Electronics - Operational Amplifiers - Discussion
Discussion Forum : Operational Amplifiers - General Questions (Q.No. 18)
18.
Input impedance [Zin(I)] of an inverting amplifier is approximately equal to:
Discussion:
5 comments Page 1 of 1.
Mano said:
10 years ago
The main problem that I am having is with the formula for input impedance: Zin = R1(1+BAol).
Where R1 is the input resistance of the opamp itself.
So if Rin and Rf (which is the feedback resistor) are equal, B will be 1.
Then by this formula, Zin will be R1(1+Aol).
In a normal inverting amplifier, following the "golden rules" the input current is (Vin - 0)/Rin.
Zin is then Vin/(Vin/Rin) = Rin.
Where R1 is the input resistance of the opamp itself.
So if Rin and Rf (which is the feedback resistor) are equal, B will be 1.
Then by this formula, Zin will be R1(1+Aol).
In a normal inverting amplifier, following the "golden rules" the input current is (Vin - 0)/Rin.
Zin is then Vin/(Vin/Rin) = Rin.
Dhanu said:
9 years ago
The input impedance, as always, is the impedance to ground for an input signal. The - input is at the same voltage as the + input which is ground. We can thus consider the - input to be at what is referred to as virtual ground. The input impedance for the overall amplifier will be simply Ri.
Zin = Ri.
Zin = Ri.
Arvind said:
9 years ago
Tell me the description.
(1)
Raina said:
10 years ago
Can anyone explain how?
Rahul sharma said:
9 years ago
Please explain how?
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