Multi-instrument setups
R&S
®
SMM100A
454
User Manual 1179.1341.02 ─ 05
A baseband signal with a sample rate f
smaple
< f
smaple, max
(i.e. smaller than the used
system clock) is interpolated, see
. The resulting modulation bandwidth
is calculated as
sample rate * 0.8
.
Estimating or defining the sample rate
The sample rate of the signal at the digital interface can be determined with one of the
following methods:
●
Estimated sample rate
Enable the instrument to evaluate the received I/Q data clock
●
User-defined sample rate
Provide both the external signal source and the receiving instrument with a com-
mon external reference signal and set the sample rate value.
Specifics of the analog I/Q interfaces
The R&S
SMM100A outputs the digitally modulated signal not only directly but also
converted to an analog I/Q baseband output signal. The R&S
SMM100A outputs the
analog baseband signal single ended or differential (non-inverted); an RF envelope
signal can be generated, too.
Differential output signal
The differential output provides symmetrical signals for differential inputs of DUTs with-
out the need of additional external electric network. To achieve an optimal and bal-
anced operating point of these inputs, ensure the correct adjustment of the used DC
voltage ("Bias") and the offset ("Offset") between inverting and non-inverting output.
Refer to the descriptions
for a description of the effect of
these parameters.
Maximum overall output voltage
The voltage of the analog output signals is defined as a combination of output voltage
of the I and Q signal components and an optional bias voltage. If the differential output
is used, an additional offset can be set, too. The values of these parameters are inter-
dependent so that the magnitude of the sum of output voltage and bias voltage must
not exceed 4V.
The following applies:
●
Single ended signal:
V
p
+ V
bias
≤
4
V
●
Differential signal:
0.5*V
p
+ |V
bias
| + 0.5*V
offset
≤
4
V
Where:
●
V
p
is the output voltage as set with the parameter
●
V
bias
is the bias voltage as set with the parameter
●
V
offset
is the offset between inverting and non-inverting output as set with the
Control and operation of external instruments
