1.At low frequencies, an op-amp has an open-loop gain A0 =10^5 and an open-loop
ID: 1832469 • Letter: 1
Question
1.At low frequencies, an op-amp has an open-loop gain A0 =10^5 and an open-loop output resistance R0 =150 . The op-amp is to be used in a non-inverting amplifierr having a voltage gain of 200. If the amplifier is designed with the assumption that the op-amp is ideal and the input resistance to the feedback network is to be 100 k, calculate the actual gain of the circuit and its output resistance.
Answer:[199.60, 0.29940 ]
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Explanation / Answer
Given
Ao = 105 , AF = 200 , Ro = 150
The relation between Ao and AF is given by
AF = Ao / D, where D = 1+Ao
D = Ao / AF = 105 / 200 = 500
The output resistance of the non-inverting amplifier is
RoF = Ro / D = 150/500 = 0.3
1 + Ao = 500
= 499 /105 = 0.00499
The feedback factor for a non-inverting amplifier is
= R1 / (R1 + RF)
0.00499 = R1 / (R1 + 100000)
R1 = 501
Voltage gain
Af = 1 + (100000/501) = 199.6
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