How Transistor works - verifying

cabraham

Honestly Bill, the rebuttals to your site have been thoroughly presented. A more fitting question is "which points in the rebuttals need clarification?" Everything I've presented is backed up with known proven science. You need to address what, if any, points I may have overlooked.

Once again, here is the thread where the matter was well discussed:

http://www.physicsforums.com/showthr...ghlight=wbeaty

BR, Claude

wbeaty

Yes, I had my chance and now it's too late!

It's a very regretful situation, but that's just how things must be.

And besides, who do I think I am?! Someone coming in at this late date, wanting to give input long after the timer has expired.

I should be ashamed.


(Also, prev msg link is bad.)

cabraham

http://www.physicsforums.com/showthr...ghlight=wbeaty

That should do it. It's never too late to ask a question. I'll clarify anything that needs to be understood better.

Claude

wbeaty

You said that you and I had a discussion, first linking to that other forum with "Rachit," then linking here where I'd posted one single message (and in that instance I never stayed around to read any responses.)

That's very odd. No, I've not been involved in any "discussion."

But now I'm wondering ...back during that enormous "current controlled" debate, did you suspect that the anonymous "Rachit" guy was actually myself? That you and I did have a discussion, but I was hiding my identity?

cabraham

I only asked the question. I don't dislike Rachit, nor anybody who opposes me. I just want to re-examine everything until concensus can be reached. I have a pet peeve just like we all do. Mine happens to be debates that never end. At some point in time there needs to be a "Supreme Court" of some kind to resolve it. The SC is not always correct, & they have reversed themselves numerous times in US history.

The current controlled model of a bjt has always been presented as an external viewpoint, focused solely on driving the bjt w/ external circuitry, not examining the internal device physics. When this point was finally uinderstood after a lengthy debate concensus was reached. It has been universally accepted, even from critics of semicon OEMs, that the current control viewpoint does not address internal physics. Rather the CC approach is beneficial for driving the device, developing networks around the bjt. In short, a constant voltage source should never be used to drive the b-e jcn.

A constant current source biases said b-e jcn very well, but a CVS would likely destroy it. Nobody, including critics, disputes this assertion. So we had universal concensus, no dissent at all, that for an external view, CC is what works best.

We also concurred w/o dissent, that when operating a bjt at a speed high enough so that internal charge distribution & transit time, is no longer negligible, then the CC model is inadequate. I still repeat this - any time internal device physics is under examination, the CC model is inadequate.

So the debate then shifted to which internal model is best. The peer reviewed app notes from OEMs, & unis say QC, charge controlled. A handful of critics say VC, voltage controlled. Scan the debate & it was eventually settled w/ full agreement that QC is the best internal model.

Do not hesitate to ask for clarification. I want to be seen here as an approachable dude. I hope that everyone feels they can talk to me freely w/o contention. If I've erred somewhere I'll accept & welcome correction. If my explanations are not effective, I'll rephrase. Please feel that you can talk to me freely w/o any repercussions. So here it is.

External model neglecting internal device physics - current control.

Internal model considering internal device physics - charge control.

Atomic level considering the limits of physics knowledge - quantum mechanics.

I'll address any questions. Best regards.

Claude

wbeaty

Hmmm, a problem.

Again: did you suspect that "Rachit" and myself were actually the same person?

cabraham

I did not assume that. I just wasn't sure. Some of his phrasings sounded like yours but that could be because he relied on your site as a reference. Just curious, Rachit is not a bad person. I just wanted to know his reasoning & sources for his contrarian position.

Don't take any of this as personal. I ask everybody else, you included, to provide sources & proof when taking a contrarian stance against a well established position in science. I provide sources & proof to support my conformist positions.

One more point, & no offense is meant. Contrarian positions are, for some folks, a lot more fun to ponder than the official viewpoint. There is something about being in a vocal minority that gives them a sense of being more enlightened than the rest. They consider the official viewpoint as "misconception, myth, based on limited anecdotal evidence, etc." What the critics need to do is carefully examine their own positions, & they will find that they make assumptions at the start that are not valid, or anecdotal, holding under limited conditions. To these folks, there is little excitement in conformist positions because one cannot take credit for it. But once a fact is established based on solid proof, there is no need to knock it down to prove oneself capable. There are many new ideas & inventions waiting to be discovered. I suggest that their effort be redirected.

