Talk:Common emitter

message: I added a description of all the parameters.  It's messy right now, though.  Not sure how else to arrange it.  Should get it right here before copying it to all the others so we aren't wasting our time. - Omegatron 02:12, August 10, 2005 (UTC)
::Its kind of redundant having the same explanation of the parameters on every amplifier article. I'm thinking about creating a new article on the BJT small signal model that explains the parameters (as you've done) and just linking to that instead. It could also cover the high frequency and other models as well. Roger 15:49, 27 April 2007 (UTC)
thread_title: Parameters

message: I didnt know it was called emitter degeneration at dc. I just thought it was called bias stabilisation. But perhaps I'm wrong (again). Any comments? Light current 02:34, 10 August 2005 (UTC)
thread_title:  Emitter degeneration 

message: Some things look wrong.
1) I believe this circuit means to use the transistor in forward-active mode. Which means we have Ve < Vb < Vc around the transistor. In the circuit of Figure 1 this translates into 0 < Vin < Vout. Thus, the voltage gain can not possibly be negative.
2) I believe in the gain/impedance table the author got mixed up between Rc (resistor from the supply circuit) and r0 (internal property of the transistor according to the hybrid-pi model). I did the calculation for the circuit of Figure 1, and although the precise relationship between beta and beta0 is not yet absolutely clear to me, it occurs that in the end you get Vout = r0 * beta0 *Vin / rPI, which is the reason why my guess is that there has been some confusion between r0 and Rc from the author. Same goes for the output impedance. Besides, the reason I had to dig a bit into this is because my physical sense told me that it's impossible that V+ would be eliminated from the result but Rc would remain.
All in all my conclusion is that the table could be correct after replacing Rc for r0 and making the voltage gain positive instead of negative. Also, if one assumes that input current enters the circuit and output current leaves the circuit, one would also have to make the current gain and output impedance negative (it would be nice to have the 2 current conventions clarified on the sketches). And, for this corrected table to be correct, in addition to the assumptions of the hybrid-pi model, after forgetting any subtle difference there might be between beta0 and beta, you'd also have to have Rc large enough so that V+ bears no influence on the current gain and output impedance.ThorinMuglindir (talk) 18:54, 8 July 2012 (UTC)
replies: text: You're right about the operating mode of the transistor; it should be operating in the forward-active mode.  However, the voltage gain is most certainly negative.  If you increase Vin, then the transistor will let more current through, thus increasing the voltage across Rc and decreasing Vout.  Basically, Rc converts a positive current gain into a negative voltage gain.alex.forencich (talk) 09:19, 29 March 2015 (UTC)

text: Also, the usual convention in two-port analysis is to consider the current going in to a port to be positive.  Under that convention, the current gain is positive. SpinningSpark 10:38, 29 March 2015 (UTC)
thread_title:  Wrong gains 

message: While this is often described as "negative feedback" ... it predates the invention of negative feedback ...
Excuse me? Am I the only one who thinks that statement is absurd?
Negative feedback is a property inherent to the system, much like gravity is inherent to massive objects; it's just a way of describing what's going on. Whether or not it's presence was intended by the designer makes no odds to the system. 142.162.46.160 (talk) 17:56, 20 May 2016 (UTC)
replies: text: And what does it mean by "predates"?  Personally, I think characterizing the common-emitter (or common-cathode) configuration (degeneration) as negative feedback is a bit of a stretch anyway, since the feedback is not from the output.  But yes, it is often discussed in such terms, for its gain stabilizing effect.   Dicklyon (talk) 18:11, 20 May 2016 (UTC)
replies: text: I wondered about that, too, and looking at negative feedback didn't help much. I suspect, though, that the theory wasn't so well understood, especially for allowing components with large (gain) variation to be used reliably in circuits. This is especially important in ICs, where it allows one to use components with large tolerance, though consistent between devices on the same chip. Gah4 (talk) 06:58, 11 April 2019 (UTC)
thread_title:  Invention of negative feedback 

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thread_title:  External links modified 

message: It is a commonly believed fallacy that a phase shift occurs in a common emitter amplifier, or, indeed any other type of transistor stage.
The assumption is based on a cursory glance at the base and collector waveforms when a sine wave is used.  
If a sawtooth is used instead, the fallacy is revealed.
A couple of illustrations show this.  
Sine_2.jpg|Caption1
Sawtooth_2.jpg|Caption2
Syncopator (talk) 11:13, 16 February 2018 (UTC)
replies: text: -- They are the same thing. Take the Fourier transform of the sawtooth wave, shift all the components 180 degrees and see what you get.  222.155.167.133 (talk) 10:33, 28 September 2018 (UTC)

text: An inversion changes the phase of all frequencies by 180 degrees.  I don't understand your objection, or your funny figure. Dicklyon (talk) 05:55, 1 October 2018 (UTC)
replies: text: Even if you don't believe that (and I do), 180 degree phase shift is commonly used to mean inversion. It might even be used where phase doesn't have meaning.  Turning a person upside down, for example, might be called a 180 degree phase shift. Gah4 (talk) 07:03, 11 April 2019 (UTC)
thread_title:  180° phase shift vs inversion.