Rohde & Schwarz SMBV100B, Руководство пользователя

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Configuring the Internal Baseband Source
R&S
®
SMBV100B
149 User Manual 1178.4460.02 ─ 03
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 3-12 , 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
.
Where b is the usable bandwidth factor and 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 = 500 MHz .
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
SMBV100B requires low oversampling factors and still provides
excellent 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.
3.6.2.4 Impact of the Enabled Number of Marker Signals on the Waveform Length
The R&S SMBV100B provides the possibility to define marker signals, that are sent to
the marker outputs in synchronicity with the I/Q output signals. Marker signals can be
either predefined or subsequently defined.
The I/Q data and marker data are located in separate memory areas of the SDRAM
and can be independently configured. Each marker signal requires 1 bit of the availa-
ble memory size. Sometimes, it is useful to generate a modulation signal without extra
marker signals to increase the maximum waveform length.
The following example explains the dependency between the number of enabled
marker signals, the available memory size, and the resulting waveform length.
Using the Arbitrary Waveform Generator (ARB)