In this chapter we review some of the basic concepts in communication systems. We will start with a brief summary of Fourier and Hilbert transforms, both of which serve as great tools to analyze RF circuits and systems. We will also present an overview of RF filters, both the real and complex domain structures, and discuss quadrature signal generation. To establish some foundation for the noise analysis presented in Chapter 4, we will also provide a summary of stochastic processes and random variables. We conclude this chapter by briefly describing the fundamentals of analog modulation schemes and analog modulators.

The majority of the material presented in this chapter is a review of various concepts that exist in signal processing, communication systems, and basic circuit theory. However, we feel it is important to present a reminder as well as a summary as throughout this book they will be referred to frequently.

The specific topics covered in this chapter are:

• Fourier series and Fourier transform;

• impulse response, poles, zeros, and network functions;

• passive and active filters;

• Hilbert transforms, polyphase filters, and quadrature signals;

• random processes, Gaussian signals, stationary and cyclostationary processes;

• amplitude, phase, and frequency modulation;

• narrowband FM and Bessel functions;

• introduction to modern digital communication.

For class teaching, we recommend focusing on selected topics from Sections 2.3, 2.5, 2.7, 2.8, and 2.9 while Sections 2.1, 2.2, and 2.4 may be comfortably assigned as reading.

Stochastic processes (Section 2.6) are crucial to attain a thorough understanding of noise in RF circuits, and particularly oscillator phase noise. For an introductory RF course, however, proper coverage of noise and phase noise may not be feasible. Consequently we defer Section 2.6 and the majority of phase noise discussion (in Chapter 8) to a more advanced course, and certainly the more astute readers. What Section 2.6 offers is a summary of selected topics that are most relevant to RF design, which will greatly complement our discussions on mixer and oscillator noise.

This chapter is devoted to reviewing some of the basic concepts used in RF design such as available power gain, matching circuits, and scattering parameters. We will also present a more detailed discussion on both lossless and low-loss transmission lines and introduce the Smith chart. Most of the material presented will be used in Chapters 4 and 6, when we discuss noise and low-noise amplifiers. Also, most of our discussions in this chapter are closely tied to the material presented in Chapter 1.

The specific topics covered in this chapter are:

• available power and matching;

• wideband and narrowband transformers;

• series–parallel transformation;

• lossless and low-loss transmission lines;

• Smith chart;

• scattering parameters.

For class teaching, we recommend focusing on Sections 3.2 and 3.3 which are crucial for the LNA design. The transmission lines, Smith chart and S-parameters, while important for RF design, could be skipped for the class. However, the material is relatively easy to follow and the interested student or engineer may study individually.

In Chapter 4 we showed that according to the Friis equation the lower limit to a receiver noise figure is often set by the first block. Moreover, the gain of the first stage helps reduce the noise contribution of the subsequent stages. Hence, it is natural to consider a low-noise amplifier at the very input of a receiver. A first look then will tell us that, for a given application, the higher the gain of the amplifier the better. However, the limit to that is typically imposed by the distortion caused by the blocks following the low-noise amplifier. As we stated earlier, there is a compromise between the required gain, noise and linearity for a given application, and a certain cost budget. These requirements may be different for a different application or standard. In this chapter we assume that these requirements are given to us, and our goal is to understand the circuit design tradeoffs. In Chapter 10 we will study receiver architectures and various tradeoffs associated with each choice of architecture.

What makes a low-noise amplifier (LNA) different from other typical amplifiers designed for analog applications is the need for the LNA to present a well-defined, typically 50 Ωinput impedance to the outside world. That, along with a relatively higher frequency of operation, limit the choice of topologies to only a handful. Most LNAs in practice use a variation thereof, one way or another.

We will start this chapter by a review of some of the basic concepts we presented in Chapter 4 and expand those a little further. We will then describe three general categories of the LNAs, namely: shunt feedback LNAs, series feedback LNAs, feedforward LNAs. We will close this chapter by considering some practical aspects of LNA design regardless of its topology.

The specific topics covered in this chapter are:

• LNA matching concerns;

• amplifier design concerns for radio frequencies;

• series and shunt feedback LNAs;

• feedforward LNAs;

• impact of substrate and gate resistance on LNAs;

• LNA layout and other practical considerations.

For class teaching, we recommend covering most of this chapter, possibly with the exception of Section 6.6 that may be assigned as reading. Sections 6.5 and 6.7 may be skipped as well if time does not permit, but we recommend presenting a brief summary at least.

By this point, we have established the need for mixers in a radio, 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 either to time variance or non-linearity, 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 and more physical understanding of the circuit.

We present both active and passive mixers, and in each case discuss the noise and linearity tradeoffs based on physical models, mostly from a receiver point of view. Although very similar in principle, we will dedicate a section at the end on upconversion mixers as well.

