Hi,
I'm trying to design an amplifier with the design specifications shown in the first image of the link.
Now I wanted to try a single common source amplifier. We're directed to use a specific nmos within cadence. Nmos4
I performed the simulations also shown in the imgur link to obtain the following
Considering the gain required is 10. I was going start by choosing a Q point from the graphs shown in the imgur link.
I chose, (11.112mA,2) @ Vgs = 2 as my Q point. This provides a transconductance gm of 10.621 mS. As well as...
Early voltage Va = 20.2 volts ... Va = ro*Id = 1818*11.112mA = 20.20
Channel Length modulation lambda= 0.0495 ... lambda = 1/Va
conduction parameter Kn = 11.97 mA/V ... Kn = 2*Id/[(Vgs-Vt)^2(1+lambda*Vds)]
Additionally you can see from my Id vs Vgs graph that Vt is roughly .7 volts.
Since I chose a 4 resistor CS design, I was going to pick R1 = 300k Ohms and R2 = 200k Ohms. To calculate Rd I had planned on working backwards from this
-10 = -gm*(ro||RL||Rd)*(Rg/(Rsig+Rg) (Rs isnt necessary bc i had planned on including by pass cap in parallel with it)...Rg = R1||R2
as I know gm, ro,RL
Once I calculated Rd, I was going to back calculate the necessary Rs value to give the proper Vgs and Vds as they're both known.
I get a negative resistance for Rd, im assuming something is wrong with my simulations OR i simply dont have a large enough gm to get the desired amplification.
I was hoping someone could point out my mistake.