Help about CMOS input impedance

[sowmya005]

Hi friends,
I would like to know the calculation of the CMOS input impedance.
How is it completely capacitance load on the CMOS input ports?
Please help.

Thanks,
Sowmya

 

[strennor]

there is no DC path from gate to source,
so the low frequency gate input impedance is only capacitance

but at high frequency, there is impedance

 

[sowmya005]

Would u pl elaborate this in timing perspective?
In order to calculate the delay for cell made of CMOS transistors,
i read that the inputs to the CMOS cell present capacitive load only.
Why only capacitive load?