Anti-Series Varactor Network With Improved Linearity Performances in the Presence of Inductive and Capacitive Parasitics

David Berthiaume,Jean-Jacques Laurin,Nicolas G Constantin

doi:10.1109/access.2021.3069090

Abstract

This paper proposes a varactor-based circuit technique intended for amplitude and phase control, with improved linearity in the presence of parasitic capacitances and parasitic inductances. The mechanism causing linearity degradation in an anti-series varactor network that includes significant parasitic elements - a key aspect that, to our knowledge, has never been reported - is first studied using an analytical approach based on multi-tone excitation. It is demonstrated that simply optimizing the ratio of diode sizes is insufficient to circumvent this linearity degradation. The underlying linearity degradation concept serves as the basis for the introduction of a modified anti-series controllable capacitance, followed by a design and practical implementation. Experimental validations with multi-tone and modulated signals demonstrate improved linearity performances with respect to the state-of-the-art when parasitic capacitances and inductances are significant. Moreover, it is shown that the complete varactor-based circuit topology proposed here, which uses the proposed modified anti-series controllable capacitance in conjunction with a second-harmonic trap filter, constitutes a very attractive alternative to the state-of-the-art anti-series/anti-parallel topology, since it reduces the required number of diodes by a factor of 2. Measurements on discrete-component designs operating at 3.6GHz, hence with significant parasitic effects, demonstrate that the proposed circuit topology improves the 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> order intermodulation distortion levels by 10.6dB and 6.6dB at output powers of 10dBm and 18dBm respectively, in comparison with the state-of-the-art topology. Measurements with a 16QAM modulated signal also show 3.9dB improvement in ACPR at 18dBm. These performances constitute improved state-of-the-art results in anti-series hyper-abrupt varactor-based electronic control.

Highlights

The aerospace industry is showing increasing interest in electronically reconfigurable antenna systems [1], [2]
In part 1) of this subsection, we demonstrate the detrimental effect of parallel parasitic capacitances in the distortion mechanism of unmatched hyper-abrupt varactor-based anti-series topologies by extending the preceding equations
EXPERIMENTAL IMPLEMENTATION AND RESULTS This section presents results from experimental measurements i) validating the improved linearity of the proposed anti-series topology in section III-A when benchmarked against a topology that does not use the proposed technique and ii) validating the complete varactor-based circuit topology proposed here, which makes use of an even-order harmonic trap

Summary

INTRODUCTION

The aerospace industry is showing increasing interest in electronically reconfigurable antenna systems [1], [2]. While many comparisons may be drawn with the priorart, the objectives pursued in this work requires high linearity performances over a wide range of tone spacing, given that our application (Fig.1) uses complex modulation schemes This aspect is compared in the column ‘‘Linearity/Power at min and max demonstrated TS’’ of Table 1. The proposed linearity improvement technique is not limited to this specific varactor and may be implemented using other hyper-abrupt varactors in flip-chip and discrete packages It is demonstrated, using multi-tone-based equations, that the linearity performance enhancement expected from the distortion-cancellation mechanism inherent to the antiseries networks in Fig., is severely degraded by the passive parasitics surrounding the varactors.

NONLINEARITIES IN PARASITIC-FREE ANTI-SERIES TOPOLOGY

EXPERIMENTAL IMPLEMENTATION AND RESULTS

CONCLUSION