Test Your EQ
— Issue #158
Each month, Test Your EQ presents
some basic engineering problems for you to test
your Engineering Quotient. What's your EQ?
|
Problem
1—A
newly-hired engineer asked one of his coworkers how to
recognize the byte value 01111110. The coworker suggested
the following circuit.
The
company guru, overhearing the conversation, suggested
the following change. Why?
Answer
Problem
2—What
is Hoth noise?
Answer
Problem 3—For
a signal that is amplitude modulated to a depth of 100%
by a sinusoidal signal, what is the ratio of the modulated
signal’s power to that of the carrier alone?
Answer
Problem
4—What
is the Boolean function realized by the following DTL
circuit?
Answer
Problem
5—A
system is designed that, for various reasons, has two
sections with separate clocks. The first section is clocked
at 16 MHz and generates a variable-rate output clock that
is fed to the second section. The second section is clocked
at 25 MHz and uses the variable-rate clock from the first
section to synthesize a sine wave output. However, when
tested with a spectrum analyzer, the sine wave output
is found to have sidebands at multiples of ±400 Hz that
start at –70 dB relative to the desired signal and don’t
drop off quickly as the frequency offset goes up. What’s
causing this?
Answer
Problem
6—The
system would perform adequately if the discrete sidebands
could be somehow converted into a relatively flat noise
floor. How might this be accomplished?
Answer
Problem
7—A
4- to 20-mA sensor used in an industrial process needs
to have galvanic isolation between its current loop and
both the power source and the equipment reading the sensor.
The following circuit is proposed as a solution. A 1-kHz
square wave oscillator feeds a MOSFET H-Bridge that is
used to drive the primary of a small audio transformer.
A resistor at the bottom of the H-Bridge samples the synchronously
rectified primary current of the transformer. The secondary
of the transformer is full-wave rectified and filtered
to drive the isolated current loop.
.
What
are some of the potential problems with this design?
Answer
Problem
8—The
following question appeared not too long ago in the Usenet
newsgroup comp.dsp:
I
am an electronics hobbyist and have a very old scanning
electron microscope. I want to use the two output channels
of a PC sound card as scan generator to drive the electron
beam over the test object and one of the inputs to receive
the video signal.
What
are some of the issues that are going to arise with this
approach?
Answer
Published September 2003
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