Why Do We Neglect Short Circuit Current When Calculating CMOS Inverter Delay?

[klen]

When calculating delay, like the fall time delay of the output, through an inverter with rc model of the transistors (assuming Cmos inverter) why do we neglect the short circuit current through the device and what are the assumptions.

Can anyone explain this?

 

[Baluncore]

By short circuit current I assume you are referring to the short period while both the upper and lower output drivers may be conducting at the same time. If it occurs, that short duration current is limited by the inductance and resistance of the path.

Any short circuit current is flowing through a potential divider comprising one complementary transistor pair. The signal is propagating perpendicular to the short circuit current and so is not effected. Any minor influence on the simple model will be taken into account by adjustment of the RC parameters.