# Common-source amplifier biased with a current mirror

#### Blythe

Joined Jun 22, 2020
3
Please set the each device's value[=RG1,RG2,RD,Vsig etc.) of common source amplifier biased with a current mirror shown in the figure meeting the following set of specifications.
*Note : MOSFET parameter Vth = 0.7V, kn = 20m, lambda = 0.01

I don't know how to get appropriate approach in this. Please some advice to me.

#### crutschow

Joined Mar 14, 2008
34,804
So, do you understand how a common-source amplifier works?

And where did you get those requirements?
"As low as possible" for he low -3dB frequency is not a spec and thus impossible to meet.

#### Blythe

Joined Jun 22, 2020
3
So, do you understand how a common-source amplifier works?

And where did you get those requirements?
"As low as possible" for he low -3dB frequency is not a spec and thus impossible to meet.
It's my assignment from university. The original problem i have to do is to design and demonstrate these specifications by using spice program. I'm able to solve some easy problems(Ex : obtaining Id when i'm given VDD, RD,RG1 and RG2) but it is abstruse for me to understand how can i approach the solution course.

#### WBahn

Joined Mar 31, 2012
30,286
If you were given the value of the current source I and the DC bias point of the gate, could you determine the small-signal voltage gain of the amplifier (without using SPICE)?

#### Blythe

Joined Jun 22, 2020
3
If you were given the value of the current source I and the DC bias point of the gate, could you determine the small-signal voltage gain of the amplifier (without using SPICE)?
I can do, maybe. I don't know what to calculate first because I don't have the value given at this point.

#### WBahn

Joined Mar 31, 2012
30,286
I can do, maybe. I don't know what to calculate first because I don't have the value given at this point.
Just reverse the calculations. You know what you want the gain to be, so figure out component values that will achieve it. Take your best shot to get started and show your work. If you truly have no idea how to start, then you are in the wrong course for where you are in your understanding and you need to take a step back and retake either this course (if you are at the end of it) or the course preceding it (if you are at the start). Otherwise you risk digging yourself a deeper and deeper hole.