Agilent Technologies N5242A, Service Manual

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5-24 Service Guide N5242-90001
Theory of Operation PNA Series Microwave Network Analyzers
Receiver Group Operation N5242A
A12 SPAM Board (Analog Description)
The A12 SPAM board contains digital and analog circuitry. For digital descriptions, refer
to
“A12 SPAM Board (Digital Description)” on page 5-32 .
In this assembly, the IF signals (A, B, C, D, and R for 4-port models and A, B, R1, and R2
for 2-port models) from the A20 IF multiplexer board go through a gain stage where small
signals are amplified to ensure that they can be detected by the analog-to-digital converter
(ADC).
All input signals are sampled simultaneously by the ADCs, where they are converted to
digital form. The ADC conversions are triggered by timing signals from the digital signal
processor (DSP) in response to commands from the central processing unit (CPU). The
digitized data is processed into magnitude and phase data by the DSP and sent to the CPU
random access memory (RAM) by way of the peripheral component interconnect (PCI) bus.
The processed and formatted data is finally routed to the display, and to the
general-purpose interface bus (GPIB) for remote operation. Refer to
“Digital Processing
and Digital Control Group Operation” on page 5-29 for more information on signal
processing.