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Analog Angle Blog

(Under)standing Your Ground

I've been occasionally asked for my view on what is the most common problem that engineers face in circuit design. My answer is simple: misuse of the word and concept of “ground.” I am not referring to the many puns, word plays, and jokes you can make using the word in various technical sentences. I have a more serious concern.

Unless your circuit (and system) has a connection to earth via an AC-line ground, or is connected by some independent wiring scheme to earth, you haven’t got a ground to stand on. Yet, as today's products increasingly become portable and battery powered, there is no true ground that you can use as a big bucket of electrons to absorb excess charge or transients, or establish a widespread potential plane. (The non-existence of a true earth ground also applies to many non-handheld products, such as autos, aircraft, and satellites.)

I know that when engineers and other specialists talk, they often use words with not quite their exact meanings, but everyone knows what is really meant (although I did attend a meeting where the term “IP” was tossed around a lot, and it turned out that one group thought they were talking about intellectual property, another thought it was an intermediate processor, and the rest thought it was Internet protocol). It's also true that when most engineers use the term “ground” — even when they don’t really have one — that they sort-of know in their hearts and heads what kind of ground it is or isn't. But over time, this mythical ground becomes the hopeful solution to a whole slew of problems with noise, transients, equipotential planes, zero-potential voltage reference points, and more.

It's really worth making the effort to be careful with your words here. If you don’t have a true earth ground, what you actually have is a common point or plane, a current return, a reference, or many other things, but that's it. Being sloppy in terminology leads to careless thinking, especially as the pressures to debug problems mount and missed schedule milestones increase. It then leads to false solutions based on projecting the availability and implications of that true earth ground.

So, if you are a new engineer to the world of real circuits (not just simulations and models), don't fall into the bad and lazy habit of casually referring to “ground” when there isn’t one. If you're a more experienced engineer, you need to be careful, too, both for yourself and for junior members of the team. Sometimes casual thinking becomes ingrained, and before you realize it, what was once just a slang term has become a technical “given” — except that it's a phantom.

Have you ever been misled or even trapped by sloppiness in technical terminology or descriptions? And how did you find out?

7 comments on “(Under)standing Your Ground

  1. Bill_Jaffa
    February 4, 2013

    My blog is about serious design issue, but we don't have to be serious all the time! What are some of the puns, word plays, and jokes around the word “ground” that you know? Do you have afavorite? Is there one which makes you moan?

  2. Brad Albing
    February 4, 2013

    Bill, I'm tellin' ya this is too serious a topic for us to be looping around with some bad puns; so I shall bypass them. I for one will remain on a higher plane and keep my feet firmly on the ground. Or earth as the call it in England.

    And no capacitor jokes either. Too politically reactive. So, no admittance to capacitor jokes, OK?

  3. Brian Dotson
    February 6, 2013

    Bill,

    This is a great blog for reminding me of the limitations of the Consumer Electronic products that I design. When I worked in the pro audio industry, we typically built a product in a steel rack package, and we used a three-wire power entry connector, with an earth ground connection on that third prong.

    However, the home audio world is built around two-wire AC connections. Furthermore, our power cord of choice, has what we refer to (for want of a better term) as a “figure eight” connector making the cord connection into the product. This means that you can't even know which of the two AC conductors is hot and which is neutral. One certainly has to think differently about double insulation for safety, and also, about how to dissipate unplanned energy coming in from ESD discharges.

  4. WKetel
    February 7, 2013

    Back in elementary electronics, course 1, ground was a zero impedance connection back to the power source return connection point. That was very convenient, but certainly misleading. Probably that is where a more correct explanation should begin. Explaining that it is usually a relatively lower impedance connection to the power supply return would be a good start. 

  5. Bill_Jaffa
    February 7, 2013

    Perhaps one of the questions you could ask a job interviewee, to see how much of their knowledge is “academic” vs “real world” is what “ground”–and what's the difference between one in theory and in practice?

  6. Brad Albing
    February 12, 2013

    You need to be careful with questions like that. You'll pro'ly weed out about 95% of your job applicants. Which might be OK – you could argue that you don't want them anyway. But if you then find that you are running out of applicants that are even remotely qualified, you may need to change your tack. Maybe hire the semi-clever ones and educate them as needed.

  7. TheMeasurementBlues
    April 17, 2013

    Bruce Archambeault says ground doesn't really exist.

    The 'Ground' Myth

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