Circuits and systems

Discover the nonlinear methods and tools needed to design real-world microwave circuits with this tutorial guide. Balancing theoretical background with practical tools and applications, it covers everything from the basic properties of nonlinear systems such as gain compression, intermodulation and harmonic distortion, to nonlinear circuit analysis and simulation algorithms, and state-of-the-art equivalent circuit and behavioral modeling techniques. Model formulations discussed in detail include time-domain transistor compact models and frequency-domain linear and nonlinear scattering models. Learn how to apply these tools to designing real circuits with the help of a power amplifier design example, which covers all stages from active device model extraction and the selection of bias and terminations, through to performance verification. Realistic examples, illustrative insights and clearly conveyed mathematical formalism make this an essential learning aid for both professionals working in microwave and RF engineering and graduate students looking for a hands-on guide to microwave circuit design.

Focusing on the core topics of radio frequency integrated circuits (RFICs) and system design, this textbook provides the in-depth coverage and detailed mathematical analyses needed to gain a thorough understanding of the subject. Throughout, theory is linked to practice with real-world application examples; practical design guidance is also offered, covering the pros and cons of various topologies, and preparing students for future work in industry. Written for graduate courses on RFICs, this uniquely intuitive and practical book will also be of value to practising RFIC and system designers. Key topics covered include RF components, signals and systems, two-ports, noise, distortion, low-noise amplifiers, mixers, oscillators, power amplifiers, and transceiver architectures. Lecture slides and a solutions manual for instructors are provided online to complete the course package.

Recent years have witnessed significant research efforts in flexible organic and amorphous-metal-oxide analogue electronics, in view of its formidable potential for applications such as smart sensor systems. This Element provides a comprehensive overview of this growing research area. After discussing the properties of organic and amorphous-metal-oxide technologies relevant to analogue circuits, this Element focuses on their application to two key circuit blocks: amplifiers and analogue-to-digital converters. The Element thus provides a fresh look at the evolution and immediate opportunities of the field, and identifies the remaining challenges for these technologies to become the platform of choice for flexible analogue electronics.

Summary

3.1 P-N JUNCTION

All modern semiconductor devices and integrated circuits (IC), which are the backbone of modern day electronics, contain at least one junction between p-type and n-type semiconductor, commonly known as p-n junction. This p-n junction is the most fundamental semiconductor device as all other devices like various types of transistors (Bipolar Junction Transistor, Field Effect Transistor, Metal Oxide Semiconductor Field Effect Transistor, etc.) require p-n junctions of various configurations, which will be discussed in subsequent chapters. Various analog and digital operations and performance like rectification, amplification, switching, logic operations require this fundamental semiconductor device. In this chapter, we will discuss various issues related to the p-n junction followed by application of such junction diodes, called p-n junction diodes, for various operations.

In chapter 2, we have been familiar with different types of semiconductors, classified in different aspects. We recall p- and n-type semiconductor, which are realized by doping an intrinsic semiconductor with different type of impurities to obtain large number of free carriers in the form of holes in p-type semiconductor and electrons in n-type semiconductor, respectively. However, these n-type and p-type semiconductors having electrons and holes in abundance are electrically neutral, as they are neutralized by the impurity ions which have created them. To be more specific, electrons are neutralized by associated donor ions, each of which has equal (opposite in sign) amount of charge as that of each electron, and holes are neutralized by acceptors ions, each of which has equal (opposite in sign) amount of charge as that of a hole, ensuring a charge neutrality. This is clearly shown in Figure 3.1. However, if we consider a semiconductor whose two sides are differently doped with acceptor and donor impurities, their effect is not like two isolated pieces of p- and n- type semiconductor due to the transport phenomena of the mobile charge carriers. Such a device is known as p-n junction and needs to be discussed in detail. It is the most fundamental semiconductor device and is the backbone of modern day electronics.

