Enabling low-distortion varactors for adaptive transmitters

Cong Huang*, Leo C.N. De Vreede, Francesco Sarubbi, Miloš Popadič, Koen Buisman, Jawad Qureshi, Mauro Marchetti, Atef Akhnoukh, Tom L.M. Scholtes, Lawrence E. Larson, Lis K. Nanver

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

26 Citations (Scopus)


A varactor diode configuration is presented for the implementation of low-distortion tunable matching networks, phase shifters, and filters. The configuration is based on varactors with an exponential C(V) relation in antiseries configuration with specific control voltage harmonic loading conditions. The resulting network combines a high capacitance tuning range with relatively low control voltages and excellent linearity. The linearity is independent of the applied control voltage and does not degrade at low tone spacing, which is ideal for the realization of adaptive transmitters and modulators. A specific Nd x -2 varactor doping profile is required for exact third-order intermodulation (IM3) cancellation. The remaining distortion is dominated by the much smaller fifth-order nonlinearities. The required impedance levels of the harmonic terminations are studied in terms of the maximum modulation bandwidth for which the proposed configuration remains linear. The doping profile optimization for quality factor, tuning range, and breakdown voltage is discussed. For experimental verification, the proposed varactor configuration has been implemented using a silicon-on-glass technology. The measurements demonstrate IM3 cancellation and indicate a superior linearity for modulated signals up to 10-MHz bandwidth.

Original languageEnglish
Article number4490422
Pages (from-to)1149-1163
Number of pages15
JournalIEEE transactions on microwave theory and techniques
Issue number5
Publication statusPublished - 12 May 2008
Externally publishedYes


  • Adaptive systems
  • Band switching
  • Impedance matching
  • Low distortion
  • Tunable filters
  • Tuners
  • Varactors


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