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IDS Vs VGS

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EngIntoHW

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I'm reading an article on MOSFET based amplifiers and saw the next figure:

class-a-jpg.59178


I think this figure is incorrect as you can't draw IDS without knowing both VGS and VDS.
Moreover, IDS is always dependant on VGS, so it doesn’t remain constant as VGS goes up.
 

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It's not incorrect: it's merely showing you the curve for one particular (unspecified) value of Vds. You'd get similar shaped curves (albeit with different slopes and plateaux) for other values of Vds.
Moreover, IDS is always dependant on VGS, so it doesn’t remain constant as VGS goes up.
Not so. The curve shows that Ids increases with Vgs up to a certain point. Beyond that point there's a plateau, where Ids is almost constant as Vgs increases.
 
Thank you.

Isn't it different than the MOSFET theory we learned?
In both Linear and Saturation equations of IDS, it is dependant on VGS.
 
In both Linear and Saturation equations of IDS, it is dependant on VGS.
Yes, even in the plateau region there will be a Vgs dependence; but very small compared to the initial part of the curve.
 
Is it being taught in college?
I've no idea. I graduated from college about half a century ago!
 
I don't see anything wrong with the device curve (Ids vs Vgs), but the "load line" doesn't make sense. Class A operation does require biasing somewhere near the middle of the curve, but I don't know what the straight line represents.
 

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Thank you very much Alec and Ron.

Ron,
Thanks for the simulation.
I guess that the straight line was an approximation.

BTW, which simulation tool did you use?
 
hi,
I was looking at this LTS Sim yesterday for another OP,, posted for reference.:D
 

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that looks more like an Ids vs. Vds curve, at one particular value of Vgs

(NOT Ids vs. Vgs at one value of Vds)

and yes it is taught in colleges...it is taught in every basic electronics course
 
that looks more like an Ids vs. Vds curve, at one particular value of Vgs

(NOT Ids vs. Vgs at one value of Vds)

and yes it is taught in colleges...it is taught in every basic electronics course
I think you're wrong. Ids vs Vds with fixed Vgs does not have a threshold voltage. Look at the curve I posted in post #7. It looks like that.
 

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