Interview with Dr. Carlos E. Saavedra

Featured Engineer

Dr. Carlos E. Saavedra

Dr. Carlos E. Saavedra - Associate Professor, Queen's University; Canada

How did you get into electronics/ engineering and when did you start?

Electronics was part of the environment I grew up in. My dad was an electrical engineer and as a kid I remember seeing all kinds of chips, PCB’s and test equipment in the space he had set up in the house for home projects. By the time I was ready to go to university, EE was a rather natural choice for me.

What are your favorite hardware tools that you use?

In the world of very-high frequency circuits, you have to think about wave propagation and scattering. As a result, we rely on test equipment that allows us measure the wave reflection and transmission properties of the circuit under test. Those instruments are called network analyzers and we have one at Queen’s that allows us to measure circuits at frequencies of up to 50 GHz. If we want to measure the power performance or the intermodulation distortion produced by an RF mixer or an amplifier, for example, we use a spectrum analyzer plus some RF signal sources. Today’s spectrum analyzers can do all kinds of measurements for which you needed separate bits of equipment just 10 or 15 years ago. That’s a nice step forward. There are other hardware items that are critical for my research work but the list is long and I’ll stop here.

What are your favorite software tools that you use?

To design radio-frequency integrated circuits (RFIC’s) we use CAD tools that allow us to do scattering parameter simulations, transient simulations, harmonic balance simulations, envelope simulations, optimization and other things. The tools that we are using right now are Cadence and Agilent’s Advanced Design System (ADS). We often run the two software programs in parallel through the Cadence-ADS dynamic link feature.

What is the hardest/trickiest bug you have ever fixed?

What we perceive as the trickiest technical challenges tend appear early in our careers as design engineers or researchers because we are still “learning the ropes.” After you’ve worked in a field for a while, the experience factor takes over and you encounter fewer and fewer bugs because you’ve learned to avoid them. To answer your question, though, in graduate school I once had to design a 28 GHz phase-locked loop circuit for direct-digital phase modulation. After simulating the circuit I went to the lab and I built it. At first the circuit did not work properly. Since we were using discrete components at the time, I checked the performance of each sub-circuit and then I looked for assembly errors but everything checked out fine. I was stumped for a while until it occurred to me that perhaps the signal strength levels inside the circuit were off. Shortly thereafter I determined that one of the passive RF mixers in the PLL was in overdrive and that fixed it.

What is on your bookshelf?

Some engineering books manage to be first-rate with regards to both the technical content and the writing style. Such books are engaging and (dare I say it?) fun to read. A couple of books of this type that I have on my shelf are: Microwave Mixers by Stephen Maas and Planar Microwave Engineering by Thomas Lee. I also have some books that I’ve read for entertainment. One of those is titled In Search of Time by Dan Falk, which describes classical and modern ideas about the nature of time. Another book I read a short while ago is Poincare’s Prize by George Szpiro.

What has been your favorite project?

Since the start of my career I’ve had the opportunity to work in a number of areas within microwave engineering such as applied electromagnetics, transceiver module design and RFIC’s. A nice thing about being a professor is that you get to select research projects that you’re going to work on. Right now my focus is almost entirely on RFIC’s and I enjoy it a lot.

What are you currently working on?

I’m working on a number of topics and I’ll discuss a few of them here. One topic area is finding new ways to reduce distortion in mixers and amplifiers. Distortion is an ever-present phenomenon in electronic circuits that gets more acute as the circuits operate at lower supply voltages. A simple way to illustrate the problem is like this: when a circuit is biased with a large dc voltage, the transistors in that circuit can handle larger RF signals before signal clipping occurs, which is a key cause of distortion. However, when the dc supply voltage is lowered, the circuit can only handle correspondingly small RF signals before the waveform starts clipping. Another set of circuits that I’m actively investigating are operational transconductance amplifiers (OTA’s) for gigahertz applications. The versatility and usefulness of OTA’s largely stems from the fact that they can be used as building blocks to make circuits with more advanced capabilities. While analog designers have been using OTA’s for a considerable period of time, it is only fairly recently that the RF community started to make more use of this class of circuits. In my group we have done a number of “firsts” with microwave OTA’s such as a reconfigurable direct-digital QAM modulator operating at 5.4 GHz and an active quasi-circulator.

What challenges do you foresee in our industry?

Statistics relating to the number of students pursuing EE degrees in North America show that enrolment in EE has declined over the last decade. If you think about it, there is a kind of paradox here because we keep hearing that North America is increasingly a knowledge-based economy. Therefore, you would think that enrolment in engineering programs should be increasing but the numbers tell a different story. It’s in everyone’s interest to reverse the above trend in order to avoid losing our technological edge with respect to both developed and emerging economies. A lot of universities, including Queen’s, are modernizing their engineering curricula to pull in more students. Companies can also help out by making more internships available to students that can eventually lead to full time jobs after graduation.

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