Oscilloscope Challenges: Answers and Winners
Oscilloscope Challenge #18: March 2008
Question
You’ve added a 2-in. wire to an oscilloscope probe tip to facilitate the measurement of a high-frequency output signal in close quarters on a crowded circuit assembly under test. You notice unexpected ringing on your measured signal. What is the quickest and most cost-effective way to attempt to eliminate the ringing?
a) Insert a small-value capacitor in series with the 2-in. wire.
b) Insert a 100-ohm resistor in series with the 2-in. wire.
c) Insert a small-value inductor in series with the 2-in. wire.
d) Redesign your assembly under test to provide a probe-accessible test point.
Answer: The correct answer is b.
Winner: The winner of the TomTom ONE GPS system (courtesy of contest sponsor Yokogawa) is Tommy Harris, Kingsport, TN.
Oscilloscope Challenge #17: February 2008
Question
Which of the following statements about active and passive probes is the most accurate?
a) Active probes are smaller and lighter in weight than passive probes.
b) Active probes operate at higher frequencies than passive probes do.
c) Passive probes exhibit less capacitive loading than active probes do.
Answer: The correct answer is b.
Winner: The winner of the TomTom ONE GPS system (courtesy of contest sponsor Yokogawa) is Phil Vogel, Lake Mary, FL.
Oscilloscope Challenge #16: January 2008
Question
When troubleshooting high-speed serial data buses, how can you minimize the effects of probe loading?
a) Choose a probe whose impedance is at least 10 times the source impedance.
b) Always use a passive probe to eliminate distortion due to an active probe’s circuitry.
c) Make sure the probe bandwidth is at least twice but no more than three times the signal bandwidth.
d) All of the above.
Answer: The correct answer is a.
Winner: The winner of the TomTom ONE GPS system (courtesy of contest sponsor Yokogawa) is Randy Garrett, Colorado Springs, CO.
Oscilloscope Challenge #15: December 2007
Question
What statement best describes digital oscilloscope sampling techniques?
a) A digital oscilloscope’s sample rate in megasamples per second must always exceed twice the frequency in megahertz of the waveform it captures.
b) Oscilloscopes can use sin x/x interpolation to reconstruct a periodic waveform based on two or more acquired samples per waveform period.
c) Equivalent time sampling is a technique that enables a digital oscilloscope to capture in real time a signal whose bandwidth in megahertz exceeds half the scope’s sampling rate in megasamples per second.
d) All of these statements are true.
e) None of these statements is true.
Answer: The correct answer is b.
Winner: The winner of the Apple iPod (courtesy of contest sponsor Yokogawa) is Diane Cuirle, Newbury, OH.
Oscilloscope Challenge #14: November 2007
Question
Read the following three statements about oscilloscopes, and then answer the question below:
1) The oscilloscope was invented in the late 19th century and was called a Braun tube.
2) The triggered oscilloscope was invented in 1946.
3) The first commercial digital storage oscilloscope appeared in 1985.
Which of these statements is true?
a) Only statement 1 is true.
b) Only statement 2 is true.
c) Only statement 3 is true.
d) All three statements are true.
e) Only statements 2 and 3 are true.
f) Only statements 1 and 3 are true.
g) Only statements 1 and 2 are true.
Answer: The correct answer is d.
Winner: The winner of the Apple iPod (courtesy of contest sponsor Yokogawa) is Norm Bingham, Wichita, KS.
Oscilloscope Challenge #13: October 2007
Question
Why might you employ an oscilloscope’s x-y mode?
1. To display voltage vs. time.
2. To display Lissajous patterns that indicate two waveforms’ phase differences.
3. To generate I-V curves.
4. All of the above.
5. None of the above.
6. Statements 1 and 2.
7. Statements 2 and 3.
8. Statements 1 and 3.
Answer: The correct answer is 7: Statements 2 and 3 are correct.
Winner: The winner of the Apple iPod (courtesy of contest sponsor Yokogawa) is David Wilson, Dunlap, TN.
