Pixel Driving Circuit With Threshold Sensing for AMOLED Uniformity
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Solution Overview
Problem
Active matrix organic light emitting diode (AMOLED) panels suffer from non-uniform brightness due to poor uniformity of driving transistor threshold voltages and OLED degradation during manufacturing.
Innovation Solution
A pixel driving circuit with a driving transistor, data writing circuit, threshold compensation circuit, sensing circuit, and light emitting element, which includes a threshold voltage sensing process and internal compensation mechanism to stabilize the driving current by compensating for threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If threshold voltage sensing is performed for all pixel units, then measurement precision of threshold voltage is improved, but loss of time increases due to the large number of pixels
Solution Approach 1:
The pixel array is divided into multiple pixel units, and the sensing process is divided into multiple sensing stages. In each sensing stage, only a subset of pixel units is sensed simultaneously. The pixel driving circuit switches between different sensing stages to complete threshold voltage sensing for all pixel units sequentially, thereby reducing the time required compared to sensing all pixels simultaneously.
Solution Approach 2:
The pixel driving circuit performs threshold voltage sensing in periodic sensing stages. Each sensing stage corresponds to a specific time period during which a particular pixel unit or subset of pixel units is sensed. By organizing the sensing process into periodic stages, the circuit efficiently manages the time required to sense all pixel units while maintaining measurement precision.
2Measurement precision
If threshold voltage sensing is performed for all pixel units, then measurement precision of threshold voltage is improved, but device complexity increases
Solution Approach 1:
The pixel driving circuit is designed to perform multiple functions: it can sense threshold voltages for different pixel units in different sensing stages, it can compensate for threshold voltage variations, and it can drive the light emitting element. By making the pixel driving circuit multi-functional, the need for separate dedicated sensing circuits for each pixel unit is eliminated, thereby reducing overall device complexity while maintaining the capability to sense all pixel units.
Solution Approach 2:
The sensing circuit, compensation circuit, and driving circuit are merged into a single integrated pixel driving circuit. This consolidation allows the circuit to share common components and control mechanisms across different sensing stages and functions, reducing the total number of discrete components and simplifying the overall device structure while enabling comprehensive threshold voltage sensing.
3Manufacturing precision
If threshold voltage sensing is performed for all pixel units, then manufacturing precision is improved, but productivity decreases
Solution Approach 1:
The pixel driving circuit performs threshold voltage sensing and compensation in advance during specific sensing stages before the actual display refresh operation. By completing the threshold voltage measurement and compensation beforehand, the circuit ensures manufacturing precision is improved without interfering with the subsequent display refresh process, thereby maintaining productivity.
Solution Approach 2:
The pixel driving circuit dynamically switches between different operating modes: sensing mode (for threshold voltage measurement), compensation mode (for correcting threshold voltage variations), and display mode (for normal operation). This dynamic switching allows the circuit to prioritize manufacturing precision during sensing and compensation phases while maintaining high productivity during display refresh phases, effectively balancing both requirements.
Data Source
AI summary
A pixel driving circuit is provided to include: a driving transistor; a data writing circuit configured to write a display data voltage from the data line to a first node in a display driving process, and sequentially write a sensing data voltage and a reset data voltage from the data line to the first node in a threshold voltage sensing process; a threshold compensation circuit configured to write a reference voltage from a reference voltage supply terminal to the first node and write a first compensation voltage to a second node in the display driving process, and write a second compensation voltage to the second node when a voltage at the first node changes from the reference voltage to the display data voltage; a sensing circuit configured to write an initialization voltage from the sensing line to the second node in the threshold voltage sensing process; a light emitting element.