What is NLDM (Non-Linear Delay Model)?
From PDVerse STA Mentor Guide · pdVerse Mentor Guide
Short Answer
NLDM stands for Non-Linear Delay Model. It represents a cell's timing arc delay (and output transition) as a two-dimensional lookup table, indexed by the input slew coming into the cell and the output capacitive load the cell is driving.
Example
A sample delay table (in ps) looks like this, with input slew values 10/40/80 ps across one axis and load values 10/30/60 fF across the other: {22,38,61 / 29,46,70 / 38,57,84} Four such 2-D tables exist per timing arc: cell_rise, cell_fall, rise_transition, and fall_transition.
Why It Matters
Real transistor delay doesn't scale in a simple straight-line way with slew and load, it curves. NLDM captures that curved, non-linear behavior by simply measuring and storing delay at a grid of representative slew/load combinations, so the tool can interpolate between them instead of using an oversimplified formula.
Mentor Note — Common Mistake
Don't expect a single delay number per cell. NLDM delay is always a lookup keyed by two inputs at once (input slew and output load), and both the rising and falling cases each get their own table.
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