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Overview
To understand the oscilloscope's sampling and acquisition modes, it is helpful to
understand sampling theory, sample rate, oscilloscope bandwidth and sample
rate.
Sampling Theory
The Nyquist sampling theorem states that for a limited bandwidth (band- limited)
signal with maximum frequency f
MAX
, the equally spaced sampling frequency f
S
must be greater than twice the maximum frequency f
MAX
, in order to have the signal
be uniquely reconstructed without aliasing.
f
MAX
= f
S/2
= Nyquist frequency (f
N
) = folding frequency
Sample Rate
The maximum sample rate of the oscilloscope is 2 GSa/s. The actual sample rate of
the oscilloscope is determined by the horizontal scale and memory depth. Turn the
Horizontal Scale Knob to adjust the sample rate.
The actual sample rate is displayed in the information area at the upper- right
corner of the screen.
The influence on the waveform when the sample rate is too low:
1. Waveform Distortion: When the sample rate is too low, some waveform details
are lost and the waveform displayed is rather different from the actual signal.
2. Waveform Confusion: When the sample rate is lower than twice the actual
signal frequency (Nyquist Frequency), the frequency of the waveform rebuilt
from the sample data is lower than the actual signal frequency. The most
common aliasing effect is the jitter on fast edges.
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