Pulse-Current Waveform Correction for Light-Emitting Device Inspection

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Solution Overview

Problem

Existing methods for inspecting light-emitting devices using pulse currents struggle to accurately apply the intended current value due to deviations from rectangular waves as pulse width shortens, leading to inconsistent characteristic value measurements.

Innovation Solution

A characteristic value correction device and method that calculates a correction coefficient based on the ratio of areas and times within the waveform of the applied pulse current, allowing conversion of actual current values to intended values for accurate characteristic inspection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If pulse width is shortened to suppress heat generation, then heat generation is reduced, but current waveform deviates from rectangular wave causing inaccurate current application

Engineering Contradiction:

Improveheat generationVSAvoidcurrent value accuracy

Core Design Contradiction:

TemperatureVSMeasurement precision

Solution Approach 1:

The patent changes the parameter of pulse width to suppress heat generation while introducing a correction coefficient that compensates for the waveform deviation. By calculating the ratio of actual current integral to target current integral, the system maintains measurement accuracy despite using shortened pulse widths that deviate from ideal rectangular waves.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If pulse current is applied for short time to inspect characteristics, then inspection speed is improved, but current value deviation increases

Engineering Contradiction:

Improveinspection speedVSAvoidcurrent value accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where the actual current waveform is measured and compared against the target rectangular wave. A correction coefficient is calculated based on the ratio of their integrals, and this coefficient is used to correct the measured characteristic values, thereby maintaining accuracy while using short pulse durations for high-speed inspection.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If correction coefficient is calculated based on area and time ratios, then current value accuracy is improved, but calculation complexity increases

Engineering Contradiction:

Improvecurrent value accuracyVSAvoidcalculation complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces complex waveform analysis with a simplified calculation method based on integral ratios. Instead of analyzing the entire waveform shape, the system calculates the correction coefficient using only the ratio of areas under the curves and the ratio of time periods, significantly reducing computational complexity while maintaining accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS12429374B2Characteristic value correction device, characteristic value calculation device, inspection device including the same, characteristic value correction method, light-emitting device, and characteristic value correction program

Publication Date: 2025.09.30 NICHIA CORP

AI summary

A characteristic value correction device includes a waveform acquiring unit, an area calculating unit, a time calculating unit, and a correction coefficient calculating unit. The waveform acquiring unit is configured to acquire a waveform indicating a relationship between an elapsed time and a first current value obtained when the pulse current is applied to a light-emitting device. The area calculating unit is configured to calculate a first area of an entire waveform and a second area of a rectangular wave portion. The time calculating unit is configured to calculate a first time between an application start time and an application end time of the pulse current and a second time corresponding to the second area. The correction coefficient calculating unit is configured to obtain a correction coefficient based on a ratio between the first area and the second area and a ratio between the first time and the second time.