Talk:Transconductance

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Objective[edit]

this Should be a general description of what the term means, and then a description of transistor and vacuum tube properties.

probably copyrighted definitions:

General: Transconductance Transconductance is a property similar to both gain and conductance. When conductance is the will to generate an current for an apply voltage at to connecting points is the transconductance the will to generate an output current at the output connecting points for and applied input voltage at the input connecting points.

Specific applications: Transconductance Amplifier An amplifier which has an transconductance instead of ordinary voltage gain. Transconductance amplifiers can be of great use in some cursuits and is are better suited to drive certain loads (consider an speaker and the speaker cable). There exists transconductance amplifiers similar to operational amplifiers usually refered to as OTAs.

TRANSCONDUCTANCE—Transconductance is a ratio of the change in plate current to a change in grid voltage with the plate voltage held constant. Transconductance (gm) is usually expressed in micromhos or millimhos.

parameter defining conditions for current flow in the channel of Field Effect Transistors (FETs); the derivative of the output current over input voltage

Split?[edit]

We have a few related concepts. Transconductance, transresistance, transadmittance, and transimpedance. Which ones should have their own articles? If they are combined into one article, what should the title be? — Omegatron 15:30, 24 July 2006 (UTC)[reply]

Transconductance is a far more widely used concept than transresistance I feel. I think transresistance is given far too much weight in the article, but I dont think it warrants its own page either.--Light current 02:22, 26 July 2006 (UTC)[reply]

This transresistance amplifier hooey seems to have been coined by Maxim. Its nothing special as its only an op amp with a FB resistor (surprise). Who else uses the terms 'transresistance' (or transimpedance). I dont think Ive heard of them before seeing them here.--Light current 02:31, 26 July 2006 (UTC)[reply]

Just because you personally haven't heard of something doesn't mean we should take it out of articles. Lots of people use the terms. — Omegatron 13:50, 26 July 2006 (UTC)[reply]

I'd say all these articles should be merged into a good discussion of two-port networks since the parameters are more or less directly as a result of two port modeling. -- mattb @ 2006-11-23T00:14Z

I don't know if this is helpful or not, but I was thoroughly confused by getting redirected here from "Norton Amplifier". I was trying to learn about Norton / current differencing amplifiers, which I now know are transimpedance amplifiers (not transconductance amplifiers), but there wasn't much information, so I started searching around and reading about transconductance amplifiers thinking that was what I wanted. It took me a while to figure out where I'd gone wrong, so my suggestion would be to either add a section/note here to explain what Norton/current-mode/transimpedance amplifiers do or to not have the URLs corresponding to those terms redirect here. (It'd almost be better just to get a "not found" page than for it to take one to this page as it is right now.) — Preceding unsigned comment added by 50.77.60.241 (talk) 21:57, 17 February 2016 (UTC)[reply]

Removed from page[edit]

Yet another term, this time coined by National Semiconductor in the early 1970s with the introduction of their LM3900 [1], is the eponymous Norton amplifier. The Norton amplifier produces an output voltage proportional to the difference between the currents flowing into its two inputs.

What has this to do with transconductance?--Light current 02:17, 26 July 2006 (UTC)[reply]

That would be a transresistance amplifier, not transconductance. — Omegatron 13:41, 26 July 2006 (UTC)[reply]

Norton Amplifier?[edit]

"Norton Amplifier" redirects to this article, but the term is found nowhere in the text. — Preceding unsigned comment added by 62.153.130.147 (talk) 08:56, 16 May 2013 (UTC)[reply]

I've now put a short article at that title. SpinningSpark 09:36, 25 September 2021 (UTC)[reply]

transistors[edit]

In the transresistance section, or maybe somewhere else, one might mention that the name "transistor" came from transresistance, even though it isn't the right quantity for a bipolar transistor. (They are usually modeled as current controlled current sources.) In any case, using transconductance for bipolar transistors is strange. They were named transistors because they don't have transconductance. Gah4 (talk) 21:54, 24 September 2021 (UTC)[reply]

Bipolar transistors don't have transconductance? Transconductance is defined quite generally for any two-port. I don't see the basis for your claim. SpinningSpark 09:06, 25 September 2021 (UTC)[reply]

The advantage of the bipolar transistor is its high transconductance which leads to high bandwidth and low offset and noise voltage. (my emphasis) SpinningSpark 09:40, 25 September 2021 (UTC)[reply]

The whole idea of transconductance for tubes and FETs is that it is, more or less, constant, given some other parameters. That is, that they model as voltage controlled current sources. I haven't thought about common base for a while, which is the way early bipolar transistors were used, but as common emitter, and for emitter follower, they model as current controlled current sources. In any case, I believe the story of the naming is well known, though I didn't look for a WP:RS. Gah4 (talk) 14:27, 25 September 2021 (UTC)[reply]

I don't dispute the naming of transistor, or that its transconductance is not constant. But that was not what you actually said. By the way, emitter follower is a voltage source surely, not a current source. SpinningSpark 15:12, 25 September 2021 (UTC)[reply]

Emitter follower is a current amplifier. The emitter voltage is 0.7V less (or 0.7V more for PNP) than the base, and it pulls just enough base current to drive the needed output current. Unlike the common emitter circuit, where you usually need excess base current to be sure it is in saturation. (Usually.) Gah4 (talk) 06:08, 26 September 2021 (UTC)[reply]

Agreed it is a current amplifier, but that does not make it a current source. The output current is almost entirely dependent on the load, while the output voltage is almost entirely dependent on the input voltage. Those are the features of a voltage dependent voltage source. Compare with an independent voltage source, the output current is also entirely dependent on the load. This source backs me up. SpinningSpark 10:19, 26 September 2021 (UTC)[reply]

...and this source says even more clearly that it is a voltage source. SpinningSpark 10:24, 26 September 2021 (UTC)[reply]

Hmm. From the outside, they look like voltage controlled voltage sources. From the transistor's viewpoint, though, they are current controlled current sources. I was not so long ago playing with ECAP and SPICE, including bipolar transistor models. In any case, they aren't characterized by transconductance. Reminds me also of Cathode follower, which came before emitter followers. Gah4 (talk) 06:13, 27 September 2021 (UTC)[reply]