TRANSISTOR AMPLIFIER DESIGN Ampli®ers are among the basic building blocks of an electronic system. While vacuum tube devices are still used in high-power microwave circuits, transistorsÐ silicon bipolar junction devices, GaAs MESFET, heterojunction bipolar transistors (HBT), and high-electron mobility transistors (HEMT)Ðare common in many RF and microwave designs. This chapter begins with the stability considerations for a two-port network and the formulation of relevant conditions in terms of i