Rohde & Schwarz R&S SMU200A, Руководство по обслуживанию

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Instrument Design and Function Description R&S SMU200A
1007.9845.82 3.8 E-6
Overvoltage Protection (Option for SATT3)
By disconnecting the instrument output with a relay, the overvoltage protection prevents damage to the
instrument as a result of an impermissible external voltage being supplied at the output. The disconnect
threshold depends on the attenuator configuration. The voltage at the RF output is evaluated via limiter
diodes and RF detectors as well as logically linked comparators. If the trigger threshold at the
comparator input is exceeded, the RF relay at the output is switched off. If option high power is installed
too, the bypass relays are switched accordingly.
Electronic Attenuator 6 GHz SATT6C
The SATT6C module is an adjustable RF attenuator pad with integrated overvoltage protection. The
module has an RF input and RF output. The insertion loss of the module can be electronically set from
approx. 5 dB to 130 dB in steps of 5 dB. The switches used are CMOS switches. In the model
1400.3400.06, a relay path can be used to bypass the attenuator pad in order to decrease insertion
loss. This bypass is referred to as high-power path. The overvoltage protection is at the module output.
If RF powers exceeding 30 dBm are fed in on the RF output, a relay separates the RF output from the
adjustable attenuator pads. In this state, the module triggers a software interrupt and the firmware
generates an error message. Switching off the instrument also interrupts this connection and changes
the signal generator's RF output to high impedance, which protects the module.
Baseband Section
The baseband section is in the first compartment directly behind the front module controller. All
baseband modules (exceptions: Baseband inputs ) are addressed via the PCI bus. The signal (I and Q)
flows from front to rear; a point-to-point connection is implemented in each case. Each module receives
the data flow (I and Q , Path A and B for both) from the previous module, processes the data from case
to case and forwards the data to the next module. The modules must therefore fill slots 1D to 6D
starting from the rear, otherwise the data transfer would be interrupted.
Data Transfer
The sample clock of the whole baseband is 100 MHz. The data is multiplexed seven-fold at this clock
rate and transferred from module to module by means of differential LVDS transmission (as defined by
TIA644).
IQ Bridge
This is simply an auxiliary module. If a slot does not have a standard module, the auxiliary module is
used to feed the IQ data flow through this slot. This is necessary in the following case (see also
Table
3-1 Overview - module replacement , on page 3.46):
Option Baseband Input is fitted:
Since this option has a fixed slot assignment, the remaining free slots must each be fitted with an IQ
Bridge module up to the next baseband module.