Page 100 - Analog Circuit Design Art, Science, and Personalities

Jim Roberge

assistant and include an interview as an important component of performance eval-
uation. This approach ensures that the student’s time in the laboratory is spent pro-
ductively. It also discourages an occasional student from “borrowing“ results from
a similar topic assigned in a previous year.
The subjects all depend heavily on classroom demonstrations, performed real
time, to illustrate concepts as they are introduced. These demonstrations make it
very clear that the material is applicable to practical systems. There is also real edu-
cational benefit in the (fortunately rare) event that a real-time deinonstration fails.
The students realize that they are in good company when one of their experimental
attempts fails.
Teaching assistants are an important part of the instructional team in all of these
courses. Fortunately, assignment to one of these courses is viewed highly by grad-
uate students interested in design, and we always have our choice of very talented
and industrious applicants. In addition to their other responsibilities, these teaching
assistants have developed many of the demonstrations that we use.
Two of the courses are undergraduate level. These courses are typically taken by
juniors and seniors and usually have an enrollment of 50 or more. This group meets
for two 1 -hour lectures a week. These lectures facilitate the introduction of new
material, particularly when accompanied by demonstrations. but the size tends to
discourage teacher-student interaction. The students also meet for two 1 -hour reci-
tation sections a week in groups of 25 or fewer. These sections are generally taught
by faculty, although occasionally graduate students who have demonstrated both
extreme familiarity with the material and excellent teaching ability teach them. New
material is often introduced in recitation sections. but the format permits more inter-
action and question-answer type teaching.
The graduate course typically has an enrollment of 12 to 15 graduate students
plus a few very gifted undergraduates. It meets an average of 4 hours a week.
One of the undergraduate courses focuses on active-circuit design. In addition to
the usual introductory electrical engineering subjects, prerequisites include a mod-
erate aniount of circuit discussion. Thus students enter the active-circuit subject with
a good background in seiniconductor device operation, facility with models that
include dependent. sources, and a basic appreciation ola number of circuit topologies.
A major theme that unifies much of this coursework involves the design of both
linear and switching circuits for specified dynamic performance. Emphasis is given
to techniques that can be used to estimate performance while retaining insight and
providing guidance for improving operation. Thus, for example, numerical methods
that basically prwide a “binary” answer as to whether design objeclives have been
met are only used as an adjunct to methods that provide greater design guidance.
The analyses of linear amplifiers is introduced with a review of the common-
emitter amplifier, and its dynamics are estimated via the Miller-capacitance approx-
imation. The development leads to the introduction of the method of open-circuit
time constants. This technique is used to estimate the dynamic performance of more
complex topologies arid to provide design insight. Such issues as the conditions
under w1iichj.l. is closely correlated with performance and the maximum bandwidth
that can be achieved (assuming an unlimitcd number or devices arc availablc)
subject tG specified constraints are explored.
This portion of the subject culminates with the students conducting a multipart
design exercise. They are given specifications such as “design an amplifier with a
voltage gain of 250 and a bandwidth of 5 MHz.” Additional parameters such as
source and output resistance and dynamic range are specified. The use of fairiy
docile device types and restricted supply power consumption is also specified.

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