OLED Pixel Driving Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The instability of threshold voltage in driving thin film transistors in OLED pixel driving circuits leads to non-uniform panel display, reduced brightness, and decreased luminous efficiency due to aging of materials, causing inconsistent current flow through OLEDs.
Innovation Solution
An OLED pixel driving circuit with a 5T1C structure, including multiple P-type thin film transistors and a capacitor, where the scan signals control the transistors through distinct stages to isolate the current flow from the threshold voltage, ensuring consistent current flow during the light-emitting stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 2T1C OLED pixel driving circuit is used, then the device complexity is low, but the uniformity of panel display deteriorates due to threshold voltage variations in driving thin film transistors
Solution Approach 1:
The driving circuit is segmented into multiple functional stages: initialization stage (setting initial voltage), threshold voltage storage stage (storing threshold voltage), and light-emitting stage (driving OLED). This segmentation allows different transistors to perform different functions at different times, isolating the current flow from threshold voltage variations.
Solution Approach 2:
The circuit uses dynamic switching of multiple thin film transistors (T1-T6) based on scan signals to transition between different operational states. The transistors are dynamically configured to either connect or disconnect specific nodes, enabling the circuit to adapt its topology based on the driving stage, thereby eliminating the direct correlation between threshold voltage and OLED current.
2Productivity
If driving thin film transistors are used for extended periods, then the productivity is high, but the reliability deteriorates due to material aging and threshold voltage drift
Solution Approach 1:
The circuit performs preliminary actions during the initialization stage by setting an initial voltage on the gate of the first thin film transistor before the light-emitting stage begins. This preliminary voltage setting compensates for threshold voltage drift that occurs during extended operation, ensuring stable OLED current flow throughout the display period.
Solution Approach 2:
The circuit incorporates feedback mechanisms where the threshold voltage of the first thin film transistor is stored and reused in subsequent driving cycles. By storing the threshold voltage in the capacitor and using it to set the initial voltage, the system creates a feedback loop that compensates for aging effects and maintains consistent OLED current over time.
3Reliability
If the turn-on voltage of driving thin film transistors increases due to aging, then the reliability improves in terms of voltage stability, but the luminous efficiency deteriorates due to reduced current flow through OLEDs
Solution Approach 1:
The circuit changes the voltage parameters dynamically by setting different voltages on the gates of different transistors based on the operational stage. During the light-emitting stage, the gate of the first thin film transistor is set to a specific voltage that compensates for aging effects, ensuring that the voltage difference across the OLED remains optimal for maintaining high luminous efficiency despite threshold voltage drift.
Data Source
AI summary
An OLED pixel driving circuit includes a first thin film transistor, a second thin film transistor, a third thin film transistor, a fourth thin film transistor, a fifth thin film transistor, a sixth thin film transistor, a capacitor and an OLED. A gate of the third thin film transistor receives a second scan signal, both a source of the third thin film transistor and a source of the fourth thin film transistor receive a data voltage or an initial voltage. A gate of the first thin film transistor is connected to a source of the second thin film transistor and one terminal of the capacitor, another terminal of the capacitor being grounded.