Figure 2-3 OIP3 Test Setup

Use the following guidelines for two-tone OIP3 measurement:

1. Figure 2-3 shows the combination of two signal generator outputs using an in-phase power splitter and combiner. Use an optional 3dB to 6dB attenuator at the signal-generator outputs to prevent the generators from interacting, resulting in signal-generator IMD3 spurs.
2. Set both the signal generator outputs to a power level and frequency spacing so that the signal generator yields the desired output power, ${\mathrm{P}}_{\mathrm{O}\mathrm{U}\mathrm{T}}$, at the device.
3. Keep the output power level within the TRF1218 linear operating range. As a general rule, keep the total output power level approximately 6dB to 8dB less than the 1dB compression point. See the device data sheet for the supported output power levels.
4. For the OIP3 test, the two tones can be spaced by the specified frequency.
5. Set the spectrum analyzer attenuation setting appropriately so that the spectrum analyzer nonlinearity does not affect the measurements.
6. Keep spectrum analyzer RBW and VBW settings identical for main tone and IM3 products.

For output IP3 calculation, take into account the combined losses at the desired frequency band between the TRF1218EVM output to the spectrum analyzer input. The combined power loss(${\mathrm{P}}_{\mathrm{L}\mathrm{O}\mathrm{S}\mathrm{S}}$) is due to the resistive match at DUT output, PCB output trace, RF coax cable, 180° passive balun, and any attenuator pads used for external matching. Equation 2 gives the calculated OIP3.

where

• ${\mathrm{P}}_{\mathrm{I}\mathrm{N}\_\mathrm{S}\mathrm{A}}$ = Input power per tone into the spectrum analyzer
• ${\mathrm{P}}_{\mathrm{L}\mathrm{O}\mathrm{S}\mathrm{S}}$ = Power loss from the device output to the spectrum analyzer input
• $\mathrm{I}\mathrm{M}\mathrm{D}3$ = Higher power of the two intermodulation distortion products recorded at either 2f1 – f2 or 2f2 – f1
• ${\mathrm{P}}_{\mathrm{I}\mathrm{N}\_\mathrm{S}\mathrm{A}}+{\mathrm{P}}_{\mathrm{L}\mathrm{O}\mathrm{S}\mathrm{S}}={\mathrm{P}}_{\mathrm{O}\mathrm{U}\mathrm{T}}$ is the amplifier output power per tone