Propagation delay isn't purely about distance: it's about the time needed for the output to settle in reaction to inputs. That includes capacitive delays: containers of electrons having to fill up.
Say we are talking about some gate with a 250 picosecond propagation delay.
But light can travel 7.5 cm in that time; way, way larger than the chip on which that gate is found, let alone that gate itself. That tells you that the bottleneck in the gate isn't caused by the input-to-output distance, which is tiny.
Say we are talking about some gate with a 250 picosecond propagation delay.
But light can travel 7.5 cm in that time; way, way larger than the chip on which that gate is found, let alone that gate itself. That tells you that the bottleneck in the gate isn't caused by the input-to-output distance, which is tiny.