What is cell delay and why is max transition important?

o   Cell Delay:  the time it takes for a signal change at the input of a standard cell (like an AND gate, OR gate, flip-flop) to propagate and cause a corresponding change at its output. It's typically measured between the 50% voltage points of the input and output waveforms. Cell delay depends on:

o    The intrinsic characteristics of the cell's transistors.

o    The transition time (slew) of the input signal.

o    The capacitive load on the output pin (output capacitance).

o    Voltage and temperature conditions.

o   Why Max Transition is Important (Relation to Cell Delay):  

o    cell delays are not fixed values. They are highly dependent on how fast the input signal transitions.

o    Libraries contain cell delay (and output transition) as a function of input transition and output load.

o    If the actual input transition time exceeds the maximum value used during characterization (i.e., violates max_trans), the timing model becomes invalid, and the STA tool cannot accurately predict the cell's delay.