Common-Mode Reference Signal Generation Using Shunt Resistor and Capacitive Divider
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Solution Overview
Problem
Conventional xDSL modems face performance degradation due to common-mode noise from unwanted signals like AM radio, which degrades the signal-to-noise ratio and data throughput, requiring additional hardware components for digital signal processing-based noise cancellation.
Innovation Solution
A method and apparatus generate a common-mode reference signal by sampling the common-mode current at a node between the common-mode filter source and a shunt resistor, eliminating the need for a high-voltage transformer by using a shunt resistor and center tap capacitors to provide galvanic isolation, allowing for effective noise cancellation without additional isolation transformers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional common mode filter with additional winding is used to generate reference signal, then common-mode noise can be detected, but galvanic isolation of at least 1500 volts breakdown voltage cannot be maintained without additional high-voltage transformer
Solution Approach 1:
The patent introduces an intermediary approach by using capacitive coupling instead of direct galvanic isolation. The common mode filter inductor with its magnetic core acts as an intermediary that provides magnetic coupling while the capacitive divider network provides the necessary isolation, eliminating the need for additional high-voltage transformers while maintaining the required 1500 volts breakdown voltage isolation.
Solution Approach 2:
The patent replaces the mechanical/electromagnetic isolation transformer with an electrical field-based solution using capacitive coupling. The common mode filter inductor's magnetic field and the capacitive divider network work together to provide both signal coupling and voltage isolation, substituting the need for a separate isolation transformer.
2Reliability
If additional high-voltage transformer is used for isolation, then galvanic isolation requirement is met, but system cost and complexity increase
Solution Approach 1:
The patent makes the common mode filter inductor multi-functional by using it both for common-mode noise filtering and for generating the reference signal through magnetic coupling. This eliminates the need for separate isolation components, reducing system cost while maintaining the required galvanic isolation through the capacitive divider network.
Solution Approach 2:
The patent merges the functions of common-mode filtering and reference signal generation into a single integrated circuit approach. The common mode filter inductor serves dual purposes, and the capacitive divider network provides both isolation and signal coupling, consolidating multiple functions into fewer components to reduce cost and complexity.
3Ease of operation
If common-mode reference signal is sampled from center tap of primary winding, then reference signal is obtained, but direct connection to RF noise canceller violates safety isolation requirements
Solution Approach 1:
The patent introduces a capacitive divider network as an intermediary between the common mode filter inductor and the RF noise canceller. This intermediary provides both signal coupling and the required safety isolation, allowing the reference signal to be accessed while maintaining the 1500 volts breakdown voltage isolation requirement.
Solution Approach 2:
The patent replaces direct electrical connection with capacitive coupling to provide safety isolation. The capacitive divider network uses electrical field coupling instead of direct conductive connection, maintaining safety isolation while providing reference signal accessibility to the RF noise canceller.
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 enhances the signal-to-noise ratio and data throughput by effectively isolating and canceling common-mode noise, improving modem performance without the need for costly high-voltage transformers, thus maintaining safety and efficiency standards.
Implementation Method 1
an additional winding on the magnetic core of the common mode filter inductor that couples the input lines to the receiver
Implementation Method 2
sampling the common-mode current at a node between the common-mode filter source and a shunt resistor
Data Source
AI summary
A method and apparatus to generate a common-mode reference signal. A common-mode current is received at a common-mode current sensing circuit. The common-mode current is sampled at a node between the common-mode current sensing circuit and a shunt resistor. The resulting voltage across the shunt resistor from the applied common-mode current is used as a common-mode reference signal.