5.1 Introduction

This chapter describes the most important techniques used for MMIC amplifier design. The classical theory and analysis of S-parameters, two-port stability and unilateral transducer gain are briefly reviewed. The key impedance matching techniques and DC biasing circuits are described before introducing the five major MMIC amplifier topologies: the reactively matched amplifier, the lossy match amplifier, the feedback amplifier, the distributed amplifier and various forms of actively matched amplifier. Finally, the design of low noise and high power amplifiers is considered. For further information on the mathematical treatment of microwave amplifier design, the reader is referred to one of the many excellent texts on this subject [1 6]. The justification for not covering this topic in great detail is that MMIC amplifier design techniques are rather different from conventional microstrip MIC amplifier design. This is partly because the size limitations of MMICs have forced designers to develop new topologies, and partly because the low component parasitics on MMICs have enabled more complicated circuit topologies to be used. In addition, the extensive use of CAD has removed the need for many of the original graphical and analytical methods of matching network synthesis and amplifier design (e.g. [7, 8]), although a good understanding of the principles of amplifier design is still vital.

Compared with hybrid-MIC amplifiers, MMIC amplifiers have the major advantages of low cost and excellent reproducibility when manufactured in large quantities. However, MMIC amplifier performance can suffer from their small size because...