What would you ask an analog-centric job interviewee?

I’ve always found that interviewing someone for an entry-level, analog-focused position to be a challenge. It’s hard to know what is sensible to ask him or her at that point in the candidate’s career. After all, you don’t want to have unrealistic expectations of what they should know if they are just out of school or have just a year or two of experience when compared to what you, as the interviewer, have learned over the years.

I was reminded of this challenge when I read another “history of engineering” book, and the author recounted the questions he was asked “back in the day” as he applied for a starting position. Since this was in the early days of electricity and before electronics, the questions were largely related to power engineering, including big motors, AC versus DC transmission, fuses, and similar topics. All those topics are still important, but not at the core of analog “circuit design” questions I usually need to ask.

Still, the book’s section made me stop and wonder: what would I ask for now in a starting-level position? I came up with a few possibilities. I also decided that asking about tradeoffs in choosing a design approach or component value might provide insight into how well the candidate understands the underlying issues beyond just repeating routine “book knowledge.” After all, a large part of engineering is really about qualitative understanding and quantitative assessment of the tradeoffs associated with various design decisions.

I decided that once I got past the basics of Ohm’s Law and discussed the schematic diagram of a single-ended op-amp set for a gain of 100, I would go into these questions:

1) What’s the difference between high-side versus low-side drive or switching as shown in Figure 1? What are the system implications (pros and cons) of each topology?

Figure 1. There are significant operational differences between high-side switching of a load (left) versus low-side switching (right). (Image: The Bald Engineer)

2) What are some approaches to consider for current sensing, along with their relative merits? (Answers could include IR drop across and in-line sense resistor, Hall effect device, and transformer, among others.) Extra credit: What about galvanic isolation for current sensing? Where and why is it needed?

3) What are some of the issues and differences when using a resistor in a high-side sensing topology versus low-side current sensing (as seen in Figure 2)?

Figure 2. As with load switching, high-side current sensing (left) has major circuit and system implications when compared to low-side sensing (right). (Image: Analog Devices)

4) Speaking of resistors for current sensing, what’s a good starting point for scaling the IR-voltage drop across the resistor (I usually say “about 100 milliohms”)? What are the tradeoffs of using smaller and larger values here?

5) What’s the difference between a low dropout regulator (LDO) and a switching regulator? What are their relative strengths and weaknesses? Low noise but inefficient for the LDO, and higher noise but very efficient for the switcher are generally true statements; however, there are some exceptions that we will ignore here.

6) Can you identify and distinguish these “ground” symbols in Figure 3?23wesx What’s the difference between chassis ground, Earth ground, and signal ground (also called “common”)?

Figure 3. There is no concept more misused and subject to misunderstanding in electrical engineering than the simple one known as “ground.” (Image: *NI/National Instruments*)

Extra credit

While we’re discussing so-called grounds, I would also ask about galvanic isolation on the AC line: how is it achieved? Why is it needed? Which applications benefit from it, and what are some that require it?

Then there’s thermal…

Consider asking some basic thermal questions, as this is an important issue in many designs. I’d go beyond the obvious points of keeping the system cool, such as using a fan or a heat sink on a single component. I would ask:

7) What are the differences between conduction, convection, and radiation for the transfer of heat, and the implications with respect to keeping a component or system cool, as shown in Figure 4?

Ohm — Figure 4. Understanding the three heat-transfer mechanisms is a fundamental requirement for effective engineering design. (Image: sciencenotes.org)

As a practical example, explain which of those three thermal mechanisms is involved, and how, when bright sunlight causes melting under a thin layer of ice on a black driveway on a below-freezing day.

8) Finally, I might end with two simple thermal questions that indicate insight into thermal principles. First, why do farmers spray their oranges to keep them from freezing as the temperature starts to drop below freezing, as long as it doesn’t go below around 28°F/-2°C (seen in Figure 5)? After all, basic “common sense” would say that any ice forming on the fruit is actually encouraging them to freeze!

analog — Figure 5. Most people would say it’s crazy to spray oranges with water as the temperature drops – but thermal principles explain why it makes sense. (Image: *X/Twitter*)

For another real-world thermal question: why is the mist spraying out of an aerosol can so cold?

Certainly, there are many more basic questions that could be asked, but interview time is limited. These are among the ones that came to mind for an analog-focused circuit-related position, especially as I sought to understand trade-offs and their pros and cons. Even if they are perhaps too challenging, depending on the interviewee’s experience, I think they will be good starting points for a revealing discussion.

References

Low-Side vs High-Side Transistor Switch, The Bald Engineer
AN-105: Current Sense Circuit Collection Making Sense of Current, Analog Devices
Chassis, Earth and Signal Grounding: Terminology and Symbols, National Instruments (NI)
Heat Transfer – Conduction, Convection, Radiation, Science Notes

Comments

Martin Rowe says

July 14, 2025 at 12:42 pm

“What’s the difference between high-side versus low-side drive or switching as shown in Figure 1? What are the system implications (pros and cons) of each topology?”

The answer is, as always, “it depends.”

What if something breaks? Do you want the load pulled up or down in an open circuit? For example, thermocouple circuits often have a 1 Mohm pull-up resistor. Why? because of the thermocouple, breaks, the sensing circuit will see a high voltage and could shut down any heaters.

As for “ground,” there is no such thing. It’s a return line for the current. EMC engineer Bruce Archambeault would always say “ground is for carrots and potatoes.”
https://www.testandmeasurementtips.com/emc-summit-gives-engineers-tips-and-fundamentals/

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