Doubt about NMOS Transistor in Microcap: Varunag

In summary, there is some doubt about the accuracy of NMOS transistor models in the simulation software Microcap. This is due to discrepancies in the results obtained from simulations and the expected behavior of the transistor. Further investigation and verification of the models is necessary to ensure accurate and reliable results in future simulations.
  • #1
varunag
25
0
I was making a model of a NMOS transistor in Microcap. It was part of an assignment. I was supposed to make graph with changing value of V_{BS}. But after a certain value of V_{BS}, I got negative current. It came to my mind it is not possible. But, I couldn't think of a reason instantly, as to why current can't flow in the opposite direction.
Here V_D = 2.5V, V_G = 1.5V, source is grounded and V_B = 4V. I hope that a reasoning could be given without other parameters of the transistor, yet if other parameters are required I would give them.

I myself will look about this and share it with everyone.

-varunag
 
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  • #2
It's fairly unclear what your test circuit looks like, but, yeah, a MOSFET will conduct equally well between drain and source, in either direction--according to bias.
 
  • #3
I found the problem with the design. When we give positive supply to the body, we are making the body-source junction reverse bias.(I have not mentioned in my query that source is grounded, but I suppose that could be expected by the way I had given the values)
And on further increasing the body voltage, we make the body-drain junction reverse bias as well. Making these junctions reverse bias, we are changing the way the transistor works. I could only figure out this.

I hope someone could give a reason more suitable.

-varunag
 
  • #4
Not all mosfets are four terminal. Most commercial decretes are three terminal.
I don't know what "negative current" means.
 
  • #5
Phrak said:
Not all mosfets are four terminal. Most commercial decretes are three terminal.
I don't know what "negative current" means.

Well we know 4 terminal mosfets. And we usually short the body with the source. only this time we tried to give some voltage to the body, to check the theoretical relations we have. It seems the first order model used by "Microcap" software, is inadequate to deal with this, and we need to check with higher models.
 
  • #6
varunag said:
Well we know 4 terminal mosfets. And we usually short the body with the source. only this time we tried to give some voltage to the body, to check the theoretical relations we have. It seems the first order model used by "Microcap" software, is inadequate to deal with this, and we need to check with higher models.

Not if MicroCap can be used for a circuit simulation with body effect considered. And that is described very briefly here: http://www.zenex.fi/microcap/files/9rm.pdf , on page 484. So there's probably a small glitch with your model.
 
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1. What is an NMOS transistor?

An NMOS (N-channel Metal-Oxide-Semiconductor) transistor is a type of field-effect transistor (FET) that is commonly used in digital electronic circuits. It is made up of a source, drain, and gate and operates by controlling the flow of electrons between the source and drain using an electric field created by the gate.

2. How does an NMOS transistor work?

An NMOS transistor works by creating a channel of electrons between the source and drain when a voltage is applied to the gate. This allows for current to flow from the source to the drain, which can be controlled by varying the voltage on the gate. When no voltage is applied to the gate, the channel is closed and no current flows.

3. What is the purpose of using an NMOS transistor in a circuit?

NMOS transistors are commonly used in digital circuits as switches or amplifiers. They can be used to control the flow of current and create logic gates, which are essential for building digital circuits. They are also used in various other applications such as voltage regulators and amplifiers.

4. How do I use an NMOS transistor in Microcap?

To use an NMOS transistor in Microcap, you will need to create a circuit diagram and specify the parameters of the transistor such as its dimensions, material, and other properties. You can then simulate the behavior of the transistor in the circuit and analyze its performance using Microcap's tools and features.

5. What are some common issues or doubts about NMOS transistors in Microcap?

Some common issues or doubts about NMOS transistors in Microcap include understanding the simulation results, selecting appropriate parameters for the transistor, and troubleshooting any errors or unexpected behavior in the circuit. It is important to have a good understanding of the theory behind NMOS transistors and their behavior in order to effectively use them in Microcap.

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