Sketch Vin-Vout in MOS transistor

[anhnha]

Can you help me check my work and tell me what is the application of the circuit?

Homework Statement

Sketch Vout versus Vin as Vin varies from 0 to VDD. Identify important points.

Homework Equations

MOS transistor equations in triode and saturation modes.

The Attempt at a Solution

 

[rude man]

I'm not going to check your math but I can tell you that this configuration is known as the common-gate configuration, analogous to the common-base mode of a BJT.

EDIT: the purpose is to improve frequency response by eliminating the so-called "Miller effect". Put a small capacitance Cgd in the common-source configuration & you will see this. The price is a lower input impedance.

Adding Rf reduces the gain ∂Vout/∂Vin but it does linearize it somewhat (for low values of -Vin, or in cutoff mode, ∂Vout/∂Vin = R/Rf where R = Rd||Rf.