Acquiring Waveforms
3-24
TDS5000 Series User Manual
Actual high-frequency
waveform
Apparent low-frequency
waveform due to aliasing
Sampled points
Figure 3- 8: Aliasing
Eliminating Aliasing. To quickly check for aliasing, slowly increase the horizontal
scale (time per division setting). If the shape of the displayed waveform changes
drastically or becomes stable at a faster time base setting, your waveform was
probably aliased.
To avoid aliasing, sample the input signal at a rate more than twice as fast as the
highest frequency component. For example, a signal with frequency components
of 500 MHz would need to be sampled at a rate faster than 1 Gigasamples/sec-
ond to represent it accurately and to avoid aliasing. The following tips may help
you eliminate aliasing on a signal:
H Adjust the horizontal scale.
H Push the AUTOSET button.
H Switch the acquisition to Envelope mode. Envelope mode searches for
samples with the highest and lowest values over multiple acquisitions and
can detect faster signal components over time.
The following table shows which acquisition fea tur es and modes are incompatible
with other feature s or modes:
Incompatible with Control/Feature Explanation
Reference Waveforms
(Ref1--Ref4)
Voltage Offset Offset is an acquisition control
not a display control
Single shot acquisition Average Acquisitions continue until the
specified number of wave-
forms have been acquired and
averaged
Incompatible Modes
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