Differential Opto Isolator Common Mode Transient Immunity
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Solution Overview
Problem
Opto-isolators face limitations in common mode transient immunity (CMTI) due to parasitic capacitance between light sources and photodetectors, leading to undesirable output signals from transient currents, especially when light sources and photodetectors are fabricated within a single package.
Innovation Solution
The implementation of a pair of photodetectors configured to generate photocurrents of opposite signs or directions in response to a light signal, combined differentially to reject or attenuate common mode transient noise, with a differential amplifier generating an output electric signal based on the difference between these photocurrents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If light sources and photodetectors are fabricated within a single package to improve integration, then device integration is improved, but parasitic capacitance increases leading to degraded common mode transient immunity
Solution Approach 1:
The photodetector is segmented into two separate photodetectors, each generating photocurrents that flow in opposite directions. This segmentation allows the photocurrents to be combined differentially, which rejects common mode transient noise while maintaining the integrated package structure.
Solution Approach 2:
The invention changes the configuration parameter of the photodetector from a single device to a pair of devices with opposite current directions. This parameter change enables differential signaling that is inherently immune to common mode transients, resolving the contradiction between integration and CMTI.
2Device complexity
If a single photodetector is used to simplify the device structure, then device complexity is reduced, but common mode transient noise cannot be rejected leading to degraded signal integrity
Solution Approach 1:
The single photodetector is segmented into two separate photodetectors configured to generate photocurrents in opposite directions. This segmentation enables differential processing that rejects common mode noise, preserving signal integrity while maintaining relatively simple device structure.
Solution Approach 2:
The invention converts the harmful effect of common mode transient noise into a beneficial differential signal processing approach. By using two photodetectors with opposite current directions, the common mode noise affects both equally and is rejected through differential subtraction, while the differential signal components are preserved and amplified.
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 significantly enhances the common mode transient immunity of opto-isolators, allowing them to withstand higher transient voltage gradients without erroneous output, thereby improving data integrity and safety across the isolation barrier.
Implementation Method 1
a light source coupled to the input terminal and configured to transmit a light signal representing an input electric signal
Implementation Method 2
a first photodetector configured to receive the light signal and generate a first photocurrent in response to the light signal
Data Source
AI summary
Isolators and methods for operating the same are described for opto-isolators with improved common mode transient immunity (CMTI). In some embodiments, a pair of photodetectors are provided in the opto-isolator and configured to generate photocurrents of opposite signs or directions in response to a light signal. Photocurrents from the pair of photodetectors are combined in a differential manner to represent data transmitted in a light signal, while common mode transient noise at the two photodetectors is attenuated or eliminated.