|Author:||Cheung, Chi-pong Dickie|
|Title:||A case study on EMC compliance for an electronic product design and manufacture|
|Subject:||Electromagnetic compatibility -- Case studies|
Telephone answering and recording apparatus -- China -- Hong Kong -- Case studies
Hong Kong Polytechnic University -- Dissertations
Department of Electronic Engineering
|Pages:||86,  leaves : ill. ; 30 cm|
|Abstract:||This dissertation reports on the investigations into the EMC problems associated with an electronic product designed and manufactured in Hong Kong. The product in this case study is a digital answering machine, using a fairly high speed DSP chip, with a 32.768MHz clock frequency to perform the voice recording and playback functions. It is a low cost product. The plastic case used does not provide any shielding to the high frequency signals. The difficult to handle EMC problems for this kind of product are the radiated emissions. The way to solve this EMC problem is to find emission sources and the radiating media. The use of double-sided PCB, without ground plane nor power plane as with the more costly four-layered PCB, adds much constraints to the possible solutions. In this project, the noise sources are associated with the DSP chip which runs on high clock speed. All the signal lines spreading from this chip will be carrying high speed switching currents and radiating high frequency energies. The major problems are centered around the harmonics of the DSP clock. Improvement work is concentrated on the PCB layout design, i.e. grounding, component placement and high speed track termination, etc. After careful design and layout, a prototype unit was constructed. Test and measurement were carried out to verify EMC. A step-by-step analysis on the critical aspects of the layout design based on the EMI measurements performed, yield some appropriate amendments to the PCB layout. This design, verification and redesign cycle was repeated until EMC compliance was achieved. This dissertation discusses the analysis and design consideration on three modifications. As long as EMC compliance design is fully considered in the product development stage, these design modifications should add little extra cost on the final product.|
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