NLDM (non-linear delay model)
Beginner
A small table that tells how slow a building block is, depending on what goes into it and how much it has to drive.
Novice
Liberty’s way of storing a cell’s delay: a small table whose rows are how quickly the input signal changes and whose columns are how much load the output drives. The tool reads between the entries.
Expert
Two-dimensional tables of delay and output transition, measured in circuit simulation at a grid of input-transition and load values. Tools interpolate inside the grid and extrapolate, less accurately, outside it. Advanced nodes add current-source models (CCS, ECSM), but synthesis runs well on NLDM.