Oscilloscope Bandwidth And Sample Rate - Teledyne T3DSO2000 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.
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.
Attenuation
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 components have a
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greater amount of attenuation.
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