The OPA690 provides good distortion performance into a 100-Ω load on ±5-V supplies. Relative to alternative solutions, this device provides exceptional performance into lighter loads, while operating on a single 5-V supply. Increasing the load impedance improves distortion directly. Remember that the total load includes the feedback network; in the noninverting configuration (see Figure 7-1), this total load is sum of R_F + R_G, while in the inverting configuration the total load is just R_F. Also, providing an additional supply-decoupling capacitor (0.1 µF) between the supply pins (for bipolar operation) improves the 2nd-order distortion.

In most op amps, increasing the output voltage swing increases harmonic distortion directly. The new output stage used in the OPA690 actually holds the difference between fundamental power and the 2nd- and 3rd-harmonic powers relatively constant with increasing output power until very large output swings are required
(> 4 V_PP). This feature also shows up in the 2-tone, 3rd-order intermodulation spurious (IM3) response curves. The 3rd-order spurious levels are moderately low at low output power levels. The output stage continues to hold the distortion levels low even as the fundamental power reaches very high levels. Section 6.11 shows that the spurious intermodulation powers do not increase as predicted by a traditional intercept model. As the fundamental power level increases, the dynamic range does not decrease significantly. For two tones centered at 20 MHz, with 10 dBm/tone into a matched 50-Ω load (that is, 2 V_PP for each tone at the load, which requires 8 V_PP for the overall two-tone envelope at the output pin), Figure 6-50 shows 47-dBc difference between the test tone powers and the 3rd-order intermodulation spurious powers. This performance improves further when operating at lower frequencies.