A simplified analytical model for nonlinear distortion in RF bipolar circuits

The nonlinear behavior of common-emitter (CE) and single-balanced BJT mixer (SBM) circuits is described by a simple closed-form interpretable analytical expression. The third-order intermodulation distortion (IM3) calculated by this approach is in good agreement with harmonic-balance results of an APLAC circuit simulator for different input signal level, biasing current, emitter degeneration and operating frequency range. In addition, the model can successfully identify the bias currents that lead to a minimum or maximum amount of distortion. Therefore, it provides an easy guideline for the designer to directly optimize the linearity performance among other conflicting performance parameters; gain, noise and power dissipation.