Improved Nonlinearity Model With Variable Knee Sharpness

In 1980, the writer proposed an instantaneous nonlinearity model with variable knee sharpness. In 1996, Litva and Lo found that it gave incorrect results for a two-tone intermodulation test, and in 2000, Loyka diagnosed the reason: nonanalyticity. Further study showed that no problem exists with typical real-world signals; nevertheless, this paper presents a new model that eliminates the problem entirely. For context, it also discusses envelope models and their application to radio-frequency power amplifiers.