TABLE OF CONTENTS This chapter focuses on microwave amplifier circuit design. A simple microwave amplifier consists of an active device, such as a transistor, an input- and output-matching circuit, and a power supply bias circuit. We begin with the two-port S-parameters for RF and microwave transistors and an operating environment for the finished amplifier. For example, we can design a circuit that amplifies signals from a generator with a 50 ohm impedance and deliver these amplified signals to a 50 ohm load. The transistor S-parameters along with some mapping functions are used to determine the correct impedance, which will terminate the input and output of the transistor. Matching circuits are designed to transform these impedances to the actual source and load impedances where the amplifier is to be used. We will use the circuit synthesis methods discussed in Chapter 5 to build input- and output-matching circuits.
Section 6.2 explains how S-parameters are presented in transistor data sheets. The S-parameters are different for each transistor and depend on how the transistor is packaged. Furthermore, the S-parameters vary with frequency and bias point. Several tables of S-parameters in the manufacturer's data sheets indicate a representative bias voltage and current. Also listed are the magnitude and phase of the two-port S-parameters at different frequencies.
Section 6.3 introduces the concept of amplifier stability. We will be working with transistors that amplify signals over a wide frequency range and are potentially unstable. An unstable transistor can oscillate and make the circuit useless as an amplifier. We...
