CMOS Fluorescence Intensity Measurement With Pulse-Width Modulation
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Solution Overview
Problem
Existing fluorescence measurement devices face challenges in accurately measuring fluorescence intensity due to noise interference from peripheral circuits, particularly when using CMOS image sensors, and difficulty in modulating excitation light intensity, especially with LED light sources.
Innovation Solution
A fluorescence intensity measurement device that emits modulated pulse-shaped excitation light and uses a CMOS image sensor to detect fluorescence, calculating intensity based on duty ratios and light intensities of excitation light with different pulse widths to remove noise components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the exposure time of the CMOS image sensor is lengthened to increase sensitivity, then the sensitivity is improved, but noise from peripheral circuits notably appears
Solution Approach 1:
The patent applies periodic action by modulating the excitation light intensity at a specific frequency (e.g., 100 Hz) and synchronously detecting the fluorescence signal. The CMOS image sensor captures images at multiple time points during the periodic cycle, and the fluorescence intensity is calculated by combining these images with known duty ratios. This periodic modulation allows the system to distinguish the fluorescence signal from the DC component of peripheral circuit noise, achieving high sensitivity measurement while suppressing noise.
2Object-affected harmful factors
If intensity modulation of excitation light is performed using Fourier transform to remove noise, then noise removal is improved, but accurate modulation is difficult when using LED light sources due to non-linear voltage-current characteristics
Solution Approach 1:
The patent uses periodic pulse-width modulation of the excitation light instead of continuous intensity modulation. By controlling the duty ratio of periodic pulses, the system achieves effective intensity modulation without requiring precise control of LED current. The fluorescent substance emits light only during the pulse periods, and the CMOS sensor captures images at multiple phases of the periodic cycle. This approach bypasses the non-linear LED characteristics problem while still enabling noise removal through synchronous detection.
Solution Approach 2:
The patent introduces an intermediary calculation method that uses the known duty ratios of the modulated excitation light and the captured image intensities to compute fluorescence intensity. Instead of directly modulating LED intensity through voltage control (which is difficult due to non-linearity), the system uses the duty ratio as an intermediary parameter that can be precisely controlled and used in the fluorescence intensity calculation formula, thereby achieving accurate modulation效果 without directly controlling LED current.
3Measurement precision
If a CMOS image sensor is cooled to increase sensitivity, then the sensitivity is improved, but there are limits in cooling the CMOS image sensor
Solution Approach 1:
The patent replaces the mechanical cooling system with an electrical/optical modulation and synchronous detection system. Instead of physically cooling the CMOS image sensor to reduce thermal noise, the system uses periodic excitation light modulation and calculates fluorescence intensity by combining multiple images captured at different phases. This substitution eliminates the need for complex cooling mechanisms while achieving high sensitivity through noise rejection rather than thermal management.
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 device effectively removes noise from peripheral circuits and improves measurement sensitivity by calculating fluorescence intensity using duty ratios, even with direct current components in excitation light, while maintaining a simple configuration and synchronized light emission and detection.
Implementation Method 1
In a case where a light source of excitation light includes light emitting diodes (LEDs)
Implementation Method 2
a fluorescence intensity measurement device that emits modulated pulse-shaped excitation light and uses a CMOS image sensor to detect fluorescence
Data Source
AI summary
A fluorescence intensity measurement device includes: a light source to emit, to a measurement target, a plurality of pieces of pulse-shaped excitation light of which a pulse width is modulated; a CMOS image sensor to detect, as an image for each pulse of a piece of the plurality of pieces of pulse-shaped excitation light, fluorescence emitted from the measurement target by the piece of the plurality of pieces of pulse-shaped excitation light; and a controller to calculate a fluorescence intensity of the fluorescence. The controller calculates the fluorescence intensity of the fluorescence, based on two duty ratios of the two pieces of pulse-shaped excitation light having different pulse widths, and two light intensities obtained from the images detected by the two pieces of pulse-shaped excitation light.