Gated Fluorescence Detection Circuit for Saturation-Free Readout
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Solution Overview
Problem
Current fluorescence detection systems face challenges in accurately detecting resonant fluorescence emissions due to amplifier saturation and crosstalk caused by the high spectral power density of excitation sources, leading to degraded bandwidth and linearity, especially when dealing with materials having short fluorescence lifetimes.
Innovation Solution
A pulsed light source is used with a gated control signal to drive a single or multiple LEDs, coupled with a two-stage amplifier system where the gain of the first stage is reduced during excitation and increased when the light is off, and the output is digitized for analysis, minimizing amplifier saturation and crosstalk through balanced source impedances and programmable gain and offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous light source is used for excitation, then the fluorescence emission can be continuously detected, but the spectral power density of the excitation source causes crosstalk and amplifier saturation
Solution Approach 1:
The patent applies periodic pulsing of the light source at frequencies much higher than the fluorescence lifetime, converting continuous excitation into periodic pulses. This allows the detector to distinguish between excitation light and fluorescence emission through frequency domain separation, eliminating crosstalk and amplifier saturation while maintaining continuous detection capability.
Solution Approach 2:
The patent dynamically adjusts the gain of the amplifier system in synchronization with the pulsed light source. The gain is increased during the pulse period and decreased during the off period, optimizing the signal-to-noise ratio while preventing amplifier saturation from the high-power excitation source.
2Measurement precision
If the gain of the amplifier is increased to detect weak fluorescence signals, then the sensitivity is improved, but the amplifier becomes saturated by the strong excitation source
Solution Approach 1:
The patent uses periodic gating of the amplifier in synchronization with the pulsed light source. The amplifier gain is activated only during the fluorescence emission period and deactivated during the excitation pulse, allowing high gain for weak signal detection without saturation from the strong excitation source.
Solution Approach 2:
The patent implements dynamic gain control where the amplifier gain is continuously adjusted based on the timing of the pulsed excitation source. This allows the system to maintain optimal sensitivity for fluorescence detection while automatically preventing saturation from the excitation source through real-time gain modulation.
3Measurement precision
If a pulsed light source is used to reduce crosstalk, then the signal-to-noise ratio is improved, but the detection bandwidth is reduced
Solution Approach 1:
The patent employs high-frequency periodic pulsing of the light source at frequencies much higher than the fluorescence lifetime. This high-frequency modulation maintains adequate detection bandwidth while still providing sufficient time separation between excitation and emission to achieve high signal-to-noise ratio through gated detection.
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
This approach enables accurate detection of resonant fluorescence signals with minimal distortion, improving bandwidth, linearity, and dynamic range, and allows for digital control of gain and offset to normalize detector performance across various applications.
Implementation Method 1
A resonant fluorescence detection system uses a pulsed light source such as a single light emitting diode (LED) or multiple LEDs
Implementation Method 2
The light pulse is coupled into the material under test. Resonant fluorescence emissions from the test material are coupled into a photodiode that converts the radiation to an electrical current
Implementation Method 3
The current is amplified in an amplifier system, which may comprise first and second stage amplifiers
Data Source
AI summary
A light source is gated ON and OFF in response to a pulsed signal. Photo emissions from the light source are coupled to a material under test. Resonant fluorescent emissions from the material are coupled to a photodiode. Current from the photodiode is coupled into an amplifier system comprising a first and second amplifier stages. The first amplifier stage is gated to a low gain when the light source is turned ON and the gain is increased when the light source goes from ON to OFF. The second amplifier stage has digitally programmable offset and gain settings in response to control signals. The output of the second amplifier stage is digitized by an analog to digital converter. A controller generates the pulse control signal and the control signals.