Reconfigurable Impedance Matching Networks for Radio Receivers

University dissertation from Lund Institute of Technology

Abstract: Mobile phones become smaller but include more advanced functions for every new generation. This paradox is possible since reduced transistor size and increased integration of digital building blocks free space for new functions. Unfortunately, not all components are easily integrated or scaled, such as the antenna, since its performance is dependent on the size. Shrinking mobile phone size results in increased impedance mismatch, as the available antenna volume and the length of the ground plane are reduced. As a consequence, the performance of the whole mobile phone transceiver is degraded, since the noise increases and the output power decreases with increased mismatch. In this work, study of reconfigurable matching networks, and their improvement of receiver and transmitter performance with mismatched antennas, has been performed. In the general introduction, the matching network is introduced as an Impedance Tuning Unit (ITU) and the behaviour from the fundamental building blocks to system aspects are studied. Also, interaction with other building blocks in the receiver chain, such as low noise amplifier, mixer, and filter, is investigated. It is shown that noise performance and power transfer are improved by introducing an ITU, which has the ability to change its matching configuration. It is also shown that it is possible to realize an ITU for receivers in CMOS. Paper I and II examine antenna design and aspects such as shielding and coupling. Paper III is a parameter study of a switched capacitor. In paper IV, V, and VI ITU topologies are simulated and measured for 0.35 um and 0.13 um and for 2.4 to 2.5 GHz and 470 to 702 MHz. The results are presented together with system aspects relevant for receivers.

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