# Pspice related Homework

#### MarsG

Joined Sep 12, 2015
24
I need help in figuring out this Pspice related homework assignment, I am first to solve the CS amplifier by hand ( calculate Rout, Rin, and voltage gain) then compare it to the Pspice sim, im not sure how to get the by hand calculations since im missing a few things like ID which is needed in order to obtain r0, im also not sure how to create the Pspice sim, Does Vsig=Vsin?
I attached below the question and the hand drawn circuit with the values.

#### WBahn

Joined Mar 31, 2012
28,514
What's preventing you from finding ID?

#### MarsG

Joined Sep 12, 2015
24
What's preventing you from finding ID?
Not knowing VD, VD=VDD-ID*RD = -(VD+VDD/RD)= ID, two unknowns

#### MarsG

Joined Sep 12, 2015
24
I got Rin = 120k and for Vgs = (R2/R1+R2)*VDD = 3V, i think i can get Id Now since VGS= VG-VS

#### MarsG

Joined Sep 12, 2015
24

#### WBahn

Joined Mar 31, 2012
28,514
I got Rin = 120k and for Vgs = (R2/R1+R2)*VDD = 3V, i think i can get Id Now since VGS= VG-VS
Which resistor is R1 and which is R2?

The expression (R2/R1+R2) is not dimensionally consistent. R2/R1 is dimensionless and you then try to add R2, a resistance, to a dimensionless number.

How are you getting that Vgs is 3V. Even if your equation were presented correctly, it would not yield 3V nor would it yield Vgs.

#### MarsG

Joined Sep 12, 2015
24
R2= 300k and R1 is 200k, the resistances in parallel at gate

#### WBahn

Joined Mar 31, 2012
28,514
How are those resistances in parallel (remember, you looking for the DC operating point at this stage)?

How do you get 3V?

Why is the 300 kΩ resistor in the numerator?

NOTE: On your first diagram it looks like your supply voltage is 15 V, not +5 V. Probably just an imaging artifact.