Achieving Effective Amplifier Designs

Oct. 5, 2009
In Design of RF and Microwave Amplifiers and Oscillators, Second Edition, Pieter L.D. Abrie offers expanded derivations and problem sets to make this material more accessible and easier to master. The author focuses on both iterative and ...

In Design of RF and Microwave Amplifiers and Oscillators, Second Edition, Pieter L.D. Abrie offers expanded derivations and problem sets to make this material more accessible and easier to master. The author focuses on both iterative and analytical synthesis techniques for designing linear amplifiers. In building on the first edition, he provides new material by considering a wide range of bias schemes including Class A, B, AB, E (nonlinear only), F, and Doherty amplifiers, as well as designing for amplifier stability and conditionally stable amplifiers. Details on the design of low-noise amplifiers (LNAs) are provided as well. In addition, this edition notes the influence of harmonic terminations on power performance. Models are presented for square spiral inductors and metal-insulator-metal (MIM) capacitors, which can be used to design monolithic-microwave-integrated-circuit (MMIC) amplifiers at microwave and millimeter frequencies.

One of the book's highlights is the power-parameter approach introduced in Chapter 2, which helps design engineers estimate the output power (1-dB compression point) of linear amplifiers. With this approach, a linear amplifier's output power is limited by the maximum amplitudes of the current and voltage associated with the transistor model's intrinsic current source. The output power extracted from a transistor can be limited in either current or voltage. Such limitations can be complicated or improved by harmonics. In a Class F amplifier, for example, the square-voltage waveform allows the fundamental tone voltage swing to be larger than the supply voltage (minus the knee voltage) with a corresponding increase in power. The use of square waveform signals can increase efficiency as well.

This approach requires a smallsignal model, the direct-current (DC) operating point at full power, and four boundary lines on the DC or pulsed current/voltage (I/V) curves of each transistor that is used. The transistors' power parameters can be derived from the small-signal model. Power parameters support the calculation of all operations typically associated with noise parameters and S-parameters including feedback, loading, cascading, and changes in configuration.

Using the power-parameter approach, the author asserts that it is easy to find optimum external load values associated with any intrinsic load. In fact, one can simply generate loadpull contours for any linear-amplifier stage and find the external terminations associated with the required intrinsic harmonic terminations.

This technique allows engineers to avoid nonlinear analysis techniques. In many cases, the power-parameter technique allows close-to-optimum designs to be created without load-pull information or an accurate large-signal model. In addition, the power-parameter approach can generate solutions that may be refined in nonlinear circuit simulators.

To design realizable RF and microwave circuits, the author emphasizes that one must have some knowledge of the parasitic elements associated with practical components. Hence, the book details the importance of accurate models for basic circuit elements including inductors, capacitors, and resistors. Skin and proximity effects also are covered in the discussions of model and simulation development. When just two conductors are in close proximity, the influence of the proximity effect will be relatively small compared to that of the skin effect. When more conductors are used, however, the effects should be taken into account.

The volume goes on to discuss resonant circuits and the design of narrowband impedance-matching networks, coupled coils and conventional transformers, and the transmission-line transformers that are widely used in RF and ultra-high-frequency (UHF) circuits. Also detailed are film resistors, single-layer parallel-plate capacitors, spiral inductors, and microstrip discontinuities. Wideband impedance-matching networks are detailed as well.

With its points punctuated by equations and graphics like Smith Charts, this book seeks to help the engineer design amplifiers more successfully. The CD-ROM that is packaged with the volume contains upgraded programs, which are integrated into a single Visual C++ program (LSM) with a menu-driven interface. According to the author, both single- and doublematching problems can be solved with LSM and the LSM executable that is licensed within the book.

Design of RF and Microwave Amplifiers and Oscillators, Second Edition by Pieter L.D. Abrie is available from Artech House for $139 (ISBN 978-1-59693-098-8). For more information, visit

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