Talk:Differential amplifier

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differential amplifier

Added differential amplifier schematic. Rohitbd 10:45, 19 December 2005 (UTC)[reply]

Isn't it a bit confusing that there are two incompatible expressions for Vout? Isn't the real situation that Vout is a sum of Ad(...) + Ac(...) ? Perhaps this is obvious to everyone, but I am worried that someone unfamiliar to electronics and/or engineering-math, might be confused, and draw erroneous conclusions. --Avl 10:28, 9 February 2006 (UTC)[reply]

Made the change. Hope it is clearer now. Rohitbd 16:35, 7 March 2006 (UTC)[reply]

I like your version better. Thanks. — Omegatron 16:45, 7 March 2006 (UTC)[reply]

My pleasure...! :-) Rohitbd 19:46, 7 March 2006 (UTC)[reply]

I think it is easy to understand now. Good work! --Avl 10:05, 25 March 2006 (UTC)[reply]

gain etc[edit]

This article is very difficult to follow, for example, neither common mode gain nor differential mode gain are defined and average reader wouldn't even have a clue what an op amp is. --RichardJ Christie 11:48, 10 September 2006 (UTC)[reply]

How can both sides be the same?[edit]

The diagram seems contradictory. If you increase the Vin for either side, the corresponding Vout will drop. While this might make sense for the negative side, how does it make sense for the positive side? How does it make sense that increasing the voltage on Vin+ will decrease the voltage on Vout+ ? 69.226.224.138 17:56, 26 September 2006 (UTC)[reply]

The gain is negative, by convention. - mako 19:31, 26 September 2006 (UTC)[reply]

but still even if the gain is negative that means if we inc the Vin for negative side then Vout will increase...pls explain —Preceding unsigned comment added by 59.94.208.55 (talk) 21:19, August 26, 2007 (UTC)

patent[edit]

The article mentions that the long tailed pair was patented by Blumlein in 1936. What is the patent number? —The preceding unsigned comment was added by TobinFricke (talk • contribs) 18:19, August 20, 2007 (UTC).

I think the article refer to the uk patent 482,470 who deal with a differential pair. But if i refer to the analog's book Op Amp Applications Handbook the inventor of the long tailed pair seem to be O. H. Schmitt in 1938. Yves-Laurent 23:48, 20 August 2007 (UTC)[reply]

Examples: Long Tailed Pair[edit]

If the diff amp is analzed as a cascade of 2 single ended amplifiers, the first amplifier acts as an emitter follower (aka common collector ) amplifier and drives the second amplifier, acting as common base amplifier. The article is erroneous in calling the 2nd amplifier of the cascade a common emitter amplifier. The input to a common base amplifier is its emitter as stated; the emitter could not be an input to a common emitter amplifier because it is common to both the input and output.

Also the article should describe the circuit's action from input to output, with the emitter follower's action described first.

The differential amplifier has excellent performance for single ended signals, and indeed is most frequently found amplifying them as the input of an operational amplifier. The reason for this excellent single ended performance is that the emitter follower amplifies only current, while the common base transistor amplifies only voltage. This circumvents the speed limitations of the Miller effect which is present in the common emitter amplifier connection. —Preceding unsigned comment added by 131.243.35.178 (talk) 22:57, 10 April 2008 (UTC)[reply]

Emitter constant current source[edit]

The following section was removed from the above metioned section. Its more confusing than helpfull, and partially doubling existing parts.--Ulrich67 (talk) 19:02, 11 November 2015 (UTC)[reply]

"The same arrangement is widely used in cascode circuits as well. It can be generalized by an equivalent circuit consisting of a constant current source loaded by two connected in parallel voltage sources with equal voltages. The current source determines the common current flowing through the voltage sources while the voltage sources fix the voltage across the current source. The emitter current source is usually implemented as a common-emitter transistor stage with constant base voltage driving with current the two common-base transistor stages. So, this arrangement can be considered as a cascode consisting of cascaded common-emitter and common-base stages."

Biasing[edit]

Wording of footnote nb4 was confusing. It began "It is interesting fact that the negative feedback as though has reversed the transistor behavior . . ." I reworded it to begin " Interestingly, it is as though the negative feedback has reversed the transistor behavior . . ." If I misinterpreted it, please improve my wording. Hebeckwith (talk) 08:31, 27 February 2021 (UTC)[reply]