Browse Prior Art Database

VIBRATION NOISE CANCELLATION IN MOBILE RADIOS

IP.com Disclosure Number: IPCOM000008360D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2002-Jun-10
Document File: 1 page(s) / 56K

Publishing Venue

Motorola

Related People

R. Seiler: AUTHOR

Abstract

This paper describes a method to reduce vibra- tion noise occuring in electronic equipment, for example in mobile radios.

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Technical Developments

VIBRATION NOISE CANCELLATION IN MOBILE RADIOS

by R. Seiler

INTRODUCTION

  This paper describes a method to reduce vibra- tion noise occuring in electronic equipment, for example in mobile radios.

PROBLEM TO BE SOLVED

  Mobile radios are typically exposed to vibration in use, which may cause undesirable electrical signals in sensitive circuits on the printed circuit board (PCB). This phenomena is known as micro- phonics. Such undesirable signals appear as noise and for example, can lead to a private line (PL) decoder falsing, or add hum to a transmitted signal. A significant amount of development effort is spent to reduce these noise levels to a tolerable extent by improving housing constructions, shieldings, circuit stability etc.

PROPOSED SOLUTION

  Often, such vibration noise is picked up by one or more chip resistors, made of piezoceramic material, which are mounted on the PCB close to the sensi- tive circuits such as modulator, high gain stages, or VCO steering line circuits. The output signal is, after conditioning (filtering, amplification etc.), routed to a phase shift circuit and then subtracted from either the received or transmitted audio.

  As digital signal processor (DSP) power becomes faster and less expensive, such circuits and associated tasks can be realized in software. In that case, the signal from the pickup would after ampli- fication be routed through an Analog to Digital Converter to the DSP which would do the signal...