Perturbation Analysis and Experimental Verification of Intermodulation and Harmonic Distortion for an Anti-Series Varactor Pair

Nonlinear distortions in an anti-series varactor pair (ASVP) are analyzed by a perturbation method. To the authors' knowledge, this paper presents the first derivation of an analytical expression that explicitly shows intermodulation and harmonic distortions of the ASVP. In addition to canceling the expected even-order distortion, the third-order distortion can be suppressed simultaneously when a certain condition is satisfied. We also find that the second- and third-order distortions can be greatly suppressed without dependence on dc bias voltage if the varactors in the ASVP have an ideal abrupt p-n junction. These theoretical predictions are verified by measuring the second- and third-order harmonic distortions of an ASVP. The experimental results show that the second-order harmonic distortion is suppressed by approximately 20 dB. The third-order harmonic distortion is suppressed to the same extent in the theoretically predicted dc bias voltage range.