Pixel Defect Detection via Inspecting Current Measurement
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Solution Overview
Problem
Conventional methods for detecting pixel defects in display devices are limited in accuracy due to small capacitance differences and low currents involved, making it difficult to determine if the threshold voltage of driving transistors is within a normal range.
Innovation Solution
A method that involves turning on specific transistors in a pixel to create a path for an inspecting current, using a current detector connected to the data line to determine if the threshold voltage is within a reference range, by applying appropriate voltage levels during an inspection period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the conventional method measures the charging time of the storage capacitor to detect pixel defects, then the detection process can be performed, but the detection accuracy is limited because the capacitance of the storage capacitor is smaller than that of parasitic capacitors in data lines
Solution Approach 1:
The patent changes the measurement parameter from storage capacitor charging time to inspection current magnitude. By applying a test voltage to the data line and measuring the resulting inspection current that flows through the driving transistor, the method achieves higher detection accuracy because the current magnitude is more significantly affected by threshold voltage deviations than the charging time of the small storage capacitor.
Solution Approach 2:
The patent introduces an inspection current as an intermediary measurement quantity. Instead of directly measuring the threshold voltage or the charging time of the storage capacitor, the method measures the inspection current that flows through the driving transistor when a test voltage is applied to the data line. This intermediary current provides a more sensitive indicator of threshold voltage deviations.
2Measurement precision
If the conventional method measures the current flowing through the driving transistor during storage capacitor discharge, then the threshold voltage can be detected, but the current is very small (a few nano-amperes) making accurate detection difficult
Solution Approach 1:
The patent changes the operational parameters by applying a test voltage to the data line during an inspection period, which causes a much larger inspection current to flow through the driving transistor. This inspection current is significantly larger than the nano-ampere range currents in conventional methods, enabling accurate detection with standard measurement equipment.
3Measurement precision
If the capacitance of the storage capacitor is increased to improve detection accuracy, then the detection precision would improve, but the pixel circuit area and complexity would increase
Solution Approach 1:
The patent uses the data line as an intermediary element to apply test voltage and measure inspection current. This approach leverages existing pixel circuit components (driving transistor, data line) without adding new circuit elements, thereby maintaining simple pixel structure while achieving high detection accuracy through clever use of the inspection current measurement.
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 method improves detection accuracy by using a higher inspecting current to determine if the pixel is normal or defective, preventing defective products from being shipped by accurately identifying threshold voltage deviations.
Implementation Method 1
detecting an inspecting current flowing in a path corresponding to the first through fourth transistors using a current detector that is connected to the data line
Data Source
AI summary
A method of detecting a pixel defect for detecting a defect of a pixel including first to fourth transistors, connected to a data line, and receiving a scan signal and an initialization control signal includes turning on the first through fourth transistors by changing the scan signal and the initialization control signal to have a turn-on voltage level in an inspection period, detecting an inspecting current flowing in a path corresponding to the first through fourth transistors using a current detector that is connected to the data line, determining that a threshold voltage of the second transistor is within a normal range when the inspecting current is within a reference range, and determining that the threshold voltage of the second transistor is out of the normal range when the inspecting current is out of the reference range.