Embedded Isolation Filter for RF Noise Reduction
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Solution Overview
Problem
In RF input designs, DC current biasing is susceptible to interfering noise due to the proximity of noise-generating components, leading to unwanted modulation and performance degradation in RF receivers, especially with increasing connection pin density and board thickness.
Innovation Solution
An embedded isolation filter is placed as close as possible to the RF device on a printed circuit board, comprising two buried inductors and one horizontal capacitor forming an LC 'pi' filter, reducing noise coupling through the use of an adaptor or interposer board connected to the main circuit board.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If components are placed closer to the RF device to reduce noise coupling, then noise reduction performance is improved, but manufacturing precision and assembly difficulty increase
Solution Approach 1:
The patent embeds the isolation filter components (inductors and capacitor) directly within the PCB layers surrounding the RF device, nesting the filter structure within the board itself rather than placing it as a separate external component. This eliminates the need for precise external component placement while achieving minimal distance from the RF device pins.
Solution Approach 2:
The patent transitions from a two-dimensional surface mounting approach to a three-dimensional embedded structure using multiple PCB layers. The inductors are formed using vertical via structures and trace patterns across different layers, allowing the filter to be positioned extremely close to the RF device without increasing surface area or complicating assembly.
2Productivity
If connection pin pitch is reduced to increase device density, then productivity is improved, but noise coupling increases due to greater proximity to noisy nodes
Solution Approach 1:
The patent introduces an isolation filter as an intermediary circuit between the noisy digital nodes and the sensitive RF supply pins. This filter acts as a mediator that allows the coexistence of high-density pin arrangements by blocking noise propagation paths while maintaining electrical connectivity.
Solution Approach 2:
The patent segments the power supply network into isolated zones using the filter structure, separating the noisy digital power domain from the clean RF power domain. This segmentation allows high-density pin placement by creating controlled noise boundaries that prevent interference between adjacent pins.
3Productivity
If board thickness is increased to accommodate higher density pins, then productivity is improved, but noise coupling increases due to longer Vias with more coupling potential
Solution Approach 1:
The patent extracts the isolation filter function from the traditional external component placement and embeds it directly into the PCB structure. This extraction eliminates the need for long external trace runs and allows the filter to be positioned at the exact location where noise coupling occurs, neutralizing the via length issue.
Solution Approach 2:
The patent incorporates the isolation filter design into the PCB manufacturing process itself, creating the inductor and capacitor structures during board fabrication rather than adding them as separate components. This preliminary action ensures the filter is already in place to counteract via coupling effects before signals are routed through the board.
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 configuration significantly reduces noise coupling, achieving a 40 dB noise reduction at 1 GHz and maintaining 30 dB noise reduction across the cell and wireless band region, outperforming standard methods by being 100 times quieter at high frequencies.
Implementation Method 1
The components—often two inductors and one capacitor—form a noise reduction filter for DC bias currents known as an isolation filter
Implementation Method 2
This allows the RF supply to be have a relatively higher impedance than, for example, its digital counterpart
Data Source
AI summary
The present disclosure relates to reducing unwanted RF noise in a printed circuit board (PCB) containing an RF device. An isolation filter is embedded in a PCB containing an RDF device. By placing the isolation filter as close as possible to the RF device in order to dramatically reduce unwanted RF noise due to unavoidable coupling between Vias and planes in the PCB structure.