Common Mode Suppression Circuit for Isolated Voltage Domains
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Solution Overview
Problem
Existing communication methods between isolated voltage domains face limitations in transient immunity due to common-mode interference, particularly in applications like electric vehicles where large voltage differences can lead to damage from current surges and high voltage transients, and existing galvanic isolation techniques like differential signaling have undesirable tradeoffs such as signal propagation delays and power consumption.
Innovation Solution
A common-mode suppression circuit using a transformer with inductor arrangements on both sides, configured to suppress common-mode signals by circulating common-mode currents to a ground reference voltage, thereby isolating the sending and receiving sides of differential signal lines and enhancing data communication reliability across voltage isolation barriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If differential signaling with capacitive coupling is used for galvanic isolation, then isolation between voltage domains is achieved, but signal propagation delays and power consumption increase
Solution Approach 1:
The patent replaces capacitive coupling with inductive coupling using a transformer. The transformer uses magnetic field coupling between primary and secondary windings to transfer signals across the isolation barrier, eliminating the need for capacitive coupling and associated propagation delays while maintaining galvanic isolation between high-voltage and low-voltage domains
Solution Approach 2:
The patent changes the coupling mechanism from capacitive to inductive by introducing a transformer with primary and secondary windings. This parameter change in the coupling method allows for better signal propagation characteristics while maintaining the isolation function, as the magnetic coupling provides a more direct signal transfer path compared to capacitive coupling
2Reliability
If differential signaling is used for galvanic isolation, then voltage domain isolation is achieved, but common-mode interference and transient immunity deteriorate
Solution Approach 1:
The patent converts the harmful common-mode interference into a beneficial effect by using the transformer's common-mode rejection ratio (CMRR). The transformer naturally rejects common-mode signals while passing differential signals, turning the isolation barrier into an active filter that eliminates common-mode noise and transients rather than just blocking them
Solution Approach 2:
The transformer acts as an intermediary device between the high-voltage and low-voltage domains. It provides galvanic isolation while selectively coupling differential signals and blocking common-mode interference, serving as both an isolator and a filter in one component
3Reliability
If isolation barriers are used between voltage domains, then circuit protection is achieved, but device complexity increases
Solution Approach 1:
The transformer serves multiple functions simultaneously: it provides galvanic isolation between voltage domains, couples differential signals across the isolation barrier, and rejects common-mode interference. This multi-functionality reduces overall system complexity compared to using separate components for each function
Solution Approach 2:
The patent merges the isolation function with the signal coupling function into a single transformer component. The primary and secondary windings of the transformer simultaneously provide both the isolation barrier and the signal transfer path, eliminating the need for separate isolation capacitors and coupling circuits
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 suppresses common-mode interference, improving the reliability of data communication between isolated circuits by mitigating common-mode transients and maintaining differential-mode signal integrity, suitable for high-voltage applications like electric vehicles.
Implementation Method 1
The transformer is configured to transfer energy from the first side to the second side via the first and second inductor arrangements
Implementation Method 2
configured to suppress common-mode signals by circulating common-mode currents to a ground reference voltage
Data Source
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AI summary
In one or more embodiments, a circuit is configured to receive a differential signal from a transmitter that is isolated from the receiver circuit and that includes a common-mode suppression circuit and signal combining circuit coupled to the corresponding lines carrying the differential signals. The common-mode suppression and signal combining circuits are configured to suppress common-mode signals of differential signals communicated on the set of differential signal lines and combine to form of differential-mode components of the differential signals.