Summary

12.1 INTRODUCTION

In electronics, an integrated circuit (also known as IC, microcircuit, microchip, silicon chip or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that is manufactured on the surface of a thin substrate of semiconductor material. A hybrid Integrated Circuit is a miniaturized electronic circuit constructed of individual semiconductor devices, as well as passive components, bonded to a substrate or circuit board. Integrated circuits are used in almost all electronic equipment and have revolutionized the world of electronics.

To a large extent, the demand for miniaturization was driven by the demands of the American Space Program. For some time, people had been thinking that it would be a good idea to be able to fabricate an entire circuit on a single piece of semiconductor. The first public discussion of this idea is credited to a British radar expert, Geoffrey William Arnold Dummer (1909–2002), in a paper presented in 1952. Jack Kilby's first prototype was a phase-shift oscillator comprising of five components on a piece of germanium, half an inch long and thinner than a toothpick. Although manufacturing techniques subsequently took different paths from those used by Kilby, yet he is considered as the pioneer in the area of IC fabrication.

ICs are polarized and every pin is unique in terms of both location and function. Most ICs use either a notch or a dot to indicate the pin numbers and its counting sequence. This is depicted in Figure 12.1.

12.2 IC: ADVANTAGES AND DISADVANTAGES

The main advantages of ICs over those made by interconnecting discrete components are as follows:

1. Extremely small size, i.e. thousands times smaller than discrete circuits. It is because of fabrication of various circuit elements on a single chip of semiconductor material.
2. Very small weight owing to miniaturized circuit.
3. Very low cost because of simultaneous production of hundreds of similar circuits on a small semiconductor wafer. Owing to mass production, IC costs as much as an individual transistor.
4. More reliable because of elimination of soldered joints and need for fewer interconnections.
5. Lower power consumption because of their smaller size.
6. Easy replacement as it is more economical to replace them than to repair them.
7. Increased operating speed because of absence of parasitic capacitance effect.
8. Close matching of components and temperature coefficients because of bulk production in batches.

Summary

10.1 INTRODUCTION

In Chapter 6, we derived various small-signal models of BJT, followed by detailed analysis of the BJT amplifiers for CE, CB and CC configurations. In designing such small-signal amplifier the main focus is on amplification linearity and magnitude of gain. Since signal voltage and current in the small-signal amplifier is restricted to small amplitude for maintaining linearity, their power handing capability or the power efficiency with which it delivers AC power to the load at the expense of DC power are of secondary concern. A voltage (current) amplifier provides voltage (current) amplification primarily to increase the applied input voltage (current). Thus, in general, these small-signal amplifiers are not capable of delivering large amount of power to a passive load. But most of the practical electronic amplifiers (starting from audio amplifier to switching power supply) require a final output stage capable of delivering large power to the load. Such amplifier/amplifying stage at the output stage of a practical amplifier circuit is known as power amplifier. It can be designed using BJTs, MOSFETs and various special semiconductor devices like thyristors. However, we will consider only BJTs while discussing the design of such amplifiers.

10.2 PERFORMANCE CHARACTERISTICS OF POWER AMPLIFIERS

The quality of power amplifiers is characterized by the following parameters:

• Power handling capability: The amplifier must be capable of delivering the required amount of power to the load in an efficient manner. This demands that the power dissipation in the transistors be as low as possible.
• High power conversion efficiency: Power conversion efficiency is another important figure of merit of a power amplifier defined as the ratio of AC power delivered to the load to the DC input power. It is expressed as,

We will calculate the power conversion efficiency η of different types of power amplifiers. A high value of η is desired as it utilizes less DC power to deliver same output AC power to the load.

• Low total harmonic distortion: Since a power amplifier deals with relatively large signals, the small-signal approximations and resultant linear equivalent circuit models are not applicable here due to the nonlinearities of the transistors while dealing with large signals. Even though power handling capability and high conversion efficiency are major design criteria in power amplifiers, linearity still remains an important criterion.

