Figure 3-4 Two-Tone OIP3 Test Setup

Use the following guidelines for two-tone OIP3 measurement:

1. As shown in Figure 3-4, combine two signal generator outputs using an in-phase power splitter/combiner. 6dB attenuators are recommended at the RF signal generator outputs to increase isolation between the two signal generators and minimize IMD3 spurs.
2. Set both the RF signal generator outputs to a power level and frequency spacing such that the signal generator yields the desired output power (P_OUT) at the device.
3. TI recommends that the output power level be within the linear operation range of the TRF0108-SP and TRF0108-SEP devices. For example, set the power on the signal generators such that the power at the device output results in approximately –4dBm per tone. As a general rule, TI recommends to keep the total output power level approximately 6 to 8dB lower than the 1dB compression point. See the device datasheet for the output power levels supported by the device.
4. Set the two tones on the signal generator according to the desired center frequency and the frequency spacing.
5. Set the spectrum analyzer attenuation setting appropriately so that the spectrum analyzer non-linearity does not affect the measurements.
6. Keep spectrum analyzer RBW and VBW settings identical for the main tones and the IM3 products.
7. For output IP3 calculation, take into account combined losses at the desired frequency band between the device output to the spectrum analyzer input. The combined power loss is due to PCB output trace, RF coax cable, and any external attenuator pad used. The calculated OIP3 is given by Equation 1.
   Equation 1. $\mathrm{O}\mathrm{u}\mathrm{t}\mathrm{p}\mathrm{u}\mathrm{t}\mathrm{}\mathrm{I}\mathrm{P}3=\frac{{\mathrm{P}}_{\mathrm{I}\mathrm{N}\_\mathrm{S}\mathrm{A}}-\mathrm{I}\mathrm{M}\mathrm{D}3}{2}+{\mathrm{P}}_{\mathrm{I}\mathrm{N}\_\mathrm{S}\mathrm{A}}+{\mathrm{P}}_{\mathrm{L}\mathrm{O}\mathrm{S}\mathrm{S}}$

   where,

   • P_{IN_SA} = Input power per tone into the spectrum analyzer
   • P_LOSS = Power loss from the device output to the spectrum analyzer input
   • IMD3 = Higher power of the two intermodulation distortion products recorded at either 2f1 – f2 or 2f2 – f1
8. In Equation 1, P_{IN_SA} + P_LOSS = P_OUT is the amplifier output power per tone.