Download R&S AMU200A Operating Manual

R&S®AMU200A
Instrument Function
Baseband Signal - Baseband Block
pling. By the same procedure the instantaneous amplitude of the various waveforms can
be scaled to a common RMS level.
Typical applications for the multi segment mode are described in the section ​"Typical
Applications for Multi Segment Waveforms" on page 312.
Multi carrier waveforms consisting of up to 512 carriers modulated by user-selectable
baseband signals can be created in order to simulate complex multi carrier scenarios with
different baseband signals (e.g. CDMA2000 or 3GPP FDD).
Waveform sample rate
The Arbitrary Waveform Generator includes a resampling unit that interpolates the input
samples to reach a target digital output I/Q sample rate before digital-to-analog conversion (DAC). The input sample rate finput is given by the default sample rate tag of the
waveform file or is set by the user in the ARB panel.
The R&S AMU uses a 100 MHz system clock and a sample rate of 100 MSamples/s.
The resampling lowpass limits the signal bandwidth to a maximum of 1.36 x finput. Within
a bandwidth of 0.68 x finput the resampler lowpass is distortion-free. Thus, an externally
created waveform file have to provide a sample rate finput that is high enough for perfect
signal reconstruction.
For distortion-free resampling the lower bound of the required sample rate finput is calculated by:
finput ≥ Signal bandwidth / 0.68
In case of digital modulation this means that the oversampling factor (finput =symbol rate
x oversampling factor) that is applied for impulse forming is high enough.
The lower bound of the oversampling factor is given by:
oversampling factor ≥ signal bandwidth / (symbol rate x 0.68)
Example:
For the WCDMA standard 3GPP FDD with root raised cosine filter (α = 0.22) and a symbol
rate (chip rate) of 3.84 MHz the minimum oversampling factor is calculated as follow:
3.84 MHz x (1+0.22) / (3.84 MHz x 0.68) = 1.794
A modulation signal with a sample rate of 100 MHz is passed directly to the digital-toanalog converter (DAC), i.e. the resampling unit is bypassed (see figure below). After the
DAC the signal is finally limited to a maximum bandwidth of 80 MHz.
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