Oscilloscope Bandwidth Tutorial
B
3000 X-Series Oscilloscopes Advanced Training Guide
121
Example
Let’s now walk through this simple example:
If the signal has an approximate rise/fall time of 1 ns (based on a 10% to
90% criteria), then the maximum practical frequency component (f
knee
) in
the signal would be approximately 500 MHz.
If you are able tolerate up to 20% timing errors when making parametric
rise time and fall time measurements on your signals, then you could use
a 500 MHz bandwidth oscilloscope for your digital measurement
applications. But if you need timing accuracy in the range of 3%, then a
scope with 1 GHz bandwidth would be the better choice.
Let’s now make some measurements on a digital clock signal with
characteristics similar to this example, using various bandwidth scopes....
Table 1
Multiplying factors to calculate required scope bandwidth based
on desired accuracy
Required Accuracy
Require Bandwidth
20%
f
BW
= 1.0 x f
knee
10%
f
BW
= 1.3 x f
knee
3%
f
BW
= 1.9 x f
knee
Determine the minimum required bandwidth of an
oscilloscope with an approximate Gaussian frequency
response to measure a 1 ns rise time (10-90%)
f
knee
= 0.5/1 ns = 500 MHz
20% timing accuracy:
Scope bandwidth = 1.0 x 500 MHz = 500 MHz
3% timing accuracy:
Scope bandwidth = 1.9 x 500 MHz = 950 MHz