Rohde & Schwarz M3SR Series 4100, Service Manual, Page: 46 / 138

R&S M3SR Series 4100 HF Transceivers Synthesizer - Function
6124.9007.82.01 1.10
1.3.2.2 Synthesizer - Function
The Synthesizer generates 2 RF signals and reference frequencies for other modules:
¾ LO1: First Local Oscillator
¾ LO2: Second Local Oscillator
¾ 100K_REF: Reference signal for other modules (100 kHz sine wave)
¾ 10K_REF: Reference signal for other modules (10 kHz square wave)
All generated frequencies are synchronised by an internal 10 MHz OXCO or by an external 1, 5 or
10 MHz reference frequency.
Essentially, the Synthesizer contains five functional blocks (see Fig. 1.4):
¾ Control
¾ 10 MHz Loop
¾ LO2 LOOP
¾ Cleaning Loop
¾ LO1 Loop
The communication of the Synthesizer with the Radio Controller is performed via the RCB (Radio
Control Bus). Via this bus the FLASH circuit is programmed, frequency and RX/TX information are
written, interrupts are captured, calibration functions are enabled/disabled and ready information of the
Synthesizer are read.
Control
The control circuit controls the hardware of the Synthesizer and is made
up of
an FPGA, a CPLD and a
FLASH device to convert the RCB (Radio Control Bus) signals to different control lines on the board
needed in the other functional blocks. Among other tasks, the FPGA receives BCD coded RX or TX
frequency updates via the Radio Control Bus. This frequency information is converted to the binary RX
or TX frequency.
A pre-tune learning process (self calibration) is implemented. The automatic calibration circuit supports
in-system measurements and adjustments to obtain values for VCO pre-tuning and Loop-Gain-
Compensation without using a PC or similar. The determined values are stored in a FLASH memory.
Via the BIT ADC the output levels, power supply voltages and temperature are monitored permanently.
The 100 kHz sine wave and 10 kHz square wave signals are generated in the FPGA by frequency
divider.