Light Sensor Dark Current Elimination Duo Switch-Capacitor
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Solution Overview
Problem
Conventional light sensors face inefficiencies in eliminating dark current, especially in high-temperature and low-illumination environments, such as under mobile phone display screens, where dark current grows exponentially, impacting sensed current accuracy.
Innovation Solution
A light sensor circuit comprising a first switch-capacitor circuit to convert dark current into voltage, a second switch-capacitor circuit to convert sensing current into voltage, and a reverse capacitor to deduct dark voltage from sensing voltage, generating an output voltage that isolates lux voltage, with synchronized switching units and capacitors to prevent saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional dark current elimination methods are used, then the circuit complexity is low, but the dark current elimination efficiency is poor and measurement precision deteriorates in high-temperature low-illumination environments
Solution Approach 1:
The patent divides the photodiode into two separate photodiodes: one exposed to ambient light for sensing and one shielded for dark current measurement. This segmentation allows independent measurement of dark current without affecting the sensing function, resolving the contradiction by achieving high measurement precision through structural division while maintaining reasonable circuit complexity.
Solution Approach 2:
The patent introduces a reverse capacitor as an intermediary element that subtracts the dark current voltage from the sensing voltage. This intermediary mechanism enables precise dark current elimination through voltage subtraction, improving measurement precision while adding only one critical component to the circuit.
2Measurement precision
If longer measurement time is used, then the measurement precision improves, but the response speed decreases and productivity deteriorates
Solution Approach 1:
The patent performs dark current measurement in advance by using a shielded photodiode that continuously measures dark current independently of the sensing process. This preliminary measurement of dark current allows for rapid subtraction from the sensing signal, achieving high measurement precision without requiring extended measurement times, thus maintaining fast response speed and productivity.
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 fast, efficient, and sensitive elimination of dark current, allowing accurate lux voltage measurement within 1-2 ms in low illumination environments, preventing switch-capacitor saturation and enhancing measurement sensitivity.
Implementation Method 1
Light sensors generally use photodiodes to sense optical signals and convert them into electrical signals
Implementation Method 2
a first switch-capacitor circuit to convert a dark current of a first photodiode, without being exposed to ambient light, into a first voltage
Data Source
AI summary
The present invention provides a light sensor with dark current elimination. A dark current from a covered photodiode and a sensed current from a photodiode are respectively transformed to a dark voltage and a sensed voltage by a controlled integration circuit. A reverse capacitor receives the dark voltage and the sensed voltage to cancel out for each other, and outputs a corrected sensing voltage.