ELT / TCT Reference Sheet

Measuring Output Impedance

 

Knowing the output impedance, ZOUT, of a device is often useful to the technician. The technique outlined below will allow the technician to easily and accurately measure the output impedance of a unit.

 

Procedure For Measuring Output Impedance:

 

  1. Connect the input source, usually a function generator, to the input of the unit under test (UUT), as shown below.
  2. Set the output of the signal source to an acceptable range. In the case of an amplifier, be sure the input is not so large that it will result in distortion of the amplifier output signal.


  3. Carefully measure the signal at the output of the UUT.
            This is the unloaded output voltage, VUL.


  4. Connect a load resistor, RL, to the output of the UUT as shown below. The load resistance should be approximately equal to the theoretical output impedance of the UUT.


  5. Carefully measure the signal at the output of the UUT. This is the loaded output voltage, VL.

  6. The output impedance may now be found using: