Nice analysis! 0:35 and 8:38. Yes, maybe not for a typical audio amplifier but there are some niche audio applications. (Perhaps, not so common now.) Examples are moving coil phono or microphone pre-amp inputs. There, the low input impedance is appropriate. An additional trick that was commonly applied, is to use transistors with large emitter areas (e.g. a power transistor), for low noise. The low Rbe value reduced thermal noise. It is true though, that common base is more at home in RF applications where the much better bandwidth of the common base amp is a big bonus, compared to the other common transistor amp configurations.
*Your teaching methodology is truly outstanding among the currently existent and constantly growing sea of youtube resources.* I wish you had been posting content 12 years ago when I was still in college lol. I remember when I first I got into BJT design topology, the notation in analysis kept scrambling my brain! I did finally nail it, but looking back it seemed to have been presented in a manner that made it much more difficult than it needed to be.
Hi Professor Fiore why have not you considered base dynamic resistance .. for voltage gain.. output over input it is not required for calculation , but does it remains active behind the scenes...please clear this Sir.
As always in these sorts of analyses, we make certain assumptions and simplifications in order to speed the process. The question is, are these simplifications still leading to a reasonably accurate result? If you compare the results of our calculations to the results of the simulations, you can see that the agreement is very high. Indeed, most of the variation seems to be coming from non-linearities (i.e., distortion). In short, why chase down second order effects if all you're looking for is an overall performance metric?
I'm still confused, why can't we just give the base a resistor that large enough to increase the Zin, so that to reduce the loading effect. As Zin will equal: Re // (r'e + Rb//Inf ). Thanks you.
You're forgetting the difference between Ib and Ie. When you're looking at the emitter from the base, everything in the emitter appears beta times larger, right? The inverse is also true. When you're looking at the base from the emitter, everything in the base appears beta times smaller.
@ElectronicswithProfessorFiore oh my dumb, forgot that it is the ib there, thanks you so much. But I still wonder if we can put a huge resistor there that even after a beta time smaller, it could still large enough for a raise in Zin. Will there be any side effect from that? You give me the confidence to attend the analog circuit class again after a long break in fear, I just want thanks you again prof.
@@phile7420 You could do that to raise the Zin, but then the approximation that the base is at ground is no longer true and you'll see a reduction in both voltage gain and upper frequency limit. You're paying 10 dollars (euros, whatever) to save 1. Not a good tradeoff. Glad the channel is helping you. That's why I'm here.
Common base amplifiers do not get the "beta multiply" effect. You see that when the input is applied to the base, not when it is applied to the emitter.
Second time around... The distortion information was more meaningful this time. If we have a r'e of 50 Ohms and we added 50 Ohms to the emitter (to give r'e + Re = 100 Ohms, we'd half the Avout.), what would happen to the distortion?
@@ElectronicswithProfessorFiore so.... amplification is directly proportional to distortion? That is, if I halve the amplification through the addition of Re, then I halve the distortion? (I'm sorry that I'm struggling with this and I appreciate your patience).
@@simonyoungglostog Sort of. What's happening here is that adding Re is a form of negative feedback (this is discussed in some detail in the Op Amps sequence). With negative feedback, you sacrifice gain in order to get other things you want (lower distortion, wider bandwidth, increased/decreased Zin/Zout). The more you sacrifice, the more you get.
Nice analysis!
0:35 and 8:38. Yes, maybe not for a typical audio amplifier but there are some niche audio applications. (Perhaps, not so common now.) Examples are moving coil phono or microphone pre-amp inputs. There, the low input impedance is appropriate. An additional trick that was commonly applied, is to use transistors with large emitter areas (e.g. a power transistor), for low noise. The low Rbe value reduced thermal noise. It is true though, that common base is more at home in RF applications where the much better bandwidth of the common base amp is a big bonus, compared to the other common transistor amp configurations.
*Your teaching methodology is truly outstanding among the currently existent and constantly growing sea of youtube resources.* I wish you had been posting content 12 years ago when I was still in college lol.
I remember when I first I got into BJT design topology, the notation in analysis kept scrambling my brain! I did finally nail it, but looking back it seemed to have been presented in a manner that made it much more difficult than it needed to be.
If only I had a time machine ;-)
In any case, tell your friends and co-workers, maybe they can benefit!
Thank you. I'm guessing that this arrangement has advantages that are yet to be discussed (compared to CE).
+ and -, as usual. On the plus side, no Miller effect as it's non-inverting (= higher f2).
EXCELLENT PRESENTATION! I FIND THAT SYMBLE FOR CURRENT SOURCE STRANGE,I THOUGHT IT WAS A DIAMOND SHAPED?
You see both. Often the diamond form is used specifically for a controlled current source. TINA's is sort of a combo.
Hi Professor Fiore why have not you considered base dynamic resistance .. for voltage gain.. output over input it is not required for calculation , but does it remains active behind the scenes...please clear this Sir.
As always in these sorts of analyses, we make certain assumptions and simplifications in order to speed the process. The question is, are these simplifications still leading to a reasonably accurate result? If you compare the results of our calculations to the results of the simulations, you can see that the agreement is very high. Indeed, most of the variation seems to be coming from non-linearities (i.e., distortion). In short, why chase down second order effects if all you're looking for is an overall performance metric?
Thank you very much Sir
I'm still confused, why can't we just give the base a resistor that large enough to increase the Zin, so that to reduce the loading effect. As Zin will equal: Re // (r'e + Rb//Inf ).
Thanks you.
You're forgetting the difference between Ib and Ie. When you're looking at the emitter from the base, everything in the emitter appears beta times larger, right? The inverse is also true. When you're looking at the base from the emitter, everything in the base appears beta times smaller.
@ElectronicswithProfessorFiore oh my dumb, forgot that it is the ib there, thanks you so much.
But I still wonder if we can put a huge resistor there that even after a beta time smaller, it could still large enough for a raise in Zin. Will there be any side effect from that?
You give me the confidence to attend the analog circuit class again after a long break in fear, I just want thanks you again prof.
@@phile7420 You could do that to raise the Zin, but then the approximation that the base is at ground is no longer true and you'll see a reduction in both voltage gain and upper frequency limit. You're paying 10 dollars (euros, whatever) to save 1. Not a good tradeoff.
Glad the channel is helping you. That's why I'm here.
WHY DID YOU NOT MULTIPLY r'e times beta in parallel Re?
Common base amplifiers do not get the "beta multiply" effect. You see that when the input is applied to the base, not when it is applied to the emitter.
Second time around...
The distortion information was more meaningful this time. If we have a r'e of 50 Ohms and we added 50 Ohms to the emitter (to give r'e + Re = 100 Ohms, we'd half the Avout.), what would happen to the distortion?
Assuming you turned up Vin to get a comparable load voltage, you'd see the distortion drop by a similar percentage.
@@ElectronicswithProfessorFiore so.... amplification is directly proportional to distortion? That is, if I halve the amplification through the addition of Re, then I halve the distortion? (I'm sorry that I'm struggling with this and I appreciate your patience).
@@simonyoungglostog Sort of. What's happening here is that adding Re is a form of negative feedback (this is discussed in some detail in the Op Amps sequence). With negative feedback, you sacrifice gain in order to get other things you want (lower distortion, wider bandwidth, increased/decreased Zin/Zout). The more you sacrifice, the more you get.