Rohde & Schwarz R&S SMU200A, Руководство по обслуживанию

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Instrument Design and Function Description R&S SMU200A
1007.9845.82 3.4 E-6
Option Low Phase Noise
The option B22 provides two high quality quartz reference oscillators, working on 10 MHz and 100 MHz.
The 100 MHz oscillator is synchronised to the 10 MHz oscillator or, with reference set to external, to a
40 MHz signal from the SSYN module.
The 100 MHz signal is fed to the standard synthesis, where it replaces the step frequency to get a
cleaner spectrum. The thereby missing frequency resolution is replaced by the resolution of the DDS.
To generate a clean 1200 MHz LO signal for the output module, the 100 MHz signal is multiplied by
four, filtered, tripled and filtered again.
To provide the clock signal for the module DAC-board it is fractional divided to 12.8 MHz.
IQ Output Module 3GHz IQOP3
The module consists of two submodules, the Level Control Module (LCM) and the RF Module (RFM).
Level Control Module LCM
The LCM consists of the following functional units:
•
Baseband processing with switchover matrix, adjustable voltage sources, IQ swap switch, 3 dB
attenuator and imbalance setting for the I/Q modulator
•
Baseband power meter
•
Digital gain and level control with DSP
•
LF AM, pulse and Levatt matrix
Baseband Processing
The LCM is used to select and process baseband signals for the I/Q modulator. Two different baseband
inputs of the module can be selected, one for differential input signals with a restricted input frequency
range from internal sources and one that is an asymmetrical input for externally supplied signals. In
addition, the Q channel can also be switched to the LF AM input at a narrower bandwidth. To adjust the
module and I/Q modulator on the RFM, the module input can also be switched over to adjustable
voltage sources or to ground. The polarity of the I baseband signal can be inverted. An attenuator with
four stages in 3 dB steps can be used to raise or lower the baseband level for optimal balance of the I/Q
modulator. High-resolution gain control can be used to set the baseband level of the I and Q signals in a
range of approx 1.5 dB. To create the broadband AM, a DC voltage can be added to the I signal.
Baseband Power Meter
The baseband power is the sum of the squares of the I and Q input signals situated orthogonally to one
another. The baseband power meter squares the I and Q signals. Input offsets are compensated for by
additive, adjustable DC voltages (DACs). The squared signal I
2
is scaled in such a manner as to
compensate for the different steepnesses of the two squaring devices. The sum of the squared signals
is determined, and a DC voltage for reducing the output offset is added. The steepness scaling and the
output offset can be adjusted via DACs.
Digital Gain and Level Control with DSP
A digital control on the LCM is used to control the gain or the output level of the IQOP3 RFM and
IQOP6. The control consists of a digital signal processor, two ADCs with anti-aliasing filters and a DAC
for controlling the gain control elements on the IQOP3 RFM or IQOP6.