Oscilloscope Bandwidth And Sample Rate - Teledyne T3DSO1000A Series User Manual

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
However, the theory assumes there are no frequency components above f
case) and it requires a system with an ideal brick- wall frequency response.
0dB
-3dB
Attenuation
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.
0dB
-3dB
Attenuation
Limiting oscilloscope bandwidth (f
reduces frequency components above the Nyquist frequency (f
So, in practice, an oscilloscope's sample rate should be four or more times its
bandwidth: f = 4fBW. This way, there is less aliasing, and aliased frequency
S
components have a greater amount of attenuation.
40 User Manual
Frequency
Aliased frequency
components
f /4
S
Frequency
f f
N S
f f
N S
) to 1/4 the sample rate (f
BW
= 2f .
S BW
(f in this
MAX BW
/4)
S
).
N