Configuring the Internal Baseband Source
R&S
®
SMW200A
303User Manual 1175.6632.02 ─ 16
Converted to analog, the signal is output directly at the BNC connectors I and Q
outputs of the instrument.
4.7.2.3 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 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 4-16 depicts the stages involved in the processing and resampling of a
waveform in the ARB.
Figure 4-16: Processing of the waveform files in the ARB
f
input
= Waveform sample rate
b = Usable bandwidth factor; b = 0.4 (R&S SMW-B10) and b = 0.4165 (R&S SMW-B9)
f
SysClk_max
= SystemClock
max
= SampleRate
max
= 200 MHz (R&S SMW-B10/-K522) and 2.4 GHz (R&S SMW-
B9/-K526)
Impact of the Resampling Filter
As illustrated in Figure 4-16, 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
.
Where b is the usable bandwidth factor and its value depends on the installed options:
●
b = 0.4 (R&S SMW-B10)
●
b = 0.4165 (R&S SMW-B9)
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
= 200 MHz fed in the standard base-
band generator ensures the Usable_Bandwidth
max
=
80
MHz. After the DAC, this signal
features a RF_Bandwidth
max
= 2*b*f
input
=
2*0.4*200 MHz
=
160 MHz.
Impact of the Oversampling Factor
Waveforms generated by the R&S WinIQSIM2 software can be optimized by choosing
a suitable integer oversampling factor.
Using the Arbitrary Waveform Generator (ARB)
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