Single stage amplifier with current mirror biasing

[CKaiL]

Homework Statement

Homework Equations

I_D= kn (Vgs - Vth)^2

The Attempt at a Solution

I asked to find the current I _D , M2. [/B]

I think in order to solve this question I need to find Vgs but how do I do that?

R_C1 = 2k ohm
R = V_DD - Vgs / I _D ,M2

V_DD = 5V , and R = 2k ohm and I have 2 unknown variable. Vgs and I _D ,M2

I think i need to make use of this I_D= kn (Vgs - Vth)^2 to solve this question

 

[rude man]

Homework Statement

Homework Equations

I_D= kn (Vgs - Vth)^2

The Attempt at a Solution

I asked to find the current I _D , M2. [/B]

I think in order to solve this question I need to find Vgs but how do I do that?

R_C1 = 2k ohm
R = V_DD - Vgs / I _D ,M2

V_DD = 5V , and R = 2k ohm and I have 2 unknown variable. Vgs and I _D ,M2

I think i need to make use of this I_D= kn (Vgs - Vth)^2 to solve this question

Good idea! But you must first find I_D for M1. Combine your last equation with another expression for I_D summing currents at the drain.
Then, you assume M1 and M2 have identical I-V characteristics so knowing I_DM1 gives you I_DM2, and you're done.

 

[CKaiL]

Could I have more information why the characteristics are identical for M1 and M2? They only have the same value for Vth while their Kn is different by a factor of 2?

I forgot to mention that I D,M1 is also given as 2mA for this question so I D, M2 is also 2mA?

 

[rude man]

Could I have more information why the characteristics are identical for M1 and M2? They only have the same value for Vth while their Kn is different by a factor of 2?

I didn't see that, sorry.

I forgot to mention that I D,M1 is also given as 2mA for this question so I D, M2 is also 2mA?

No. For any MOSFET in the 'saturation' region with λ = 0, which this is since Vgs > Vth & Vds > Vgs - Vth),
I = k(Vgs - Vth)².
So, since k2 = 2k1, what is I,M2 if I,M1 = 2 mA?

 

[CKaiL]

Hi

So I find the value for Vgs by subbing in Vth and I D,M1. Once I gotten the value of Vgs , i sub this value into the equation to find i D,M2 with a k2? Am I correct?

 

[rude man]

Hi

So I find the value for Vgs by subbing in Vth and I D,M1. Once I gotten the value of Vgs , i sub this value into the equation to find i D,M2 with a k2? Am I correct?

No point in solving for Vgs. From my last post it should be obvious that I_M2 = 2I_M1. Solve for I_M1 as I discussed earlier.

 

[CKaiL]

Sinc k2 = 2k1 , I2 = 2I1. I2 = 4mA?

 

[CKaiL]

I have another question for this. I am asked to find the small signal parameter of the 2 MOSFET .
The formula are
Output resistance in the small signal equivalent circuit of a MOSFET operating in the saturation region is given as R₀ = 1 /(channel length modulation * Current I_D)

I have I_D value for both 1_D M1 and 1_D M2 but in this question , channel length modulation for both are equal to 0
when you sub in these value , you will get an error.

 

[rude man]

Sinc k2 = 2k1 , I2 = 2I1. I2 = 4mA?

Good guess!

 

[rude man]

I have another question for this. I am asked to find the small signal parameter of the 2 MOSFET .
The formula are
Output resistance in the small signal equivalent circuit of a MOSFET operating in the saturation region is given as R₀ = 1 /(channel length modulation * Current I_D)

I have I_D value for both 1_D M1 and 1_D M2 but in this question , channel length modulation for both are equal to 0
when you sub in these value , you will get an error.

Suppose the channel modulation was a very small number but not zero - what would be the output resistance then?

 

[CKaiL]

hmm good guess meaning is ID , M2 = 4mA correct or wrong?

For channel length modulation
In the picture it says that the channel length modulation is equal to 0 for channel length modulation M1 and channel length modulation M2.

 

[CKaiL]

I would also like to check if this is a configuration of a Common source with source degeneration single stage amlifer?

 

[rude man]

hmm good guess meaning is ID , M2 = 4mA correct or wrong?
Correct.

For channel length modulation
In the picture it says that the channel length modulation is equal to 0 for channel length modulation M1 and channel length modulation M2.

I know. I asked you what kind of number you would get if the channel modulation was a small number but NOT zero.

 

[rude man]

I would also like to check if this is a configuration of a Common source with source degeneration single stage amlifer?

What terminal is common to the input and output?
What is the definition of "source degeneration"? You want answers on a platter and we're not allowed to give you that - which is to your benefit.

 

[CKaiL]

The source is connected to the gate and Output is connected to the drain

 

[rude man]

The source is connected to the gate and Output is connected to the drain

 

[rude man]

Yes, but what terminal is common to the input and the output? What is the input referred to, and what is the output referred to?

 

[CKaiL]

Input is connected to the gate , Output is connected to the drain. Source is connected to neither input or output

 

[CKaiL]

I am looking at the amplifier at M2

 

[rude man]

I am looking at the amplifier at M2

Good.
An input is a voltage. A voltage is always between two points.
An output is also a voltage. Same thing.
So, again - what terminal is common to input and output?

 

[CKaiL]

There don't seem to be a common terminal between the input and output if I look at M2 only.The only common terminal I see between the input and output is between M1 and M2 terminal where the body of the M1 (output) is connected to the input of M1

 

[rude man]

There don't seem to be a common terminal between the input and output if I look at M2 only.The only common terminal I see between the input and output is between M1 and M2 terminal where the body of the M1 (output) is connected to the input of M1

Talking M2 only. Re-read what I said about how voltages always need two points.
The input is between G and S.
The output is between D and S.
See any common terminal yet?