Design challenges in a product - Part 1

EMI/EMC is a major roadblock for any product release. If everything works fine, you can release the product on time to market or else your engineers might be breaking their heads to crack the EMI/EMC problems. Now if we dig deeper, where can the EMI/EMC problems start? If you ask this question to an audience of electrical engineers, they say, PCB Layout. While most agree to this, electrical designer engineers should think what the actual source of noise is and provide all the recommendations to the Layout engineer. The review gate in a PCB design should not only focus on functional but also should keep an eye on the potential EMI problems. While most of the electrical engineers and Layout engineers try to follow PCB Layout design tips, the main challenge is how you fit those recommendations in your PCB Layout design.

With the design timelines squeezed and competition at our feet, electrical designers have no other choice to use off-the-shelf modules for power supply. It could either be based on the AC-DC module or DC-DC module. The image above shows radiated emission graph of CQB50W12-72S24 module  from CINCON in Radiated emission test under horizontal orientation. If you observe the radiated emission test waveform, you see that you don't have enough margin and the radiations are very close to the allowed level. This is the case with most of the power converter modules available in the market. Moreover, the Radiated emissions test are done on these modules with almost an ideal kind of PCB Layout. The layer count, ground plane impedance, component placement for the input filtering and other circuitry around the DC-DC converter are all placed ideally by vendor on their PCB under test as they have all the room to play around on their evaluation kit.

Now coming to our original design with these power converters, we neither have the room to play around like the vendor evaluation board or achieve the same ground and power planes as like evaluation board. Adding to that the board density adds up causing more problems. The end result of these is the affected impedance of ground and power planes which causes EMI/EMC failures. Now you can imagine the situation of electrical engineer and layout engineer and especially the EMI/EMC engineer who most of the times comes into picture post failures in the compliance tests. 

While putting the pressure on PCB Layout is not correct, it is the primary responsibility of electrical engineer to design circuitry which can reduce emissions and involve EMI/EMC engineer from the beginning of product life cycle. The most important point here is adding intense review cycles to the design is the major key to a successful release.