Differential Signal Filter with Shared Reactive Impedance
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Solution Overview
Problem
Conventional multiple conductor systems experience significant unrequired over-coupling from common mode to differential mode due to construction element tolerances, particularly in capacitors and coils, leading to inadequate common mode suppression, which is insufficient for stringent applications like the automobile industry.
Innovation Solution
The implementation of a serial connection of reactive impedances in the attenuation or filter elements, where one reactive impedance is shared across all elements, significantly reduces tolerance-related deviations, enhancing common mode suppression by assigning a second reactive impedance to all filter elements, which can be capacitive or inductive, and optionally including additional ohmic resistances for improved stability and frequency behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional single reactive impedance per filter element is used, then device complexity is low, but common mode suppression is insufficient due to tolerance deviations
Solution Approach 1:
The reactive impedance in each filter element is segmented into multiple series-connected reactive impedance elements (at least two). This segmentation reduces the impact of individual element tolerances on the total impedance, thereby improving common mode suppression. The total impedance remains the same, but the tolerance distribution across multiple smaller elements reduces overall deviation.
Solution Approach 2:
Multiple filter elements with series-connected reactive impedance elements are merged in parallel within each filter stage. The parallel combination of multiple reactive impedance paths further reduces the overall tolerance impact and enhances common mode suppression. This merging approach allows the system to achieve higher reliability while managing complexity through standardized modular design.
2Reliability
If higher order low passes or cascading filters are used, then common mode suppression improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies local quality by making the reactive impedance elements in series within each filter element have different nominal values. This local differentiation optimizes the frequency response and common mode suppression at specific frequency ranges without requiring a complete redesign of the entire filter system. The selective variation of impedance values at local levels achieves enhanced performance while maintaining ease of manufacture through modular construction.
3Ease of manufacture
If capacitors and coils with standard tolerances are used, then manufacturing cost is low, but tolerance-related deviations in capacity or inductivity values cause overcoupling from common to differential mode
Solution Approach 1:
The reactive impedance is segmented into multiple series-connected elements, which reduces the impact of individual component tolerances. Even when using standard tolerance capacitors and coils, the series combination of multiple elements with different nominal values results in a total impedance with reduced relative tolerance, thereby minimizing overcoupling from common to differential mode.
Solution Approach 2:
By assigning different nominal values to the reactive impedance elements in series within each filter element, the patent optimizes the local impedance distribution. This local quality variation ensures that tolerance deviations in individual components do not translate directly into large total impedance deviations, thus reducing overcoupling while maintaining ease of manufacture with standard components.
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 achieves a substantial increase in common mode suppression, exceeding the 50 dB requirement for stringent applications, with reduced quality in both differential and common modes, thereby improving signal integrity and reducing unrequired current or voltage peaks.
Implementation Method 1
The attenuation or filter elements are usually frequency filters which are constructed using passive components. For example, an RC module is frequently used as a first order low pass.
Implementation Method 2
The reactive impedances can preferably be designed according to claims 2 and 3 either as capacities or as inductive resistors.
Implementation Method 3
The reactive impedance which is the decisive influence for the suppression of the common mode is dramatically reduced when an individual reactive impedance, namely the second reactive impedance which is arranged in the second partial branch is to the same degree a component of all the attenuation or filter elements.
Data Source
AI summary
The electric multiple conductor system (1) is used for the transmission of signals in differential mode, and has two signal lines (5, 6) and a shared reference line (7). Each signal line (5, 6) includes an attenuation or filter element (13, 14) with a connection branch (15, 16), which runs between a branch node (20, 21) in the respective signal line (5, 6) and the reference line (7). The attenuation or filter elements (13, 14) of the respective signal lines (5, 6) are nominally of the same size. Each connection branch (15, 16) respectively includes a serial connection of a first partial branch (17, 18) having a first reactive impedance (23, 24) and a second partial branch (19) having a second reactive impedance (25). The second partial branch (19) is a shared component of all attenuation or filter elements (13, 14). The multiple conductor system (1) achieves a very high level of common mode suppression.