UE RF Components and System Design

The radio frequency (RF) unit is one of the most important blocks in the mobile phone. Apart from cellular system modems, mobile phones house several other wireless systems. All the wirless systems have RF front-end units and digital baseband units. This chapter covers the RF systems for a cellular system's modem. The basic building blocks of RF system are RF front-end module (FEM), RF transceiver unit, and frequency generation unit. The mixer circuit converts the RF signal to low frequency baseband signal, so that it can be sampled by the analog-to-digital converter (ADC). The chapter explains how the conversion from the RF frequency to baseband frequency can be done in one or several stages based on the receiver downconversion technique. Optimizing the design of a communications receiver is inherently a process of compromise. There are several factors that govern the performance of a radio receiver, such as RF noise figure (NF) and image rejection (IR).