OLED Pixel Circuit Current Calibration for Uniformity
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Solution Overview
Problem
Active matrix organic light emitting diode (OLED) displays face challenges in maintaining image uniformity and accounting for degradation over time due to non-uniform behavior of thin film transistors, which requires additional transistors and lines for monitoring and compensation, ultimately decreasing pixel density.
Innovation Solution
A system for controlling pixels in OLED displays that includes a pixel circuit with a drive transistor, storage capacitor, reference voltage source, programming voltage source, and a controller to manage current and voltage levels, allowing for calibration and compensation without the need for additional transistors or lines, thereby maintaining image quality and pixel density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If monitoring systems are added to measure time dependent parameters for compensation, then image uniformity and degradation compensation are improved, but pixel density decreases due to additional transistors and lines
Solution Approach 1:
The patent combines the monitoring and compensation functions into the existing pixel circuit by utilizing the drive transistor itself for current measurement during programming cycles. The controller integrates multiple functions (programming, monitoring, compensation) into a unified control sequence, eliminating the need for separate monitoring circuits and additional transistors.
Solution Approach 2:
The drive transistor serves multiple functions: it drives the light emitting device during emission cycles and simultaneously acts as a monitoring element during programming cycles. The controller performs multiple tasks including voltage programming, current measurement, degradation monitoring, and compensation calculation using the same hardware resources, making the system multi-functional without adding components.
2Adaptability or versatility
If additional transistors and lines are incorporated for monitoring and compensation, then degradation compensation capability is improved, but manufacturing complexity increases
Solution Approach 1:
The monitoring and compensation functionality is merged into the existing pixel circuit structure, utilizing the drive transistor and storage capacitor that are already required for basic operation. This integration approach avoids additional fabrication steps and reduces manufacturing complexity while maintaining degradation compensation capability.
Solution Approach 2:
The pixel circuit performs self-monitoring and self-compensation by using its own drive transistor to measure current and the controller to calculate compensation values. The system serves itself by leveraging existing components for dual purposes, eliminating the need for separate monitoring circuits and simplifying the manufacturing process.
3Measurement precision
If the storage capacitor stores voltage difference between reference and programming voltage, then compensation precision is improved, but circuit complexity increases
Solution Approach 1:
The storage capacitor is pre-charged to the reference voltage before the programming voltage is applied. This preliminary action establishes a known baseline voltage that enables precise measurement of the voltage difference. The controller then calculates compensation values based on this pre-established reference, improving measurement precision without requiring complex real-time measurement circuits.
Data Source
AI summary
A system for controlling a display in which each pixel circuit comprises a light-emitting device, a drive transistor, a storage capacitor, a reference voltage source, and a programming voltage source. The storage capacitor stores a voltage equal to the difference between the reference voltage and the programming voltage, and a controller supplies a programming voltage that is a calibrated voltage for a known target current, reads the actual current passing through the drive transistor to a monitor line, turns off the light emitting device while modifying the calibrated voltage to make the current supplied through the drive transistor substantially the same as the target current, modifies the calibrated voltage to make the current supplied through the drive transistor substantially the same as the target current, and determines a current corresponding to the modified calibrated voltage based on predetermined current-voltage characteristics of the drive transistor.