Summary

13.1 INTRODUCTION

Operational amplifier or OPAMP is one of the most important building blocks in all aspects of analog circuitry. It becomes the universal analog IC because of its wide range of application in analog signals processing. It can function as a line drive, comparator (one bit A/D), amplifier, level shifter, oscillator, filter, signal conditioner, actuator driver, current source, voltage source, and many other applications.

The OPAMP is a multistage two-input differential amplifier that is designed to be an almost ideal control device, specifically a voltage-controlled voltage source. Basically, it is an abstraction of ideal voltage amplifier with very high gain. We will employ the OPAMP to construct more complex circuits using its simple, abstract model. The equivalent circuit of OPAMP is shown in Figure 13.1.

The integrated circuit OPAMP usually consists of a cascade of three stages:

a) Input stage: May contain one or two differential amplifier stages
b) Intermediate stage: Emitter follower and DC level shifter.
c) Output stage: Driver stage (Class B amplifier)

Internally, the OPAMP itself is a moderately complicated circuit and its design is beyond the scope of this book. The heart of the OPAMP is its input stage acting as differential amplifier using BJT/MOSFET. This differential input stage gives the OPAMP its high input resistance and a high gain with very little noise. It also converts the differential input voltage to a single-ended output. A typical OPAMP also has a second stage similar to the first stage, which provides additional amplification and level shifts the output voltage to zero when both inputs are equal. OPAMPs may also have an output stage similar to the buffer, due to which OPAMP exhibits low output impedance.

Symbolic representation of the operational amplifier shown in Figure 13.2, suggests that it as a two-port device. The two ports are an input and an output port. A + V voltage (for example, 15 V) is applied at the ‘plus’ power port and a –V voltage (for example, −15 V) is applied at the ‘minus’ power port. An input voltage (the control) applied across the non-inverting and inverting input terminals of the OPAMP is amplified by a large amount and appears at the output port.

Summary

INTRODUCTION

Electronics, evolved from the word ‘electron’ (a sub-atomic particle carrying negative charge), is the branch of science and engineering dealing with the study, design and use of devices that depend on the conduction of electricity through vacuum, gas or semiconductor, contributed by the transport phenomenon of the electrons. Earlier, electronics or electronics engineering used to be considered as an integral part of electrical engineering. However, due to the tremendous growth of electronics and its unprecedented applications in various fields over the last few decades, it has evolved as a separate branch of engineering. In addition, due to its widespread application in almost all possible branches of engineering and science, acquiring basic understanding of electronics and fundamentals of electronic devices has become a common requirement for students of all engineering disciplines.

Before we discuss the details of the preliminary concepts required to understand the basic ideas of electronics, let us have a look at the chronological growth of modern electronics:

Summary

INTRODUCTION

The invention of various semiconductor devices and the chronological growth in the field of microelectronics in electronics industry is the backbone of most of the modern electrical/electronic and communication gadgets that have dramatically changed human life, leading to a new technology-driven society. One of the most remarkable breakthroughs to drive technology in the last few decades is the invention of transistor, a three terminal device that is extremely useful and almost an integral part of any analog or digital circuit. The first version of transistor was invented by Dr William Shockley and his co-workers Walter H Brattain and John Bardeen in Bell Lab, USA in 1947. Owing to various operational advantages like low power requirements, high efficiency, etc., coupled with its ultra-compact size, the transistor became very popular since its invention and replaced the previously used vacuum tube-based systems. Over time, the first transistor invented by Shockley et al (point-contact transistor) went through several rounds of modification, resulting in various new variants of the transistor, which include Bipolar Junction Transistor (BJT), Field Effect Transistor (FET), Metal Oxide Semiconductor Field Effect Transistor (MOSFET), etc.

In this chapter, we will discuss the construction of a transistor, basic principle of operation and its two most important applications, namely amplification and switching, in detail. Advanced concept regarding transistor operation and various other functionalities will be discussed in subsequent chapters.

