This paper describes a Adaptive Impedance Tuning Circuit which can be adaptively tuned between circuit's characteristic impedance and the arbitrary load impedance. The Adaptive Impedance Tuning Circuit is consisted of such parts as mismatch sensor, impedance tuner and tuning algorithm. Each parts's design methods proposed in other papers are compared with their advantages and disadvantages. And we propose simple design method for Adaptive Impedance Tuning Circuit using a λ/4 transmission line and π-network. Calculation formulas and selection algorithm from calculated values of a complex load impedance are proposed and simulation using induced calculation formulas and selection algorithm is performed. Simulation results show good agreement with theoretical predictions.
An adaptive impedance tuning circuit (AITC) is used to compensate for the impedance between the arbitrary load impedance and the characteristic impedance of interest. An AITC is required for correct and accurate load impedance measurements. A new type of mismatch measurement circuit that measures the arbitrary load impedance more accurately is proposed and its performance against existing methods is compared. The proposed circuit exhibits a significant performance improvement compared with the conventional method, and it could be applied to different communication systems that have a variety of input signal strengths.Introduction: In an electrical system, maximum power transfer between a load and a source is achieved when impedances of the load and the source are matched with respect to each other, which minimises reflection losses between the load and the source. In RF communication, the characteristic impedance of the front end is substantially constant, but the antenna impedance varies considerably with frequency and external circumstances. One way to solve this problem is to use an adaptive matching circuit instead of a fixed matching circuit. To correctly apply an adaptive impedance tuning circuit (AITC), accurate measurement of the load impedance is required. To respond rapidly to the continuously changing circumstances, a method for calculating the load impedance directly without iteration is a more efficient way than a method with iterations [1]. This Letter details a load impedance measurement method using a sectioned λ/4 transmission line (TL) without iterative calculations. The sectioned-TL-based method and theory has been presented in several papers [2,3]. According to [2], the TL should be divided into several parts, and each part must be measured, so this technique requires complex calculations. In addition, this technique is difficult to implement. The technique in [3] is simplified to a three-point measurement on a λ/4 TL; however, the calculation method for selecting the exact results is not presented.This Letter presents a calculation method for directly measuring the load impedance by only measuring the voltages at three points on the λ/4 TL without iteration, and suggests a selection algorithm for determining the exact measurement values from several calculated load impedances. In addition, a new type of mismatch measurement circuit is proposed. This novel circuit measures the arbitrary load impedance more accurately by using a high-impedance sampling TL and sampling capacitors. By comparing the performance with the conventional method that uses coupling resistors, the superior performance of the proposed circuit is demonstrated.
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