“Distortion-Free” Varactor Diode Topologies for RF Adaptivity

Abstract

Varactor diode-based circuit topologies, which can act as high-Q "distortion-free" tunable capacitive elements, are presented. These diodes are implemented in a novel ultra low-loss silicon-on-glass technology, with resulting measured Q's of over 200 at 2 GHz. The measured IM3 improvement compared to traditional single varactor tuning techniques is greater than 30 dB.

RF Technology Enablers for Software-Defined Radios

“…However, improved varactor diode-based circuit topologies, along with a high performance varactor diode process technology, have recently been demonstrated with very low distortion [17]. In addition, a silicon-based process technology was demonstrated with diodes Q's ranging from 100 to over 500 at 2 GHz, with capacitance values up to 50 pF, and with extremely low parasitic capacitances [18]. These developments revive interest in varactor diodes as a viable tuning approach for high-performance SDR frontends.…”

LOW THIRD-ORDER INTERMODULATION DISTORTION IN Ba_0.6Sr_0.4TiO₃ THIN FILM INTERDIGITAL CAPACITORS

“…Antiparallel and back-to-back circuit topologies were introduced and experimentally verified for achieving minimum distortions [7]. Since then, several research groups have demonstrated the effectiveness of implementing this idea in BST, MEMS and varactor diode technologies to enhance linearity of the devices [8][9][10][11]. A linearity improvement technique based on BST-stacked parallel-plate capacitors has been analysed by connecting several capacitors in series, which reduced the RF swing across each capacitor [8,12].…”

Improved hybrid sige HBT class-ab power amplifier efficiency using varactor-based tunable matching networks

“…3), which form a so-called varactor stack (VS). A high ohmic resistor and two diodes in anti-parallel configuration have been used to realize sufficiently high impedance for the VS center tap, in order to avoid linearity degradation for narrow tone spacings [7]. Each VS is independently controlled through its center-tap voltage to achieve the desired capacitance variation and impedance transformation.…”

“…2) are implemented using the TU Delft siliconon-glass technology, which has been customized for the implementation of ultra low-loss high performance varactors (Q>100@2GHz). By using these varactors in an anti-series configuration, a tunable capacitor with extremely low distortion is realized [7]. The inductors were implemented using bond-wires to facilitate some additional adjustment of the inductances values as well.…”

“…Recent work [7], demonstrated ultra-low loss (Q>100@2GHz) ultra-low distortion anti-series configured varactor diodes which can act as nearideal tuning elements [8]. By using a customized silicon-on-glass technology, these varactor topologies were used to implement two continuous-tunable matching networks, which provide low-loss and lowdistortion and a 1:10 impedance transformation range [9].…”