Adaptive impedance-matching techniques for controlling L networks

Authors:
André Van Bezooijen;Maurice A. De Jongh;Freek Van Straten;Reza Mahmoudi;Arthur H. M. Van Roermund
Affiliations:
EPCOS Netherlands B.V., Nijmegen, The Netherlands;EPCOS Netherlands B.V., Nijmegen, The Netherlands;NXP Semiconductors, Nijmegen, The Netherlands;Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands;Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
Venue:
IEEE Transactions on Circuits and Systems Part I: Regular Papers
Year:
2010

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Abstract

The link quality of mobile phones suffers from antenna mismatch due to fluctuating body effects. Techniques for adaptive control of impedance-matching L networks are presented, which provide automatic compensation of antenna mismatch. To secure reliable convergence, a cascade of two control loops is proposed for independent control of the real and imaginary parts of impedance. A secondary feedback path is used to enforce operation into a stable region when needed. These techniques exploit the basic properties of tunable series and parallel LC networks. A generic quadrature detector that offers a power-independent orthogonal reading of the complex impedance value is presented, which is used for direct control of variable capacitors. This approach renders calibration and elaborate software computation superfluous and allows for autonomous operation of adaptive antenna-matching modules.