Keysight N5221A/22A Service Guide 5-23Theory of OperationReceiver Group OperationA12 SPAM Board (Analog Description)The A12 SPAM board contains digital and analog circuitry. For digitaldescriptions, refer to “A12 SPAM Board (Digital Description)” on page 5-29.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 again stage where small signals are amplified to ensure that they can bedetected by the analog-to-digital converter (ADC).All input signals are sampled simultaneously by the ADCs, where they areconverted to digital form. The ADC conversions are triggered by timing signalsfrom the digital signal processor (DSP) in response to commands from thecentral processing unit (CPU). The digitized data is processed into magnitudeand 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 thegeneral-purpose interface bus (GPIB) for remote operation. Refer to “DigitalProcessing and Digital Control Group Operation” on page 5-26 for moreinformation on signal processing.6 DCOM Digital ground7 PulseSyncIn Pulse generator synchronization trigger input (TTL)8 RFPulseModIn RF source pulse modulation drive input (TTL)9 DCOM Digital ground10 Pulse1Out Programmable pulse train output #1 (TTL)11 Pulse2Out Programmable pulse train output #2 (TTL)12 Pulse3Out Programmable pulse train output #3 (TTL)13 Pulse4Out Programmable pulse train output #4 (TTL)14 NC No connect15 DCOM Digital groundTable 5-4 PULSE I/O Connector Pin AssignmentsDB-15 Female ConnectorPin Name Description
