# CMOS inverter with gate of PMOS transistor always grounded

If there is a CMOS inverter such that the gate of the PMOS transistor is always attached to the ground and the input voltage is only applied to the gate of NMOS, then how would the inverter behave, as in: Will it be similar to a NMOS inverter with a resistor connected between its source and Vdd supply?

I need to calculate the Vout for Vin =0 and Vin=2.5 volts and the switching voltage ( where Vin = Vout); thus I would like to find the equations characterizing the behaviour of the inverter.

So, for any Vin, the PMOS is always saturated and it can be replaced by an resistor of resistance same as ON resistance of the PMOS and the current flowing throught it would always be the saturated current. Please tell me if my approach is correct or if not, how should I tackle this problem?

To clarify, the devices are all short channel and channel length modulation is ignored.

Here is a schematic:

• If you provide a link to the schematic we can add it in for you. Commented Sep 9, 2012 at 8:29
• I put the schematic on google plus .... heres the link : plus.google.com/u/0/photos/104893953340544861875/albums/… thanks a lot for your help Commented Sep 9, 2012 at 8:33
• any help guys .... Commented Sep 9, 2012 at 11:33
• Back in the days before CMOS logic became common, NMOS chips were designed in which the load for each logic gate was a depletion-mode PFET acting as a current source. But in that case, the PFET's gate was connected to its source. I'm having trouble imagining why you'd want to use an enhancement-mode PFET with its gate grounded, which would needlessly complicate the physical layout. Commented Sep 9, 2012 at 14:15
• Minor nit: I don't think NMOS chips used PFETs. I think you mean depletion-mode NFETs. I would expect that in CMOS unless one uses extra processing steps to control depletion-mode FET behavior a long and skinny PFET would make a better passive pull-up than would an NFET. Commented Nov 25, 2013 at 20:08