# Small singal amplifer. How to calculate

Discussion in 'Homework Help' started by Maintenance Man, Sep 19, 2011.

1. ### Maintenance Man Thread Starter New Member

May 12, 2010
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0
Hi to all
Could someone please help me figure VE, IE, VRL and VCE of a small common emitter amplifier using a voltage divider as the input on base. I just would like to know the formuals. Thank you very much for your help.

2. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,990
1,115
For this diagram

Base current is equal to :

$Ib = \frac{Vth - Vbe}{ Rth + (\beta+1)*Re}$

$Vth = Vcc*\frac{R2}{R1+R2}$

$Rth = *\frac{R1+R2}{R1*R2}$

And emitter current

$Ie = Ib*(\beta+1)$

$Ve = Ie * Re$

Collector current

$Ic = Ib*\beta$

$Vc = Vcc - Ic * Rc$

$Vce = Vc - Ve$

VRL ??

The voltage gain is equal

$Av = \frac{Rc||RL}{re} = gm * Rc||RL \approx 40 *Ic *(Rc||RL)$

$re = \frac{Vt}{Ic} \approx \frac{26mV}{Ic}$

$gm = \frac{1}{re} = \frac{Ic}{26mV} \approx 40 *Ic$

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Last edited: Sep 19, 2011
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