Rohde & Schwarz R&S SMU200A, Руководство по обслуживанию

Страница: 128 / 294

R&S SMU200A Instrument Design and Function Description
1007.9845.82 3.1 E-6
3 Repair
This chapter describes the design of the R&S SMU, measures for tracing errors down to module level
and, in particular, the replacement of modules. Options are denominated without headers, so option
B102 means R&S SMU-B102.
Instrument Design and Function Description
A detailed schematic of the Vector Signal Generator design is presented in the block diagrams (see
chapter 5). The following functional description of the instrument refers to the block diagram.
RF-Section
Standard Synthesis Module SSYN
The Standard Synthesis (SSYN) module generates a frequency range from 200 MHz to 3025 MHz
(extended divider range starting at 500 kHz) with an internal resolution of approx. 2
µ
Hz. The actual
frequency synthesis generates the frequency band from 731 MHz to 1512.5 MHz. All further output
frequencies are generated by frequency doubling or frequency division. In addition, the module contains
the 10 MHz reference frequency as well as a fixed frequency oscillator at 1040 MHz that is
synchronized to the reference. Its output signal is used to generate the lower frequency band down to
100 kHz (by down-conversion) on the IQOP3 module.
The SSYN module supplies additional fixed frequencies obtained from the 1040 MHz reference by
division, and these serve as reference signals for other modules (DAC IF).
The individual function modules are described below.
Reference Loop
The Reference Loop submodule contains a high-quality, 1040 MHz ceramic resonator oscillator. The
oscillator is set to a stable reference frequency in a control loop with a frequency divider in the reverse
path. The control bandwidth can be set in two stages. The reference frequency can be the 10 MHz
OCXO located on the board (internal reference mode), an externally applied reference frequency
(EXTREF_IN) of 5 MHz, 10 MHz or 13 MHz (external reference mode).
The 1040 MHz reference signal is distributed to the individual modules of the synthesizer via several
power splitters and buffer amplifiers.
A variable frequency (REFVAR) is derived from the CRO 1040 MHz via a programmable divider. This
frequency is used either by the DAC IF board as a reference (12.8 MHz).
The oscillator frequency of 1040 MHz is required as a reference frequency for the other function
modules of the synthesizer and is also available to the IQOP3 for down-conversion (REF 1040). The
output level for the IQOP3 is kept constant by a level control.