AMOLED Pixel Circuit Current Measurement and Brightness Correction
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Solution Overview
Problem
The lifetime of organic light emitting diodes in AMOLED displays is unstable, causing uneven brightness due to changes with time and temperature, leading to issues with display uniformity.
Innovation Solution
An AMOLED pixel circuit is designed with an additional thin film transistor and current measurement circuit, allowing for real-time measurement and correction of drive current, which is used to adjust the signal voltage to maintain consistent brightness across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 2T1C pixel circuit is used for AMOLED display, then the structure is simple and power consumption is low, but the brightness uniformity deteriorates due to organic light emitting diode property changes over time and temperature
Solution Approach 1:
The pixel circuit is divided into multiple functional modules: a first thin film transistor for signal input, a second thin film transistor for current control, a capacitor for voltage storage, and a third thin film transistor for measurement control. This segmentation allows each component to perform its specific function optimally while maintaining overall system reliability.
Solution Approach 2:
The patent introduces a feedback mechanism where the drive current is measured through the third thin film transistor and fed back to the signal voltage drive circuit. This feedback loop enables real-time adjustment of the signal voltage to compensate for organic light emitting diode property changes, thereby maintaining brightness uniformity across different pixels and over time.
2Use of energy by moving object
If current driving method is used in AMOLED, then the lighting efficiency is high, but the lifetime stability deteriorates causing uneven display
Solution Approach 1:
The patent makes the pixel circuit dynamic by introducing real-time current measurement and signal voltage adjustment. The third thin film transistor enables dynamic control of the measurement process, and the signal voltage drive circuit dynamically adjusts the gate voltage of the second thin film transistor based on measured current values, allowing the system to adapt to changing conditions over time and temperature.
Solution Approach 2:
The feedback mechanism measures the actual drive current through the third thin film transistor and uses this information to adjust the signal voltage. This closed-loop control compensates for lifetime degradation and property changes of the organic light emitting diode, maintaining stable performance throughout the device's operational life.
3Reliability
If additional thin film transistor and current measurement circuit are added, then the brightness uniformity is improved, but the device complexity increases
Solution Approach 1:
The third thin film transistor serves multiple functions: it acts as a current measurement element, a control element for the measurement process, and part of the feedback mechanism. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in device complexity while achieving improved brightness uniformity.
Solution Approach 2:
The patent merges the current measurement function with the existing pixel circuit structure by integrating the third thin film transistor into the signal path. The current measurement circuit is combined with the signal voltage drive circuit, creating a unified system that performs both driving and measurement functions without requiring completely separate measurement apparatus.
Data Source
AI summary
The present invention provides an AMOLED pixel circuit. The third thin film transistor (T3) are located between the first, the second thin film transistors (T1, T2), and the control line (Control) is employed to input the control signal for controlling on and off of the third thin film transistor (T3), and thus controlling the AMOLED pixel circuit to measure the drive current with the current measurement circuit (1) and correcting the signal voltage with the signal voltage drive circuit (2), or displaying normally. The drive current entering the organic light emitting diode (D) in respective pixels can be corrected to solve the issues of unstable brightness and uneven display caused by the properties of the organic light emitting diode (D), which is changing along with the time and temperature, and to improve the display effect.