Agilent Technologies N5230A, Service Manual, Page: 126 / 262

5-6 Service Guide N5230-90014
Theory of Operation PNA Series Microwave Network Analyzers
Synthesized Source Group Operation N5230A
Synthesized Source Group Operation
The source group produces a stable output signal by phase locking a synthesized
voltage-controlled oscillator (VCO). Refer to
Table 5-2 on page 5-8 for the full frequency
range of the source. The outputs at the front panel test ports are swept, stepped or CW
signals. Maximum leveled output powers are listed in
Table 5-1 on page 5-4 . For a simple
block diagram of the source group, refer to Figure 5-2 .
In this section the following are described:
• Basic Operation
• Frequency Offset Operation (Option 080)
• A7 and A9 Fractional-N Synthesizer Boards
• A6 and A8 Multiplier Boards
• A19 Switch/Splitter/Leveler/Amplifier/Multiplier (SSLAM)
• A10 Frequency Reference Board (including rear-panel interconnects)
• A16 Test Set Motherboard (including rear-panel interconnects)
Basic Operation
Table 5-2 on page 5-8 lists the L.O. harmonic number, the synthesizer frequencies (A7 and
A9), and the main source frequency (A19) within the analyzer for each band. This table is
referred to throughout this chapter and also appears on the overall block diagram at the
end of
Chapter 4, “Troubleshooting.”
The A10 frequency reference board produces a constant phase locked reference signal of
5 MHz that is sent to the A7 and A9 fractional-N synthesizer boards.
The A7 fractional-N synthesizer board produces an LO signal that is sent through the A6
multiplier to the A20 mixer brick. The frequency is synthesized such that the mixing
product of this LO signal with the test signal output is a constant 7.66 MHz when the spur
avoidance function is OFF. With the spur avoidance function ON, this IF signal is set to
various values between 1 and 12 MHz, at source frequencies below 40 MHz, to avoid
generating spurious responses. This IF signal is sent to the A5 SPAM board for digital
processing.
The A9 fractional-N synthesizer board produces an incident signal that is sent through the
A8 multiplier board and then the A19 SSLAM to the front panel outputs. A portion of this
signal is either split (R1 and R2 channels) or coupled (A and B channels) off and sent to the
A20 mixer brick where it is mixed with the LO signal from the A6 multiplier board to
produce the 7.66 MHz IF signal.
The A7 and A9 fractional-N synthesizer boards each contain their own phase lock circuitry.
The A7 board is used to phase lock the LO signal while the A9 board is used to phase lock
the test signal. This makes it possible for the LO signal to be tuned to a different frequency
than the test signal, which is necessary since the LO signal is normally 7.66 MHz higher
than the test signal. Since the A7 and A9 fractional-N synthesizer boards each receive
their 5 MHz input reference signal from the exact same source, their outputs remain
in-phase even though they are at different frequencies.