Small signal, transient, DC analysis

[wantedSpidy]

How would carry out the analysis experimentally? In the lab given a power source, a function generator and an oscilloscope.

And what the heck do they mean!!!

The device in question here is an N MOSFET.

 

[blahblah99]

Originally posted by: wantedSpidy
How would carry out the analysis experimentally? In the lab given a power source, a function generator and an oscilloscope.

And what the heck do they mean!!!

The device in question here is an N MOSFET.

They mean you need to do some research and go over your lecture notes before asking for help on your homework question. I'm not going to do your homework for you, but I'll give you a little hint.

Those three terms are three different analysis on paper, and different measurements in the lab. I would start with the DC analysis first since it's very difficult to analyze the other two without the DC analysis.

 

[wantedSpidy]

Here's the deal, its a random asssignment which we never learned anything about ..

Actually I'm looking for not how to do it, but what they each mean, and whats the point of doing them?

 

[BrownTown]

Well, the small signal analysis tells you how the MOSFET would work in small signal operations. Like for example if you are using it as an amplifier then you have a DC bias voltage with an AC signal superimposed on the DC, the small signal analysis tells you how that small AC signal will be manipulated. In an amplifier this means determining the gain of the amplifier, the input and ouptput resistances, the maximum output voltage etc... The DC analysis is how the MOSFET reacts under pure DC conditions. So at what voltages it is operating in the triode or saturation regions, and how it behaves in those regions. Transient analysis I'm not totally sure what they want, so i'll just say they want to know how the MOSFET will react to transients .

EDIT: see, there are a bunch of characteristic constants associated with any particular MOSFET, and when you do the analysis in lab you are trying to determine what they are so you can model the MOSFET more accurately and understand how it will react under all sorts of conditions.

 

[CycloWizard]

Originally posted by: wantedSpidy
Here's the deal, its a random asssignment which we never learned anything about ..

Actually I'm looking for how to do it, but what they each mean, and whats the point of doing them?

Sounds like it might be time to switch majors if you're saying that already.

 

[wantedSpidy]

Originally posted by: CycloWizard

Originally posted by: wantedSpidy
Here's the deal, its a random asssignment which we never learned anything about ..

Actually I'm looking for how to do it, but what they each mean, and whats the point of doing them?

Sounds like it might be time to switch majors if you're saying that already.

I'm curious as to why you said that .....

I just felt the need to confirm my thoughts about the topic, because of my limited background as of now.....

 

[BrownTown]

I would just have to point out that any circuits textbook would go into considerable depth about exactly what these are and what you need to do in lab in order to do them. So if you have a testbook it should take you no time at all to find the right chapter and start reading. If no text book is available there are probably tons of good sources on the internet about this subject. The fact of the matter is that you are not gonna get someone here at Anandtech to spend hours writing a detailed explaination about MOSFETs just so you can save the 5 minutes it takes to look it up in google or in a book.

 

[wantedSpidy]

Originally posted by: BrownTown
EDIT: see, there are a bunch of characteristic constants associated with any particular MOSFET, and when you do the analysis in lab you are trying to determine what they are so you can model the MOSFET more accurately and understand how it will react under all sorts of conditions.

Yeah, so basically the point is to confirm the paramters you extract experimentally match the given paramter values right? Like comapre experimental results with HSPICE analysis and see whether our lambda, kp and VTO constants are right?

 

[CycloWizard]

Originally posted by: wantedSpidy
I'm curious as to why you said that .....

I just felt the need to confirm my thoughts about the topic, because of my limited background as of now.....

It sounds like you're probably a sophomore who already hates what he's doing.

 

[bobsmith1492]

Originally posted by: CycloWizard

Originally posted by: wantedSpidy
I'm curious as to why you said that .....

I just felt the need to confirm my thoughts about the topic, because of my limited background as of now.....

It sounds like you're probably a sophomore who already hates what he's doing.

Hey, maybe he just needs some encouragement? He's obviously a freshman/sophomore - although maybe a junior. I think we did mosfets in EGR315.

The best thing you can learn, though, is how to learn on your own.

It's another thing sometimes if a master of the subject is nearby and can easily and quickly explain (i.e. in class and/or lab, not online!).

 

[wantedSpidy]

I am actually a sophmore, but I'm more of a signals and systems/Digital Logic guy.
This was my first devices course, it was mroe of a project class, and the theory was never done.
So I was looking for some guidance so I could get off on the right foot.

 

[BrownTown]

heh, well if you are a digital logic type guy than MOSFETs are pretty much the biggest deal in your life so you might want to get a good understanding of those .

 

[wantedSpidy]

yeah, I realized that. I was only doing stuff in VHDL and Verilog, up till now. I just knew how MOSFETS worked without actually knowing the intricate details of the device.
Now I have to learn all this stuff on my own, thanks to our great prof, who didn't go over anything in class.....

 

[BrownTown]

I find the route your school is taking in the teaching of microelectronics to be somewhat interesting in that they are teaching you high level logic design before teaching you lower level device characteristics. At least where I go to school it is the other way around, but I guess each school can do it their own way and you end up learnign it all in the end.

 

[TuxDave]

Originally posted by: BrownTown
I find the route your school is taking in the teaching of microelectronics to be somewhat interesting in that they are teaching you high level logic design before teaching you lower level device characteristics. At least where I go to school it is the other way around, but I guess each school can do it their own way and you end up learnign it all in the end.

Rutgers kinda did both at the same time. Sophomore year you take Digital Logic Design so you learn your NAND and NORs and K-maps and really simple VHDL. However you also take Microelectronic Devices at the same time so you learn MOSFET device physics and single stage amplifiers.

But yeah, if you're talking about full system RTL/VHDL, that was a senior level class so by then we're way past the device basics.

 

[bobsmith1492]

We studied digital systems (logic operations and such) before the actual device characteristics. Really, they're not that connected; by the time you need to know exactly how the transistors in your NAND gate operate to design circuits using them, you'd be at such a high level (high speed circuits, etc.) that you would have had ample time to take the device physics classes.

I don't see why you'd study low-level characteristics before typical logic operation; (basic) logic is much less complicated, hence lower-level.

 

[wantedSpidy]

I mean the order is up to us, there are 4-5 core courses and there's no particular order.
I just happened to do the core courses in digital logic, before the devices ones. There are loads of people who do it the other way round.

Its just that they changed the curriculum recently and this was the first time with the new structure, so it was kinda wayward ......