hw3 due feb23

got current source I into the drain of a mosfet, to amplify, need q1 in saturation
1. Vgs>Vthresh -> Vov>0
2. Vds>Vgs-Vthresh -> Vds>Vov

solution: table 6.3 p550-552
gmRo = A0 = 2LVa'/Vov = 2*4e-7*20e6/0.25 ~~ 64V/V
Idsat = 1/2 * kn' * W/L*Vov*Vov -> W/L = 16 -> W=6.4e-6m

using a separate mosfet to provide a load for a current mirror in place of a resistor
only time you get amplification out of the q1/q2 combo is when both are in saturation
we use IC instead of discrete components because of power requirements and size requirements

analysis of figure 6.18
KVLs: Vo+V-Vdd = 0
V=Vsd2
Vo=Vdd-V=Vdd-Vsd2

note that Vsg3 = Vsg2
note Iref sets Vsg3 by current mirror
assume W/L is same for q2 and q3
q2/q3 must be in saturation always
point A occurs when q2 enters saturation
this A occurs at the voltage where V=Vsg2-|Vtp|
recall that Vov2=Vgs2-|Vtp|
point 1 occurs where Iref intersects the Vsg2 curve and Vsg2 is greater than Vov2 for q2 makes q2 in saturation
note: slope of Vsg2 curve is 1/Ro2 = delId2/delVsd2
must overlay fig6.18b onto c
transistor q2 is called active load for q1
note from fig b and the KVL: Vo = Vdd-Vsd2
then, when Vsd2=0 -> Vo = Vdd
when Vsd2=Vsg2-|Vtp| aka point A
Vo = Vdd-(Vsg2-|Vtp|)
and other A  translates to fig c point A, so between 0<=Vsd2<=Vdd-(Vsg2-|Vtp|), q2 will be in triode region
now from A on fig c at a slop of 1/Ro2 draw a line from A to the Id axis

for q1 to remain in saturation, point B must occur at Vob where Vob>=Vgs1-Vtn
then Vgs1 ranges between Via and Vib in order for q1 to remain saturated

the points on fig b can be computed as follows:
Voa = Vdd-(Vsg2-|Vtp|) = Vdd-Vov2
Vob = Vdd-(Vsg1-|Vtn|) = Vib-Vtn
Av = delVo/delVi = -(Voa-Vob)/(Vib-Via) = gmRo