Agilent Technologies 2000 X-Series, User Manual

Page: 158 / 352

158 Agilent InfiniiVision 2000 X-Series Oscilloscopes User's Guide
12
Acquisition Control
Oscilloscope Bandwidth Required
The oscilloscope bandwidth required to accurately measure a signal is
primarily determined by the signal's rise time, not the signal's frequency.
You can use these steps to calculate the oscilloscope bandwidth required:
1 Determine the fastest edge speeds.
You can usually obtain rise time information from published
specifications for devices used in your designs.
2
Compute the maximum "practical" frequency component.
From Dr. Howard W. Johnson's book, High- Speed Digital Design – A
Handbook of Black Magic , all fast edges have an infinite spectrum of
frequency components. However, there is an inflection (or "knee") in the
frequency spectrum of fast edges where frequency components higher
than f
knee
are insignificant in determining the shape of the signal.
f
knee
= 0.5 / signal rise time (based on 10% - 90% thresholds)
f
knee
= 0.4 / signal rise time (based on 20% - 80% thresholds)
3 Use a multiplication factor for the required accuracy to determine the
oscilloscope bandwidth required.
See Also Choosing an Oscilloscope with the Right Bandwidth for your
Application
, Agilent Application Note 1588
( "http://cp.literature.agilent.com/litweb/pdf/5989- 5733EN.pdf" )
Required accuracy Oscilloscope bandwidth required
20% f
BW
= 1.0 x f
knee
10% f
BW
= 1.3 x f
knee
3% f
BW
= 1.9 x f
knee