User manual

Acquisition and Setup

R&S

RTO

16User Manual 1316.0827.02 ─ 06

2.1.2.1 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 usually specified in GHz: f

ADC

1 / T

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, and

the rate of recording waveform samples - the number of waveform samples per second

- is the sample rate. The higher the sample rate, the better is the resolution and the more

details of the waveform are visible.

Maximum sample rate on R&S RTO1044

R&S RTO1044 can work with double maximum realtime sample rate compared to other

R&S RTO instruments. This high sample rate is achieved by interleaving two channels:

channel 1 and 2 are interleaved, and also channel 3 and 4. Interleaving assumes that

only one of the paired channels can be used - either channel 1 or channel 2, and either

channel 3 or 4.

Using a channel on R&S RTO oscilloscopes is more than displaying it. In the background,

without displaying the channel, it can serve as trigger source, as source of a math wave-

form, cursor or automatic measurement. As soon as the second channel of a pair is used

in one way or another, the interleaving mode is disabled and the realtime sample rate is

limited to the usual value of 10 GSa/s.

Minimum sample rate and aliasing

A sufficient resolution is essential for correct reconstruction of the waveform. If the signal

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. However, the

theorem assumes ideal conditions, so the Nyquist sample rate is usually not sufficient.

Basics