Capacitive Isolation Link With Passive Common-Mode Suppression
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Solution Overview
Problem
Galvanic isolation barriers in electronic devices often allow common mode signals to pass through, which can cause damage to sensitive circuitry, as existing suppression methods like clamping diodes or transistor networks either prevent communication or introduce noise and power dissipation issues.
Innovation Solution
A common mode suppression circuit using two passive RLC filter circuits, each coupled between a capacitor and a low-impedance node, effectively filters out common mode signals while allowing differential signals to pass, reducing power dissipation and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If clamping diodes or transistor networks are used to suppress common mode signals, then common mode signals are suppressed, but communication is prevented or noise and power dissipation are introduced
Solution Approach 1:
The patent introduces an intermediary common mode suppression circuit between the capacitive coupling elements and the receiver. This circuit acts as a mediator that selectively suppresses common mode signals while allowing differential communication signals to pass through, thereby resolving the contradiction between suppression effectiveness and communication integrity without introducing excessive power dissipation.
Solution Approach 2:
The suppression circuit utilizes parameter changes in impedance characteristics across different signal modes. By designing the circuit to present high impedance to common mode signals and low impedance to differential signals, it achieves selective suppression without the continuous power dissipation associated with active clamping diodes or transistor networks.
2Object-affected harmful factors
If clamping diodes or transistor networks are used to suppress common mode signals, then common mode signals are suppressed, but noise is introduced
Solution Approach 1:
The common mode suppression circuit serves as an intermediary that passively filters common mode signals without introducing active noise-generating components. Unlike clamping diodes or transistor networks that may introduce switching noise or thermal noise, this intermediary circuit uses passive impedance matching to achieve suppression cleanly.
Solution Approach 2:
The patent employs simple passive components (resistors, capacitors, inductors) in the suppression circuit rather than complex active devices. These passive elements are inherently low-noise and do not require power supply connections that could introduce noise, providing clean common mode suppression.
3Object-affected harmful factors
If expensive capacitors are used to block common mode signals, then common mode signals are blocked, but cost increases
Solution Approach 1:
The patent segments the common mode suppression function from the signal coupling function. Instead of requiring expensive high-voltage capacitors to perform both coupling and common mode blocking, the design separates these functions: standard capacitors handle coupling while a dedicated suppression circuit handles common mode rejection, reducing overall component cost.
Solution Approach 2:
The intermediary suppression circuit provides common mode blocking functionality without requiring the capacitors themselves to have high common mode rejection ratios. This allows the use of lower-cost capacitors that would otherwise be insufficient for common mode suppression on their own.
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 signals, preventing damage to sensitive circuitry while maintaining communication across the galvanic isolation barrier with reduced power dissipation and noise, and allows the use of less expensive capacitors, leading to cost savings.
Implementation Method 1
The common mode suppression circuit includes a first passive RLC filter circuit coupled between the first capacitor and a low-impedance node, and a second passive RLC filter circuit coupled between the second capacitor and the low-impedance node
Data Source
AI summary
In some examples, a device is arranged to include a galvanic isolation barrier between first and second voltage domains. The device includes first and second capacitors arranged across the galvanic isolation barrier. The first and second capacitors are configured to communicate differential signals between the first and second domains. The device also includes a common mode suppression circuit arranged in the second voltage domain and configured to suppress a common mode signal communicated by the first and second capacitors. The common mode suppression circuit include a first passive RLC filter circuit coupled between the first capacitor and a low-impedance node. The common mode suppression circuit also includes a second passive RLC filter circuit coupled between the second capacitor and a low-impedance node.