Why digital engineers don't believe in EMC (reprinted)

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Why digital engineers don't believe in EMC (reprinted) [Copy link]

	I recently attended a local (Seattle) meeting of the IEEE Electromagnetic Compatibility (EMC) Society, which is not where I live, but I highly recommend it to you, where you can learn more about the basics of EMC and get a lot of free advice. After listening to Bill Ritenour's presentation on electrostatic shielding for gasoline pumps, we began to focus on another question, namely: what is the advantage of teaching EMC concepts to people with a purely digital background? After much discussion and reflection, I am now able to point out the basic reason why many digital engineers have difficulty dealing with EMC issues. Contrary to some opinions in the analog world, it is not because they can't speak, nor because they didn't study hard in school, and it has nothing to do with the individual engineer. Instead, the root underlying reason for many of today's EMC difficulties is an attitudinal problem, namely: digital engineers don't believe in EMC. This unfortunate situation is caused by many factors, and our educational institutions, the manufacturers of instruments (integrated circuits, simulation tools, etc.), and the poor performance of engineering management have all contributed to this unfortunate situation. Our organizations, vendors, and managers have inadvertently promoted five misconceptions that have prevented many new digital engineers from properly understanding EMC, or even from believing in its existence. For new digital engineers fresh out of school, it is at best a myth. The more you know about the five misconceptions, the more you can understand the perspectives of many digital engineers, thus helping you solve the inevitable EMC problems. Ⅰ Digital engineers do not believe that electric current circulates Digital schematics show that digital signals are passed from gate to gate on the logic net. These signals are transmitted as electrons that always circulate, but the schematics do not show the return path of the signal flow. Many digital engineers believe that the return path is irrelevant. If the logic driver acts as a voltage source and the input acts as a voltage sink, they infer the reason to worry about current. Oscilloscope and logic analyzer manufacturers mainly promote voltage state probes, which adds to the misunderstanding of EMC. If a good current sensing probe has a very small probe tip that is close to active, you can see the current flow on a single BGA ball, which becomes a "reality" rather than a purely theoretical concept. For example, if you are going to work with a digital engineer on a common state cable radiation problem, you first need to make sure that the engineer really understands the fact that current circulates. Ⅱ Digital Engineers Do Not Believe in H Field I attribute this type of misunderstanding to the education system, which focuses on electronic domain effects rather than magnetics. This is a product of the vacuum tube era, which was characterized by very high circuit impedance. For example, the plate circuit of a vacuum tube might have an impedance of 100,000 ohms, which is much higher than the impedance of free space (377 ohms), so most of the near-field energy around the plate circuit will be in the electronic field state, and most of the cross-coupling and parasitic coupling problems will produce electronic field or capacitive effects. Today's high-speed digital system circuits are low impedance, close to 50 ohms, which is much lower than the free space impedance of 377 ohms, and most of the near-field energy around digital circuits is in the magnetic field state, not the electronic field state, so crosstalk, ground bounce and interference problems in high-speed digital systems involve the circulation of current, magnetic field and inductance. In the EMC world, it is common knowledge that most of the near-field energy around digital circuit boards is magnetic, but digital engineers do not understand it. III Digital Engineers Don't Believe Gates Are Differential Amplifiers Typical product data sheets rate input voltage sensitivity in absolute volts, but there is no clear statement that the gate responds only to the difference between the input pin voltage and a specified reference pin voltage, nor is it clear which is the specified reference pin. (For TTL, this is the cathode power rail; for ECL, this is the anode line.) This lack of clarity leads many engineers to believe that the gates sense "absolute zero" volts, as if some magic wire were running from the chip to the center of the earth to find the "true" ground reference voltage. As a result, they fail to understand the problems that arise when the ground voltages at two points in the system are not equal. Of course, no manufacturer will admit that their chip is susceptible to ground shift, so it is not surprising that they cannot say more about this. In addition, the architecture of such systems allows ground shifts between chips, which is likely to cause failures, and may generate a lot of EMI, and face ESD and other immunity problems, which is a serious problem. Most digital engineers do not take the time to consider the existence of different ground voltages in the system and the effect it has on performance, or the mechanisms that implement ground shifts. IV Digital engineers do not believe in electromagnetic waves Despite the numerous examples of electromagnetic fields encountered in their work (e.g., microwave popcorn and television), many digital engineers still do not believe that such effects occur in digital systems. The root cause is that the fluctuations do not exist in Spice devices. A generation of circuit designers believed that the world of Spice-based software simulation was a representation of real circuits operating under real conditions, but they did not understand that this was limited. Digital designers fresh out of school believed that Spice could not do E&M fields, so they must not exist. Simulation certainly has its role, and in general, if you know what to simulate, it can work wonders. But if you work on research such as EMC, the advantages of simulation are over-sold, and the problem is that we do not necessarily know what effects will have the greatest impact, and simulation cannot do anything about it. Samuel Clemens once said, "We can never predict the disaster." Ⅴ Digital engineers do not believe that understanding EMC will help our careers This is a management problem, and it's not hard to see why it happens. Let's assume Joe is a brilliant product designer and digital genius who has just finished his EMC work and got his latest product to pass FCC and EC regulations at first glance. What he is is what happened next, as predicted. Joe's design career is over, and he will never design another processor at the company. Instead, he starts solving Fred's EMC problems, then Bob's, and then the rest of the world. He efficiently eliminates them, reuses his EMC experience, and others get paid for getting a wet processor board working again. In today's business world, the typical digital engineer is only rewarded for digital functionality, not for the full preparation for production. in conclusion I would like to change this situation. We can rely on our EMC experts, signal integrity experts and all the smart researchers in universities to help eliminate the above five misunderstandings, so as to help us reduce the EMC problems we will face in the next decade. This will greatly improve the future of the computer industry. I hope that our local EMC society meeting will be joined by more digital colleagues. You will not regret it.

ehk

Education needs a major reform

rain

I think the problem of education reform is quite serious. I hope it can attract the attention of relevant departments. We need talents and reject waste.