Oscilloscope Bandwidth Tutorial
B
4000 X-Series Oscilloscopes Advanced Training Guide
161
Step 3: Calculate scope bandwidth
The third step is to determine the oscilloscope bandwidth required to measure this
signal, based on your desired degree of accuracy when measuring rise times and
fall times.
shows multiplying factors for various degrees of accuracy for
scopes with a Gaussian frequency response.
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.
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
