Customer Reviews

Wideband Amplifiers

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Finding a book that addresses a topic from the famous MIT Radiation Laboratory Series feels almost like encountering a new version of the bible. The RL Series has provided firm anchors to analog circuit designers throughout the past six decades and represents as such an almost untouchable set of classic texts. Yet, it was high time for comprehensive updates of these texts to see the light of day. For example, the Valley-Wallman's "Vacuum Tube Amplifiers" has first appeared in 1948. Since that time the transistor has been invented, the computers have become an important engineer's design tool and the engineering practice has resulted in many new insights into the field of electronic amplifiers. Authors Peter Staric and Erik Margan have successfully addressed this challenge with their book "Wideband Amplifiers" published by "2006 Springer" of Netherlands.

Just like the Radiation Lab Series, the content of "Wideband Amplifiers" rests on firm understanding of theoretical underpinnings of topics addressed. And just like the former, the "Wideband Amplifiers" is enriched with engineering guidance, stemming from unmistakable hands-on experience. But what gives this book its special vital value is its match to the world of semiconductors and computers.

As the title "Wideband Amplifiers" suggests, the authors have paid particular attention to bandwidth extending techniques. The inductive peaking has received a thorough analysis, starting with a clever introduction of this powerful technique. The many variations of Bessel, Butterworth and real pole circuits are richly illustrated with time and frequency responses, providing the designer with an important warning to consider both while pursuing either.

The same diagrams display also the uncompensated responses, giving the designer a measure of benefit extracted from increased circuit complexity. Each diagram is accompanied by the actual circuit schematics that would produce the relevant responses. The authors have gone even a step further and have provided the methods for calculation and design of cylindrical T-coils and their coupling coefficients. To the practicing engineer this will be an additional welcome shortcut on the path from theory to implementation. To the analytically minded the mathematical derivations of all responses will open the path to creative experimentation before committing a design to implementation.

The authors have taken a noncommittal stand with respect to frequency and time domain approaches of circuit design. As we have hinted earlier this forces the designer who pursues a response in one domain to pay attention also to the behaviour in the other domain. The Fourier and Laplace transforms, tying together the two domains have received an extravagant treatment in the very first chapter of this book. It is likely the most complete set of analytical tools to be found in a non-mathematics book.

Rather than offloading the forward and inverse transformations to the tables as is commonly done, the authors have not shied away from entering the slippery field of contour integration, integration around poles and other complex mathematical constructs underlying the inverse transformations. Yet, they have tied all these mathematical abstractions to the electrical circuitry and have brought them down to earth with many beautiful illustrations. If one wanted desperately to come up with a missing mathematical tool it would be the implicit convolution. By allowing the transfer of unspecified boundary conditions between domains the implicit convolution greatly expands the usability of transforms. Unfortunately, this powerful technique is not widely publicized.

Having obviously enjoyed the beauty of exact mathematical predictability of passive peaking circuit behaviour, the authors bid farewell to exact calculations in the third chapter. Here the amplification part of the book's title joins the wideband part, which was so thoroughly addressed in the second chapter. The semiconductor cascode amplification and the JFET source follower receive the lion's share of the attention. Special needs of oscilloscope amplifiers are addressed and again reveal the hands-on familiarity with the subject. The knowledge acquired in the second chapter is here well integrated with the active elements and is thoroughly analyzed from the viewpoint of the ultimate goal, i.e., wideband amplification.

In the fourth chapter new options offered by multi-stage amplifiers are addressed. The possibility of cascading unequal stages opens a whole new spectrum of possibilities. The predictability of performance by analytical means is again available and the authors make ample use of it. A systematic positioning of Butterworth and Bessel poles dependent on the number of amplification stages takes up much of the chapter's allocated space. Unlike all known classical texts of this genre, this book provides tables of Butterworth and Bessel poles up to the 10-th order. As was the case in earlier chapters, the authors again carefully allocated equal space to frequency and time domain performance questions.

Chapter 5 starts with an implementation of a seven pole two stage amplifier whose bandwidth has been inductively peaked and optimized for time response. This amplifier and most of the following circuits addressed in this chapter should be an oscilloscope designer's wish-come-true. It would include the design of an input attenuator without the bothersome "hook-effect" and a delightful transition from discrete amplifier implementations to integrated versions. Modern operational amplifiers and a variety of integrated components are used in powerful combinations to meet the needs of an oscilloscope or a number of other electronic test instruments.. Issues like linearity, slew rate, overdrive recovery and even error corrections are addressed in this chapter richly endowed with ideas and circuits.

In the sixth chapter the reader is led from the classical mathematics of linear, time invariant, causal systems to its digital equivalent. Again the frequency and time domains receive full attention but this time within the Matlab environment. As the filtered amplification ideas are being developed they are examined with this powerful digital tool. At the same time the readers are familiarized with ways of casting their own ideas into the language that the Matlab Signal Processing Toolbox can understand.

An important contribution of this chapter is a proposed method, which overcomes the known divergent responses of Fourier transform to temporal step inputs. In the classical analog environment of previous chapters this problem was overcome by the use of Laplace transform. The method developed here is applicable to sampled data only. It is successfully used throughout the chapter for evaluation of time responses obtained from sampled spectral data by means of the Fast Fourier Transform algorithm. A thorough analysis of errors stemming from the digital nature of signals and from their digital processing is another indicator of the hands-on experience of the authors.

Chapter seven is an implementation of the groundwork developed in chapter 6. The nitty-gritty question of how to get from calculated poles to resistors, capacitors and inductors is addressed here. A rarely encountered analysis of a cascade of an analog and a digital filter is also found in this chapter. Even the complex task of overall optimization of such structures is discussed.

Among other issues addressed, which testify to a thorough familiarity of the authors with the gaps between theoretical and actual performance, of even the best designs, is the question of aliasing. The spurious responses arising from aliasing are vividly illustrated in both time and frequency domain and methods for combating them with windowing are discussed. A proof of authors' successful struggle with aliasing in general, is visible from the beautiful graphs that make the perusal of this book a pleasant experience. But its value to a designer of wide band amplifiers, striving for ultimate performance is unprecedented.

Zvonko Fazarinc

"Wideband Amplifiers" is an excellent book for a postgraduate student of circuit design, or a professional engineering reference. Good qualitative explanations of underlying principles before mathematical treatment. A down to earth writing style attempts, with considerable success, to lift the veil from this often feared part of the `dark art' of analogue design. Highly recommended.

J