Rohde & Schwarz SMM100A, Руководство пользователя

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Configuring the internal baseband source
R&S
®
SMM100A
151 User Manual 1179.1341.02 ─ 05
f
input
is retrieved from the waveform (the default sample rate tag) or is defined by the
corresponding parameter in the ARB user interface.
The Figure 4-12 depicts the stages involved in the processing and resampling of a
waveform in the ARB.
Figure 4-12: Processing of the waveform files in the ARB
f
input
= Waveform sample rate
b = Usable bandwidth factor
f
SysClk_max
= SystemClock
max
= SampleRate
max
Where:
●
f
SysClk_max
= SystemClock
max
= SampleRate
max
= 600 MHz
●
b = 0.4165
Impact of the resampling filter
As illustrated in Figure 4-12 , the filter in the resampling stage is distortion-free for sig-
nals with the following maximum baseband bandwidth:
Usable_Bandwidth
max
[MHz] = b* f
input
.
The usable bandwidth factor b equals b = 0.4165.
An externally created waveform file has to provide a sample rate f
input
that is high
enough for perfect signal reconstruction. For distortion-free resampling the lower
bound of the required sample rate
f
input
is then calculated as follows:
f
input
≥
Usable_Bandwidth / b
Thus, a modulation signal with a sample rate f
input
= 600 MHz fed in the baseband gen-
erator ensures the Usable_Bandwidth
max
. After the DAC, this signal features a
RF_Bandwidth
max
= 2*b*f
input
= 2*b*600 MHz = 1 GHz .
Impact of the oversampling factor
Waveforms generated by the R&S WinIQSIM2 software can be optimized by choosing
a suitable integer oversampling factor.
Conventional ARB generators often assume oversampling factors of 4. The ARB gen-
erator of the R&S
SMM100A requires low oversampling factors and still provides excel-
lent signal quality in terms of EVM and ACP.
A reduced sample rate saves significantly the amount of memory or allows an
increased signal cycle time, and vice versa.
Using the arbitrary waveform generator (ARB)