Adaptive RF Front-Ends for Hand-held Applications by Andre van Bezooijen, Reza Mahmoudi, Arthur H.M. van Roermund

By Andre van Bezooijen, Reza Mahmoudi, Arthur H.M. van Roermund

The RF front-end – antenna blend is a crucial a part of a cellular phone simply because its functionality is particularly appropriate to the hyperlink caliber among hand-set and mobile community base-stations. The RF front-end functionality suffers from alterations in working surroundings, like hand-effects, which are frequently unpredictable.

Adaptive RF Front-Ends for handheld Applications provides an research at the influence of fluctuating environmental parameters. in an effort to conquer undesired habit assorted adaptive keep watch over tools are taken care of that make RF frond-ends extra resilient: adaptive impedance keep an eye on, and adaptive strength control.

Several adaptive impedance keep an eye on ideas are mentioned, utilizing a priori wisdom on matching community houses, with the intention to simplify strong 2-dimensional keep an eye on. A commonplace safety suggestion is gifted, in accordance with adaptive energy keep an eye on, which improves the ruggedness of an influence amplifier or preserves its linearity less than extremes. It includes over-voltage, over-temperature, and under-voltage protection.

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For the realization of stand-alone modules, in this book so-called functional control techniques have been explored (see Fig. 1 under Book approach) because these techniques are well suited for analog and mixed-signal circuit implementations. These functional control techniques make use of a priori knowledge on control properties of tunable LC-networks that are often visualized as rotations over circle segments in a Smith chart. For 2-dimensional functional control techniques detection of the complex values of impedance and admittance is very desirable.

These conclusions are visualized in Fig. 9. For the sake of mathematical simplicity, the analysis is performed on a nonsaturated power amplifier. For a saturated PA, however, all trends are similar, but the impacts are more pronounced. Since saturation limits the average current flowing through the power transistor, a relatively small collector current will flow at zero degrees mismatch and low supply voltage, whereas a relatively large current will flow at +/À180 mismatch and high supply voltage.

The biasing voltage UBIAS is unsuited for actuation, because, at high power, the currents of a class-AB power transistor are determined by self-biasing due to RF and not by the biasing applied from the external reference voltage UREF. Controlling the input power PIN downwards is effective in avoiding all undesired behaviors, except for the maximum output power that reduces. In conclusion, actuation of the power transistor input power is most suited in avoiding undesired transistor behavior, while information, correlated to undesired behavior, is obtained from detection of one or more multiply dependent variables.

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