218 Keysight InfiniiVision 3000T X-Series Oscilloscopes User's Guide
13 Acquisition Control
Oscilloscope Bandwidth and Sample Rate
An oscilloscope's bandwidth is typically described as the lowest frequency at
which input signal sine waves are attenuated by 3 dB (-30% amplitude error).
At the oscilloscope bandwidth, sampling theory says the required sample rate is f
S
= 2f
BW
. However, the theory assumes there are no frequency components above
f
MAX
(f
BW
in this case) and it requires a system with an ideal brick-wall frequency
response.
However, digital signals have frequency components above the fundamental
frequency (square waves are made up of sine waves at the fundamental frequency
and an infinite number of odd harmonics), and typically, for 500 MHz bandwidths
and below, oscilloscopes have a Gaussian frequency response.
Figure 35 Theoretical Brick-Wall Frequency Response
f
S
f
N
-3dB
Attenuation
Frequency
0dB
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