SIG
L
ENT
SDS1000X User Manual
37
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.
0dB
-3dB
Attenuation
f
N
f
S
Frequency
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.
f
S
/4 f
N
f
S
Frequency
Limiting oscilloscope bandwidth (f
BW
) to 1/4 the sample rate (f
S
/4)
reduces frequency components above the Nyquist frequency (f
N
).
So, in practice, an oscilloscope's sample rate should be four or more times its bandwidth:
f
S
= 4fBW. This way, there is less aliasing, and aliased frequency components have a
greater amount of attenuation.
Aliased frequency
compoments
Attenuation
0dB
-3dB
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Summary of Contents for SDS1102X
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Page 19: ...SIGLENT SDS1000X User Manual XVII www biall com pl...
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Page 89: ...SIGLENT SDS1000X User Manual 69 Figure 28 Relative Window Trigger www biall com pl...
Page 91: ...SIGLENT SDS1000X User Manual 71 Figure 29 Interval Trigger www biall com pl...
Page 95: ...SIGLENT SDS1000X User Manual 75 Figure 32 Runt Trigger www biall com pl...
Page 109: ...SIGLENT SDS1000X User Manual 89 Figure 44 SPI Trigger www biall com pl...
