Test Your EQ
— Issue #157
Each month, Test Your EQ presents
some basic engineering problems for you to test
your Engineering Quotient. What's your EQ?
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Problem
1—Consider
the logic expression Y = A.B.C! + B.C + C.A!. This is
called the sum of products (SOP) notation. The normal
way to implement it would be to use AND, OR, and NOT gates.
But it is sometimes required to implement such expressions
using only NAND or NOR gates. Explain how would you implement
it using only NAND gates. The aim here is to guess the
NAND gate structure required to implement the expression
by simply looking at the expression with no calculations
involved.
Answer
Problem
2—What
1-bit changes in the following circuit may cause glitches?
Answer
Problem 3—A simple electronic combination lock
has four toggle switches, each of which may be either
up or down. One of the switches is disconnected and has
no effect on the lock, but you don't know which one. What
is the smallest set of combinations you can devise that
is guaranteed to open the lock?
Answer
Problem
4—If two of the four switches are known to be
nonfunctional, how many combinations must be tried in
order to open the lock?
Answer
Problem
5—Dither
often helps the A/D conversion process by eliminating
the nonlinear effects of quantization. However, sometimes
it isn't practical to add the dither signal directly to
the signal being measured, especially if there are multiple
signals being measured through an analog multiplexer.
In that case, it is possible to add the dither to the
A/D reference voltage instead. What pitfall must be avoided
when using this approach?
Answer
Problem
6—You are given a power transformer that has
many leads coming out, but none of them are labeled. How
can you figure out its winding ratios and relative phases
using only an AC voltage source, a resistor, and a volt/ohm
meter?
Answer
Problem
7—How can a signal generator and oscilloscope
speed up the process of identifying transformer windings?
Answer
Problem
8—An amplifier has a mid-frequency gain A0 =
100, an upper cut off frequency fH = 40 kHz, and a lower
cutoff frequency fL = 20 Hz. For a negative feedback transfer
ratio B (beta) = 0.1, find the following: the overall
gain at mid frequency; the upper cutoff frequency with
feedback; and the lower cutoff frequency with feedback.
Answer
Published August 2003
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