Imposed Biasing Problem

[Gilster]

Hi,

I've been stuck for hours and I was hoping anyone can help. I'm not even sure how to start the problem. Am I supposed to find the value of the resistor R or find different w/l values for the mosfets? How do I approach the problem? Any help is greatly appreciated. Thanks.

 

[tompham]

Hi Gllster

Assume all nmos in edge of saturation ---> Vds = Vdsat and let X = W/L, kn = UnCox

For M3: Vdd - Vss = I3*R3 + Vdsat3 (1)
X3 = 2*I3/kn * Vdsat3*Vdsat3 (2)
From (1) and (2) ---> X3

You can do same thing to find X1 and X2.

Now from relative of Mx with M1 or M2 or M3 in current mirror --> Ix/I1 = Xx/X1

And you can find value of R from equation: Vdd - Vss = Ix*R + Vdsx = Ix*R + Vgsx = Ix*R + Vtn + Vdsatx = Ix*R + Vtn + Vdsat1 = Ix*R + Vtn + Vdsat2 = Ix*R + Vtn + Vdsat3

(Note Vdsat1 = Vdsat2 = Vdsat3 and Vgs = Vtn + Vdsat)

Note Vdsatx = Vdsat1 = Vdsat2 = Vdsat3