Adaptive Impedance-Matching Techniques for ControllingLNetworks

The link quality of mobile phones suffers from antenna mismatch due to fluctuating body effects. Techniques for adaptive control of impedance-matchingLnetworks 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 parallelLCnetworks. 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.