Keysight N5227A Service Manual page 150

Theory of Operation
Digital Processing and Digital Control Group Operation
• A16 SPAM Board (Digital Description)
• A21 CPU Board (including rear-panel interconnects)
• A55 Hard Disk Drive
A16 SPAM Board (Digital Description)
The A16 SPAM board contains digital and analog circuitry. For analog descriptions, refer to
Board (Analog Description)" on page
The digital signal processor (DSP) receives digitized data from the digital circuitry of the A16 SPAM board. It
computes discrete Fourier transforms to extract the complex phase and magnitude data from the analog IF
signal. The resulting raw data is written into the main random access memory (RAM). The data taking
sequence is triggered either externally from the rear panel or by firmware on the A21 CPU board.
A21 CPU Board
The A21 CPU board contains the circuitry to control the operation of the analyzer. Some of the components
include the central processing unit (CPU), memory (EEPROM, ROM, RAM), bus lines to other board
assemblies, and connections to the rear panel. Some of the main components are described next:
• CPU
• Main RAM
• Rear Panel Interconnects
CPU . The central processing unit (CPU) is a microprocessor that maintains digital control over the entire
instrument through the instrument bus. The CPU receives external control information from the keypad, any
USB device, LAN or GPIB, and performs processing and formatting operations on the raw data in the main
RAM. It controls the DSP, the video processor, and the interconnect port interfaces. In addition, when the
analyzer is in the system controller mode, the CPU controls peripheral devices through the peripheral port
interfaces.
Front panel settings are stored in SRAM, with a battery providing at least five years of backup storage when
external power is off.
Main RAM . The main random access memory (RAM) is shared memory for the CPU and the DSP. It stores
the raw data received from the DSP while additional calculations are performed on it by the CPU. The CPU
reads the resulting formatted data from the main RAM, converts it to a user-definable display format, and
writes this to the video processor for display.
5-34
5-28.
PNA Series Microwave Network Analyzers
"A16 SPAM
Service Guide N5227-90001
N5227A