What is input slew, and why does it change a cell's delay?
From PDVerse MMMC Interview Masterclass · pdVerse Mentor Series
Direct answer
Slew is how fast a signal transitions between logic levels — a sharp, fast edge versus a slow, lazy one. A slower input edge makes the receiving cell switch more gradually, which increases its own delay and the sharpness of its output edge.
Mentor explanation
Picture an inverter fed by a nice, crisp input transition versus the same inverter fed by a mushy, slow-rising input. In the second case, the inverter spends longer in its linear region before it fully switches, so its output also takes longer to respond and its own output edge comes out slower. That's why slew isn't just a side detail — it's one of the two main inputs (along with load) into every delay lookup in the library, and it also propagates forward, degrading the next stage's input slew too.
Example or conceptual chain
Slow input edge -> gradual switching -> higher cell delay and a slower output edge.
Key takeaways
- Slew is how fast a signal transitions between logic levels — a sharp, fast edge versus a slow, lazy one.
- A slower input edge makes the receiving cell switch more gradually, which increases its own delay and the sharpness of its output edge.
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