# How to change the threshold of voltage difference between source and drain when the gate voltage is zero

#### achen

Joined Sep 11, 2022
18
The NMOS configuration is as below.
the gate voltage is 0 V
the source voltage is fixed to 0 V, the drain voltage is swept from -2 V to 2V.
We can see that the threshold of voltage difference between source and drain is very little, at drain voltage around -0.01 V.
What parameter of this NMOS shown in the second graph (Level1_Model) I can change in order to have the threshold voltage difference much negative, say -10 V ?

#### Attachments

• 89.5 KB Views: 24
• 57.9 KB Views: 22

#### Papabravo

Joined Feb 24, 2006
21,307
I'm not sure why you think there is one.

#### dl324

Joined Mar 30, 2015
17,125
Threshold voltage is Vto.

#### DickCappels

Joined Aug 21, 2008
10,246
The threshold ad drain current as a function of gate-to-source voltages at different drain-source voltages is a function of the design (including the manufacturing process) of a given MOSFET.

You can modulate the the transfer function of the gate by adding a second gate, then you would be uding a dual gate MOSFET.

#### Papabravo

Joined Feb 24, 2006
21,307
The threshold ad drain current as a function of gate-to-source voltages at different drain-source voltages is a function of the design (including the manufacturing process) of a given MOSFET.

You can modulate the the transfer function of the gate by adding a second gate, then you would be uding a dual gate MOSFET.
Could you clarify the phrase: "The threshold ad drain current ..."?
I'm not sure what the "ad" means and the sentence above is unclear to me in its meaning.

I am aware of the ability to fabricate a range of MOSFETS with differing amounts of drain current at Vgs=0 V. Essentially sliding the characteristic Id versus Vgs curve from that of a depletion mode MOSFET to an enhancement mode MOSFET. Is this what we are talking about?

Last edited:

#### DickCappels

Joined Aug 21, 2008
10,246
If your (@Papabravo ) question is directed to me, that was a typo -typed on my phone. It should read "The threshold and drain current as a function of gate-to-source voltages at different drain-source voltages..."

#### Papabravo

Joined Feb 24, 2006
21,307
If your (@Papabravo ) question is directed to me, that was a typo -typed on my phone. It should read "The threshold and drain current as a function of gate-to-source voltages at different drain-source voltages..."
Yes, it was, and thank you for the clarification. Am I correct that we are talking about the intercept of the characteristic curve with the Vgs=0V axis?

#### DickCappels

Joined Aug 21, 2008
10,246
Last edited:

#### WBahn

Joined Mar 31, 2012
30,295
The NMOS configuration is as below.
the gate voltage is 0 V
the source voltage is fixed to 0 V, the drain voltage is swept from -2 V to 2V.
We can see that the threshold of voltage difference between source and drain is very little, at drain voltage around -0.01 V.
What parameter of this NMOS shown in the second graph (Level1_Model) I can change in order to have the threshold voltage difference much negative, say -10 V ?
Are you taking into account that, for the basic MOSFET, the drain and source are interchangeable? Thus when you take the drain voltage to -2 V, what you have in effect is a NFET with a Vgs of 2 V and a Vds of 2 V. More to the point, what you have is a diode-connected FET.

Now playing into this is where the body is connected. Also, especially for discrete MOSFETs, the drain and source regions may not be symmetric.