Objectives

At the end of the study of this chapter a student should be:

1. familiar with the modelling of different types of active devices

2. able to develop a suitable model of a device for a particular computer analysis

3. familiar with nonlinear d.c. analysis, small-signal a.c. analysis and large-signal transient analysis of simple electronic circuits

4. familiar with the Newton–Raphson algorithms and be able to determine the d.c. operating points of circuits for further analysis, and

5. familiar with the applications of some computer programs.

In recent years computational methods have been very popular for analysing and designing electronic circuits. It is now possible to design integrated circuits having thousands of transistors on a single chip. Such designs cannot be carried out experimentally at the bench. As very large scale integrated circuits make the fabrication of faster and cheaper computers possible, computer aided design is being used more and more to build such circuits. In this chapter, we will discuss various transistor models and parameters needed for computer analysis, different types of analysis and computer programs.

Computer aided design models

Renewed interest in transistor modelling took place in the sixties and seventies with the advent of computer aided design. Various models which had been developed during this period fell into two main categories, the first being single lump models in which transistor terminal currents are described in terms of quantities determined from terminal measurements; the second category of models is completely described by five basic transistor equations (two continuity equations, two current density equations and Poisson's equation) derived from the donor and acceptor concentration pattern.

Objectives

At the end of the study of this chapter a student should be:

1. familiar with the operation of the differential amplifier, its voltage gain, common-mode gain and common-mode rejection ratio

2. familiar with constant current sources and current mirror circuits

3. capable of explaining the principle of Darlington connections

4. able to design level shifting circuits

5. familiar with multistage amplifiers and able to calculate their input and output impedances and overall current and voltage gains

6. able to design class A, class B and tuned amplifiers

7. familiar with different types of heat sinks and able to choose the right heat sink for a particular circuit

Linear integrated circuits

Complete multistage amplifiers and other linear devices can be constructed on a single chip of silicon occupying a very small volume by using modern techniques for the fabrication of integrated circuits. In the case of monolithic integrated circuits, all components may be manufactured on the chip by a diffusion process. A diffusion isolating technique is used to separate the various components from each other electrically. The design techniques used for the construction of these integrated circuits are basically the same as those used to build circuits employing discrete components, although, in many cases some modification in techniques is needed.

The operational amplifier is the most common type of integrated circuit (small scale integration) which is widely used with different forms of external circuitry to build summers, subtractors, integrators, filters, etc.

Objectives

At the end of the study of this chapter the student should be:

1. familiar with the main imperfections in operational amplifiers, able to describe their effects on the output and stability of various circuits, and compensate for the errors due to them.

2. able to design several important linear and nonlinear circuits using operational amplifiers: phase shifting circuits, instrumentation amplifiers, comparators, precision rectifiers and logarithmic amplifiers.

3. familiar with different methods of design of active filters and able to choose the right design for a particular need.

4. able to describe the operating principles of multivibrators and triangular wave generators, and design these circuits given the specifications.

5. able to solve differential equations using summers, integrators and potentiometers, and apply amplitude and time scaling if necessary.

6. familiar with the principles of inverse function generators and able to design dividing, square rooting and RMS circuits using multipliers and operational amplifiers.

The name operational amplifier is derived from the fact that the amplifier was originally used to perform electronically various mathematical operations such as differentiation, integration, addition and subtraction. However, due to its versatility its use has been extended to other types of electronic circuits mainly in the fields of instrumentation and control engineering. The availability of inexpensive high performance operational amplifiers in the form of integrated circuits has obviously extended their use especially in analogue electronic circuits and systems.

Objectives

At the end of the study of this chapter a student should be:

1. familiar with three basic functional blocks of a phase-locked loop

2. familiar with the principle of operation of a phase-locked loop as a whole

3. able to determine important PLL parameters such as lock range and acquisition range

4. familiar with typical applications, both in electro-mechanical and telecommunication systems.

The phase-locked loop (PLL) is a very useful and versatile building block in the frequency domain. It is available from manufacturers as a single integrated circuit. It helps to synchronise the output signal of an oscillator with a reference signal in both frequency and phase. While synchronised in frequency, the phase difference between the output signal and the input signal is zero, or very small. It works in much the same way as a general feedback loop which acts in most control systems, e.g., electronic, mechanical, as shown in Fig. 5.1. Here the input is a function of the desired output. If the output is different from the desired value, the mixer produces an error signal which is then amplified and corrects the output. Although its concept has been known since 1932, its application was restricted until the 1960s, when it first became available in an integrated circuit form.

Components of phase-locked loops

The PLL contains a phase detector, a low-pass filter and a voltage-controlled oscillator in an arrangement as shown in Fig. 5.2.

Objectives

At the end of the study of this chapter a student should:

1. be able to design different types of digital-to-analogue (D-to-A) converters

2. be familiar with various kinds of analogue-to-digital (A-to-D) converters; their advantages and disadvantages and be able to construct them

3. be familiar with the errors in the converters

4. be conversant with the design of discrete multiplexers and demultiplexers and be familiar with their limitations and errors

5. be familiar with the principles of sample-and-hold circuit and be able to design them

6. be able to develop a suitable data acquisition or distribution system for a particular need and find the accuracy of such a system.

