An Adaptive Impedance Matching System for Mobile Communication Terminals (移動通信ワークショップ)

概要

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An adaptive impedance matching system is proposed for antennas in mobile communication terminals. This system employs only a simple algorithm for convergence, therefore does not require any complicated mathematical formulation for modeling of the system itself as well as its nonlinear control elements. Also the proposed system utilizes only simple digital circuits as a sequencer and basic analog circuits. In addition to that, the appropriate range of the control elements (varactors) is investigated. As a figure of merits, the present system is evaluated with an amount of improvement of the impedance mismatch between the adaptive matching circuit and the RF front end over a fixed-capacitance matching system. With a parametric simulation, appropriate range of the capacitance for the varactors, which can make the improvement in the mismatch considerably small while the antenna impedance fluctuates, is estimated. Moreover, a good improvement is also confirmed even by using a varactor with a wider range than the appropriate one, through limiting the range of the capacitance. Finally, a method to keep the good improvement is shown. It is realized through holding the control voltages to the varactors once the impedance mismatch becomes less than a certain threshold value. As a result, the improvement in the mismatch is observed by about 6.0dB in time average over the fixed-capacitance matching system.
社団法人電子情報通信学会の論文
2004-02-25