[SOLVED] nMOS Invertor with Depletion load - Calculating Switching Voltage

[ECE101]

Hi,

For an nMOS Invertor with Depletion load, I'm trying to calculate the switching voltage and current at this point.



Both devices will be operating in the Linear region but how do I calculate this?

Thresholds are 1V and -3V.

(W/L)pd / (W/L)pu = 4

 

[erikl]

Neglecting the Vds dependency (λ=0):

I2 = Kn*( W/L)*(|Vgs2| - Vth2)²
I1 = Kn*(4W/L)*(Vgs1 - Vth1)²
I2 = I1
4(Vgs1 - Vth1)² = (|Vgs2| - Vth2)²
2(Vgs1 - Vth1) = (|Vgs2| - Vth2)
Vgs1 = Vi
2*(Vi - 1V) = 0 + 3V
Vi - 1V = 3/2 V = 1.5V
Vi = 2.5V = Switching Voltage

I1 = I2 = Kn*(W/L)*9 = current at this point

Nice homework!

 

[ECE101]

Thanks for the answer erikl!

"I2 = Kn*( W/L)*(|Vgs2| - Vth2)2"

Can you explain how this is derived?
Why can we neglect the Vds dependency?

Apologies for the stupid questions!

This is the answer we have been given, however I'm struggling to understand how he gets his answer of 2.31V

I understand why both are operating in the linear region, "equating the currents" is the problem...

 

[erikl]

"I2 = Kn*( W/L)*(|Vgs2| - Vth2)²"
Can you explain how this is derived?

This is standard for the medium to strong inversion region. Any book on MOS will tell you this.

Why can we neglect the Vds dependency?

At least in first approximation.

"equating the currents" is the problem...

That's what I did.