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Advanced High-Speed Signal Propagation
A Workshop for
Experienced Digital Designers
What's Advanced about Advanced High-Speed
Signal Propagation?
Try this pop-quiz (ten questions).
The following material is covered in the
course "High-Speed Digital Design". If you
have already taken that class, or you make
70% or better on this quiz, you are ready
for the advanced course. If you score less
than 70%, you may, of course, still attend,
and you'll learn a lot, but you will
comprehend the material at a deeper level if
you first take Dr. Johnson's original course,
High-Speed Digital Design.
The answers appear at the end of the quiz.
1. In a synchronous digital system, the highest
frequency of interest for purposes of signal
integrity is approximately:
a)
The velocity of signal propagation divided
by the signal path length
b) One half divided by the rise or fall time of the signal, whichever is less
c)
The third harmonic of the clock
d)
The processor's internal clock frequency
e)
The fifth harmonic of the clock
2.
Which of the following trace configurations
is the fastest:
a)
Microstrip with heavy soldermask
b)
Stripline
c)
Offset stripline
d)
Embedded microstrip
e)
Microstrip with no soldermask
3.
When two fifty-ohm traces rise out of the
plane of the pc board and flow through the
air (as when passing through connector pins
or component bodies) the resulting crosstalk
is caused mostly by:
a)
Far-field radiation
b)
Inductive coupling
c)
Electron leakage currents
d)
Aluminum migration
e)
Capacitive coupling
4.
What can happen when you violate the setup
and hold times on a flip flop?
a)
The Q output goes to a voltage halfway
between zero and one and stays there
b)
The output assumes an imaginary value equal
to 1+j
c)
The flip-flop loses sync., causing a series
of errors
d)
Output transitions occur much later than the
specified CLK->Q interval
e)
The flip-flop circuit burns up
5.
In which way is a single-ended oscilloscope
probe NOT likely to distort your signal:
a)
The input capacitance of the probe loads
your signal
b)
Non-linearity in the vertical amplifier
makes rising edges appear earlier than
falling ones
c)
The limited bandwidth of the probe distorts
and slows the shapes of rising and falling
edges
d)
The dc input resistance of the probe draws
extra drive current from your circuit
e)
The inductance of the ground wire associated
with the probe sets up a resonance
6.
On a long transmission line, the value of an
external series-terminating resistor should
equal:
a)
The load resistance of the receiver minus
the source resistance of the driver
b)
17 ohms
c)
The smallest value that stops ringing just
before the clock setup time
d)
The transmission line Z0 minus the source
resistance of the driver
e)
33 ohms
7.
A diode-clamping termination at the end of a
trace can sometimes improve signal quality,
but never does as well on a long
transmission line as:
a)
A resistor in the middle of the line
b)
An "H" distribution
c)
Modulating the line width
d)
The R-C termination (resistor and capacitor
in series)
e)
A purely resistive termination at the
source, end, or both
8.
What is the primary effect of an
interruption (hole or slot) in the reference
plane underneath a high-speed trace?
a)
Decreases power-supply noise
b)
Weakens the physical board structure,
causing warping
c)
Increases crosstalk among all traces that
cross the same hole or slot
d)
Prevents signal from crossing the hole or
slot
e)
Exacerbates the "swiss cheese" effect
9.
Which of the following adjustments would
increase the lead inductance of a
surface-mounted bypass capacitor?
a)
Changing the layout to use a smaller
component body
b)
Moving the power and ground planes closer to
the surface of the board where the capacitor
sits
c)
Adding more vias
d)
Using fatter vias
e)
Adding traces in series with the mounting
pads
10.
At the end of an unterminated transmission
line, a ringing waveform tells you that:
a)
The source impedance of the driver is too
low
b)
The Z0 of the transmission line is too low
c)
The receiver has too much inductance
d)
The source impedance of the driver is too
high
e)
It's Miller time
Answers: 1b, 2e, 3b, 4d, 5b, 6d, 7e, 8c, 9e,
10a
There are Three Ways to
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