OLED Driving Transistor Threshold Voltage Sensing
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Solution Overview
Problem
Organic light emitting diode (OLED) display devices face issues with current variation due to threshold voltage deviations, leading to degradation and non-uniform display quality, especially when the gate and drain electrodes of the driving transistor form a diode structure, making it impossible to sense a positive threshold voltage and resulting in varying current flow through the OLED.
Innovation Solution
The OLED display device incorporates a source follower structure for the driving transistor, allowing the gate electrode voltage to be maintained constant, enabling the transistor to sense the threshold voltage and compensate for deviations, thereby maintaining consistent current flow through the OLED regardless of positive or negative threshold voltage deviations, and eliminates the need for a light emitting control transistor to sense the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the gate and drain electrodes of the driving transistor are connected to form a diode structure, then the device complexity is reduced, but the measurement precision of threshold voltage is worsened because it becomes impossible to sense a positive threshold voltage
Solution Approach 1:
The patent divides the driving transistor into separate gate and drain electrodes that are not connected, allowing independent control and measurement. This segmentation enables the gate electrode to be controlled by a capacitor while the drain electrode can sense the threshold voltage, resolving the contradiction between simplified structure and measurement capability.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element connected to the gate electrode of the driving transistor. This capacitor stores and applies voltages that enable threshold voltage sensing without requiring a direct connection between gate and drain, thus maintaining measurement precision while keeping the structure relatively simple.
2Measurement precision
If a light emitting control transistor is used to sense the threshold voltage, then the measurement precision of threshold voltage is improved, but the device complexity increases
Solution Approach 1:
The patent extracts the threshold voltage sensing function from a separate light emitting control transistor and integrates it into the driving transistor itself. By using the driving transistor's own gate and drain electrodes in combination with a capacitor, the sensing function is achieved without adding extra transistors, thus improving measurement precision while avoiding increased device complexity.
Solution Approach 2:
The driving transistor is designed to perform multiple functions: it serves as both the current source for the OLED and the threshold voltage sensing element. The gate electrode controls the current while the drain electrode senses the threshold voltage, eliminating the need for a separate light emitting control transistor and reducing overall device complexity.
3Adaptability or versatility
If the driving transistor operates with varying threshold voltage, then the adaptability to different operating conditions is improved, but the stability of current flow through the OLED is worsened
Solution Approach 1:
The patent implements a feedback mechanism where the threshold voltage sensed at the drain electrode is used to adjust the voltage applied to the gate electrode via the capacitor. This feedback loop compensates for threshold voltage variations, ensuring that the current flow through the OLED remains stable despite changes in the driving transistor's threshold voltage characteristics.
Solution Approach 2:
The patent dynamically changes the voltage parameter applied to the gate electrode of the driving transistor based on the sensed threshold voltage. By adjusting this voltage parameter in response to threshold voltage variations, the system maintains stable current flow through the OLED while adapting to different operating conditions and transistor characteristics.
Data Source
AI summary
An organic light emitting diode display device may include a first transistor connected between a data line and a first node; a second transistor connected between the first node and a second node; a third transistor connected between a reference voltage line and a third node; a fourth transistor connected between a initialization voltage terminal and the second node; a driving transistor having a source electrode connected to the second node, a gate electrode connected to the third node, and a drain electrode connected to a high electric potential voltage terminal; a first capacitor connected between the first node and the drain or source electrode of the driving transistor; a second capacitor connected between the first node and the third node; and a light emitting diode connected to a low electric potential voltage terminal and to the second node.