In Noninverting Amplifier, the op-amp parameters are given as follows:
A = 200,000, Zin = 1MΩ and Zout=100Ω.
Calculate the amplifier output impedance (with negative feedback)
r1 = 10kΩ
r2 = 10kΩ
a) Zout_f = 100 Ω
b) cannot be determined.
c) Zout_f = 10 mΩ
d) Zout_f = 1 mΩ
The formula for calculating the output impedance of a noninverting amplifier with negative feedback is:
Zout_f = (A + 1) * Zout / (A * (1 + Vin/Vout)^2 - 1)
Where A is the open-loop gain of the op-amp, Zout is the op-amp's output impedance, Vin is the input voltage and Vout is the output voltage. In this case, we can assume that Vin is equivalent to Vout, since the noninverting amplifier has unity gain (i.e. Av = 1 + Rf/Ri). Therefore, Vin/Vout is equal to 1.
Plugging in the given values, we get:
Zout_f = (200,001) * 100Ω / (200,000 * (1 + 1)^2 - 1)
Zout_f = 10 mΩ
Therefore, the answer is option c) Zout_f = 10 mΩ.
To calculate the amplifier output impedance with negative feedback, we can use the formula:
Zout_f = Zout / (1 + A * (r2 / r1))
Given A (open-loop voltage gain) = 200,000, Zin (input impedance) = 1MΩ, Zout (output impedance) = 100Ω, r1 = 10kΩ, and r2 = 10kΩ, we can substitute these values into the formula:
Zout_f = 100Ω / (1 + 200,000 * (10kΩ / 10kΩ))
Simplifying further:
Zout_f = 100Ω / (1 + 200,000)
Zout_f = 100Ω / 200,001
Zout_f ≈ 0.0005Ω
Therefore, the amplifier output impedance (with negative feedback) is approximately 0.0005Ω.
The closest option is d) Zout_f = 1 mΩ.