Approximate method for hand computation of nonlinear distortion performance of varactor tuning circuits

The nonlinear distortion performance of varactor tuning circuits excited by an arbitrary number of input sinusoids with arbitrary amplitudes is analysed using an exponential series representation of the charge/voltage characteristic of the varactor diode. The special case of relatively small input-signal amplitudes is considered in detail and approximate closed-form expressions are obtained for the output harmonics and intermodulation products of any order. The simple expressions can be used for quick estimation of the nonlinear distortion performance of varactor tuning circuits using hand computation.