I always refute the critics with solid immutable laws like conservation of energy & charge, Kirchoff's 2 laws, Maxwell's equations, etc. These are Gibraltars of science. Any theory which cannot conform to these laws are nothing but heresy. To prove the contrarian view requires disproving these well proven laws.

Any theory which is contradicted by said laws cannot be taken seriously. The critics are the ones spreading myths & misconceptions. Everything we need to know is taught at the accredited unis in engineering (full) & physics curricula. Web sites preaching info which counters the uni teachings must be scrutinized, & I always find that assumptions are made early which are invalid, & hence produce invalid conclusions.

But admission of an error is rare. Once a critic has boldly declared the engr/phy community to be wrong, mountains of evidence refuting their erroneous view is futile. They are then in a position where they must defend their contrary view,& attack the official view just to save face. That is why I tend to be careful about debating an issue. If I am not experienced in a topic, I tend to trust those who are. Nothing is worse than taking a hard stand on an issue I am not an expert on, then after others present evidence to the contrary, I realize "Oh s***, I'm wrong!" I avoid that by debating only when I know the facts.

Oh well, I do run on. Best regards.

Claude

Studiot

Probably the two most famous counterexamples to this declaration are

The gross miscalculation of the age of the Earth by Lord Kelvin.

The address to the Royal Society by Oliver Heaviside "Gentlemen, shall I refuse my dinner because I do not fully understand the process of digestion?"

cabraham

I stand by what I posted. One person, such as Lord Kelvin, does not disprove my point. Lord Kelvin put his foot in his mouth on more than one occasion, esp in his later years. The unis teach what is known at this moment to the best of their ability. New discoveries will be made & the science/uni canon will be updated to reflect new info.

As far as OH & dinner goes, that is hardly a rebuttal to my point. I didn't say that all is known. Rather, if we wish to understand how to utilize a bjt to its full effectiveness, unis are a good source, as are semicon OEMs.

The internal physics involves QM, of which the science community has only a limited understanding. We have much to learn about QM, & the unis provide only a limited amount of enlightenment here, because man's knowledge of QM is limited.

I hope that clears up my statement. BR.

Claude

wbeaty

Nope, I've never been on that forum. I think I registered long ago when I was adding forums to the big list on my Electronics Hobbyist page. I suspect that Rachit is this one professional chip designer who uses SED and other newsgroups, and appears to be a big fan of my articles. He probably emailed me a few times years ago.

wbeaty

What contrarian position? What do you mean exactly?

My transistor article comes right out of standard textbooks. It's what I was taught in EE classes at the U. of Rochester. It's all based on the main bjt equation, the DC transconductance equation or "Shockley's Equation" which describes the effect of the potential barrier in the BE junction of the bjt: Ic=Is*(e^(Vbe/vt)-1). That equation appears in vast numbers of EE textbooks, if not all of them. I think Horowitz and Hill devote an entire chapter to it. In Art of Electronics, first they go over Ic=hfe*Ib and the "little man in the transistor." Then they drop the simple stuff and delve into professional-level design techniques. IIR, Sedra and Smith do the same. (Might you recall the undergrad semiconductor physics text you yourself used back in school?)

But my transistor article was written for the Electricity exhibit at the Boston Museum of Science (well, the initial version was.) Therefore my goal is to explain diode switching to little kids and grandmothers. I cannot introduce any math at all. I can't even use the central concept of "diode potential barrier." In order to translate the diode equation Id=Is*(e^(Vd/Vt)-1) into everyday language, I focus on visualizing the changing width of the depletion zone; the variable insulating region found in all PN junctions.

The general public can't deal with Id=Is*(e^(Vd/Vt)-1), but many of them can understand a thin flat insulator which dynamically grows and shrinks in thickness, and which presents a barrier between two conductors. My original transistor article was intended to have several animations where the Depletion Zone is depicted as glass, and the rest of the carrier-filled semiconductor material is depicted as metal. Also, I planned articles covering Diode first, then BJT later, so everyone can pick up a critical concept: the BJT is really just a fancy kind of diode switch.

