Agilent Technologies E4440A, Service Manual

Page: 118 / 436

118 Chapter 5
Troubleshooting the Synthesizer Section
A11 Reference Assembly Description
A11 Reference Assembly Description
Purpose. The A11 reference assembly provides a phase locked 10 MHz
signal to other boards and assemblies in the instrument. The 10 MHz
reference is phase locked either to an internal reference source or to an
externally applied signal. Any external signal between 1 MHz and
30 MHz can be selected by the user to phase lock the 10 MHz reference
signal.
Signal Path . The 10 MHz signal is routed to the A12 synthesizer
assembly, the A8 analog IF assembly, the A26 CPU assembly, the A13
front end driver board, the option slots on the A25 motherboard, and
the rear panel 10 MHz output connector. In addition, a 50 MHz signal
and a 300 MHz signal are routed to the A10 3rd converter assembly.
The 50 MHz signal is used for calibration purposes, and is switched on
when amplitude calibration is performed. The 300 MHz signal is used
as a second LO for the 3rd Converter assembly, and is always active.
The reference assembly utilizes a phase-lock loop which provides
stabilization for all the internal reference oscillators used throughout
the instrument.
The reference assembly performs the following function:
• phase locks the 100 MHz VCXO to, either, an internal 10 MHz
frequency reference, or to an external standard, user selectable
between 1 MHz and 30 MHz.
• provides a phase-locked 300 MHz (100 MHz
×
3) 3rd LO signal to the
A10 3rd Converter assembly.
• provides a phase-locked 600 MHz (100 MHz
×
6) signal to the A9 2nd
LO assembly.
• provides a 600 MHz (100 MHz
×
6) signal to the A12 Synthesizer
assembly.
• provides the reference unlock detector which, through the A26 CPU
assembly, warns the user that the reference lock loop is unlocked.
• provides a phase-locked 50 MHz (100 MHz
÷
2) internal calibrator
signal to the A10 3rd Converter assembly.
• provides the 10 MHz phase-locked reference for various assemblies
in the instrument.