Oscilloscope Challenge #12: September 2007
Question
What is the function of an oscilloscope’s timebase?
a) Allow a user to set the time at which signal acquisition should begin.
b) Control the speed at which the instrument draws a trace horizontally.
c) Control the vertical deflection of a trace.
d) Statements a and b are correct.
e) Statements a, b, and c are all correct.
Answer: The correct answer is b.
Winner: The winner of the Apple iPod (courtesy of contest sponsor Yokogawa) is Mohamed Shaltot, Phoenix, AZ.
Oscilloscope Challenge #11: August 2007
Question
Which of the following is true about color-graded or intensity-graded persistence in an oscilloscope?
a) Color or intensity persistence indicates the type of trigger in use.
b) Color or intensity persistence uses a signal’s history to indicate its frequency of occurrence and how the signal changes over time.
c) Persistence is available in analog oscilloscopes only.
d) Color or intensity persistence lets you see a signal's frequency components.
Answer: The correct answer is b.
Winner: The winner of the Apple iPod (courtesy of contest sponsor Yokogawa) is Rodney Adams, Seattle, WA.
Oscilloscope Challenge #10: July 2007
Question:
Which of the following statements about making bit-error-rate (BER) measurements on serial buses is true?
a) A BER tester can make quantitative bit-error-rate measurements.
b) An oscilloscope can allow you to qualitatively observe the behavior of a serial data channel, but it cannot make quantitative BER measurements.
c) An oscilloscope can make quantitative BER measurements.
d) Statements (a) and (b) are true.
e) Statements (a) and (c) are true.
Answer: The correct answer is e.
Winner: The winner of the 30-Gbyte iPod (courtesy of contest sponsor Yokogawa) is Vishnu Dave, Baltimore, MD.
Oscilloscope Challenge #9: June 2007
Question:
Which of the following oscilloscope features are applicable to serial-bus troubleshooting?
a) Persistence mode
b) Bus-specific triggering functions
c) Pre- and post-triggering capability
d) Both a and b
e) Both b and c
f) All of the above
Answer: The correct answer is f.
Winner: The winner of the 30-Gbyte iPod (courtesy of contest sponsor Yokogawa) is Jon Radlick, Warren, MI.
Oscilloscope Challenge #8: May 2007
Question:
The figure represents an oscilloscope persistence view of traffic on a serial bus (an eye diagram). What does the red arrow represent?
a) One clock cycle.
b) One unit interval (UI).
c) One-half unit interval (UI).
d) Both a and b.
e) Both a and c.
Answer: The correct answer is b.
Winner: The winner of the 30-Gbyte iPod (courtesy of contest sponsor Yokogawa) is Marilyn Langley, San Jose, CA.
Oscilloscope Challenge #7: April 2007
Question:
Which of the following statements best describes a mixed-signal oscilloscope?
a) It combines an analog front-end with digital data storage.
b) It combines analog-input oscilloscope channels with logic-analysis channels.
c) A mixed-signal oscilloscope is any scope that includes analog and digital components.
d) A mixed-signal scope is any scope that can be used to troubleshoot a mixed-signal device under test (DUT).
Answer: The correct answer is b.
Winner: The winner of the 30-Gbyte iPod (courtesy of contest sponsor Yokogawa) is David Danielson, Chelsea, MI.
Oscilloscope Challenge #6: March 2007
Question:
Which of the following oscilloscope tips are accurate and can be found in the Test & Measurement World archives?
a) For troubleshooting PCI Express-class buses, as a general rule of thumb, a scope's bandwidth should be 1.8 times the maximum data rate of interest.
b) Digital scopes can measure serial-data signal integrity and help isolate problems caused by factors such as noise, crosstalk, and radiation from other electronics products.
c) Both statements a and b are accurate, and the tips can be found in the Test & Measurement World archives
d) Neither statement a nor statement b is accurate, and neither tip can be found in the archives.
Answer: The correct answer is c.
Winner: The winner of the 30-Gbyte iPod (courtesy of contest sponsor Yokogawa) is Tom Lemke, Cedar Rapids, IA.
