OLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The variation in threshold voltage of transistors in OLED display devices leads to uneven light emission across multiple pixel circuits, resulting in inconsistent display performance due to manufacturing process variations.
Innovation Solution
A pixel circuit design incorporating multiple transistors and capacitors that compensates for the threshold voltage of the driving transistor, ensuring the driving current is independent of the transistor's threshold voltage, thereby stabilizing light emission and preventing afterimages and brightness issues during gray scale transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional 3T1C pixel circuit structure is used, then the device complexity is low, but the light emission uniformity deteriorates due to threshold voltage variations
Solution Approach 1:
The patent changes the circuit parameters by introducing additional transistors (T4, T5, T6) and capacitors (C2) to create a threshold voltage compensation mechanism. This modifies the electrical parameters of the pixel circuit to compensate for manufacturing variations in transistor threshold voltages, thereby improving light emission uniformity while maintaining reasonable device complexity
Solution Approach 2:
The patent implements a feedback mechanism where the threshold voltage of the driving transistor is compensated through additional circuit elements. The compensation circuit measures and adjusts for threshold voltage variations, creating a feedback loop that corrects for manufacturing process deviations and ensures consistent light emission across all pixels
2Ease of manufacture
If transistor threshold voltage varies due to manufacturing process, then the device complexity remains the same, but the display quality deteriorates due to uneven light emission
Solution Approach 1:
The patent converts the harmful effect of threshold voltage variations into a beneficial compensation mechanism. By introducing additional circuit elements, the design actively measures and compensates for threshold voltage deviations, turning the manufacturing variability problem into an opportunity for improved display uniformity through systematic correction
3Use of energy by moving object
If a simple 3T1C circuit is used, then the power consumption is low, but the light emission stability deteriorates during gray scale transitions
Solution Approach 1:
The patent applies preliminary action by resetting the driving transistor and anode before gray scale transitions occur. The additional transistors and capacitors are configured to perform preliminary resetting operations, ensuring that the pixel is in a known stable state before transitioning to new gray levels, thereby preventing display defects and ensuring stable light emission
Data Source
AI summary
A pixel circuit and a display device are provided. The pixel circuit includes a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a driving transistor, a first capacitor and a second capacitor. A threshold voltage of the driving transistor is compensated through a cooperation of the transistors and the capacitors in a source following manner, such that a driving current generated by the driving transistor for driving a light emitting element to emit light is independent from the threshold voltage of the driving transistor itself. In addition, the driving transistor and the anode of the light emitting element are reset through the cooperation of the transistors, thereby avoiding from grabbing a different threshold voltage after a gray scale transition, thus avoiding afterimages and insufficient brightness of the first frame after the gray scale transition.