Electronics and Communication Engineering - Analog Electronics - Discussion
Discussion Forum : Analog Electronics - Section 1 (Q.No. 9)
9.
Gain of the amplifier is 'A'. Then the I/P impedance and O/P impedance of the closed loop amplifier shown below would be
Answer: Option
Explanation:
By using Miller theorem circuit can be redrawn as
.
Discussion:
11 comments Page 1 of 2.
Shadan said:
8 years ago
Since we know that Input impedance of Amplifier is high and output impedance is low so If Zin is input impedance and Input current Ii then Ii not flow in amplifier because of amplifier high input impedance so it goes through Feedback impedance then,
Ii=Vi-Vo/Z.
Take common Vi then,
=Vi(1-Vo/Vi)/Z,
= Vi(1-A)/Z. (A= Vo/Vi).
So input impedance Zi= Vi/Ii= Vi/Vi(1-A)/Z.
= Z/1-A.
And output impedance is Zo= Vo/Ii.
Zo= A*Vi/Vi(1-A)/Z.
= ZA/1-A.
Thanks.
Ii=Vi-Vo/Z.
Take common Vi then,
=Vi(1-Vo/Vi)/Z,
= Vi(1-A)/Z. (A= Vo/Vi).
So input impedance Zi= Vi/Ii= Vi/Vi(1-A)/Z.
= Z/1-A.
And output impedance is Zo= Vo/Ii.
Zo= A*Vi/Vi(1-A)/Z.
= ZA/1-A.
Thanks.
(7)
Krishna said:
6 years ago
Miller theorem is used to analyse an amplifier in which a resistor is present between o/p and i/p node.
Zi = (Z/1-A) & Zo =(Z*A/A-1).
Zi = (Z/1-A) & Zo =(Z*A/A-1).
(1)
Vikas said:
7 years ago
You are right @Vijay.
But here I0=Ii because current is not flowing through amplifier. Its flow through feedback.
But here I0=Ii because current is not flowing through amplifier. Its flow through feedback.
Vijay said:
7 years ago
@Shadan.
Shouldn't the output impedance be Zo=Vo/Io i.e. Io=output current?
Shouldn't the output impedance be Zo=Vo/Io i.e. Io=output current?
Mahesh said:
10 years ago
What about input impedance? How to calculate it?
Vinoth said:
7 years ago
Zi=Z/1-A but the answer is Zi=Z/A-1.
Lak said:
9 years ago
Please, can anyone explain this?
(1)
Rajitha said:
7 years ago
@Vinoth.
Actually Zi=Z/1-A.
Actually Zi=Z/1-A.
Hemanrh said:
5 years ago
Thank you @Shadan.
Gayatri said:
7 years ago
Thank you @Shadan
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