A somewhat physical interpretation of can be
found, if the effective carrier velocity
used in the
compact models for the transconductance
is interpreted as
bias dependent group velocity. then describes the phase
information of this group velocity. This explains on one hand,
why the absolute values of are in the order of magnitude
of extracted delay times, on the other hand why a direct
interpretation as the delay time of the device is not
appropriate. On the other hand, typical delay times are extracted
from the inverse of
values for analog or from ring
oscillators for digital applications.