BJT: CONSTRUCTION AND TERMINALS

A Bipolar Junction Transistor, popularly known as BJT, is a three-terminal semiconductor device with two junctions between them. As shown in Figure 4.1(a), the structure of a transistor resembles a sandwich in which a very narrow and lightly doped p-region is sandwiched between two n-regions. Such a transistor is named as n-p-n transistor. A complementary structure of Figure 4.1(a), as shown in Figure 4.1(b), consists of an n-region sandwiched between two p-regions, resulting in a p-n-p transistor. The term ‘bipolar’ in BJT signifies the presence of two different types of carriers, electron and hole, and the resultant current is the combined contribution of both the carriers. As indicated in Figure 4.1, the three regions of the transistor are named as emitter (E), base (B) and collector (C).

Summary

4.1 INTRODUCTION

4.2 BJT: CONSTRUCTION AND TERMINALS

Summary

P-N JUNCTION

A p-n junction is formed from a single crystal intrinsic semiconductor in which one side is doped with acceptor impurity, i.e. trivalent atoms (p-region), and the other side is doped with donor impurity, i.e. pentavalent atoms (n-region).

Summary

INTRODUCTION

In Chapter 4, we discussed the basic construction, characteristics, various modes and principle of operation of bipolar junction transistor (BJT) in detail. Subsequently, in Chapter 5, we dealt with biasing techniques of the transistor in an elaborate manner. In addition, we understood the fundamental concept of BJT acting as an amplifier in a qualitative manner. While biasing a transistor our main goal is to fix a proper operating point, also known as Q point, based on the specific applications. This is achieved by proper choice of the bias resistor and DC voltages. Once this Q-point is finalized, we apply the AC signal in the input side of the biased transistor circuit. Thus, complete analysis of an amplifier consists of DC analysis followed by an AC analysis. In this chapter, we will focus on the AC analysis of the BJT circuits in an elaborate manner with special emphasis on design of the BJT-based linear amplifiers. One important ingredient in the AC analysis and design of linear amplifiers is to replace the BJT with proper equivalent circuits. Such replacement of BJTs with equivalent circuits, known as ‘modeling’ of the BJT, is applicable under small signal approximations. This assumes the amplitude of the applied AC signal is small enough to consider that BJT is essentially operated in active region and its characteristics can be approximated by linear relations. Such linear relations between input and output signals of the BJT allow superposition theorem applicable in BJT circuits and we can obtain the total response of the BJT circuit by separately determining the response due to i) DC sources alone (called biasing), and ii) AC sources. Figure 6.1 shows a schematic diagram of an electronic circuit driven by both DC and AC input. While the purpose of the DC input is to ensure that the device operates in the desired region of operation, i.e. bias the device properly, AC input provides the required functionality like amplification, switching, etc. By applying the small-signal models of the device, thereby linearizing their performance, we apply the superposition theorem to obtain the overall response of the circuit by separately obtaining the individual responses due to DC input and AC input, as shown in Figure 6.1.

Summary

INTRODUCTION

IC: ADVANTAGES AND DISADVANTAGES

The main advantages of ICs over those made by interconnecting discrete components are as follows:

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3 - Linear Behavioral Models in the Frequency Domain

Nonlinear Circuit Simulation and Modeling

Radio Frequency Integrated Circuits and Systems

Organic and Amorphous-Metal-Oxide Flexible Analogue Electronics

Chapter 3 - P-N Junction and P-N Junction Diode

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7 - Field-Effect Transistors

Chapter 12 - Integrated Circuits

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Chapter 10 - Power Amplifiers

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Chapter 13 - Operational Amplifier

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1 - Introduction to Electronics: Basic Ideas

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4 - Bipolar Junction Transistor

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Chapter 4 - Bipolar Junction Transistor

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3 - P-N Junction and P-N Junction Diode

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9 - Oscillators and Multivibrators

Frontmatter

6 - Modelling of BJT and Design of Amplifiers

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Dedication

12 - Integrated Circuits

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Contents

Acknowledgements

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Nonlinear Circuit Simulation and Modeling

Radio Frequency Integrated Circuits and Systems

Organic and Amorphous-Metal-Oxide Flexible Analogue Electronics

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