While it is merely a nuisance to experience radio interference, it is definitely a serious matter if an ABS, stability control, or airbag suffers a malfunction because a vehicle passes a TV tower too closely. Thus, mastering EMC is a basic requirement for automotive electronics designers. Part one of this article explains basic strategies and provides useful hints.
EMC, or electromagnetic compatibility, is the ability of an electronic device (or a module, printed circuit board, or integrated circuit) to operate in an electromagnetically distorted environment while keeping its own distortions below certain thresholds so that other devices do not suffer any serious adverse effects. For many people this field of expertise seems more like a form of black magic: No matter what work is done related to EMC, not only will something completely unexpected and unpredictable happen. Worse than that, it can be assumed that things will always take a turn in the wrong direction. It will become apparent through this article whether this viewpoint is accurate and what engineers can do to gain more facility in this field.
Those involved in the field of electronics, especially in the automotive sector, will certainly have been confronted by EMC-related issues more than once. The phenomenon of radio interference is nearly as old as the invention of radio itself and at an early stage led to the definition of guidelines for noise suppression. The other part of EMC, the immunity against distortions, only began attracting attention around fifty years ago.
Not only is the number of electronic control units in cars on the rise, so too is the number of electronic devices frequently used inside the cars, such as cell phones, portable navigation devices, wireless headsets, which may also cause interference.
Making matters even worse is that more and more of devices of this kind operating at higher and higher frequencies are constantly being introduced to the market. Higher frequencies imply that smaller structures can behave like an antenna and cross-coupling needs to be considered even for relatively small coupling capacitances. It is therefore only natural that there has been a growing need to define certain rules of the game over the past decades.
Nowadays all car manufacturers are highly aware of the fact that EMC testing is an important part of car electronics development and understand that EMC issues become costlier the later they are discovered. That is the reason why they do not just rely on a final test inside the car but insist on tests of the electronic control unit (ECU) and even on test results of the integrated circuits used in the design before deployment in vehicles.
All around the world a wide variety of test methods have been developed for both unwanted electromagnetic emissions as well as the susceptibility for electromagnetic distortions. In the meantime, all integration levels are covered and over the past 10 years the various standardization committees have devoted their time to the IC level.
As a semiconductor manufacturer, Atmel is confronted primarily with IC-level and ECU-level tests. Unfortunately, not only have there been quite a large number of different standards established (perhaps a bane to testing specialists), at the same time, many OEMs apply these standards in slightly different ways.
Read this complete article here, which details EMC tests, frequency selection, and PCB layouts, courtesy of Automotive Designline Europe.
Part 2 of this feature discusses methods for suppressing high-frequency noise.