Rohde & Schwarz SMW200A - Impact on the Enabled Number of Marker Signals on the Waveform Length

Configuring the Internal Baseband Source
R&S
®
SMW200A
304User Manual 1175.6632.02 ─ 16
Conventional ARB generators often assume oversampling factors of 4. The ARB gen-
erator of the R&S SMW 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.
4.7.2.4 Impact on the Enabled Number of Marker Signals on the Waveform Length
The R&S SMW 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 whereas each marker signal requires 1 bit of the
available 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.
Example: Calculating the maximum waveform length
The calculation in this example is based on an instrument equipped with option
R&S SMW-B10 (256 Msamples).
●
Total Memory Size = 256 MB
●
Required Memory Size (per complex sample) = 32 bits + 3 bits = 35 bits = 4.375
bytes, where:
– The raw I/Q samples are stored as 16-bit values;
That is, for I/Q data = 2 x 16 bits = 32 bits (16 bits per I/Q channel)
– Each software defined marker requires 1 bit;
That is, for 3 enabled markers = 3 x 1 bit = 3 bits
●
Maximum Waveform Length (with 3 markers) = 256 MB / 4.375 bytes = 58 Msam-
ples
●
Theoretical Maximum Waveform Length (no markers) = 256 MB / 4 bytes
= 64 Msamples
Hence, a memory size of 256 MB yields a maximum waveform length of 58 Msamples
if three markers are enabled. The maximum waveform length increases to 64 Msam-
ples, if the internal hardware markers are used, and the complete memory is available
for I/Q data.
The minimum length of a waveform is 512 samples. A waveform shorter than this value
is automatically repeated until it reaches the minimum length.
Using the Arbitrary Waveform Generator (ARB)