Sampling Rate; Aliasing - TiePie Handyscope HS4 DIFF-5MHz User Manual

Figure 3.7: "connecting" the samples
3.3

Sampling rate

The rate at which the samples are taken is called the sampling rate, the number
of samples per second. A higher sampling rate corresponds to a shorter interval
between the samples. As is visible in figure 3.8, with a higher sampling rate, the
original signal can be reconstructed much better from the measured samples.
Figure 3.8: The effect of the sampling rate
The sampling rate must be higher than 2 times the highest frequency in the input
signal. This is called the Nyquist frequency. Theoretically it is possible to recon-
struct the input signal with more than 2 samples per period. In practice, 10 to
20 samples per period are recommended to be able to examine the signal thor-
oughly.
3.3.1

Aliasing

When sampling an analog signal with a certain sampling rate, signals appear in the
output with frequencies equal to the sum and difference of the signal frequency
and multiples of the sampling rate. For example, when the sampling rate is 1000
Sa/s and the signal frequency is 1250 Hz, the following signal frequencies will be
present in the output data:
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Chapter 3