A5 System Board - Keysight N9912A Service Manual

Theory of Operation
Measurement Group
Power Management Circuitry
The circuitry on the A4 RF board has five special sections that may be powered
down for the purpose of power management. These sections may be
selectively powered down (via "load switching") when not required for the
current operating mode of the analyzer.
The sections that may be selectively powered down are:
— Source—most of the source synthesizer circuitry
— LO—most of the LO synthesizer circuitry
— SA—most of the first, second, and third converter circuitry
— Reflectometer—put into a low power state
— High-Band Pre-amp—high band section of the pre-amp turned off
The load switching for the Source, LO, and SA sections is accomplished on the
A5 system board via the Analog Power Supply Load Switching circuitry.
The load switching for the Reflectometer and High-Band Preamp is
accomplished on the A4 RF board.
Other Circuitry
The CPLD (Complex Programmable Logic Device) communicates wit5h the
FPGA on the A5 system board via Serial Bus [A]. It provides the digital control
for the functions on the A4 RF board. It also reads the VCO unlock signals.
Serial Bus [B] allows the System Monitor on the A5 system board to read two
temperature sensors and the ID EPROM for the A4 RF board.
RF1 temperature sensor (NA Temp Sensor) is near the RF OUT connector on
the side of the A4 RF board that is away from the A5 system board. This
temperature sensor is nearest the NA circuitry.
RF2 temperature sensor (SA Temp Sensor) is located through the A4 RF board
from FL1202 on the A5 system board side of the A4 RF board. This temperature
sensor is nearest the SA circuitry.

A5 System Board

The A5 system board controls all of the functions of the analyzer and digitizes
the RF IF signal from the A4 RF board.
The A6 SOM (System on Module) board is mounted directly on the A5 system
board.
All external connections for the analyzer come through the A5 system board
except for the RF IN and RF OUT ports.
The A5 system board also controls the power switching and power
management.
5-10 Keysight N9912A Service Guide