Opto-isolator Common Mode Pulse Compensation via Auxiliary Current Source
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Solution Overview
Problem
Opto-isolators face performance issues due to common mode pulses between the ground references of transmitter and receiver ICs, causing capacitive coupling that affects the drive current of LEDs and leads to errors in signal transmission, particularly when the slope of the common mode pulse exceeds 10 KV/μsec, resulting in reduced optical output and incorrect logic signals.
Innovation Solution
An opto-isolator design that includes a sensor to detect common mode pulses and an auxiliary current source to adjust the drive current of the LED, either increasing or decreasing it based on the pulse slope to compensate for parasitic capacitance effects, ensuring accurate signal transmission by maintaining appropriate drive current levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the transmitter and receiver ICs are integrated within the same IC package to reduce size, then the overall size of the opto-isolator is reduced, but capacitive coupling between the ground reference of the receiver IC and the LED drive leads increases, causing common mode pulse interference
Solution Approach 1:
The invention segments the current path by introducing a dedicated sense lead separate from the drive leads. This segmentation allows the sense lead to measure the actual current reaching the LED without being affected by capacitive coupling to the receiver ground, thereby resolving the interference problem while maintaining compact integration
Solution Approach 2:
The invention introduces an intermediary sense lead that acts as a mediator between the drive circuitry and the LED. This sense lead provides a reference path that is electrically isolated from the receiver ground capacitive coupling, enabling accurate current sensing despite the harmful capacitive effects in the integrated package
2Speed
If the slope of common mode pulse exceeds 10 KV/μsec, then the transient component increases, but this causes significant current to be pulled through parasitic capacitance, reducing LED drive current and optical output
Solution Approach 1:
The invention implements feedback by continuously monitoring the actual current through the sense lead and using this information to adjust the drive current dynamically. When common mode pulses with high slopes cause current diversion through parasitic capacitance, the feedback mechanism detects this and compensates by increasing the drive current to maintain the required LED current and optical output
Solution Approach 2:
The invention performs preliminary action by proactively adjusting the drive current based on detected common mode pulse conditions. Before the pulse can significantly degrade the signal, the system anticipates the current diversion through parasitic capacitance and pre-compensates by modifying the drive current, ensuring reliable signal transmission even with fast rising edges exceeding 10 KV/μsec
3Device complexity
If traditional opto-isolator design is used without compensation, then the device structure remains simple, but common mode pulses cause errors in logic signal transmission
Solution Approach 1:
The invention enables self-service by allowing the opto-isolator to automatically detect and compensate for its own interference problems. The sense lead monitors the actual current conditions, and the control circuitry autonomously adjusts the drive current to compensate for common mode pulse effects, eliminating the need for external compensation circuits or complex shielding structures
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 effectively compensates for common mode pulse-induced errors by adjusting the LED drive current, maintaining proper operation of the opto-isolator across a range of pulse slopes from 10 kV/μsec to 40 kV/μsec, preventing errors and ensuring reliable logic signal transfer.
Implementation Method 1
the close proximity of the transmitter and receiver circuits results in capacitive coupling between the ground reference of the receiver IC and the leads that drive the transmitter LED
Implementation Method 2
an electrical-to-optical converter, such as a visible or infrared light emitting diode (LED), that converts the electrical signal into an optical signal
Implementation Method 3
an optical-to-electrical converter, such as a photodiode, that converts the optical signal back into an electrical signal
Data Source
AI summary
In an opto-isolator, common mode pulses that occur are compensated for by either adding current to the electrical-to-optical converter (EOC) drive current to compensate for a decrease in the EOC drive current caused by the occurrence of a common mode pulse or by pulling some of the drive current away from the EOC to compensate for an increase in the EOC drive current caused by the occurrence of a common mode pulse.