In order to process analogue signals which are continuous and of varying magnitude over a period of time, with the aid of computers, conversion of analogue currents or voltages into digital codes is essential. Again, conversely, in order to control machines with the help of computers, digital signals have to be converted into analogue currents and voltages. A typical system is shown in Fig. 7.1. Here the analogue sensors measure physical quantities such as temperatures, pressures, etc., and the analogue controls switch on (or off) heaters, pumps and so on.

Sometimes it is necessary to acquire or distribute more than one signal simultaneously. This can be achieved by using the time-sharing techniques. The time required for acquiring data from many sources, or distributing data to many controls can be reduced dramatically if a single channel is time-shared for transferring data.

This book is intended particularly as a text for undergraduate students of electrical and electronic engineering at the intermediate level of a degree course. Some material may, however, be appropriate to the final year. Each topic has been deliberately selected and emphasis has been given to operational amplifier circuits and their applications, data acquisition circuitry and computer aided analysis and design. Other useful topics which have been covered in some detail are analogue filter circuits and phase-locked loops. A list of the prerequisite knowledge for this text is given in the first chapter.

This book is most appropriate for students because (i) a specific subject area, analogue circuits for more advanced students has been highlighted and (ii) particular attention has been given to a descriptive treatment of practical details and applications, e.g. CAD rather than theoretical analysis, because these areas are often neglected and are essential for practising engineers. Therefore it is hoped that students and engineers alike will find this text useful and informative, but less analytical than many other books presently available, and thus be able to cover a wider range of topics within a given period of time. Several carefully chosen problems set at various levels of difficulty are included at the end of each section to help readers gain a better understanding of the topics under discussion.

I would like to thank my parents and my immediate colleagues both academic and industrial for their encouragement and advice in the preparation of the manuscript.

In recent years there has been rapid progress in electronic circuit design and the main reason for this is the advance in digital techniques. This volume differs from the texts which are available on the market nowadays in two respects. Firstly it covers only analogue electronic circuits and systems; secondly basic electronics is omitted so that appropriate emphasis can be given to the design of the most popular and useful analogue electronic circuits. The following are prerequisites for studying this text:

1. (a) P-N junction diodes: principles of operation both in the forward and reverse mode, characteristic equation, resistance and junction capacitance, Zener diodes.

2. (b) Junction transistors: principle of operation, common-emitter (CE), common-collector (CC) and common-base (CB) configurations, static characteristics, definition of active, cut-off and saturation regions, the concept of load lines and the need for biasing, the transistor as an amplifier.

3. (c) Amplifiers: voltage and current gains (Av and Ai), input and output resistance (Rin and Rout), frequency response concept, the use of the h-parameter model of the transistor for circuit analysis, midband frequencies of the CE, CC and CB configurations and calculation of Av, Ai, Rin and Rout for each case.

4. (d) Field effect transistor: principle of operation, static characteristics, load lines, biasing circuits, use as an amplifier.

5. (e) Positive and negative feedback and their advantages and disadvantages.

6. (f) Operational amplifiers: ideal amplifier, analysis of inverting, noninverting, differential, buffer and summer amplifiers, use of operational amplifiers as integrators and differentiators.

Objectives

At the end of the study of this chapter students should be:

1. familiar with radio frequency carrier waves and low frequency information signals

2. familiar with the principles of different types of modulation

3. able to choose a suitable method of modulation for transmission of a particular signal.

In a communication system radio frequencies are used to carry information which is most often of low frequencies from one place to another mainly because of the ease with which the high frequency waves can propagate around the world by multiple reflections from the ionosphere and at very high frequencies antennae of modest size can form narrow beams. Ranging from roughly 3 kHz to 300 GHz radio frequencies are widely used in telephone systems, radio and television broadcasting, satellite communications and also in radio detection and ranging. Usually the information is at audio frequency and is transposed onto the radio frequency to be carried from one point to another. The process of transposition is known as modulation. There are several ways to modulate a radio wave. In this chapter we will discuss different types of modulators and also demodulators. The latter are used to recover information from modulated waves at the receiving point.

Amplitude modulation

In this type of commonly used modulator a sinusoidal carrier wave is made to vary in amplitude in sympathy with the magnitude of the low frequency information signal.

Objectives

At the end of the study of this chapter a student should be:

1. familiar with the conditions of sinusoidal oscillations

2. able to understand the principles of LC oscillators

3. familiar with the principle of operations of RC oscillators

4. able to construct crystal oscillators.

In electronics periodic signals of various shapes such as sinusoidal, triangular, rectangular and pulses are often needed to perform different types of operation. Although the term oscillator is generally referred to a generator of sinusoidal signals, while a rectangular-wave generator is more commonly known as a multivibrator, an oscillator generates an a.c. output signal without requiring any form of input signal. Sinusoidal oscillators are mainly used in radio frequency transmitters and receivers. Square-wave or pulse generators are used in almost every type of digital equipment. In this chapter we shall mainly concentrate on sinusoidal oscillators.