TABLE OF CONTENTS In Chapter 8, we introduced noise and noise figure in mathematical terms. In this chapter, we will show how this information applies to transistor amplifiers. Two-port S-parameters and noise characteristics are published by microwave manufacturers to ensure that the transistor can be easily utilized in an amplifier design. We have introduced a mathematical representation of noise created by a two-port. The noise added by the two-port is characterized by a few quantities that are essential to the two-port and the input reflection coefficient. Some transistor data sheets show noise parameters for a particular transistor at several frequencies.
Many applications, such as communication and radar receivers, require amplifiers that add a minimal amount of noise to the receiver signal. It is necessary to design amplifiers with a specified noise figure to gurantee the proper operation of the receiver. If the amplifier is narrowband, we may be able to design the input matching circuit in a way that the source reflection coefficient corresponds to the minimum noise figure source impedance. We know this will yield an amplifier with the lowest possible noise figure for a particular transistor. However, the optimum noise figure reflection coefficient may lie in the region of potential instability. Moreover, we may want to trade a little noise for a higher gain. This chapter shows how to design low noise amplifiers by finding the constant noise figure circles, using more than one transistor amplifier stage and setting the proper bias point of the transistor.
Section 9.2 discusses...
