AMOLED Pixel Circuit Threshold Extraction With Charge-Pump Feedback
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Solution Overview
Problem
Active matrix organic light emitting device (AMOLED) displays face challenges in extracting threshold voltage and mobility parameters from pixel drivers due to aging, which affects image quality, and this requires additional components in the driver circuit, reducing the pixel aperture.
Innovation Solution
A data extraction system for AMOLED displays that includes a pixel circuit with a drive transistor, an organic light emitting device, and a charge-pump amplifier, utilizing a controller to control electronic switches and provide a programming signal to extract threshold voltage and mobility parameters with minimal components, maximizing pixel aperture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional components are added to extract threshold voltage and mobility parameters from pixel drivers, then image quality is maintained through compensation, but the pixel aperture area is reduced
Solution Approach 1:
The existing drive transistor and programming circuit are made to serve dual purposes: driving the OLED pixel and extracting threshold voltage and mobility parameters. By using the same components for both driving and characterization functions, no additional components are required, thus preserving pixel aperture while enabling image quality compensation through parameter extraction
Solution Approach 2:
The pixel driver circuit extracts its own threshold voltage and mobility parameters using its existing components without requiring external measurement equipment or additional circuitry. The drive transistor and programming voltage circuitry characterize themselves by measuring their own electrical characteristics during normal operation, eliminating the need for separate extraction components that would reduce pixel aperture
2Area of moving object
If a simple driver circuit with minimal components is used to maximize pixel aperture, then pixel aperture area is maximized, but extraction of threshold voltage and mobility parameters becomes challenging
Solution Approach 1:
The system measures the actual threshold voltage and mobility of the drive transistor and uses this feedback information to adjust the programming voltage. By implementing a feedback loop that continuously monitors and compensates for transistor parameter variations, the system achieves accurate parameter extraction and compensation using only the existing minimal components, without requiring additional measurement circuitry
Solution Approach 2:
Traditional parameter extraction methods that would require additional physical measurement equipment are replaced by electrical measurement techniques using the existing programming voltage circuit. Instead of adding mechanical or external electrical measurement devices, the system uses voltage programming and current measurement through the existing transistor to extract parameters, maintaining pixel aperture while enabling characterization
Data Source
AI summary
A system to improve the extraction of transistor and OLED parameters in an AMOLED display includes a pixel circuit having an organic light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input to provide the programming signal, and a storage device to store the programming signal. A charge-pump amplifier has a current input and a voltage output. The charge-pump amplifier includes an operational amplifier in negative feedback configuration. The feedback is provided by a capacitor connected between the output and the inverting input of the operational amplifier. A common-mode voltage source drives the non-inverting input of the operational amplifier. An electronic switch is coupled across the capacitor to reset the capacitor. A switch module including the input is coupled to the output of the pixel circuit and an output is coupled to the input of the charge-pump amplifier.