Loukas Chevas 1, Matthias Bucher 1, Nikolaos Makris 1,2, Ioannis Spiridon Fosteris 1, Nikolaos Fasarakis 1, Antonios Stavrinidis 2,1, Maria Kayambaki 2, Athanasios Kostopoulos 2
and George Konstantinidis 2
Methodology for Harmonic Distortion Characterization and Modelling of GaN HEMT Varactors
Instruments 2026, 10(3), 37;
2 Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, 70013 Heraklion, Greece
Abstract: The bias-dependent capacitance of varactors can introduce harmonic distortion into the circuits where they are utilized. A gate capacitance model valid through inversion–depletion has been presented for GaN HEMT varactors in the drive for their utilization in monolithic GaN ASICs. This work focuses on the circuit and the methodology employed to accurately measure on wafer the harmonic distortion caused by one such device. The circuit is presented and its design considerations and operation trade-offs are discussed, followed by a presentation of the measurements resulting from its use. Second- and third-order harmonic distortion is recorded and presented, with Verilog-A model simulations used to fit the measured data. The model consists of a charge-based expression of the HEMT varactor capacitance, with a minimal number of parameters. The good fit of the model is demonstrated, proving both the suitability of the circuit used for the measurements and the validity of the capacitance model for real-world applications.
Fig: Measurement setup schematic for the harmonic distortion characterization of HEMT varactors and V(f) characterization of the HEMT varactor. Inset is the parallel impedance combination measured by the LCR meter. (a) Cgc(Vg) for fixed frequencies. (b) Cgc(f) for fixed Vg levels. (c) Rp(Vg) for fixed frequencies. (d) Rp(f) for fixed Vg levels.
Aknowlegements: This research was partially funded by the European Union under the project AGAMI_EURIGAMI (ID:101102983).
Data Availability Statement: The measurement data generated and analyzed during the present study are available from the corresponding author upon reasonable request.
