188 Agilent InfiniiVision 3000 X-Series Oscilloscopes User's Guide
12 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
1 Ghz bandwidths and below, oscilloscopes have a Gaussian frequency
response.
Figure 34 Theoretical Brick-Wall Frequency Response
f
S
f
N
-3dB
Attenuation
Frequency
0dB
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