- #1

kelvin56484984

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## Homework Statement

assume β=200,Vt=26mV,Vbe(on)=0.7V

Find the voltage gain Vo/Vs

How to find the Rth , Vs ,then find the voltage gain?

I try to draw the circuit diagram below

## Homework Equations

## The Attempt at a Solution

Vth=[R2/(R1+R2)]*15

Vth=1.63V

Which method should I use to find Rth?

Rth=R2//R1

=5.53k ohm

or

I see this formula Rth=0.1Re(1+β) on my book

Rth=0.1Re(1+β)

=10.3k ohm

I assume Rth=R2//R1

Vth=Rth*Ib+Ie*Re+Vbe

Vth=Rth*Ib+(1+β)*Ib*Re+0.7

Ib=8.57μA

Rπ=Vt/Ib

Rπ=26m/8.57μ

Rπ=3.03k ohm

Assume my small signal model diagram is correct

Vb=ib*Rπ

Vo=-βib*Rc

But how to find the Vs

then I can find the voltage gain(Vo/Vs)?

=[Vo/Vb]*[Vb/Vs]