Color Sensor Calibration via On-Chip RGB to XYZ Transformation
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Solution Overview
Problem
Current colour sensors in the LED market face challenges in achieving high device-to-device accuracy and repeatability, particularly in transforming RGB counts to CIE XYZ tristimulus colour space, due to variance in filter materials and silicon-related effects, leading to inadequate Δu′v′ resolution across operating temperatures.
Innovation Solution
A colour sensor arrangement comprising a colour sensor, processing unit, memory, and control unit that generates and processes channel signals to produce calibrated tuples of colour signals, allowing for on-chip colour transformations and storage of calibration data, enabling accurate device-to-device tolerances and colour temperature measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard process manufacturing with common filter materials is used, then device cost is kept low, but device-to-device accuracy and colour temperature measurement precision deteriorate
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements on each individual device during manufacturing and storing the resulting calibration data in memory before the device is shipped. This pre-calibration approach captures device-specific variations in filter characteristics and silicon effects, enabling accurate colour measurements without requiring expensive custom-filtered devices. The calibration data is used to generate correction factors that compensate for manufacturing variations.
Solution Approach 2:
The patent employs parameter changes by transforming the raw RGB channel signals into calibrated colour space coordinates (such as CIE XYZ or CIE L*a*b*) using device-specific calibration parameters stored in memory. The calibration process determines optimal transformation parameters for each device, accounting for variations in filter spectral curves, absorption coefficients, and silicon temperature coefficients. This allows standard devices to achieve high measurement precision through software-based parameter adjustment.
2Measurement precision
If device-to-device tolerance is minimized through wafer or post-package trimming, then detection accuracy improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies the copying principle by creating a digital replica of each device's optical characteristics through calibration measurements. Instead of physically modifying devices to match a standard, the system captures each device's unique spectral response and creates corresponding calibration data that copies the device's actual behaviour. This digital twin approach allows accurate colour measurements without complex physical trimming or matching processes.
Solution Approach 2:
The patent replaces mechanical/physical trimming processes with software-based calibration. Instead of using wafer trimming or post-package mechanical adjustments to match devices to a reference standard, the system uses computational methods to characterize and correct each device's response. This substitution of mechanical systems with software processing significantly reduces manufacturing complexity while maintaining or improving measurement accuracy.
3Device complexity
If colour space transformations are performed off-device, then device complexity is reduced, but device-to-device tolerance varies and reliability deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing device-specific transformation parameters in memory during the calibration phase. These pre-computed parameters account for each device's unique characteristics and are ready for immediate use during operation. This eliminates the need for complex real-time calculations and ensures consistent application of the same transformation parameters, improving reliability and reducing device-to-device variation.
Solution Approach 2:
The patent introduces an intermediary element in the form of calibration data stored in memory, which acts as a mediator between the raw sensor signals and the final colour space coordinates. This intermediary layer contains device-specific correction factors and transformation parameters that ensure accurate and consistent colour measurements across all devices, regardless of manufacturing variations. The intermediary calibration data bridge ensures that off-device transformations produce reliable and repeatable results.
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
The solution provides very accurate device-to-device tolerances and improved colour temperature accuracy, meeting the high standards required by the LED market, by integrating calibration data and performing colour transformations on-chip, thus enhancing the reliability of colour sensing solutions.
Implementation Method 1
The colour sensor is arranged to generate at least a first channel signal which is indicative of a colour of light incident on the colour sensor
Data Source
AI summary
A color sensor arrangement comprises a color sensor arranged to generate at least a first channel signal being indicative of a color of light incident on the color sensor. A processing unit is connected to the color sensor and arranged to generate a tuple of color signals by processing the at least first channel signal. A memory is connected to the processing unit and a control unit is connected to the processing unit and to the memory. Furthermore, the control unit is arranged to receive calibration data relating the tuple of color signals to a calibrated tuple of color signals and arranged to store said calibration data (M) by means of the memory. An interface is connected to the processing unit and comprises an interface terminal.