Differential Amplifier with Two stages

[jay_help]

Homework Statement

Hello everyone,
Here's my problem : I have to determine the bias voltages of the amplifier to ensure saturation of each transistor (Vb1, vb2 and vb3).

Relevant Equations

Vdd = 3.0V, Vinp = 1.5V, Vinn = 1.5V, Voutp = 1.5V, Voutn = 1.5V, Vds of transistor 1 = 0.4V).

What I tried to do :

First I tried to calculte vb1 :

Saturation => Vds > Vgs - vth
Vds > Vgs - vth
Vd - Vs > Vgs - vth
Vd= Vb1
Vb1 > Vgs - vth + Vs
Vs= Vss
Result : Vb1 > 0.4 - vth + Vs

I don't know if it's correct and don't know what to do for the two others.

 

[AvroArrow]

Can someone help me ? Thank you ! A:This is a common circuit used in analog design. It is usually combined with an resistor in series with the gate to provide a voltage divider bias. For Vb1, you have it right. Vgs must be greater than Vth and the source voltage (Vss), so Vb1 must be greater than Vgs-Vth + Vss. For Vb2, it is similar. Vds must be greater than Vgs-Vth, so Vb2 must be greater than Vgs - Vth + Vss. For Vb3, it is a bit different. Since Vds=Vgs, Vb3 must be equal to Vgs - Vth + Vss.