- #1

Granger

- 168

- 7

## Homework Statement

I have the following circuit with MOSFET (cascode amplifier).

[![enter image description here][1]][1] [1]: https://i.stack.imgur.com/BAqQh.png

Information given:

##V_t=1V##

##I_1=20\mu A##

##k=10 \mu AV^{-2}##

Knowing that ##V_b## is 5V determine the minimum value of the output voltage so that both transistors are saturated.

## Homework Equations

3. The Attempt at a Solution [/B]

I'm kinda confused on how to proceed on this.

First of all, don't we need VDD? How to relate VB with this?

I started by assuming both transistors had the current I_1 (I assume this is correct).

Then I used the MOSFET equation for saturation ##i_D=k(v_ {GS}-Vt)^2## to determine ##v_{GS}## in both transistors. obtaining 2.4 V.

Then I applied the boundary condition for saturation ##v_{DS}=v_{GS}-V_t## and so obtained for both transistors ##v_{DS}=1.4V##

So the minimum value of ##v_O## is 2.8V.

This is incorrect, the answer should be 4V. I'm really not understanding how to proceed... Can someone give me an hint on how to do this? Thanks!

#### Attachments

Last edited by a moderator: