What will happen if we swap the transistors of an inverter?

[Narveer]

In a simple inverter circuit, if the PMOS in the Pull-Up Network is
replaced by an NMOS and if the NMOS in the Pull-Down Network is
replaced by a PMOS transistor, will the design work as an non-
inverting buffer? Justify your answer.

[sonal aggarwal]

i think if we swap the pullup and pull down transistors in cmos inverter then it no longer perform the inverting function.it simply becomes the buffer.

[sonal aggarwal]

if we apply 1 input to nmos pullup transistor it connects vdd rail to output and hence we get 1 output.so its acts like buffer.

[Narveer]

If we swap the transistors of an inverter that means NMOS will acts as
pull-up transistor and PMOS acts as pull-down.

So
1. when input is HIGH then PMOS is in cut-off region and NMOS pull-up
output to HIGH state. But output voltage will Vtn( i.e threshold
voltage for NMOS) less than VDD. NMOS is BAD-1 switch.

2. When input is LOW then NMOS is in cut-off region and PMOS pull-down
output to LOW state. But output voltage will Vtp( i.e. threshold
voltage for PMOS) high than VSS. PMOS is BAD-0 switch.

So we have less output voltage swing and less noise margins.

Nmh(Noise margin in HIGH state)= Voh-Vih
Mml(Noise margin in LOW state)= Vil-Vol

Voh= Maximum output voltage available in high state
Vih= Minimum input that can be considered as high
Vil= Maximum input voltage that can be considered as low
Vol= Minimum output voltage available in low state

On Mar 8, 4:06 pm, sonal aggarwal <sonal.aggarwa...@gmail.com> wrote:
> On Tue, Mar 8, 2011 at 2:52 PM, sonal aggarwal

> <sonal.aggarwa...@gmail.com>wrote: