How to test 3rd Order Intercept Point of an amplifier

The third-order intercept point (IP3) is a measure of the linearity of an amplifier. It is the point at which the fundamental and third harmonic output signals have the same power level, and can be used to determine the distortion characteristics of an amplifier.

To test the third-order intercept point of an amplifier, you will need the following equipment:

1. Signal generator
2. Spectrum analyzer
3. Power meter
4. Two attenuators with known attenuation levels

The following steps can be followed to test the third-order intercept point of an amplifier:

1. Set up the signal generator to produce a two-tone signal with frequencies f1 and f2, where f2 = 2f1.
2. Use one of the attenuators to reduce the output power of the signal generator to a level suitable for the amplifier input.
3. Connect the amplifier input to the signal generator output through the attenuator.
4. Connect the amplifier output to the spectrum analyzer input.
5. Set the spectrum analyzer to display the output spectrum of the amplifier.
6. Adjust the input power level until the output spectrum of the amplifier shows the two-tone signal at frequencies f1 and f2.
7. Measure the output power level of the two-tone signal using the power meter.
8. Increase the input power level until the output power of the third harmonic signal at 3f1 is equal to the output power of the fundamental signal at f1.
9. Measure the output power level at this point using the power meter.
10. Calculate the third-order intercept point (IP3) using the formula:

IP3 = P1 + (P3 – P1)/2

where P1 is the power level of the fundamental signal and P3 is the power level of the third harmonic signal at the point of equal power.

Note that the attenuator used between the signal generator and the amplifier should be adjusted so that the input power level of the amplifier does not exceed its maximum specified input power.