how to build a BJT model and a MOSFET model using laplace transform

Dear friends:
Firstly,I must be sure whether BJT or MOSFET can transform using laplace transform.Secondly,If it can transform,I want to know how to finish .

I will appreciate your help!
small hill!

Laplace transform is only applicable to linear systems, transistors are highly non-linear devices. How do you imagine to model it with laplace?

I think you refer to a linear model applicable to small signals, then coming from s-parameters. You could be interested in the following article:

http://www.truefork.org/Academia/BIJSTELLpaper.pdf

FvM said:

Laplace transform is only applicable to linear systems, transistors are highly non-linear devices. How do you imagine to model it with laplace?

Click to expand...

Dear FvM:
If transistors can not imagine to model it with laplace,please you list other ways.especially,how to build a mathematical model
of transistors in the actual circuit.

Thanks so much for response!

small hill

You didn't tell which aspects of transistor behaviour you want to model. In circuit simulation, transistors are usually modelled by non-linear equations, e.g. Gummel-Poon model for BJT.

FvM said:

You didn't tell which aspects of transistor behaviour you want to model. In circuit simulation, transistors are usually modelled by non-linear equations, e.g. Gummel-Poon model for BJT.

Click to expand...

Dear FvM:
I can use non-linear differential equation to define the current of BJT model in circuit. But why can operational amplifier circuit show laplace model.example,Active low-pass filtering amplifier ciruit.

according to the structure of operational amplifier ,I realize operational amplifier is made up of lots of BJT.could you tell me why BJT cannot be shown in Laplace.then operational amplifier can be shown.

Thanks so much for response!
small hill

Analysis of active filters and many other OP circuits is presuming small-signal operation, linearizing the non-linear transfer characteristic around the bias point. The same can be done for analysis of transistor circuits. It uses small signal transistor models, see https://en.wikipedia.org/wiki/Transistor_model#Small-signal_linear_models

Also albbg is talking about small signal transistor models in post #3.

FvM said:

Laplace transform is only applicable to linear systems, transistors are highly non-linear devices. How do you imagine to model it with laplace?

Click to expand...

Dear FvM:
If I can understand when Transistor works in the area of linear,transistor can be transformed using laplace.however,when transistor runs in the area of non-linear,it cannot be modeled in any mathematics method。

please give me some detailed replies!
small hill!

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albbg said:

I think you refer to a linear model applicable to small signals, then coming from s-parameters. You could be interested in the following article:

http://www.truefork.org/Academia/BIJSTELLpaper.pdf

Click to expand...

Dear albbg:
If I can understand when Transistor works in the area of linear,transistor can be transformed using laplace.however,when transistor runs in the area of non-linear,it cannot be modeled in any mathematics method。

please give me some detailed replies!
small hill!

Nonlinear systems can be well described by nonlinear differential equations, also transistors. Transient analysis of circuit simulators is using it extensively.