Oscilloscope Challenge #5: February 2007
Question
Which of the following statements offers the best advice for choosing oscilloscope bandwidth (and can be found in the Test & Measurement World archives)?
a) You should select an oscilloscope having a front-end analog bandwidth that is greater than or equal to the clock rate of the serial bus you are troubleshooting.
b) You should select an oscilloscope having bandwidth equal to or greater than three times the highest frequency component of the signal you want to observe.
c) The Nyquist theorem indicates that, for digital-signal measurements, you should choose a scope for which the signal-under-test’s digital clock rate is twice the scope’s analog bandwidth.
Answer: The correct answer is b
Winner: The winner of the 30-Gbyte iPod (courtesy of contest sponsor Yokogawa) is James Larrabee, Rochester, NY.
Oscilloscope Challenge #4: January 2007
Question
The eye diagram provides a way for characterizing the jitter that is present on serial-bus digital signals. Which of the following best describes the relationship of oscilloscopes to eye diagrams?
a) The eye diagram is a frequency-domain representation and cannot be displayed by an oscilloscope.
b) The eye diagram is a frequency-domain representation that you can obtain by performing a fast Fourier transform (FFT) on data captured by a digital storage oscilloscope.
c) An oscilloscope can display eye diagrams directly.
Answer: The correct answer is c
Winner: The winner of the 30-Gbyte iPod (courtesy of contest sponsor Yokogawa) is Bridgett Schultz, Minneapolis, MN.
Oscilloscope Challenge #3: December 2006
Question
Select the best reason for using a digital oscilloscope with serial-data-bus triggering and analysis capabilities when designing or troubleshooting serial data buses:
a) Such an oscilloscope can generate simulated bus traffic to help determine real-world bus performance.
b) Such an oscilloscope can display both decoded serial bus data and physical-layer waveform data together at one time.
c) Such an oscilloscope can provide statistical information about bus loading and bus disturbances.
d) All three of the above choices are key reasons for using a digital oscilloscope for serial bus analysis and troubleshooting.
Answer: The correct answer is b.
Winner: The winner of the 30-Gbyte iPod (courtesy of contest sponsor Yokogawa) is Stanley Perkins, San Diego, CA
Oscilloscope Challenge #2: November 2006
Question
Many of today’s digital oscilloscopes provide special features for users who are designing or troubleshooting serial data buses. In addition to displaying serial bus waveform(s), what other serial-bus-related feature (or features) do digitial oscilloscopes most commonly offer?
a) Triggering on a specific bus event (e.g., a device address)
b) Generating a bus event to test how the bus responds
c) Decoding serial bus data
d) Monitoring bus loading levels and alerting a user if certain conditions are met
e) a & b only
f) c & d only
g) a & c only
h) a, b, c & d are all common serial-bus-related features found on oscilloscopes
Answer: The correct answer is g.
Winner: The winner of the 30-Gbyte iPod (courtesy of contest sponsor Yokogawa) is Roy Olund, Seattle, WA.
Oscilloscope Challenge #1: October 2006
Question
You are using your digital oscilloscope with serial data bus triggering and analysis capabilities to display the waveforms of the data bus you are troubleshooting. However, on the scope, the waveform bits aren’t very square—i.e., they appear quite rounded. What is the best choice for adjusting the oscilloscope and improving the quality of the measurement, assuming the bandwidth of the scope is sufficient for the signal being measured?
a) Increase the V/div setting
b) Increase the display persistence
c) Increase the T/div setting (e.g., 20 ms/div to 50 ms/div)
d) Increase the data points/acquisition (that is, memory) setting (e.g., 100 kpoints to 1 Mpoints)
Answer: The correct answer is: d) Increase the data points/acquisition (that is, memory) setting (e.g., 100 kpoints to 1 Mpoints)
Winner: The winner of the 30-Gbyte iPod (courtesy of contest sponsor Yokogawa) is Gene Schneider, Consulting Engineer, ICOM.
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