Illuminance Sensor Circuit Topology for Spectral Accuracy
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Solution Overview
Problem
Existing illuminance sensors face challenges in achieving accurate spectral-response characteristics close to human spectral luminous efficacy due to errors in current mirror circuits and high circuit complexity, particularly in low illuminance conditions and when dealing with light sources having significant infrared components.
Innovation Solution
An illuminance sensor design incorporating a first and second light receiving element with different spectral-response characteristics, utilizing an integrating analog-digital conversion circuit for precise current conversion and subtraction, eliminating the need for current mirror circuits and reducing circuit complexity by integrating and comparing voltage outputs to achieve a spectral-response characteristic approximating human spectral luminous efficacy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a current mirror circuit is used to subtract currents from photodiodes with different spectral-response characteristics, then the spectral-response characteristic can be adjusted to approximate human spectral luminous efficacy, but measurement precision deteriorates due to large errors from transistor property variations
Solution Approach 1:
The patent extracts the problematic current mirror circuit from the system and replaces it with separate analog-digital conversion circuits for each photodiode. This removes the source of measurement errors while preserving the ability to achieve desired spectral-response characteristics through digital processing of the converted signals.
Solution Approach 2:
The patent substitutes the analog current subtraction mechanism (current mirror circuit) with a digital signal processing approach. By converting currents to digital values separately and then performing subtraction digitally, the system eliminates the precision errors inherent in analog current mirror circuits while maintaining the spectral adjustment capability.
2Measurement precision
If multiple photodiodes and current mirror circuits are used to achieve accurate spectral-response characteristics, then the spectral measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex analog current mirror circuits with simpler analog-digital conversion circuits. Each photodiode connects to its own ADC, eliminating the need for precise current mirroring and subtraction circuitry. This substitution dramatically reduces circuit complexity while maintaining or improving measurement precision through digital processing.
Solution Approach 2:
The patent changes the operating parameters of the photodiodes by applying different reverse bias voltages. This allows each photodiode to be optimized for specific wavelength ranges, improving spectral measurement capability without requiring complex circuit arrangements. The parameter change approach simplifies the overall system design.
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 enables accurate illuminance measurement with low circuit complexity, effectively approximating human spectral luminous efficacy and reducing errors, especially in low illuminance conditions and with diverse light sources.
Implementation Method 1
The photodiode PD1 has a current Iin1 flowing therethrough in correspondence with environmental brightness. The photodiode PD2 has a current Iin2 flowing therethrough in correspondence with environmental brightness.
Data Source
AI summary
Disclosed are an illuminance sensor which has a spectral-response characteristic approximate to the spectral luminous efficacy and which has a low circuit complexity, and a display device including the illuminance sensor. The illuminance sensor includes (i) a current output circuit which, with use of a bitstream signal of a first analog-digital conversion circuit for carrying out an analog-digital conversion with respect to a first current flowing through a first light receiving element, outputs a current corresponding to the first current and (ii) a second analog-digital conversion circuit which receives a third current obtained by subtracting a current from a second current flowing through a second light receiving element and which thus carries out an analog-digital conversion with respect to the third current.