IEEE Solid-State Circuits Magazine - Summer 2014 - 45

Great Lessons from the Back of the Envelope
I have had the rare opportunity of learning electronics from some of the
world's best scientists in the field. For sure, Prof. Rinaldo Castello has a special
place among them. Back in 2001, I had just become a PhD student. I arrived
in Pavia in April that year, visiting the Microelectronics Laboratory led by Prof.
Castello where I remained until the end of 2001. It was an intense period of
time during which I learned far more than I was able to understand at the
moment. I was surrounded by nice people, bright minds, and participated
in many exciting discussions. Besides Rinaldo, I had the chance of meeting
other great people, Prof. Francesco Svelto and Prof. Andrea Baschirotto, just
to name a few, as well as many fellow-students at the time who are now
well established professionals both in academia and industry worldwide and,
most importantly, still dear friends. In addition, I recall with pleasure all the
smart and friendly people working at the "Studio di Microelettronica". The
atmosphere was very stimulating and friendly, as Rinaldo wanted it to be.
Coming from a University where a new curriculum in IC design techniques was being devised in those years, and having a stronger background
in solid-state devices physics and signal processing, and much less in analog
circuit design, arriving to Pavia was quite an experience. When I first talked

operate the circuit like this-and he waved his hands simultaneously up
and down as to mimic a common-mode voltage applied at the input
of the circuit-the signal does not get through; when you use it like
that-and he swung his hands alternately to mimic a differential-mode
signal-the circuit amplifies". And that was it: as simple as it sounded,
it was the very core of the problem. I wish I had the same capability of
communicating complex concepts in such a simple way to my students.

Every now and then, during a
technical conversation, Rinaldo
would come up with what he calls
"i conti della serva", something I
would liberally translate as "back
of the envelope calculations".
A very deep understanding and knowledge of every detail of a circuit or
a system, and yet the capability of reducing it to very simple concepts, is
a characteristic of Prof. Castello's that is both unique and inspiring. Every
now and then, during a technical conversation, Rinaldo would come up
with what he calls "i conti della serva", something I would liberally translate as "back of the envelope calculations". He would scratch some quick
numbers on a piece of paper-or even better do the calculations on the
fly in his mind-and predict the outcome of a lengthy simulation on the
spot, with ridiculous accuracy. I think that many people would be very
interested in knowing his set of small rules to get to those results, and see
them published someday. For sure, the take-home message I got observing him at work-a serious and rigorous scientific approach to the technical problems, followed by some simple, concise, yet exact wrap-up-is
an important lesson I will take with me during all my professional life.

Figure S3: Anatomical Theatre at University of Padova. (Photo
courtesy of Wikipedia.)

to Rinaldo about technical topics, I could only get a small part of what he
wanted to communicate to me. The reason for that was not that he talks in
an unclear way or maybe in jargon. On the contrary, he knows the subject
so deeply that while he says something, he always implies much more. In
other terms, he talks the language of the IC designer. When some years later,
while chatting with him at a conference, I realized that I was finally able to
communicate with him (almost) at his level, I thought-indeed, with some
pride-that I was on a good way to become an IC designer myself.
Prof. Castello not only has always been a reference point for me from
a technical and research-related standpoint. He is also a terrific teacher.
Once, I heard his suggestions to a PhD student who was about to do
some TA activities, which I found brilliant. Concerning the operation
of the differential pair, and the doubts of the TA on how to explain it to
the students, Rinaldo said: "they just have to understand this: when you
Digital Object Identifier 10.1109/MSSC.2014.2327711
Date of publication: 26 August 2014

-Andrea Bevilacqua
About the Author
Andrea Bevilacqua (M'04, SM'14) received the Laurea, and Ph.D. degrees
in electronics engineering from the University of Padova, Padova, Italy, in
2000, and 2004, respectively. From 1999 to 2000, he was an intern with
Infineon Technologies, Munich, Germany. In 2001 he visited the Microelectronics Laboratory of the University of Pavia, Italy. From 2002 to 2003, he
was a Visiting Scholar with the University of California, Berkeley. Currently,
he is an Assistant Professor with the Department of Information Engineering,
University of Padova. His current research interests include the design of RF/
microwave integrated circuits and the analysis of wireless communication
and radar systems. Dr. Bevilacqua has been serving as a member of the TPC
of IEEE ESSCIRC since 2007, and is TPC Co-Chair of IEEE ESSCIRC 2014. He
was a member of the TPC of IEEE ICUWB from 2008 to 2010. He was an
Associate Editor of IEEE TCAS-II from 2011 to 2013 and was nominated "Best
Associate Editor" for TCAS-II for 2012 to 2013. He is author or coauthor of 22
journal papers and 32 conference papers. He holds 2 patents. His h-index,
according to the Scopus database, is 11.

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