# Pass Transistor CMOS power dissipation

#### elettro2021

Joined Feb 8, 2022
14
Hello,I have following circuit

and I need to prove that this circuit has non-zero static dissipation.
Assume the inverter switches ideally at VDD/2, neglect body effect, channel length modulation and all parasitic capacitance.

Now When A=B= VDD, the voltage at node x is VX=VDD-VtN,but how can I prove analytically that there is no static power dissipation for inverter cmos? Because P=(Vdd^2)/Rp how can I compute equivalente resistance Rp for PMOS M2?

#### ericgibbs

Joined Jan 29, 2010
15,673
hi e2021,
As this is Homework we must see your best attempt at answering, we can then help.?
E

#### elettro2021

Joined Feb 8, 2022
14
In this case M2 works in saturation or linear region?

#### elettro2021

Joined Feb 8, 2022
14
I made my attempt to resolve it....any help to continue??

#### elettro2021

Joined Feb 8, 2022
14
excuse me.....text error Now When A=B= VDD, the voltage at node x is VX=VDD-VtN,but how can I prove analytically that there is no zero static power dissipation for inverter cmos?

#### elettro2021

Joined Feb 8, 2022
14
M2 PMOS works in velocity saturation
Rp=Vds/Idp=Vdsat/(k'p*(w/l)*Vdsat*(2.5-2.07-0.4)) and I neglet Vdsat/2
w/l=6 k'p=30*10^-6 Vdsat=1 V
Rp=185kOhm

Is it correct my way of thinking??

#### elettro2021

Joined Feb 8, 2022
14

#### DickCappels

Joined Aug 21, 2008
8,794
Are both transistors on at any time?

#### elettro2021

Joined Feb 8, 2022
14
No....the logic function performed by this circuit is a NAND gate... any help??

Last edited:

#### DickCappels

Joined Aug 21, 2008
8,794
What are the threshold voltages of M1 and M2?

#### elettro2021

Joined Feb 8, 2022
14
threshold voltages of M1 and M2 ....please view image.....Vtn=0.43 and Vtp=-0.4...

#### elettro2021

Joined Feb 8, 2022
14
any help????

#### DickCappels

Joined Aug 21, 2008
8,794
Let's call the threshold 0.4 V. The gates are There is 1.25V of forward bias between each transistor's gate and source, so there is conduction overlap during most of the transition on the input.

That's as far as I can go as I have not studied MOSFETs in depth. The fellow who was helping you is a moderator here and will in all likelihood be aware of where you are with your problem and back to help you.

#### ericgibbs

Joined Jan 29, 2010
15,673
Hi e2021,
If possible, I would have helped you, but unfortunately, your query is not in my area of expertise.

E

#### DickCappels

Joined Aug 21, 2008
8,794
:bump: