Common Emitter Amplifier

A video showing how to do AC analysis of a common emitter amplifier. AC analysis involves figuring out the voltage gain, the input impedance and the output impedance of the amplifier.

[jakerankin]

If anyone is wondering why the output impedance is found by treating Rc as if its in series with the load when its clearly in parallel in the diagram, its because in the simplified amplifier model (the triangle) we model the output as a thevinin equivalent circuit with the output impedance being the thevinin equivalent resistance. Its kind of unexplained in the video but him opening up the current source is just the usual step you take to finding thevinen resistance, which ends up being just Rc. And so when you put together the output as a thevinin equivalent circuit in the final model you have Zout as Rc in series with the load.

Very helpful video by the way i just wanted to clear this up because it stumped me for a while

[baustin]

my god, you explained this much more clear than my microelectronics professor. bless your soul.

[bjarneb]

best series on BJT's possible, i've learned alot and it all makes sense now, thank you very much

[louisnkotto]

Eleven years later I come across this masterpiece.
Thank you so much

[Kevin]

Good video, confirmed a different method I learned for solving these beasts.  Highly satisfying when you make your calculations, build it, and your in a close ballpark to actual values.

[RTD]

Great explanation - the best I've seen on YouTube.

[jessmac]

Great video and explanation. Very clear. I wish I’d found your videos weeks ago. Subscribed and bookmarked

[Pechette-]

Thank you very much ! Your videos helped me tremendously in understanding this topic, and the use of "t-model" is a lot more easier to work with.

[hermandjens]

I know you made this vidio many years ago, but it helped me understand the effect of impedance today thank you!

[shuyuchen]

Thank you so much David, this cleared my doubt for long time and thanks to people who asked the question about Re, since I got the same questions!!

[thePrinceOfPurpose]

You are very good at explaining electronics. Thank you for posting this video.

[sarahsshadow]

You are going to save me in my christmas exams... great tutorial, thank you!

[Foxkoun]

Between your video and alot of back and forth in the book I'm much more confident about this material.

[renruida]

Great Tutorial. Finally understood how these things work

[davyemak]

Thanks you sir!! Clear explanation with the best audio and visual effect!! More easy to understand than the explanation of my lecturer at institute!!! 

[darkstar]

If only my prof could explain as well as you did! Thanks!

[benji]

you are a great teacher. these are wonderful tutorials

[sky_kryst]

There are very few professors who can explain this with such simplicity. And thank god you're on the internet!

[hbrt]

To those asking where the RE went in the AC analysis, it was shorted by the bypass capacitor. Capacitors are shorted in AC and therefore current passe through the shorted component to avoid the resistance.

[qaderexpert]

best explanation, you made everything simple and clear. Thank you so much