Keysight Technologies N5247B, Service Manual

Page: 196 / 566

5-26 Keysight N5247B Service Guide
Theory of Operation
Synthesized Source Group Operation
5-
A15 Version 7 Digital to Digital Synthesizer (DDS) Assembly (S/N
Prefixes
≥
6021 Only)
For instruments with s/n prefixes
≥
6021, there are three A15 Digital
Synthesizer (DDS) assemblies: N5240-60222 contains two DDS chips
(standard 2-port and an optional N5240-60102 containing a four DDS chip
assembly, is required for 4-port models and for adding a 3rd source (Option
XSB, requires Option 422 or Option 423).
The A15 Direct Digital Synthesizer (DDS) assembly uses an internally
generated 10 MHz reference signal that is derived from the 100 MHz OCXO
circuit (if present, this signal may be locked to an external reference).
The 100 MHz OCXO signal is coupled off to a divide-by-10 section and the
resulting 10 MHz synchronized clock-signal is output from the DDS carrier
board to the input of the A16 SPAM board (SPAM CLK) and to the rear panel
(REF OUT).
The DDS assembly’s carrier board’s also produces a 19.2 GHz signal that is
split and sent to each of the DDS Slugs to drive the LO, SRC1, SRC2, and SRC3
(SRC3 requires, Option XSB).
In bands 2 to 21, the DDS Slug’s output is used to produce the output
frequencies of 10 MHz to 6 GHz that is transmitted to the DDS assembly
multiplier section as listed in Table 5-2 on page 5-21 .
In bands 21–52, the DDS Slug’s signal is passed through a doubler circuit
where bands 21–24, 27–32, 35–43, and 47–52 are sent directly to the output
of the DDS assembly while bands 25–26, 33–34, and 44–46 are passed
through another doubler circuit then to the output of the DDS assembly to
produce the output frequencies listed in Table 5-2 on page 5-21 .
Refer to the NOTE notice on page 5-1 . The output of the A15 13.5 GHz DDS
assembly (the LO synthesizer section) is a frequency value higher than the
output of the source 1 and source 2 13.5 GHz synthesizer portions of the DDS
assembly. This is because the output of the A15 13.5 GHz synthesizer
assembly is routed through the A25 LO multiplier/amplifier 26.5 board to the
A27 and A28 mixer bricks where they are mixed with the test signals to
produce a 7.606 MHz IF signal for each of eight receivers (A–D and R1–R4).
Refer to “A27 and A28 Mixer Bricks” on page 5-53 for a more complete
description.