Electronics - Digital Switching

A: Pick the wrong topology and the clock’s phase noise balloons with temperature, pushing the modem into intermittent loss of frame and a failed SAT. LVDS fanout buffers are designed for controlled differential swing, low additive jitter, and predictable behavior across telecom temperature ranges, even when input coupling details are fuzzy. CMOS single-ended parts look tempting but their threshold drift and ground bounce show up fast at 156 MHz. TTL with pull-ups turns trace impedance into timing uncertainty. ECL is fast, but the negative rail and power integrity risk are a commissioning trap with missing as-builts.

A: Miss this by an order of magnitude and the CPLD overheats during burn-in, delaying commissioning. The gate charge model gives P ≈ Q × V × f, so 25 nC × 3.3 V × 5 MHz lands near 0.4 W. The ‘only during edges’ intuition hides the fact that energy is lost every cycle. Treating charge as capacitance without checking units leads to fantasy numbers. Assuming tens of watts ignores that current pulses are brief, not continuous.

A: Assume the wrong polarity and you can hard-drive a shared bus, corrupting data and possibly cooking an IO during first power. Incomplete as-builts mean neither symbol nor net name gets blind trust. Tracing the signal path or probing the upstream logic output under known states resolves the ambiguity without energizing the bus fight. Assuming defaults or generic symbols is how latent errors slip through FAT.

A: Ignore the physics and you pass pre-compliance but fail again at the certified lab, blowing schedule. IEC 61000 emission limits exist to control RF energy generated by fast transitions. Series resistors tame dV/dt and dI/dt right where noise is born. Mains ferrites help conducted paths but don’t touch radiated board-level noise. Test setup tricks and thicker copper miss why the limit exists.