# Ex. 1-13 Sedra Smith

Discussion in 'Homework Help' started by sandman42, Aug 24, 2007.

1. ### sandman42 Thread Starter New Member

Aug 22, 2007
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0
Hi,

here I am with another question:

Given the attached circuit, the exercise says. "An amplifier with a voltage gain of 40 dB, and inpur resistance of 10 kohm and an output resistance of 1kohm is used to drive a 1kohm load. What is the value or Avo?"

If I understand correctly, Av=Vo/Vi, Vo is the V on RL, so Vo= (RL * Avo* Vi)/(RL+Ro), so Av= (RL * Avo)/(RL+Ro), therefore Avo=((RL+Ro)*Av)/RL.

With the given data that makes twice of Av. Av= 40dB= 100 so Avo should be 200.

As usual, I trust answers, but I thought that, since in a coupled amplifier, not all the voltage supplied gets transferred to the load, but only a fraction due to output resistance that must be kept lower than load resistance, i.e. Ro << RL, so how can Av and Avo have the same value?

Or, (since english is not my native language), does "An amplifier with a voltage gain of 40 dB" means "An amplifier with Avo=40dB", since the Av is the overall gain, i.e. when the load is applied, so if for example RL were 1 Mohm, Av = 99% Avo?

Thanks

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2. ### JoeJester AAC Fanatic!

Apr 26, 2005
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Look at that right hand schematic. You set the Avo to 200 ... what is the voltage across the Load resistor?

Then change the load resistor to 1 M ohm and answer the same question ... what is the voltage across the load resistor.