AMOLED Pixel Circuit Voltage Extraction for TFT Aging Compensation
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Solution Overview
Problem
Existing display technologies face challenges in maintaining image uniformity and accounting for degradation in active matrix organic light emitting diode (OLED) displays due to non-uniform behavior of thin film transistors (TFTs) across panels and over time, which can lead to decreased pixel density with the incorporation of additional transistors and lines for monitoring systems.
Innovation Solution
The method involves extracting the OLED voltage of a selected pixel by programming it in stages where the current is independent of and dependent on the OLED voltage, measuring differences in programming voltages, and using current-voltage characteristics to determine the effective OLED voltage, while accounting for TFT aging, thereby allowing for compensation and maintaining image quality without decreasing pixel density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If monitoring systems are incorporated to measure time dependent parameters for compensation, then image uniformity and degradation accounting are improved, but pixel density decreases due to additional transistors and lines
Solution Approach 1:
The patent combines the monitoring function with the existing pixel circuit by using the same transistor and line infrastructure for both display programming and monitoring measurements. The pixel circuit performs dual functions: displaying image information and measuring time-dependent parameters like threshold voltage shifts, eliminating the need for separate dedicated monitoring components that would reduce pixel density.
Solution Approach 2:
The pixel circuit is designed to perform multiple functions using the same components. The same transistor controls both the display programming current and the monitoring measurement current. The same pixel line carries both display data and monitoring signals at different times, making the circuit universal and avoiding additional transistors or lines that would compromise pixel density.
2Adaptability or versatility
If additional transistors and lines are added for monitoring systems, then compensation capability is improved, but device complexity increases
Solution Approach 1:
The monitoring capability is merged into the existing pixel circuit structure. The same transistor that controls display programming also performs monitoring measurements by controlling current flow through the OLED. This integration avoids adding separate monitoring transistors and lines, thereby maintaining circuit simplicity while achieving compensation capability.
Solution Approach 2:
The pixel circuit performs self-monitoring using its own components without requiring external monitoring hardware. The circuit measures its own time-dependent parameters (such as threshold voltage shifts) by controlling current flow through the OLED and measuring the resulting voltage drops, enabling compensation capability without increasing device complexity.
3Measurement precision
If multiple programming stages are used to extract OLED voltage, then measurement precision is improved, but time consumption increases
Solution Approach 1:
The patent uses periodic programming stages to extract OLED voltage. First, a programming stage sets the transistor to a known state with current independent of OLED voltage. Then, a second programming stage measures the voltage-dependent current. By periodically alternating between these stages and using the monitor line to read measurements, the system achieves precise OLED voltage extraction while minimizing time consumption through efficient sequential operation.
Data Source
AI summary
The OLED voltage of a selected pixel is extracted from the pixel produced when the pixel is programmed so that the pixel current is a function of the OLED voltage. One method for extracting the OLED voltage is to first program the pixel in a way that the current is not a function of OLED voltage, and then in a way that the current is a function of OLED voltage. During the latter stage, the programming voltage is changed so that the pixel current is the same as the pixel current when the pixel was programmed in a way that the current was not a function of OLED voltage. The difference in the two programming voltages is then used to extract the OLED voltage.