80 Keysight CXG, EXG, and MXG X-Series Signal Generators Service Guide
Self Test
Self Test Descriptions
503 FM DACs (Option UNT)
This test checks that the FM DACs are working. The output of each DAC is
connected directly to the ABUS. The test sets each FM DAC to output various
DC levels and measures the resultant voltage.
504 FM Attenuators (Option UNT)
This test checks that the FM attenuators are working. There are two sets of FM
attenuators: FracN and Sum. The inputs to the FM attenuators come directly
from the FM DACs while the output goes directly to their respective VCOs. The
testing is performed in CW mode and relies on the loops to maintain lock while
the FM voltages are applied. Prior to testing, the instrument frequency is set to
566.40625 MHz to allow the VCO frequencies to be close to midrange. This
puts the FracN frequency at 1500 MHz while the sum VCO frequency is at
1132.8125 MHz. The FM DAC is first set to the maximum value while the
appropriate attenuator is set. Since the VCO will maintain the same frequency,
this will cause the tuning voltage to shift in the opposite direction which is
measured. The FM DAC is then set to the minimum value and again the tuning
voltage is measured. The difference between the two voltages is then reported
back. While testing the FM DAC for the sum loop, the sum pretune DAC value
is manually shifted so that the loop maintains lock.
505 LF Out (Option UNT or 303)
This test checks that the LF Out DAC is working. The test sets the LF Out DAC
to output various DC levels and measures the resultant voltage.
506 External Modulation Inputs (Option UNT or UNW)
This test checks the two external modulation input circuits (EXT1 and EXT2).
Both are identical and include an ADC to digitize the analog signal. The digital
signals then go directly to the analog FPGA. The test uses the +1V (gain) and
ground (offset) cal signals. The test measures the output of the op-amp that
feeds to ADC as well as the digital number that the ADC generates.
507 Pulse Mod (Option UNW)
This test checks the pulse modulator. This test is performed in ALC open mode.
600 Attenuator Self Tests
The Attenuator Self Tests are designed to test the attenuator section of the A3
RF assembly. Since the attenuators are located after the ALC detector, RF
power through the attenuators cannot be tested.
601 Attenuator Voltages
This test checks the voltages used for the attenuator section.
602 LED Voltage (Model N5166B, N5171B, N5172B, N5181B, N5182B)
This test checks the voltage for the attenuator LEDs.
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