Yksipuoleisen tähtimaadoitetun piirilevyn EMC optimointi

Electromagnetic compliance, EMC, is an important aspect in today’s electronic design. Devices should not disturb other devices and also have to work in noisy environment. Tolerable interference emission levels are determined by standards. Electromagnetic interference, EMI, is a process, which involves an interference source, a coupling path and a receiver. Interferences from electronic devices are not only caused by noisy circuits like switching converters and high speed digital circuits, but also non-ideal components. Coupling methods can be divided on four categories: conductive, capacitive, inductive and radiated coupling. In printed circuit board (PCB) design, electromagnetic interferences can be affected with grounding component placement and routing. Proper PCB design decreases emissions from a device and also inside the device, but on the other hand poor PCB design may cause huge problems. Usually, all design principles can’t be implemented and therefore compromises have to be done. Standards define creepage and clearance distances and hence set limitations also directly for PCB design. In PCB, one has to consider also, that manufacturability and design rules may vary for different subcontractors. Main theories of electromagnetic interference and principles of PCB design are examined through literature review in this thesis. Standards related to examined LED driver and harmonized design rules for all manufacturing plant are also introduced. PCB design’s effects on radio frequency interference (RFI) emissions are investigated experimentally using eight test PCBs and one reference PCB. The effect of each design principle is investigated by changing only that feature in each test PCB and by trying to keep the rest of design same reference PCB. Examined features included grounding, tracking and components placement. Measurement process in conformity with CISPR 15 standard is described before measurement results introduction. The effect of the main loop size was not as significant as expected. According to measurement results, the most significant effect on radiated emissions was caused by ground trace width from all examined features