The specific topics covered in this chapter are:

• mixer basic requirements;

• active mixer operation;

• noise, linearity, and second-order distortion in active mixers;

• passive mixer operation;

• noise, linearity, and second-order distortion in passive mixers;

• LO duty cycle optimization;

• M-phase and harmonic-rejection mixers;

• transmitter mixers;

• LNA/mixer practical design example.

For class teaching, we recommend covering Section 7.1, as well as active and passive mixers basic operation (initial parts of Sections 7.3 and 7.4). A qualitative discussion may be also presented from the material presented in Section 7.8.

An unavoidable cause of electrical noise is the random thermal motion of electrons in conducting media such as wires or resistors. Active circuits comprising of MOS transistors suffer from similar random motion of electrons leading to noise. As long as communication systems are constructed from such devices, the noise will be with us. Amplifying arbitrarily weak signals to make them detectable is unrealistic, as the presence of noise sets a lower limit to the minimum detectable signal. This ultimately limits the range where the transmitter and receiver can communicate, while maintaining a minimum signal-to-noise ratio at the detector output.

This chapter starts with a review of the noise sources present in RF components and how they are modeled and dealt with in the context of two-ports. We then define the noise figure as a universal figure of merit describing the noise properties of a circuit, and link that to the minimum detectable signal in a given radio. Finally, we present the concept of minimum noise figure, and a systematic approach to optimizing the signal-to-noise in amplifiers. Most of this chapter deals with linear and time invariant circuits such RF amplifiers. However, we will also introduce the cyclostationary noise to set the foundation for the mixer and oscillator noise analysis. A detailed study of noise in time-variant or non-linear circuits such as mixers or oscillators is presented in Chapters 7 and 8 respectively, although many basic concepts discussed in this chapter are still applicable.

The specific topics covered in this chapter are:

• thermal and white noise, cyclostationary noise, and FET thermal and flicker noise;

• noise of lossy passive circuits;

• noise figure;

• minimum noise figure and noise optimization;

• introduction to phase noise;

• sensitivity;

• noise measurement techniques.

For class teaching, we recommend presenting a brief summary of Sections 4.1 and 4.2, while fully covering Sections 4.3, 4.4, 4.5, and 4.7. In particular, much of the material on noise figure definition and noise optimization (Sections 4.3 and 4.4) will be directly used in Chapter 6. Sections 4.6 and 4.8 may be assigned as reading.

In this chapter we will study the challenging problem of delivering power to an 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 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 5, such systems demand more linearity on the power amplifier, and hence achieving a respectable efficiency becomes more of a challenge.

We will start this chapter with a general description of challenges and concerns, as well as linearity–efficiency tradeoffs. We will then have a detailed description of different classes of PAs. We conclude the chapter by discussing various common techniques employed to linearize the PA, or to improve the efficiency in an attempt to ameliorate the challenging linearity–efficiency issues.

The specific topics covered in this chapter are:

• power amplifier basic operation;

• PA classes A, B, and C;

• switching power amplifiers (classes D, E, and F);

• power combining techniques;

• pre-distortion;

• envelope elimination and restoration;

• envelope tracking;

• dynamic biasing;

• Doherty power amplifiers.

For class teaching, we recommend covering Section 9.1 and selected parts of Sections 9.2–9.7 (for instance only classes A, B, and E or F). The discussion on Doherty PAs and linearization techniques may be deferred to a more advanced course, although most of the material is easy to follow, if assigned as reading.

By now we have a general idea of what receivers and transmitters look like. Nonetheless, the exact arrangement of the blocks, the frequency planning involved, the capabilities of digital signal processing and other related concerns result in several different choices that are mostly application dependent. While our general goal is to ultimately meet the standard requirements, arriving at the proper architecture is largely determined by the cost and power consumption concerns. The goal of this chapter is to highlight these tradeoffs, and present the right architecture for a given application, considering the noise, linearity, and cost tradeoffs that were generally described in Chapters 4 and 5. Moreover, we will see that the proper arrangement of the building blocks is a direct function of the circuit capabilities that we presented in Chapters 6-9.

We will start this chapter with general description of the challenges and concerns when realizing RF transceivers. We will then have a detailed description of both receiver and transmitter architectures, and present several case studies. At the end of the chapter, a practical transceiver design example is presented, along with some discussion on production related issues, packaging requirements, and integration challenges.

The specific topics covered in this chapter are:

• transceiver general considerations;

• super-heterodyne receivers;

• zero- and low-IF receivers;

• quadrature downconversion and image rejection;

• dual-conversion receivers;

• blocker tolerant receivers;

• ADC, filtering and gain control in receivers;

• linear transmitters;

• direct-modulated and polar transmitters;

• out-phasing transmitters;

• transceiver case study;

• packaging and product qualification;

• production related concerns.

For class teaching, we recommend covering only Sections 10.1, 10.2.1, 10.2.2, 10.2.3, and 10.6.1. A brief introduction to non-linear transmitters (Sections 10.6.3 and 10.6.4) may be also very helpful, if time permits. The remaining sections, and particularly Section 10.7 are easy to follow, and may be appealing to practicing RF engineers.

