The Impact of Dennard's Scaling Theory - IEEE

cult to get the idea of mixed signal
MOS ICs accepted. “When Yannis
began his graduate work around
1970,” said Dr. Paul Gray, an early
collaborator who is now Professor
Emeritus and Professor in the
Graduate School, EECS, UC Berkeley,
in an email statement, “bipolar
was used for virtually all analog
integrated circuits and most digital
circuits, which were at low integration
levels at the time. MOS was
used for memory and was just
beginning to be used for some
complex logic circuits.” CMOS was
in its infancy. “It was not easy to
see that MOS technology would
bring about the need to integrate
both analog and digital on the
same chip. This backdrop made
MOS analog circuits a somewhat
speculative proposition.”
Career Breakthrough Was
The First Useful MOS
Operational Amplifier
“Working with Paul Gray, Yannis
P. Tsividis developed and demonstrated
the world’s first useful MOS
operational amplifier,” said Dave
Hodges, Professor of Engineering,
EECS, UC Berkeley, via email. “It
was fundamental to the development
of mixed signal MOS integrated
circuits, which provide vastly
higher levels of circuit integration
than bipolar analog devices,”
the prior mainstream technology.
Before CMOS was fully developed,
the implementation of high
gain op amps in NMOS was a real
challenge, Hodges said. “Yannis
came up with some circuit ideas to
overcome this” using NMOS-only
technology. Yannis’s most lasting
contribution to the usefulness of
CMOS was his work on the adaptation
of weighted-capacitor A/D
conversion techniques to a special
kind of converter used for voice,
called a companding coder. He
and others first demonstrated this
technique, which became very
widely used in telephone systems
around the world in the 1980’s and
1990’s.”
Kirchhoff Medal
Subsequent milestones, Tsividis
said, have been “the work my students
and I did on switched-capacitor
circuit analysis and simulation;
our techniques for automatically
tuned integrated continuous-time
filters; and our work related to precision
MOS modeling for analog
and mixed-signal design.”
Dr. Tsividis, who is an IEEE Fellow,
has received two best paper
awards from the IEEE Circuits and
Systems Society, as well as the
IEEE-wide Baker best paper
award.
Master Teacher
The recipient in 2005 of the IEEE
Undergraduate Teaching Award,
Dr. Tsividis is unusual among
prominent researchers for his
enthusiasm about teaching at this
level. “I find it extremely rewarding,”
he said. “I have created a
first-year undergraduate class,
‘Introduction to Electrical Engineering,’
where we mix circuits
and electronics and attempt to
make students tinker. The idea is
to make them excited and motivated
about what they will be learning
in their follow-up classes. Just
to show you how rewarding
undergraduate teaching can be, let
me tell you a story from that class.
The class has a heavy lab component.
During an experiment on
amplifiers, a student comes to me
and says, ‘I see how, if I put a signal
in, I get a signal out, and if I do
not put a signal in, I get nothing
out. What would happen if I took
the output signal and used it as the
PEOPLE
input?’ That student had re-invented
oscillators right on the spot.”
In order to reach undergraduates,
a professor “must be willing
to find ways to explain things intuitively
to the students – not just
throw a bunch of equations at
them,” Tsividis said. “The key is to
make the math interesting, by
making clear why it’s useful.
Dumping the first circuits class on
anybody in an EE department has
often had disastrous results in the
motivation of students – I’m sure
our field has lost some of the best
minds because of this,” he said.
Interdependence of
Research and Teaching
“Whenever I want to really understand
an area different from mine,
I ask to teach a class in it,” Tsividis
said. “This is how I learned about
DSPs, communications, signals and
systems, and semiconductor
devices. Only when I am forced to
explain something carefully to others,
do I understand it fully.” As for
his graduate students, he aims
especially “to strike the right balance
between helping them and
challenging them to come up with
their own solutions.”
Shanthi Pavan, a recent Tsividis
Ph.D., who is now an assistant
professor at the Indian Institute of
Technology in Madras, India, said
in an email that he remembers
especially Prof. Tsividis’s “infectious
enthusiasm,” “clarity,” “meticulous
feedback,” and “virtually limitless
patience.” Dr. Cowan would
concur. “I don’t think people can
decide to become great teachers,”
he said. ”It has to come from the
heart.”
Yannis Tsividis received the Bachelor’s
degree in electrical engineering
from the University of
Minnesota in Minneapolis in 1972,
and the MS and Ph.D. degrees,
also in electrical engineering, from
the University of California at
Berkeley in 1973 and 1976. He is
Charles Batchelor Memorial Pro-
Winter 2007 IEEE SSCS NEWSLETTER 57