188 Keysight CXG, EXG, and MXG X-Series Signal Generators Service Guide
RF Assembly
A3 RF Assembly Overview
Additionally, the Reference section in the MXG instruments provides the
following reference signals:
— 500 MHz to synthesizer offset phase lock loop
— 1 GHz to synthesizer mixer LO
The internal reference oscillator for all the MXG instruments, as well as the
EXG microwave instruments, is an OCXO, while the internal reference oscillator
for the CXG and EXG RF instruments is a TCXO.
All the reference signals generated by the Reference section are multiplied or
divided from a 100 MHz crystal oscillator that is phase locked to either the
internal 10 MHz reference oscillator or an external signal provided by the user.
There is also a detector to sense if there is an external reference signal present.
An external reference signal must be at a frequency of 10 MHz unless option
1ER, Flexible Reference Input, is installed. With option 1ER the external
reference signal can be between 1 MHz and 50 MHz, if FREQ, More, Reference
Oscillator, Ref Oscillator Ext Freq is set to match the frequency of the
reference signal.
There are several adjustments related to the Reference section found in the
performance verification and adjustment software for these instruments, which
will be covered later in this chapter.
There are a couple of error messages that the instrument could display that
relate to this section. They are:
— 512 Reference unlocked; There is a problem with the external reference
settings or connections. If reference is internal check Ref Oscillator Tune.
— 515 Reference Missing; Reference board: 10Mhz reference signal bad or
missing
If either of these is seen, see the “A3 RF Assembly Troubleshooting” section
later in this chapter.
Synthesizer Section
There are two different Synthesizer sections used in the four different A3 RF
assemblies. All the CXG and EXG instruments have a single phase lock loop
synthesizer, while all the MXG instruments have a triple phase lock loop
synthesizer. All the phase locked loops are ultimately locked to signals from
the reference section of the assembly.
The output frequency of the Synthesizer section has a range of 750 MHz to 1.5
GHz and is supplied to the Synthesizer Multiplier / Divider section. A times four
multiplier path of the Synthesizer Multiplier / Divider section returns a 3 to 6
GHz signal to the Synthesizer section as feedback for the phase lock loop of
the synthesizer output.
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