RF Chokes on Flexible Printed Circuit for Common-Mode Noise
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Solution Overview
Problem
Electronic devices face challenges in managing electromagnetic interference (EMI) due to common-mode noise emissions, particularly in applications with limited space and weight constraints, such as wearable computing devices, where conventional EMI filters are ineffective in suppressing noise near irregularly shaped ground paths and at connector discontinuities.
Innovation Solution
The implementation of RF chokes directly on flexible printed circuits in the differential signal path, positioned adjacent to noise sources or connectors, to effectively suppress common-mode noise before it can escape and be re-radiated as EMI, utilizing common-mode coil-based designs that cancel differential signals while attenuating common-mode noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional EMI filters are used to suppress common-mode noise, then noise suppression is achieved, but device size and weight increase
Solution Approach 1:
The patent extracts the EMI filtering function from separate external components and integrates it directly into the flexible printed circuit board through embedded RF chokes. This integration eliminates the need for separate filter components, thereby suppressing common-mode noise while avoiding the weight penalty of additional discrete EMI filters.
Solution Approach 2:
The patent merges the EMI filtering function with the flexible printed circuit board structure by embedding RF chokes within the circuit board layers. This combining of filtering functionality with the existing circuit board eliminates separate filter components and reduces overall device weight while maintaining noise suppression effectiveness.
2Object-affected harmful factors
If conventional EMI filters are used to suppress common-mode noise, then noise suppression is achieved, but device volume increases
Solution Approach 1:
The patent extracts the EMI filtering function from separate external components and integrates it directly into the flexible printed circuit board through embedded RF chokes. This integration eliminates the need for separate filter components, thereby suppressing common-mode noise while avoiding the volume penalty of additional discrete EMI filters.
Solution Approach 2:
The patent merges the EMI filtering function with the flexible printed circuit board structure by embedding RF chokes within the circuit board layers. This combining of filtering functionality with the existing circuit board eliminates separate filter components and reduces overall device volume while maintaining noise suppression effectiveness.
3Object-affected harmful factors
If RF chokes are placed远离 connector to suppress common-mode noise, then noise attenuation is achieved, but EMI energy has opportunity to escape at connector discontinuity
Solution Approach 1:
The patent places RF chokes in close proximity to the connector where common-mode noise is generated, enabling preliminary suppression of EMI energy before it can escape through the connector discontinuity. This strategic positioning ensures that the filtering action occurs at the source of the problem, preventing EMI radiation rather than attempting to mitigate it later.
4Ease of manufacture
If flexible printed circuit is made rigid to mount RF chokes, then component mounting is enabled, but flexibility and weight advantages are lost
Solution Approach 1:
The patent nests the RF chokes within the flexible printed circuit board structure, embedding them between conductive layers and dielectric material. This nesting approach allows component integration while maintaining the flexible circuit board's flexibility and weight advantages, as the chokes become part of the flexible structure rather than requiring rigid mounting surfaces.
Solution Approach 2:
The patent uses the flexible printed circuit board itself as the mounting substrate for RF chokes, leveraging the flexible circuit's structure to support and integrate the filtering components. This approach maintains flexibility and weight benefits while enabling component mounting through alternative methods such as embedding or surface mounting on flexible substrates.
5Adaptability or versatility
If ground path shape changes irregularly to accommodate layout, then routing flexibility is improved, but common-mode noise is generated at shape change portions
Solution Approach 1:
The patent applies local quality by placing RF chokes at specific locations where ground path shape changes occur or where connectors are positioned. This targeted approach addresses common-mode noise generation at problematic locations without requiring changes to the overall ground path routing, thereby maintaining routing flexibility while suppressing noise at critical points.
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 solution minimizes EMI emissions by locating RF chokes close to noise sources or connectors, reducing the escape of EMI energy and providing effective EMI management in space-constrained devices like head-mounted displays, while maintaining lightweight and flexible circuit designs.
Implementation Method 1
utilizing common-mode coil-based designs that cancel differential signals while attenuating common-mode noise
Data Source
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AI summary
In an electronic device that employs high-speed differential signaling on one or more pairs of conductors in a flexible printed circuit, RF chokes are placed in the differential signal path and mounted directly on the flexible printed circuit which is used to interconnect a peripheral device, such as an image sensor, through a connector to another device component such as a main printed circuit board. The RF chokes are configured to suppress common-mode noise propagating in the differential pairs of conductors. In one illustrative embodiment, the RF chokes are located on the flexible printed circuit adjacent to the peripheral device to suppress common-mode noise near its source. In another illustrative embodiment, the RF chokes are mounted adjacent to the connector to suppress the common-mode noise before it has an opportunity to escape the flexible printed circuit at the major discontinuity presented by the connector.