OLED Driving TFT Sensing via Current Integration
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Solution Overview
Problem
Conventional external compensation methods for organic light emitting displays face challenges in accurately sensing electrical characteristics of driving TFTs due to large parasitic capacitance variations and long sensing times, especially in low-grayscale conditions, leading to inconsistent luminance across pixels.
Innovation Solution
The implementation of a current sensing method using a data driver IC with current integrators and a sample & hold unit, which applies sensing data voltage to data lines and removes common noise components, allowing for faster and more accurate sensing of pixel currents through the use of a current sensing method with reduced parasitic capacitance impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage sensing method is used in conventional external compensation, then the sensing circuit can be implemented, but the parasitic capacitance causes long sensing time and inaccurate measurements especially in low-grayscale conditions
Solution Approach 1:
The patent replaces the conventional voltage sensing method with a current sensing method. Instead of measuring voltage through parasitic capacitance (indirect mechanical-like measurement), the invention directly senses the current Ids flowing through the driving TFT using a current sensing circuit. This substitution eliminates the dependency on parasitic capacitance charging time, thereby significantly reducing sensing time while improving measurement accuracy, especially in low-grayscale conditions where voltage sensing is most problematic.
2Reliability
If external compensation method is used to compensate for driving TFT variations, then luminance uniformity can be improved, but the sensing time increases due to parasitic capacitance charging requirements
Solution Approach 1:
The patent replaces the voltage sensing mechanism that relies on parasitic capacitance charging with a direct current sensing approach. The current sensing circuit measures the actual current Ids flowing through the driving TFT without requiring capacitance charging time. This maintains the external compensation method's ability to improve luminance uniformity while eliminating the time penalty associated with voltage sensing, thus resolving the contradiction between reliability improvement and time loss.
3Measurement precision
If voltage sensing is performed after source electrode potential reaches saturation, then threshold voltage compensation can be achieved, but the sensing time becomes excessively long
Solution Approach 1:
The patent substitutes the voltage sensing method that waits for source electrode potential saturation with a direct current sensing method. The current sensing circuit continuously monitors the current Ids flowing through the driving TFT, allowing immediate detection of threshold voltage variations without waiting for capacitance charging or potential saturation. This provides accurate threshold voltage sensing information much faster, resolving the contradiction between measurement precision and sensing time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces sensing time and enhances sensing performance by directly integrating current data, providing accurate compensation for threshold voltage and mobility variations, thereby improving image consistency across pixels.
Implementation Method 1
a current integrator that integrates the pixel current
Implementation Method 2
a sample & hold unit that stores and holds an integrated value obtained from the current integrator
Data Source
AI summary
An organic light emitting display comprises: a display panel with a plurality of pixels connected to data lines and sensing lines, each pixel comprising an OLED and a driving TFT for controlling the amount of light emission of the OLED; and a data driver IC comprising a plurality of sensing units for sensing current data of the pixels through a plurality of sensing channels connected to the sensing lines, each sensing unit comprising: a first current integrator connected to an odd sensing channel; a second current integrator connected to an even sensing channel neighboring the odd sensing channel; and a sample & hold unit that removes common noise components from a first sampled value input from the first current integrator and a second sampled value input from the second current integrator while storing and holding the first and second sampled values.