Microphone RF Shielding for Wireless Device Noise Reduction
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Solution Overview
Problem
Mobile wireless communications devices face interference issues due to conducted and radiated RF energy from power amplifiers, antennas, and LCDs, which degrade receiver sensitivity and cause audio breakthroughs, particularly in GSM systems, and strong RF energy interfering with CPU input/output lines through keyboard circuits.
Innovation Solution
The implementation of RF shielding to isolate microphones from RF circuitry, power amplifiers, and antennas, along with EMI filters in LCD and keyboard connections to reduce electromagnetic interference, and the use of acoustic and RF sealing to maintain frequency response and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If circuit boards and electronic components are reduced in size and placed closer together, then device size is reduced and portability is improved, but electromagnetic interference between components increases
Solution Approach 1:
The device is divided into separate isolation compartments - a first isolation compartment for RF circuitry and a second isolation compartment for the power amplifier. This segmentation physically separates components that would otherwise interfere with each other, allowing compact overall device size while preventing electromagnetic interference between the RF receiver and power amplifier.
Solution Approach 2:
An RF shield acts as an intermediary barrier between the RF circuitry and power amplifier. The shield is positioned between these components to block electromagnetic fields, allowing the components to be placed closer together for compactness while maintaining isolation to prevent interference.
2Device complexity
If microphones are positioned close to RF circuitry for compact design, then device complexity is reduced, but microphone noise from RF energy increases
Solution Approach 1:
The microphone is placed within the second isolation compartment that is dedicated to audio components, separated from the first isolation compartment containing RF circuitry. This segmentation allows simple overall layout while protecting the microphone from RF energy that would cause audible noise and audio breakthroughs.
Solution Approach 2:
The RF shield and isolation compartments serve as intermediary barriers between the microphone and RF circuitry. These barriers block conducted and radiated RF energy from reaching the microphone, allowing close positioning for compact design while preventing RF-induced microphone noise.
3Object-affected harmful factors
If RF shielding is added to isolate microphones from RF circuitry, then microphone noise is reduced, but device complexity increases
Solution Approach 1:
The RF shield is integrated with the housing structure and circuit board layout. The first and second isolation compartments are formed as part of the overall device architecture, combining the shielding function with the structural housing rather than adding separate complex shielding components.
Solution Approach 2:
The isolation compartments serve multiple functions: they provide RF shielding to prevent interference, organize and secure components in compact arrangements, and maintain acoustic pathways for the microphone. This multi-functionality reduces overall device complexity despite adding shielding capabilities.
4Adaptability or versatility
If keyboard circuits are included for device functionality, then device versatility is improved, but RF interference to CPU through keyboard lines increases
Solution Approach 1:
The RF shield and isolation compartments act as intermediary barriers that prevent RF energy from coupling onto keyboard circuit lines and propagating to the CPU. This allows full keyboard functionality while blocking the interference path.
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 effectively reduces audible buzz and improves RF receiver sensitivity by isolating microphones from interfering energy, preventing audio breakthroughs and CPU resets, while ensuring normal device operation and compliance with interference guidelines.
Implementation Method 1
An RF shield surrounds and isolates the microphone from the RF circuitry, power amplifier and antenna and shields the microphone from radiated energy generated from the RF circuitry, antenna or power amplifier
Implementation Method 2
an acoustical tube can extend from the cover through the RF shield to the microphone
Data Source
AI summary
A mobile wireless communications device includes a housing and circuit board in the housing and having radio frequency (RF) circuitry and a power amplifier and microphone mounted thereon. An antenna is carried within the housing and operative with the RF circuitry. An RF shield surrounds and isolates the microphone from the RF circuitry, power amplifier and antenna and shields the microphone from radiated energy generated from the RF circuitry, antenna or power amplifier.