An amplifier has a voltage gain of 30 dB and current gain of

An amplifier has a voltage gain of 30 dB and current gain of 70 dB. What is the power gain in decibels? If the input resistance is 100 k, what is the load resistance?

An amplifier with a voltage gain of 40 dB, an input resistance of 20 k, and an output resistance of 75 is used to drive a 50 load. What is the value of the open circuit voltage gain? Find the value of the power gain in dB.

Solution

Ans)

   Voltage gain =20 Log(Vout/Vin)=30 dB

   Vout/Vin=10^(30/20)=31.62

Current gain =20 Log(Iout/Iin)=70 dB

Iout/Iin=10^(70/20)=3162.28

Power Gain=Pout/Pin=(Vout/Vin)*(Iout/Iin)=99991.29

Power Gain in dB=10 Log(Pout/Pin)=50 dB

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Input Resistance Rin =Vin/Iin=100 kohms

Vout/Vin=31.62 ---eq1 and  Iout/Iin=3162.28-eq2

eq1/eq2 gives

Rout=RL=(31.62/3162.28)*Rin=(31.62/3162.28)*100k

So Load Resistance RL=1000 ohms or 1k ohms

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