R&S SMJ100A, Руководство по эксплуатации, Страница: 386 / 874

Instrument Function
R&S
®
SMJ100A
370 Operating Manual 1403.7458.32 ─ 14
●
Const I/Q Test Signal: Continuous test signal with constant IQ and constant Clock
Frequency of 10 KHz. The values for each I and Q components are selectable but
constant. They are defined as a decimal number, which is decimal-to-binary con-
verted internally. The signal is provided as a 16-bit wide digital signal for both I and
Q channels.
Converted to analog, the signal is output directly at the BNC connectors I and Q
outputs of the instrument.
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 5-26 depicts the stages involved in the processing and resampling of a
waveform in the ARB.
Figure 5-26: Processing of the waveform files in the ARB
The R&S SMJ uses a 100 MHz system clock and a sample rate of 100 MSamples/s.
Impact of the Resampling Lowpass Filter
As illustrated on the Figure 5-26 , the lowpass filter in the resampling stage is a distor-
tion-free for signals with the following maximum baseband bandwidth:
BasebandBandwidth
max
, MHz = 0.31 x f
input
.
An externally created waveform file have 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 than calculated as follow:
f
input
≥
BasebandBandwidth / 0.31
A modulation signal with a sample rate f
input
= 100 MHz is passed directly to the digital-
to-analog converter (DAC), i.e. the resampling unit is bypassed. After the DAC, this
signal features a
RFBandwidth
max
= 80 MHz .
Impact of the Oversampling Factor
Waveforms generated by the R&S WinIQSIM2 software can be optimized by choosing
a suitable integer oversampling factor.
Baseband Signal - Baseband Block