For the generic amplifier shown in the figure, if we know the values of the vI,
ID: 2991195 • Letter: F
Question
For the generic amplifier shown in the figure, if we know the values of the vI, vo, Rs, and Rl, and you have a voltage meter, can you measure the output resistance Rout? Please describe the measurement procedure (hint: consider the output with or without load resistance).
For the generic amplifier shown in the figure, if we know the values of the vI, vo, Rs, and Rl, and you have a voltage meter, can you measure the output resistance Rout? Please describe the measurement procedure (hint: consider the output with or without load resistance).Explanation / Answer
Say you set your op-amp to output 5V, and you measure the voltage with an open circuit1. The current will be 0A (because the circuit is open) and the voltage you measure will be 5V. Now, you connect a resistor to the output, such that the current at the output of the op-amp is 50mA. You measure the voltage across this resistor and find it to be 4.99V. You can then calculate the output impedance of the op-amp as:
(-5V-4.99V)/(0mA-50mA)=0.2
You will note that I changed the sign of the result. This low source impedance means the op-amp can supply (or sink) a lot of current without the voltage changing much.