faustoleali1974
Newbie level 6
Dear Sirs, i'm trying to solve an exercise for an exam but i doesn't really understand how to do it
The circuit below:
**broken link removed**
LINK TO IMAGE
The exercise text: FIND THE APPROXIMATE VALUE OF THE AMPLIFIER IN THE FIGURE AT THE FREQUENCY fr:
Rcllector = 1250 Ohm
Remitter = 250 Ohm
L = 100 uH
C = 500 nF
Bo >>1
Bo * Remitter >> Rpi (resistance between base and emitter in the small signal model of the BJT)
fr = 1/(2*pi*sqrt(LC))
The solution of the exercise says:
The frequency fr is the resonance frequency of L-C parallel circuit. At this frequency the collector impedance is purely resistive (i think becouse Rcollector has a infinite impedance paralleled) SO THE GAIN IS THE ONE OF A DOUBLE LOAD CIRCUIT:
gain = Av = Vo/Vi = - Rcollector/Remitter = - 5
Can someone explain how to obtain this last formula?
---------- Post added at 03:16 ---------- Previous post was at 02:51 ----------
The formula is correct if I apply the small signal analysis that short circuit the supply with the ground but why must I obtain the gain with small signal analysis?
The circuit below:
**broken link removed**
LINK TO IMAGE
The exercise text: FIND THE APPROXIMATE VALUE OF THE AMPLIFIER IN THE FIGURE AT THE FREQUENCY fr:
Rcllector = 1250 Ohm
Remitter = 250 Ohm
L = 100 uH
C = 500 nF
Bo >>1
Bo * Remitter >> Rpi (resistance between base and emitter in the small signal model of the BJT)
fr = 1/(2*pi*sqrt(LC))
The solution of the exercise says:
The frequency fr is the resonance frequency of L-C parallel circuit. At this frequency the collector impedance is purely resistive (i think becouse Rcollector has a infinite impedance paralleled) SO THE GAIN IS THE ONE OF A DOUBLE LOAD CIRCUIT:
gain = Av = Vo/Vi = - Rcollector/Remitter = - 5
Can someone explain how to obtain this last formula?
---------- Post added at 03:16 ---------- Previous post was at 02:51 ----------
The formula is correct if I apply the small signal analysis that short circuit the supply with the ground but why must I obtain the gain with small signal analysis?
