Differential Optical Sensing Receiver for EMI Rejection
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Solution Overview
Problem
Optical sensing devices are prone to electromagnetic interference, which contaminates weak optical signals and requires significant amplification, leading to amplified interference signals, necessitating effective interference reduction before amplification.
Innovation Solution
A fully differential architecture with capacitors configured to filter electromagnetic interference and provide offset voltages to reverse-bias photodetectors, ensuring that electromagnetic interference is rejected and not amplified alongside the optical signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If amplification circuits are used to amplify weak optical signals, then the optical signal strength is improved, but electromagnetic interference is also amplified along with the signal
Solution Approach 1:
The patent divides the signal processing into separate differential paths (positive and negative) that process interference and signal components separately before combining them. The photodetector is split into multiple detectors arranged in a differential configuration, allowing the system to separate and cancel electromagnetic interference from the optical signal through differential processing.
Solution Approach 2:
The patent converts electromagnetic interference into a beneficial cancellation mechanism by using differential processing. The interference signals received by positive and negative photodetectors are subtracted from each other, transforming the harmful interference into a canceling effect that reduces noise while preserving the optical signal.
2Device complexity
If non-differential circuits are used for simplicity, then device complexity is reduced, but interference rejection capability deteriorates
Solution Approach 1:
The patent implements a segmented differential architecture where the photodetector is divided into multiple independent detectors (positive and negative) that operate in parallel. Each detector processes signals independently through separate amplification and filtering paths, enabling interference rejection while maintaining modular simplicity in each individual path.
Solution Approach 2:
The patent transitions from single-ended to differential signal processing, adding a dimensional aspect to the circuit architecture. By introducing positive and negative signal paths that operate in opposite phases, the system achieves interference rejection through differential subtraction without significantly increasing the complexity of individual signal paths.
3Object-affected harmful factors
If offset voltages are applied to reverse-bias photodetectors, then interference reduction is improved, but circuit complexity increases
Solution Approach 1:
The patent combines multiple voltage provisioning functions into a single integrated circuit that simultaneously generates offset voltages for both positive and negative photodetectors. The circuit merges voltage generation, biasing, and signal processing functions into unified blocks, reducing overall circuit complexity while maintaining the interference reduction benefits of reverse-biasing.
Solution Approach 2:
The patent implements universal voltage provisioning circuits that serve multiple functions: generating offset voltages for reverse-biasing photodetectors, providing bias currents for amplification stages, and establishing reference potentials for differential processing. This multi-functionality reduces the number of separate circuits needed while achieving comprehensive interference reduction.
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 significantly reduces electromagnetic interference, achieving more than two orders of magnitude lower input referred current detection error compared to non-differential circuits, ensuring clean optical signal amplification and processing.
Implementation Method 1
a photodetector, wherein the photodetector is reverse-biased by a first voltage between a cathode and an anode of the photodetector
Implementation Method 2
a first circuit coupled to the photodetector and configured to provide the second voltage to the photodetector; and a second circuit coupled to the first circuit and configured to provide the first voltage to the photodetector
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
An apparatus for detecting optical signals includes a photodetector. The photodetector is reverse-biased by a first voltage and a second voltage is added to the first voltage to provide an offset equal to the second voltage for the photodetector. A first circuit is coupled to the first circuit to provide the second voltage for the photodetector and a second circuit is coupled to the first circuit to provide the first voltage to the photodetector to reverse-bias the photodetector. The second circuit provides an output voltage proportional to a current of the photodetector at an output of the second circuit.