Some time ago I introduced the equation for DM radiation from a loop. I also let Howard Johnson make fun of the single ended crowd that do not believe in loops by quoting from one of his articles. (Refer to “Why Digital Engineers Don’t Believe in EMC”, IEEE EMC Society Newsletter, Spring 1998.) The whole article is available on the internet.Anyway, to continue:E = … [Read more...]
The Hybrid Ground System
We’ve already concluded that for low frequencies the Star or SPG ground works best and at the high frequencies, the so-called equipotential ground plane with a MPG system works best. No one grounding system is perfect. On top of that, most of the equipment these days operates at frequencies from DC to daylight, so the grounding design has to cover all frequencies … [Read more...]
The Equipotential Plane That Isn’t
The success of the multipoint ground (MPG) system requires having an extremely-very-low RF impedance grounding connection to an extremely-very-low RF impedance equipotential reference plane. It also helps if the conducting materials are homogeneous and the bad things are kept separate from the good ones. Does that sound easy? You’re right – it’s not! A couple of posts … [Read more...]
Twinkle, twinkle, little star . . .
We often wonder how good you are. Want to start a heated argument in the EMC community? Just start talking about grounding systems and why the Star or single point ground (SPG) system is so-o-o-o much better than those ridiculous multipoint ones being used by all those other people. Really? Are they that good? Before I answer that, let me first mention Scott … [Read more...]
Grounding Conductor Limitations!
I briefly mentioned some of the elements of grounding in the last post. Technically, there are three types of grounding systems that work: (1) the single point (a.k.a. star) ground (SPG), which uses wires; (2) the multipoint ground (MPG), which requires a ground plane or mesh; and (3) the floating (no) point ground (FPG). All three utilize some variety of RF … [Read more...]
Common Mode Emission. Can It Get Any Worse?
You betcha! Once upon a time I was in charge of EMC design for a large scale military digital telecommunications system. This system had to handle both red and black analog and digital data with the proviso that never the twain shall meet. In the lab where all the engineering tests were taking place everything went great until the cables were hung on the … [Read more...]
What’s this about CM and DM radiation?
We’ve been discussing loops all along and we are still at it. The last post looked at DM, this time it’s back to CM. These loops are the worst -- big – bad – ugly! Finding the loop may be a problem . . . but where there’s current, there’s a loop. The DM loop is easy, typically a differential pair over a ground plane in a high-speed system, the CM is some … [Read more...]
Tell Me Again Ron – What’s This About CM & DM Radiation?
Apparently, I didn’t throw enough words at the CM/DM problem in the last several posts so I’m going to add to it, but from a slightly different perspective. It’s either that or hide my email address. I’ll do DM this time, CM next time. We’ve been discussing loops all along. If there’s current, there is a loop somewhere. Finding it may be a … [Read more...]
EMC Engineers Come Bearing Gifts
It’s the holiday season again, when we celebrate the serious things in life and have some fun too.When EMC engineers come bearing gifts...tis NOT the season to be jolly. Fa-la-la, le-la-la-laa. In fact, it’s time to be worried. For to the EMC engineer, GIFTS is an acronym for: Grounding, Isolation, Filtering, Transient suppression, and Shielding. Sometimes it takes … [Read more...]
CM Feeling Bad, Check its Pulse
The last post examined CM radiation. Wow, what a problem! Over 100,000 microvolts/meter from a 3.5 ma signal. If the DM is normally the intended signal, where does the big common mode signal come from? Let’s take a look at that. The whole world seems to be enamored with high speeds. I know I could hardly wait to get a 1 GHz notebook. Did it help me … [Read more...]