Keysight CXG, EXG, and MXG X-Series Signal Generators Service Guide 195
RF Assembly
A3 RF Assembly Overview
Amplitude Modulation (Option UNT)
The AM output of the Function Generator / Trigger Control section is used to
provide the modulating signal for analog amplitude modulation. This
modulating signal is amplified in the Automatic Level Control section and
summed with the ALC reference and temperature compensation DAC outputs.
This ultimately drives the ALC modulator diodes to provide the desired
amplitude modulation of the output signal.
Pulse Modulation (Option UNW)
For Pulse Modulation, ALC is only on for a short period within the pulse
duration. Outside this short period of time, ALC is in a holding state waiting for
the next pulse.
Microwave Instruments
While the majority of the ALC control circuitry is located on the A7 Micro-Deck
assembly for microwave instruments, they do use the Low Band and Het Band
modulator diodes on the A3 RF assembly for frequencies <3.2 GHz. They also
use the ALC detectors on the A3 RF assembly for Low Band and Het Band
below 2.0 GHz. For frequencies 2.0 GHz and higher the ALC detector is located
on the A7 Micro-Deck assembly.
Function Generator / Trigger Control Section
There are three main blocks in the Function Generator / Trigger Control
Section. They are:
— LF Function Generator
— Trigger Control
—Sweep Out Interface
There are a few adjustments related to the Function Generator / Trigger
Control section found in the performance verification and adjustment software
for these instruments, which will be covered later in this chapter.
LF Function Generator
Without option 303, Multifunction Generator, option UNT, AM, FM, Phase
Modulation, or option UNW, Narrow Pulse Modulation, the LF Function
Generator is not available for independent use.
The LF Function Generator has the ability to generate analog modulating
signals for amplitude modulation, frequency modulation, phase modulation,
and pulse modulation. It also has the ability to take externally generated
analog modulating signals through the rear panel EXT 1, EXT 2, and PULSE
inputs and route them to the internal analog modulators.
The LF Function Generator generates the 9 kHz to 5 MHz signal to the RF
Output section to drive the Op-Amp Band.
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