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Measuring the output resistance of an amplifier

Mir
Intellectual 485 points


I am using an opamp to make a non-inverting amplifier. A series 50ohm resistor is placed from the output of the IC to the output node of the package. In circuit, the resistor measures 50ohms. When tested in No-load and 50% loaded condition (as recommended by some websites) anomalous readings are obtained.

What is the correct setup for measuring output impedance?

  • 0
    TI__Guru 64125 points
    Hi Mir,

    You need to force a current into the output stage of the op amp and measure the voltage drop across a sense resistor. The sense resistor forms a voltage divider with the op amps closed-loop output impedance (Zout). Therefore, Zout can be back calculated based on the voltage on the op amp output and the current flowing into the output.