The THS6212 provides good distortion performance into a 100-Ω load on a 28V supply. Relative to alternative solutions, the amplifier provides exceptional performance into lighter loads and operation on a 12V supply. Generally, until the fundamental signal reaches very high frequency or power levels, the second harmonic dominates the distortion with a negligible third-harmonic component. Focusing then on the second harmonic, 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 value is the sum of R_F + R_G, whereas in the inverting configuration this value is just R_F. Providing an additional supply decoupling capacitor (0.01 μF) between the supply pins (for bipolar operation) also improves the second-order distortion slightly (from 3 dB to 6 dB).

In most op amps, increasing the output voltage swing directly increases harmonic distortion. The Typical Characteristics sections illustrate the second harmonic increasing at a little less than the expected 2x rate, whereas the third harmonic increases at a little less than the expected 3x rate. Where the test power doubles, the difference between the fundamental power and the second harmonic decreases less than the expected 6 dB, whereas the difference between the fundamental power and the third harmonic decreases by less than the expected 12 dB. This difference also appears in the two-tone, third-order intermodulation (IM3) spurious response curves. The third-order spurious levels are extremely low at low-output power levels. The output stage continues to hold the third-order spurious levels low even when the fundamental power reaches very high levels.