Acquisition and waveform setup
R&S
®
RTP
134User Manual 1337.9952.02 ─ 12
5.1.2 Sampling and acquisition
The vertical system of a digital oscilloscope conditions the test signal in a way that the
following A/D converter (ADC) can transform the measured voltage into digital data.
5.1.2.1 Sampling and processing
The A/D converter samples the continuous signal under test at specific points in time
and delivers digital values called ADC samples. The rate at which the converter is
working is the ADC sample rate, a constant value specified in GHz: f
ADC
=
1 / T
I
The digital ADC samples are processed according to the acquisition settings. The
result is a waveform record that contains waveform samples and is stored in the
waveform memory. The waveform samples are displayed on the screen and build up
the waveform.
The number of waveform samples in one waveform record is called record length.
The rate of recording waveform samples - the number of waveform samples per sec-
ond - is the sample rate. The higher the sample rate, the better the resolution is and
the more details of the waveform are visible.
Minimum sample rate and aliasing
A sufficient resolution is essential for correct reconstruction of the waveform. If the sig-
nal is undersampled, aliasing occurs - a false waveform is displayed. To avoid aliasing
and accurately reconstruct a signal, Nyquist theorem postulates that the sample rate
must be at least twice as fast as the highest frequency component of the signal. How-
ever, the theorem assumes ideal conditions, so the Nyquist sample rate is usually not
sufficient.
Basics
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