Reversed Semilattice Filter Resonance for Common Mode Rejection
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Solution Overview
Problem
Conventional reversed semilattice filters face challenges in achieving effective common mode rejection at higher frequencies, particularly with the advent of 5G-NR cellular standards, due to increased frequency ranges and sizing requirements that make it difficult to maintain tight coupling between inductors.
Innovation Solution
Incorporating a resonant circuit within the filter structure to lower common mode impedance at specific frequencies, using configurations such as inductors coupled with capacitors or transformers with center taps, which improves signal rejection in the stop band without affecting the pass band, thereby enhancing compliance with newer cellular standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional reversed semilattice filters are used, then the filter structure is simple, but common mode rejection is insufficient at higher frequencies
Solution Approach 1:
A resonant circuit is introduced as an intermediary element between the input and output nodes of the filter. This resonant circuit acts as a mediator that specifically targets and rejects common mode signals at predetermined frequencies without interfering with the differential signal path, thereby improving common mode rejection while maintaining the overall filter structure
Solution Approach 2:
The resonant circuit is configured to provide frequency-selective common mode rejection at specific predetermined frequencies rather than across the entire frequency spectrum. This localized approach allows the filter to maintain simplicity in the pass band while providing enhanced rejection characteristics in the stop band where common mode signals are most problematic
2Reliability
If tight coupling between inductors is maintained, then common mode rejection is improved, but sizing requirements become difficult to meet at higher frequencies
Solution Approach 1:
The resonant circuit serves as an intermediary that provides common mode rejection without requiring tight physical coupling between inductors. By introducing this intermediate element, the filter achieves effective common mode rejection at higher frequencies while allowing greater spatial separation between inductor components, thus meeting sizing requirements
3Reliability
If resonant circuit is added to lower common mode impedance, then signal rejection in stop band is improved, but device complexity increases
Solution Approach 1:
The resonant circuit is designed to perform multiple functions: it provides common mode rejection at predetermined frequencies, maintains differential signal integrity in the pass band, and can be integrated into existing filter topologies. This multi-functionality justifies the added complexity by delivering multiple performance benefits from a single circuit addition
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 modified filter design achieves improved common mode rejection characteristics, ensuring better performance and compliance with stringent 5G-NR signal processing standards by effectively reducing common mode impedance at predetermined frequencies.
Implementation Method 1
The resonant circuit is configured to lower a common mode impedance for the filter at a predetermined notch frequency
Data Source
AI summary
Reversed semilattice filters with improved common mode rejection characteristics are disclosed. In one aspect, a filter may include two interior nodes coupled with an impedance that treats unwanted signals as common mode signals and provides rejection for common mode signals while passing differential signals of interest. The impedance is modified to have a resonant circuit that improves signal rejection in the stop band by lowering the effective impedance at those frequencies while leaving the pass band unaffected.