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Re: Regarding Boyk and Sussman, Cheever, etc.

Many years ago I saw part 5, but not part 6, and there are many facts that are brought out in this series of articles.
In part 5, it is interesting that Baxandall proves that the parabolic approximation cannot hold up at low currents with a fet, and higher order distortion is inevitable when fets are operating well below their normal working current.

I think this sequence of articles is about the best out there on this subject. Regarding the FET characteristics, I was coming at it from the angle of the Massobrio and Antognetti device modeling book I referenced above. Though it's nominally a text about SPICE modeling, a major portion of the book is concerned with deriving equations relating the terminal currents and voltages of the device based purely on considerations of device physics. The formula they get for a FET is pretty messy, involving, among other things, a square root term with Vgs cubed inside the square root. Then they show the usual quadratic approximation with a graph comparing the two. The graph shows them to be very close. What I took home from this was that the simple quadratic approximation was not based on device physics at all. Rather, it just happens to be a pretty accurate and much more convenient approximation to the formula obtained from device physics. I could scan these pages from the book and send them to you if you're interested.

This is the sort of thing that we should be talking about and even debating, rather than the usual.

Amen! Technical discussions are what this forum is all about. I don't know how it turned into the nightmare it did. I think people realized that it was essentially unmoderated, so they know they can come here and create havoc.

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