# Regarding MOS Model Parameters in LTSpice

#### wishfulOrange

Joined Apr 8, 2020
3
Hey, I'm trying to find MOS Model Parameters in LTSpice, the parameters I'm looking for are the Threshold Voltage and the Lambda.
So, according to my model, I do not have values for PHI, or GAMMA. I assumed (W/L) to be 1.

The approach I followed was taking the general Drain Current Equation of MOSFET, differentiating it with respect to Vgs, and trying to express Drain Current as a function of its Derivative, which I was successful in doing.
Vth=Vgs - 2*(Id/d(Id))
where d(Id) is the derivative of Id w.r.t. Vgs.

Similarly, I tried the same approach with differentiating the Drain Current Equation w.r.t. Vds, and trying to express Drain Current as a function of its derivative.
Lambda = d(Id)/(Id - Vds*d(Id))
where d(Id) is the derivative of Id w.r.t Vds

Now, both of these equations are good enough to give me Vth and Lambda when I know the value of Vgs and Vds, but it is not sufficient to find their values independent of both of them, even if it is a reasonable estimate of both of them.

It will be a great help if any of you could guide me here! Thanks in advance!

#### Bordodynov

Joined May 20, 2015
2,661
I don't understand your purpose. Are you in the field of theoretical constructions? Or do you want to find the threshold of a real transistor? I'll upset you. The real transistor has no threshold in the simplest sense. The simplest understanding of threshold is that the transistor current is equal to zero at the Vth gate voltage. There is a current at VG<Vth. There is a real definition of threshold at some fixed transistor current. The current is given differently depending on the transistor power. More transistor - more current.

#### wishfulOrange

Joined Apr 8, 2020
3
I don't understand your purpose. Are you in the field of theoretical constructions? Or do you want to find the threshold of a real transistor? I'll upset you. The real transistor has no threshold in the simplest sense. The simplest understanding of threshold is that the transistor current is equal to zero at the Vth gate voltage. There is a current at VG<Vth. There is a real definition of threshold at some fixed transistor current. The current is given differently depending on the transistor power. More transistor - more current.
I plan to design a CMOS Differential Amplifier according to predetermined specifications after I've found the necessary characteristics of NMOS and PMOS given in my MOS Model Library File.

And I would certainly need the parameters to do that, I've worked out the calculations regarding different (W/L) ratios that I'll be needing to construct the Amplifier.