This book describes circuit engineering efforts for modern mobile communication.Electronic circuits for latest mass applications like mobile phones and smart phones are realized as so-called systems on chip (SoC). Such SoCs are realized in nanometer CMOS technology and contain a lot of digital circuits for digital signal processing but they also contain analog circuits which often form the key devices for a good over-all performance. The importance of analog filters nowadays is often underestimated. They are, however, still necessary to obtain high-performance wireless receivers and transmitters.