16-06-2017, 04:32 PM
I'm getting déjà vu here 
http://golbornevintageradio.co.uk/forum/...1#pid66491
We didn't get as far as AC analysis there, sadly. And to keep it really simple for the purposes of understanding, I ignored Ib, knowing that 47k and 10k would pass plenty of current.
For AC, when calculating the "full" gain, I go down the gm.RL route, rather than RL/Re. They are mathematically equivalent, it's just that I find it far more intuitive to think of the transistors as a transconductance amplifier with a transconductance of 40 times Ic, which of course comes straight from the Ebers-Moll equation. To consider RL/Re, you really need to think in terms of negative feedback, which is an unnecessary layer for a beginner IMHO. Or you tell them to "just accept it", which many people are uncomfortable with. Teaching is all about the "story" in my experience...
http://golbornevintageradio.co.uk/forum/...1#pid66491
We didn't get as far as AC analysis there, sadly. And to keep it really simple for the purposes of understanding, I ignored Ib, knowing that 47k and 10k would pass plenty of current.
For AC, when calculating the "full" gain, I go down the gm.RL route, rather than RL/Re. They are mathematically equivalent, it's just that I find it far more intuitive to think of the transistors as a transconductance amplifier with a transconductance of 40 times Ic, which of course comes straight from the Ebers-Moll equation. To consider RL/Re, you really need to think in terms of negative feedback, which is an unnecessary layer for a beginner IMHO. Or you tell them to "just accept it", which many people are uncomfortable with. Teaching is all about the "story" in my experience...
