# amplifier

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#### chalithamalin

##### New Member
please tell me if this is a correct amplifier one or not? if it is not a correct please tell me what the wrong it has. i made an amplifier following method.

R1 = Rc, R2 = Re, R3 = Rl , R4 = Rb1, R5 = Rb2 V1 = Vcc
Where RBB = (Rb1//Rb2)

AC EQIEVELENT

Vo = gmVbe (Rc//Rl)
Vbe = Vin (rπ/ ( rπ+RBB))
Then,
Vo = gm [Vin (rπ/( rπ+RBB))] (Rc//Rl)
Vo/ Vin = gm (rπ/( rπ+RBB)) (Rc//Rl)
Av = gm (rπ/( rπ+RBB)) (Rc//Rl)
(Rc//Rl) = output impedance
( rπ+RBB) = input impedance

Gain = 10v/v
Input impedance = 20kΩ
Output impedance = 20 Ω
rπ = 4.5k Ω (2N3903)

using these values ,
gm = ?
then,
Ic = gm VT
Rc = (Vcc – Vcc*2/3)/Ic
β = 100 (I assumed it as 100)
α = β/ β+1
IE = Ic/ α
VRb2 = Vcc*1/3
Hence,
Vbe = Vb - Ve
0.7 = VRb2 - Ve
Ve = VRb2 -0.7
Re = (Ve - 0)/Ie

Then,
Rc//Rl = output impedance
Rl = ?

Rb2//Rb1 = RBB ------------------------------------(1)
{Rb2/(Rb1 + Rb2)}*Vcc = (Vcc*1/3) ------------(2)
Rb2 = ? and Rb1 = ?

This is a small signal amplifier so I used input signal in mille volts (10mV) and frequency in kHz (25kHz)

Reference : - Sedra/Smith microelectronic CIRCUITS (5th edition)

if u can't see my circuit diagram please mail me chalithamalin@yahoo.com

#### BrownOut

##### Banned
I don't see a diagram.

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