Using an Oscilloscope to Measure the Output Impedance of a Signal Source

 

Measurement Equipment:

• Oscilloscope ( Hantek DPO7000)

• Signal Generator (Hantek HDG3000)

• Load Resistor with Known Resistance

Measurement Principle:

The signal source can be modeled as an ideal voltage source in series with an output impedance Ro.

By measuring the open-circuit voltage (V_open) and the loaded voltage (V_L), and applying the voltage division principle, the following formula is derived: Ro = R_L × (V_open / V_L - 1)

 
 
 

Measurement process:

The signal generator outputs a 1kHz, 2Vpp sine wave.

The oscilloscope measures the open-circuit voltage peak-to-peak V_open as 2.02 Vpp.

After connecting a 45Ω load resistor, the peak-to-peak voltage across the load V_L is measured as 960mV.

By substituting into the formula, the result is 49.68 Ω, so the output impedance of this signal source is 50 Ω.

 
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