Rohde & Schwarz FSP3 - Processing of Measured Data - Detector Board; Fig. 3-6 Processing of Measured Data

R&S FSP Instrument Design and Function Description
1164.4556.82 3.7 E-1
Processing of Measured Data - Detector Board
The following sections explain the signal and data paths required for result processing in the various
operating modes:
A
D
12
ZF / Video
32 MHz
Digital
Do
w
n
Converter
Detector
Controller
Noise-Filter
Detectors
Counter
Magnitude
Phase
Fast
Measure
R
A
M
Trigger
S
w
eep Control
PCI Interface
PCI Bus to Host
Control
R
A
M
D
A
DDC DCON
Video
Fig. 3-6 Processing of measured data
Spectrum Analysis Using an RBW >100 kHz
In this mode, only the analog resolution filters on the IF filter board are used. The signal applied to the
A/D converter via the input IF/Video is therefore already a log video signal. The signal is continuously
sampled at 32 MHz in the ADC and digitized.
The signal path is now directly routed to DCON.
In the DCON, the data are directly applied to the noise filter. The noise filter is used to limit the video
bandwidth or to average the noise content. The signal path is routed to the detector logic where the
results are processed, i.e. peak max, peak min, sample, average and RMS values as well as the
number of measured values and quasi-peak values are determined.
With measurement data rates > 1 MHz, detector data have to be stored in the measurement RAM
because online storage is no longer possible at these high speeds. Upon completion of the sweep, the
sweep data are read by the host from the measurement RAM, processed and displayed.
Spectrum Analysis Using an RBW  100 kHz
In this operating mode, the resolution bandwidths are generated digitally with the aid of the DDC. This IC
first mixes its input IF into the baseband using an NCO, and then filters the obtained I/Q signal via an
HDF (high decimation filter) and an FIR (finite impulse response) stage. At the end of the DDC
processing chain, the I/Q signal in the CORDIC block is split into magnitude and phase. For signal
processing in the DDF, the IF signal from the IF filter module directly represents the linear IF.
For a conventional log display of the analyzed spectrum, the magnitude data is logarithmized in the
DCON between the DDC interface and the noise filter.
Further signal processing on the detector board is identical to that of operating mode RBW > 100 kHz.