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How to Measure Op-Amp Input Resistance

An operational amplifier -- or "op-amp" for short -- is an integrated electronic circuit that can be used to serve as a voltage-controlled oscillator, to generate voltage pulses, to amplify AC signals, and for several other functions within an electronic circuit. Some circuit functions -- such as AC signal amplification -- require that the impedance in both sides of a circuit must be matched properly. Since circuit impedance and resistance are closely linked, it may be necessary to measure the input or output resistance of the op-amp.

Things You'll Need

Electrical input source (such as a TTL signal generator)
Ammeter
Voltmeter
Operational amplifier installed into a circuit
Electrical ground source
Electrical test probe with alligator-clip ends
Pencil or pen
Paper
Calculator

Instructions

- 1
  Turn on the ammeter and the voltmeter. Set the ammeter scale to "DC amps." Set the voltmeter to "DC volts."
- 2
  Attach the black ammeter lead to the non-inverting input lead on the op-amp. Connect the red ammeter lead to the positive terminal on the electrical input source.
- 3
  Connect one end of the test probe to the electrical ground source. Connect the other end of this probe to the inverting input lead.
- 4
  Attach the red voltmeter lead to the op-amp's input lead. Attach the black voltmeter lead to the electrical ground source. Turn on the electrical input source.
- 5
  Divide the voltage measurement by the current measurement. This calculated value is the input resistance measurement.

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