You're totally familiar with Ic=Is*(e^(Vbe/Vt)-1), right? It's the "Ohm's Law" of the transistor.

Chunkysalsa

Interesting article to read. I don't know anything about transistor yet to contribute to your discussion.

I thought it was interesting to see you responding here when the other day my intro circuit analysis professor gave us the link to that article as a source for writing a small mini-paper on how transistors work.

Studiot

Out of interest, on what website was this 'discussion' with this 'rachit' fellow please?

I ask because I remember a member called ratch on who had a particularly frustrating discussion style on another forum. He kept referring to the amasci website.

wbeaty

Yeah, that article has attracted fairly huge web traffic, plus staggering amounts of ego-swelling congratulatory email, way too much for me to have any hope of answering. The physics educators love it. As S. Hawking discovered, any new explanations of physics, if they're purely verbal+pictures, tend to attract big crowds.

So I was a temporary minor online celeb. But you cannna makes a living on th intertubes, unlessuns you publishes a paper-based book.

wbeaty

It's the same one Claude repeatedly posted here, the one with forty-three pages. I thought you participated? See the first page of this current thread, down near the bottom.

Look back there again, it doesn't say 'ratch,' it says 'ratchit.'

cabraham

As I've stated repeatedly, there are 3 basic equations which can be labeled as "terminal relations":

1) Ic = beta*Ib

2) Ic = alpha*Ies*exp((Vbe/Vt) - 1)

3) Ic = alpha*Ie

Equation 3 is the law of transistor action. Equation 2 is often miswritten, as you just did. I've highlighted the factor "alpha" & the saturation current is "Ies". In a diode there is but one value of Is. In a bjt, there are 2 junctions each w/ their own value of "Is", due to differing doping densities in collector vs. emitter. Hence "Ics" & "Ies" are used in the Ebers-Moll equations.

All 3 equations are needed to fully describe a bjt. But only 1 of the 3 input quantities can be the directly controlled input, the other 2 being incidental, but inportant nonetheless. We can control the base current & then eq 1) gives us Ic. But this method results in beta dependency, which we usually avoid. Eq 3) is very reliable. If we set Ie to a known value, Ic is very predictable. Alpha is around 0.98 to 0.998.

We never control Ic w/ Vbe. The Ies term is very temp dependent. It also has a positive temp coefficient. A voltage source directly across the b-e jcn could kill the device. It's never done. We control a bjt by controlling its current.

In the process of doing so, a voltage develops across the b-e jcn. We use eqn 2) to compute transconductance of the device. This is the upper limit for the transconductance of the stage. The stage gm cannot exceed the devices gm.

Likewise, beta is the upper limit for the stage current gain. The stage current gain cannot exceed beta, that of the raw device.

Your presentation of bjt operation reads like a scathing indictment of OEM & uni app notes. It reads as if your version is the only valid one. My beef is that the explanation given in uni texts is spot on, & does not need any correction. You present E-M to the exclusion of the other 2. E-M is one law for bjt operation. The other 2 are just as important. A bjt is a 2 port device. It cannot be explained in 1 equation. Likewise for a FET.

As I said, to develop bjt networks, the CC model is good until storage/transit time becomes an issue at high speeds. Then QC takes over. I've used CC & QC forever, & haven't gone wrong. What have you used?

Claude

wbeaty

Yep, dead normal textbook stuff.

But I begin to suspect that you didn't read my previous message (number 45.) Hint hint.

Miswritten? No, it's simplified, just as uni texts commonly do, for devices where alpha ~= 1. Must we now go and make a list of the undergrad textbooks which do this? Does your school have an engineering library with all the current double-E texts behind the ref desk? Well, doing all that is irrelevant, for the reasons explained in my previous message.

And again as before: might you yet recall which text you yourself had in your undergrad semiconductor physics course, the one that first covered transistors?

Sure, but I think you're missing something important. Hint again: read my previous message 45, the one you quoted.

What is the goal of my transistor article?

That transistor article ...what was it's goal? What org was it written for, and who are their clients?