What would you ask an entry-level analog hire?
Article By : Bill Schweber
Asking about tradeoffs in choosing a design approach or component value might give insights into how well the candidate understands the underlying issues beyond just repeating routine "book knowledge."
I’ve always found that interviewing someone for an entry-level analog-focused position is 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 a just year or two of experience compared to what you, as the interviewer, have learned.
I was reminded of this challenge when I was reading another “history of engineering” book and the author recounted the questions that were 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, big motors, AC versus DC transmission, fuses, and similar. All those topics are still important but not in the realm of the analog “circuit design” questions I usually needed to ask.
Still, the book’s section made me stop and wonder: what would I ask now for 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 give me insight into how well the candidate understands the underlying issues beyond just repeating routine “book knowledge.” After all, working through the tradeoffs is what a large part of engineering is really about.
Eight basic questions
I figured that once I got past the basics of Ohm’s Law and began asking about a single-ended op-amp schematic set for a gain of 100, I would go into these eight questions:
- What’s the difference between high side versus low side drive or switching (Figure 1)? What are the system implications (pros and cons) of each topology?
Figure 1 The small topological difference between high-side and low-side switching of a transistor’s load has major system implications. Source: The Bald Engineer
- What are some approaches you might consider for current sensing? Answers could include IR drop across sense resistor, Hall effect device, and transformer, among others.
- What are some of the issues and differences when using a resistor in a high-side sensing topology versus low-side current sensing (Figure 2)?
Figure 2 Somewhat similar to high/low-side switching differences, current sensing using an in-line resistor on the high versus low side has system implications as well as impact on resistor voltage-drop sensing circuitry. Source: Analog Devices
- Speaking of resistors for current sensing, what’s a good starting point for scaling the IR drop across the resistor (I usually say “about 100 milliohms”)? What are the tradeoffs if using smaller and larger values here?
- 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, but there are some exceptions we would ignore here.
- Can you identify and distinguish these “ground” symbols (Figure 3). 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.” Source: National Instruments
I would also ask some basic thermal questions, as that’s an important issue in many designs; I’d go beyond the obvious points of keeping system cool using a fan or using a heatsink on a single component.
- What are the differences between conduction, convection, radiation for transfer of heat and the implications with respect to keeping a component or system cool (Figure 4)?
Figure 4 Understanding of the three heat-transfer mechanisms is a basic engineering-design necessity. Source: sciencenotes.org
- Finally, I might end with a simple thermal question that indicates insight into thermal principles: 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 28°F/-2°C (Figure 5)? “Common sense” would say that any ice forming on the fruit is actually encouraging them to freeze.
Figure 5 I suspect 99 out of 100 average people would say it’s crazy to spray oranges with water as the temperature drops, but thermal principles explain why it makes sense. Source: Twitter
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 was looking for understanding of tradeoffs and pros/cons.
What questions have you used as good indicators, especially as you have only a limited amount of time with the candidate? Are there any questions you asked in the past but no longer do, as components and priorities have evolved?
This article was originally published on Planet Analog.
Bill Schweber is an electronics engineer who has written three textbooks on electronic communications systems, as well as hundreds of technical articles, opinion columns, and product features. In past roles, he worked as a technical website manager for multiple EE Times sites and as both Executive Editor and Analog Editor at EDN. At Analog Devices, he was in marketing communications; as a result, he has been on both sides of the technical PR function, presenting company products, stories, and messages to the media and also as the recipient of these. Prior to the marcom role at Analog, Bill was Associate Editor of its respected technical journal, and also worked in its product marketing and applications engineering groups. Before those roles, he was at Instron Corp., doing hands-on analog- and power-circuit design and systems integration for materials-testing machine controls. He has a BSEE from Columbia University and an MSEE from the University of Massachusetts, is a Registered Professional Engineer, and holds an Advanced Class amateur radio license. He has also planned, written, and presented online courses on a variety of engineering topics, including MOSFET basics, ADC selection, and driving LEDs.