How to find CMOS capacitances?

[ramone]

Hello there... I have upload a picture of two chained cmos inverter using SCMOS rules. Can someone explain me how to find capacitances:
Cgd1
Cgd2
Cgate(NMOS at second inverter)
Cgate(PMOS at second inverter)

PLEASE HELP!!!

(image found at: https://obrazki.elektroda.pl/13_1157409570.JPG )

 

[darwiny]

Re: CMOS capacitances

HI,

For Cgd, it depends upon basing condition of the MOSFET (PMOS/NMOS)
When Vds < Vgs-Vt, you can assume Cgs = Cgd = 1/2 Cgtotal
Where Cgtotal = W*L*Cox
When Vds > Vgs-Vt, you can assume Cgs =0 and Cgd = 2/3 Cgtotal

May this can help!

Dar

 

[vijay_nag]

CMOS capacitances

check out the book by Sung-Mo Kang and Yusuf Leblebici. it has given a very good explanation to find out the capacitances.