Voltage Programming OLED Pixel Structure for Threshold Voltage Compensation
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Solution Overview
Problem
The voltage programming type active matrix organic light emitting diode (OLED) pixel structure suffers from current deterioration due to threshold voltage shifts in amorphous silicon TFTs, leading to non-uniform current flow and picture quality deterioration, as the existing structure cannot correct TFT threshold voltage deterioration between pixels.
Innovation Solution
The proposed pixel structure incorporates additional transistors and a capacitor configuration that includes a fifth switching transistor, a fourth switching transistor, a capacitor, and a sixth transistor, which allows for the pre-charging of the gate node with a high voltage to compensate for threshold voltage, and periodic application of a negative voltage to minimize threshold voltage deterioration, thereby maintaining reliable OLED current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If amorphous silicon TFTs are used to drive OLEDs, then manufacturing complexity is reduced and wide screen achievement is enabled, but threshold voltage shifts occur causing current deterioration and picture quality degradation
Solution Approach 1:
The capacitor is pre-charged with a data voltage during the programming phase before the OLED emission phase. This preliminary charging action stores the correct drive voltage that compensates for the TFT's threshold voltage, ensuring accurate current flow to the OLED despite TFT deterioration. The pre-stored voltage in the capacitor serves as a compensation mechanism that was prepared in advance.
Solution Approach 2:
The pixel structure implements a feedback mechanism where the capacitor stores voltage information that reflects the TFT's threshold voltage characteristics. By charging the capacitor with a data voltage that accounts for the TFT's threshold voltage drop, the system creates a feedback loop that compensates for TFT deterioration, ensuring consistent OLED current flow across different pixels and over time.
2Productivity
If continuous gate bias voltage is applied to TFTs, then OLED current flow is maintained, but threshold voltage deterioration occurs causing non-uniform current distribution
Solution Approach 1:
The capacitor is charged with a data voltage during a programming phase before the OLED emission phase. This preliminary action stores the precise voltage needed to compensate for TFT threshold voltage, ensuring that when the OLED emits light, the correct current flows despite TFT deterioration. The voltage compensation is prepared in advance rather than relying on continuous adjustment.
Solution Approach 2:
The pixel structure operates in periodic cycles: during the programming phase, the capacitor is charged with the data voltage; during the emission phase, the stored voltage compensates for TFT threshold voltage. This periodic charging and compensation mechanism ensures uniform current distribution across pixels while maintaining continuous OLED operation.
3Ease of operation
If conventional voltage programming pixel structure is used, then device operation is simplified, but TFT threshold voltage deterioration cannot be corrected between pixels
Solution Approach 1:
The capacitor is pre-charged with a data voltage during the programming phase that specifically accounts for and compensates for the TFT's threshold voltage. This preliminary voltage storage action ensures that when the OLED is driven, the correct current flows despite TFT deterioration. The compensation is built into the voltage stored in the capacitor before operation begins.
Solution Approach 2:
The capacitor serves as a feedback element that stores voltage information reflecting the TFT's threshold voltage characteristics. By charging the capacitor with a data voltage that compensates for threshold voltage drop, the system creates a self-correcting mechanism that maintains inter-pixel consistency without complicating the overall operation.
Data Source
AI summary
A pixel structure using a voltage programming type active matrix organic light emitting diode (OLED) which can minimize a current deterioration phenomenon. The pixel structure includes a fifth TFT receiving an external management signal EMS through its gate, having a drain region connected to a cathode part of an OLED, and receiving an input of an OLED current through its source-drain current path when the OLED emits light, a fourth TFT receiving a set scan signal SCAN through its gate and having source and drain regions connected to gate and drain parts of a third TFT T3; respectively, the third TFT T3 being a current driving transistor for determining the OLED current when the OLED emits light, a capacitor C having upper and lower plates connected to the gate part of the third TFT T3 and a ground voltage VSS.