Hi, I am making a current mirror for one of my classes using NMOS transistors. The required reference, Id, current is roughly 1mA, and the desired load current is 100μA. Basically, in order to lower the current to the load I need to add a resistor going from the source of the second MOSFET to ground. I have attached a schematic of the design. Here is the work I have done so far:
MOSFET parameters: Kn = 111e-6, W/L = 3, Vt = 2 V
since 1mA reference current(Id) is desired, and we know that N1 is in saturation,
Id1 = (1/2)*(Kn)*(W/L)*(Vgs - Vt)^2
plugging in our values
1mA = (1/2)*(111e-6)*(3)*(Vgs - 2)^2
Vgs = 4.582 V
therefore the resistor, Rd:
Rd = (Vdd - Vgs) / Id = (12 V - 4.852 V) / (0.001) = 7.4kΩ
I know that my desired current, Is, is 100μA and is one tenth of the reference current, Id:
Is = Id / 10
I am having trouble calculating a value for Rs to get 100uA. Is there some way I should be manipulating the Id equation that I used above? Or should I be using simple voltage division and ohms law? Thanks for any help.
Brent
MOSFET parameters: Kn = 111e-6, W/L = 3, Vt = 2 V
since 1mA reference current(Id) is desired, and we know that N1 is in saturation,
Id1 = (1/2)*(Kn)*(W/L)*(Vgs - Vt)^2
plugging in our values
1mA = (1/2)*(111e-6)*(3)*(Vgs - 2)^2
Vgs = 4.582 V
therefore the resistor, Rd:
Rd = (Vdd - Vgs) / Id = (12 V - 4.852 V) / (0.001) = 7.4kΩ
I know that my desired current, Is, is 100μA and is one tenth of the reference current, Id:
Is = Id / 10
I am having trouble calculating a value for Rs to get 100uA. Is there some way I should be manipulating the Id equation that I used above? Or should I be using simple voltage division and ohms law? Thanks for any help.
Brent
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