24
RADIO-FREQUENCY TRANSCEIVERS
The increasing demand for portable communication systems has motivated extensive research and development on wireless transceivers. The necessity for low-cost and low-power solutions along with the limited spectrum availability have introduced numerous challenges in the design of radio-frequency (RF) transceivers for wireless applications. Benefiting from the momentum of the digital market, complementary metal-oxide semiconductor (CMOS) technology has become attractive to provide affordable solutions for RF integrated circuits (IC). In this chapter, we first provide an overview of transceiver architectures, with more emphasis on the transmitters. Then, in the second part, we present examples of transceiver implementations.
24.1 TRANSMITTER ARCHITECTURES
24.1.1 Modulation Overview
In order to have better understanding of transmitter architectures, first we briefly study the modulation types by categorizing them into two groups: constant-envelope and variable-envelope modulations.
24.1.1.1 Constant-Envelope Modulation.
If the transmitter signal is specified as A(t)cos(ωct + Φ(t)), for a constant envelope modulation, as the name implies, A(t) is fixed. This gives significant flexibility in the implementation of the transmitter because the transmitter signal is not affected by any nonlinearity in the transmitter. This especially provides considerable advantage for the power amplifier (PA) using a nonlinear ...
