5-28 Service Guide N5227-90001
Theory of Operation PNA Series Microwave Network Analyzers
Receiver Group Operation N5227A
A16 SPAM Board (Analog Description)
The A16 SPAM board contains digital and analog circuitry. For digital descriptions, refer to “A1 6 SPAM
Board (Digital Description)” on page 5-34.
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 A24 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 5-31
for more information on signal processing.
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