August
2004, Issue 169
Test Your EQ:
Each
month, Test Your EQ presents some basic engineering
problems for you to test your Engineering Quotient.
What's your EQ?
|
Problem
1—A
two-layer mirror is designed to provide total cancellation
of reflected energy at a particular wavelength. The front
surface is partially reflecting. The back surface is totally
reflecting, and the thickness is such that light from
the back surface is out-of-phase with respect to the light
from the front at that wavelength (i.e., the mirror is
an odd multiple of a quarter-wavelength thick).
Keeping
in mind that the front surface also reflects internally,
creating multiple reflections before all the light escapes
again (see the diagram), what is the reflection coefficient
(K) required to achieve total cancellation of the light?
Answer
Problem
2— In
what sense does a noninverting amplifier configuration
put more strain on an op-amp relative to an inverting
amplifier configuration?
Answer
Problem 3—What is “endianess”—big endian versus
little endian—and why might one be preferred over the
other?
Answer
Problem
4—What is a data scrambler and what is it for?
Answer
Problem
5—The circuit shown below is the classic op-amp
difference amplifier, in which VOUT = RY/RX(VP
– VN).
This
circuit has several pitfalls for the unwary, however.
For example, even assuming an ideal op-amp, what is required
to achieve a high common-mode rejection ratio (CMRR)?
Answer
Problem
6—Again, assuming an ideal op-amp, what can you
say about the input impedance seen at the two input terminals?
Answer
Problem
7—Given that you eventually need to build this
circuit with a nonideal op-amp, what is the relationship
between the device’s inherent CMRR and the circuit CMRR?
