In this chapter we study the challenging problem of delivering power to antenna efficiently. The linear amplifier topologies that we have discussed thus far are fundamentally incapable of achieving high efficiency. Considering the high demand for improving battery life, this shortcoming becomes very critical when delivering hundreds of mW or several watts of power into the antenna. This issue is exacerbated in most modern radios that employ complex modulation schemes to improve the throughput without raising the bandwidth. As we discussed in Chapter 6, such systems demand more linearity on the power amplifier, and hence achieving a respectable efficiency becomes more of a challenge.

By this point we have established the need for mixers in a radio, which is to provide frequency translation, and consequently to ease analog and digital signal processing by means of performing them at a conveniently lower frequency. Since the frequency translation is created due to either time variance or nonlinearity, or often both, the small signal analysis performed typically on linear amplifiers does not hold. This makes understanding and analysis of the mixers somewhat more difficult. Although exact methods have been presented, in this chapter we resort to more intuitive yet less complex means of analyzing the mixers. In most cases this leads to sufficient accuracy but more physical understanding of the circuit.

In this chapter we review some of the basic concepts in communication systems. We start with a brief summary of Fourier and Hilbert transforms, both of which serve as great tools for analyzing RF circuits and systems. We also present an overview of network functions and the significance of poles and zeros in circuits and systems. To establish a foundation for the noise analysis presented in Chapter 5, we also provide a brief summary of stochastic processes and random variables. We conclude this chapter by briefly describing the fundamentals of analog modulation schemes and analog modulators.

This chapter is dedicated to reviewing some of the basic concepts in RF design such as available power gain, matching circuits, and scattering parameters. We also present a more detailed discussion on both lossless and low-loss transmission lines and introduce the Smith chart. In addition, we recast a follow-up discussion on a receive–transmit antenna pair viewed as a two-port system. Most of the material presented will be used in Chapters 5 and 7, when we discuss noise and low-noise amplifiers.

In this chapter we present a detailed discussion on various types of oscillators, including ring and crystal oscillators. The LC resonators and integrated capacitors and inductors have been already discussed in Chapter 1, and are essential to this chapter. Furthermore, some of the communication concepts that we presented in Chapter 2, such as AM and FM signals, as well as stochastic processes, are frequently used in this chapter.