Bi-Directional Constant Impedance Filter for Cascaded LC Isolation
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Solution Overview
Problem
Conventional electronic filters exhibit varying input impedance with frequency, impairing bi-directional communications and interacting undesirably when coupled in series, particularly in applications like DSL systems.
Innovation Solution
The development of bi-directional constant impedance filter structures that maintain a constant input impedance across a range of frequencies, allowing multiple filter sections to be cascaded without interaction, by using specific configurations and component values that ensure a consistent impedance of Z0 at both ports.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LC filter structures are used, then filtering function is achieved, but input impedance varies with frequency impairing bi-directional communications
Solution Approach 1:
The patent transforms the conventional LC filter by introducing resistive elements and transforming the circuit topology to achieve constant input impedance across frequency. Specifically, the filter is converted to a bridged-tee configuration with resistors R1=R3=Z0 and R2=2Z0, along with transformed inductor and capacitor values, to maintain Z0 impedance at the input port across all frequencies while preserving the low-pass filtering function.
2Manufacturing precision
If conventional filters with different filter responses are coupled in series, then filtering selectivity is improved, but filters interact in an undesirable fashion
Solution Approach 1:
The patent achieves filter isolation by transforming each filter section to have constant input impedance Z0. This is accomplished by changing the circuit topology to bridged-tee configuration and adjusting component values (R1=R3=Z0, R2=2Z0, and transformed L and C values) so that each filter section presents a constant resistive impedance independent of frequency, thereby eliminating interactions when filters are cascaded in series.
Data Source
AI summary
A method and apparatus to provide a bi-directional constant impedance filter. Embodiments include electric networks which give filter responses while presenting a constant impedance to a signal received at either an input or an output port for a plurality of frequencies.