The same physics shows up differently depending on whether the FPGA is driving a wide bus, memory, clocks, mixed-signal circuitry, serial links, or slow control I/O.
SSN: worst case. Many same-bank outputs switch on one edge; intermittent bit errors, false input transitions, corrupted strobes, or bank-wide noise.
Crosstalk: adjacent bus lines inject pattern-dependent errors; physical bit order matters.
SSN: bursts cause supply bounce; DQS/clock/strobe margin shrinks; failures vary with voltage, temperature, and traffic.
Crosstalk: DQ-to-DQ, DQ-to-DQS, or clock-to-data coupling causes eye closure or lane-specific errors.
SSN: a quiet input near a noisy bank sees false threshold crossings during large switching events.
Crosstalk: nearby fast edges inject narrow pulses into high-impedance or asynchronous victims.
SSN: output bursts modulate PLL jitter, ADC code noise, DAC spurs, or analog ground references.
Crosstalk: specific digital nets couple into analog traces; spur frequency tracks aggressor activity.
SSN: usually lower than wide LVCMOS, but supply noise can still add jitter.
Crosstalk: pair-to-pair or connector/cable coupling appears as eye closure, deterministic jitter, or lane-specific BER.
SSN: rare until many outputs switch loads together or thresholds are marginal.
Crosstalk: long parallel cables and high-impedance inputs pick up pulses; termination/filtering/spacing usually helps.
Sources: Microchip AN4848; AMD/Xilinx XAPP689; Altium, “Is it Simultaneous Switching Noise or Crosstalk?”; UBC, “Crosstalk-Aware Routing in FPGAs”; Design & Reuse, “How to reduce simultaneous switching output noise with a stand-alone SerDes.”