The gain of the circuit is: Rc/Re (DC gain). All about electronics is relations between impedance. Now, if you calculate impedance Re - you may calculate gain for given frequency, The same time you may calculate how Re makes effect on input impedance.
Rez = 1/(√(1/Re)∧2+Zc∧2)

Yevgeny

 

The gain of the circuit is: Rc/Re (DC gain). All about electronics is relations between impedance. Now, if you calculate impedance Re - you may calculate gain for given frequency, The same time you may calculate how Re makes effect on input impedance.
Rez = 1/(√(1/Re)∧2+Zc∧2)

Yevgeny

Yevgeny - in order to avoid misundestandings and misinterpretations You should have mentioned that the expression Rc/Re is a rather rough estimation only. (What happens for Re=0 ? Infinite gain?)
This expression may be used for RE>>1/gm only (gm=transconductance).
More correct: Av=Rc/(Re + 1/gm)

 

LvW you right.
I try explain how parallel capacitor works, that why shown Rc/Re.

Thx.
Yevgeny

 

LvW you right.
I try explain how parallel capacitor works, that why shown Rc/Re.
Thx.
Yevgeny

OK - and what happens when you bypass RE with a cap?
Your expression: Gain approaches infinity
My (correct) expression: Gain is "gm*Rc"

 

Even you add internal impedance (Re) plus Zc(ω} x β - AC gain too mach. Last time i did that calculation about 30 years ago.

Yevgeny

 

Even you add internal impedance (Re) plus Zc(ω} x β - AC gain too mach. Last time i did that calculation about 30 years ago.
Yevgeny

OK - no problem.
Just for clarification (to avoid misunderstandings):
When you speak about "internal impedance (Re)" - you mean the inverse of the transconductance re=1/gm, which is a dynamic transresistance (small letters) - and Ohms law does NOT apply. Hence, it must not be called "internal resistance".