TABLE OF CONTENTS In this section, we will discuss numerous transistor bias circuits. So far we have only shown how to design the microwave portion of the amplifiers. We have not shown how the low-frequency part of the circuit is designed. Transistors have gain because a small voltage or current at the input of the transistor can control a large output current or voltage. To achieve this, the operating state of the transistor without an input, or quiescent point, must be set properly. The data sheets contain lists of S-parameters, which are only useful when the current and voltage of the transistor match the bias conditions that correspond to those in the table. Usually, a substantial microwave and low-frequency circuit is needed to bias the transistor and make sure that power is supplied to the transistor in such a way that it is transparent to the microwave signal. There are two aspects of the transistor bias network: the bias injection circuit and the bias supply circuit. In this section, we will show ways to connect the power supply with the microwave transmission lines. We will also indicate what voltages are needed from the supply.
In most cases, a method of supplying the bias voltage and current to the transistor must be invisible to the frequencies of interest to the amplifier. Bias injection circuits are needed to connect to the transmission line. However, they should not affect the propagation of high-frequency signals through the transmission line. This is achieved by...
