Integrated LCD Test Circuit for Defect Detection
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Solution Overview
Problem
Existing liquid crystal display device testing methods are inefficient, as they require visual inspections after completion and cannot reliably detect minute current variations, leading to increased rejection rates and space requirements due to the need for numerous terminals and analog switches.
Innovation Solution
A test circuit integrated into the same substrate as the liquid crystal display elements, featuring a comparator circuit to detect selected rows or columns, an encoder circuit to encode voltage levels, and a read-out circuit to determine the selected line number, allowing for bi-directional scanning and voltage level encoding without external test devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If visual inspection is used for testing after device completion, then the testing process is simple, but the detection precision is insufficient and cannot detect minute current variations
Solution Approach 1:
The test circuit is nested within the array substrate itself, with test circuitry integrated among the pixel electrodes and TFTs. This allows the testing function to be embedded within the device structure, achieving high detection precision without adding external testing equipment or complex external test circuits.
Solution Approach 2:
The liquid crystal display device performs self-testing through integrated test circuits that can activate specific row lines and column lines, apply test voltages, and detect current variations autonomously. The device tests itself without requiring external test devices, achieving both high detection precision and simplicity.
2Reliability
If numerous terminals and analog switches are added to detect malfunction, then the detection capability is improved, but the device size increases and space requirements are not met
Solution Approach 1:
The row lines and column lines serve dual functions: they are used for normal display operation and for defect detection. The same conductive structures that drive the liquid crystal display during normal operation are reused as test signal pathways, eliminating the need for separate dedicated test terminals and switches.
Solution Approach 2:
The test circuit components (test TFTs, test signal lines, detection circuits) are merged with the display circuit components in the same array substrate. The test row lines and column lines are combined with the display row lines and column lines, allowing defect detection functionality to be integrated without increasing device area.
3Productivity
If testing is performed after device completion, then the testing process is simple, but manufacturing efficiency decreases due to wasted devices with detectable defects
Solution Approach 1:
The test circuits are constructed during the same manufacturing process as the display elements, before the device is completed and packaged. This allows defects to be detected early in the manufacturing process, enabling corrective actions to be taken before further processing steps are performed, thereby improving manufacturing efficiency by preventing waste of subsequent processing steps on defective devices.
Data Source
AI summary
A test device for detecting malfunction of a liquid crystal display device, and also provide a liquid crystal display device incorporated with such test device. The test device comprising a comparator circuit for detecting which of the rows or columns of the lines is selected, an encoder circuit receiving the detection result from the comparator circuit, a plurality of bus lines and a read-out circuit reading the voltage level of the bus lines from the encoder circuit to determine if the encoded number is identical with the number of the selected row or column line, wherein the comparator circuit, the encoder circuit, and the read-out circuit being built in the same substrate as the liquid crystal display elements.