Solve PMOS Transistor Circuit: Vthreshold, Vgs, Vgt, Vds

[Maxwell]

I have a PMOS transistor circuit set up.

These are my parameters:

Vthreshold = -0.4 V
Vgs = -3 V

Vgt = Vgs - Vthreshold = -3 + 0.4 = -2.6 V

Vds = Vgs - Vthreshold = -2.6V

I'm trying to figure out what operating region this stupid thing is in. There are so many different ways of figuring this out, that it's getting very confusing -- it seems every source uses a different notation.

I know it's not in the Cutoff region, because Vgs < Vthreshold. However, since Vds and Vgt are the same, how do I decide if it is in Linear or Saturation region?

For linear: Vgs < Vthreshold and Vds > Vgt

For saturation: Vgs < Vthreshold and Vds < Vgt

This is really starting to bug me.

If I could figure out how to find Vgd -- that is, voltage from gate to drain, I might be able to figure something out. However, my Vin = 2V and the drain is connected to a variable resistor and then to ground, I think Vgd = 2V. But I don't think this is possible since it's a PMOS, so I'm ignoring that parameter for now.

Thank you.

 

[EvLer]

what is Vgt? never have come across this...
The voltages around MOSFET usually have this relation Vgs = Vgd + Vds. So, I don't think that you can get Vds the way you did.
To determine the region of operation you need to look at inequality of this sort: Vds ? (Vgs - Vtp)
However Vds is not given... so you'd either have to know extra parameters like Id, W/L or assume a value/region and then verify.

 

[piercas]

I understand your frustration with the different notations and methods used to determine the operating region of a PMOS transistor circuit. Let me try to clarify some of the confusion for you.

Firstly, Vgt is not a commonly used parameter for PMOS transistors. It is usually used for NMOS transistors, where it represents the voltage difference between the gate and the source. For PMOS transistors, we typically use Vtp (threshold voltage for PMOS) to determine the operating region.

In your case, Vds and Vgt are not the same. Vds represents the voltage difference between the drain and the source, while Vgt (or Vtp) represents the voltage difference between the gate and the source. In order to determine the operating region, we need to compare these voltages to the threshold voltage, Vtp.

In the case of a PMOS transistor, the operating regions are as follows:

1. Cutoff region: Vgs < Vtp
2. Triode/Linear region: Vgs > Vtp and Vds > Vgs - Vtp
3. Saturation region: Vgs > Vtp and Vds < Vgs - Vtp

Since Vgs = -3 V and Vtp = -0.4 V, we can see that the transistor is in the saturation region. Vds is less than Vgs - Vtp, which is equal to -2.6 V in this case.

As for Vgd, it is not a relevant parameter for PMOS transistors because the gate is connected to the source in a PMOS circuit. The voltage difference between the gate and the source will always be zero.

I hope this helps clarify the operating region of your PMOS transistor circuit. Keep in mind that different sources may use different notations, but the underlying principles remain the same.