compensation.
Solution Approach 2:
The circuit dynamically changes the voltage parameter of the compensation capacitor to counteract threshold voltage drift. By adjusting the capacitor's stored voltage based on the driving TFT's actual threshold voltage, the system maintains constant driving current. This parameter change approach allows the circuit to adapt to threshold voltage variations without complex operational procedures.
3Reliability
If a compensation circuit is added to eliminate threshold voltage drift effects, then the image display quality improves, but the device complexity increases
Solution Approach 1:
The compensation TFT serves multiple functions: it acts as a switch during the reset phase, performs threshold voltage compensation during the compensation phase, and helps control the driving current during the driving phase. This multi-functionality reduces the need for additional dedicated compensation components, improving image display quality while minimizing the increase in device complexity.
Solution Approach 2:
The compensation circuit operates in periodic phases: a reset phase where capacitors are initialized, a compensation phase where threshold voltage drift is corrected, and a driving phase where the OLED is driven with compensated current. This periodic operation allows the compensation function to be integrated into the existing pixel circuit timing, improving image quality without requiring continuous complex circuitry.
Data Source
AI summary
The present disclosure relates to a pixel driving circuit having a pixel structure of 7T1C to compensate a threshold voltage of a driving thin film transistor (TFT) in the organic light-emitting diode (OLED). As such, the current passing through the OLED may not be related to the threshold voltage of the driving TFT. Thus, the improper image-displaying of the OLED display caused by the drifting of the threshold voltage of the driving TFT may be reduced.