In this chapter we present a detailed discussion on various types of oscillator, including ring and crystal oscillators. 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.

Given the non-linear nature of oscillators, we will offer a somewhat different view on noise compared to much of the material presented on amplifiers and mixers. This is captured in the Section 8.3.5, Cyclostationary Noise, which is a continuation of our discussion in Chapter 4. Even though we introduced the concept of phase noise in Chapter 4, we will present a detailed analysis based on the concept of energy balance, briefly touched on in Chapter 1.

Although the focus of this chapter is mainly on LC oscillators, that are widely used in RF transceivers, we will also cast brief discussions on ring and quadrature oscillators. Both schemes are not as common given the performance limitation that we shall discuss. We conclude the chapter by presenting crystal oscillators as well as a brief summary of PLL and its noise characteristics.

The specific topics covered in this chapter are:

• linear oscillators and Leeson's model;

• non-linear oscillators and the energy balance model;

• AM and PM noise;

• cyclostationary noise;

• Bank's general result;

• examples of common oscillator topologies: NMOS, CMOS, Colpitts, and class-C;

• ring oscillators;

• quadrature oscillators;

• crystal oscillators;

• phase-locked loops.

For class teaching, we recommend the linear oscillator (Section 8.1), and selected oscillator topologies from Section 8.4. If deemed necessary, a summary of Bank's results (Section 8.3.8) may be presented to improve understanding of the phase noise derivation of various topologies. A detailed discussion of phase noise (Sections 8.2 and 8.3) must be deferred to a more advanced course. Sections 8.8, 8.9, 8.10, and 8.11 may be assigned as reading.

In Chapter 4 we showed that the thermal noise of a receiver sets a lower limit on the signal detectable at the receiver input. The upper limit to the maximum signal a receiver can handle is set by the distortion, arisen from non-linearity present in the active circuits making up the receiver. However, handling a desired large input is generally not an issue as is typically managed by the proper gain control in the receiver. On the other hand, we will show in this chapter that the distortion has a far more detrimental impact on the receiver, when subject to large unwanted signals, known as blockers. Similarly to noise, the blockers will also set a lower limit on the detectable signal.

We will start this chapter with a general description of blockers and their profile in wireless systems. We will then present four distinct mechanisms that could impact the receiver performance in the presence of large blockers, namely small signal non-linearity, large signal non-linearity, reciprocal mixing, and harmonic mixing. We shall discuss the appropriate figures of merit for each case, and describe their practical impacts on modern receivers.

The specific topics covered in this chapter are:

• general description of blockers in radios;

• introduction to wireless standards;

• full duplex systems;

• second- and third-order intercept point;

• compression and desensitization;

• reciprocal mixing;

• harmonic distortion;

• noise and linearity in transmitters;

• AM–AM and AM–PM distortion;

• pulling in transmitters, and its impact on performance.

While this chapter may be very appealing for RF circuit and system engineers, for class use we recommend focusing only on a summary of Sections 5.1, 5.2, and covering Sections 5.3.1, 5.3.3, 5.3.5, and 5.4. The rest of the material may be assigned as reading. The chapter includes many practical examples of deriving blocker requirements for both receivers and transmitters for various applications, such as cellular or wireless LAN.

In this chapter basic components used in RF design are discussed. A detailed modeling and analysis of MOS transistors at high frequency may be found in [1], [2]. Although mainly developed for analog and high-speed circuits, the model is good enough for most RF applications operating at several GHz, especially for the nanometer CMOS processes used today. Thus, we will offer a more detailed study of inductors, capacitors, and LC resonators instead in this chapter. We will also present a brief discussion on the fundamental operation of distributed circuits and transmission lines, and follow up on that in Chapter 3. In Chapters 4 and 6, we will discuss some of the RF related aspects of transistors, such as more detailed noise analysis as well as substrate and gate resistance impact.

LC circuits are widely used in RF design, with applications ranging from tuned amplifiers, matching circuits, and LC oscillators. Inspired by superior noise and linearity compared to transistors, historically, radios have relied heavily on inductors and capacitors, with large portions of the RF blocks occupied by them. Although this dependence has been reduced in modern radios, mostly for cost concerns, still RF designers deal with integrated inductors and capacitors quite often.

We start the chapter with a brief introduction to electromagnetic fields, and take a closer look at capacitors and inductors from the electromagnetic field perspective. We will then discuss capacitors, inductors, and LC resonators from a circuit point of view. We conclude the chapter by presenting the principles and design tradeoffs of integrated inductors and capacitors.

The specific topics covered in this chapter are:

• capacitance and inductance electromagnetic and circuit definitions;

• Maxwell's equations;

• distributed elements and introduction to transmission lines;

• energy, power, and quality factor;

• lossless and low-loss resonance circuits;

• integrated capacitors and inductors.

For class teaching, we recommend focusing on Sections 1.7, 1.8, and 1.9, while Sections 1.1–1.6 may be assigned as reading, or only a brief summary presented if deemed necessary.