Mobile Handset Design

4

Mobile RF Transmitter and Receiver Design Solutions

4.1 Introduction to RF Transceiver

In Section 1.3.3.2 of Chapter 1, we discussed the basic building blocks of a mobile phone. For a digital mobile phone, the modem part can be broadly divided into two main blocks: (a) the RF module and (b) the baseband module. The RF module is the analog front-end module. On the receiver side it is responsible for signal reception from the air and down conversion onto the baseband signal, and on the transmitter side it is responsible for up conversion of the baseband signal to the RF signal, then transmission in the air. The baseband module deals with digital processing of the baseband signal and protocols. An ADC and DAC are placed in between the analog RF and digital baseband units. In this chapter, we will discuss the different design solutions for analog RF front-end modules. The basic building blocks of a typical radio RF front-end section of any mobile device (using digital baseband) is shown in the Figure 4.1.

1. Antenna – This acts as a transducer. It converts the incoming EM wave into an electrical signal on the receiver side and the outgoing electrical signal into an EM wave on the transmitter side. The basic principle of antenna action has already been discussed in Chapter 1, and different types of mobile phone antennas are discussed in detail in Chapter 10.
2. Tx–Rx Path Separation Block (Duplexer or Tx–Rx Switch or Diplexer) – Generally the same antenna is used for transmission as well ...