c h a p t e r 1Introduction to Communications Circuits1.1 IntroductionRadio frequency integrated circuit (RFIC) design is an exciting area for research or product development. Technologies are constantly being improved, and as they are, circuits formerly implemented as discrete solutions can now be integrated onto a single chip. In addition to widely used applications such as cordless phones and cell phones, new applications continue to emerge. Examples of new products requiring RFICs are wireless local area networks (WLAN), keyless entry for cars, wireless toll collection, global positioning system (GPS) navigation, radio frequency identi-fication (RFID) tags, asset tracking, remote sensing, ultra wideband (UWB) radios for high data rate personal area networks (PANs), mobile television reception us-ing standards such as digital video broadcast handheld (DVB-H) or digital video broadcast terrestrial (DVB-T), and tuners in cable modems. Thus, the market is expanding, and with each new application there are unique challenges for the de-signers to overcome. As a result, the field of RFIC design should have an abundance of products to keep designers entertained for years to come. This huge increase in interest in radio frequency (RF) communications has re-sulted in an effort to provide components and complete systems on an integrated circuit (IC). There has been much research aimed at putting a complete radio on one chip. Since complementary metal oxide semiconductor (CMOS) is required for the digital signal processing (DSP) in the back end, much of this effort has been de-voted to radios in CMOS technologies [1–3]. However, bipolar design continues to be used in the industry because of its higher performance. CMOS traditionally had the advantage of lower production cost, but this is becoming less true as technology dimensions become smaller. In the future, both of these technologies will probably be replaced by radically different technologies. In any case, as long as people want to communicate, engineers will still be building radios, and contrary to popular belief, most of the design concepts in RFIC design are applicable regardless of what technology is used to implement them.The objective of a radio is to transmit and receive signals between the source and destination with an acceptable quality and without incurring a high cost. From the user’s point of view, quality can be perceived as information being passed from source to destination without the addition of noticeable noise or distortion. From a more technical point of view, quality is often measured in terms of bit error rate, and acceptable quality might be to experience less than one error in every million bits. Cost can be seen as the price of the communications equipment or the need to replace or recharge batteries. Low cost implies simple circuits to minimize circuit area and low power dissipation to maximize battery life.