RF and Microwave Circuit and Component Design for Wireless Systems

CHAPTER SEVEN

Switches

7.1 INTRODUCTION

Semiconductor control circuits (i.e., switches, phase shifters, attenuators, modulators, etc.) have been used extensively in radars, communication systems, electronic warfare, wireless applications, instruments and other systems for controlling the signal flow or to adjust the phase and amplitude of the signal. At RF, microwave, and millimeter-wave frequencies, many of the problems of bandwidth, switching speed, power handling, high dynamic range, low voltage operations and high operating frequency have already been solved. One of the most suitable MMIC components is the switching circuit. When MMIC technology first received acceptance, switch products played a key role. In microwave systems, the transmitter and receiver portion is called a transceiver, and it requires several switches (low and high power). Low-power switches are used in phase shifters and attenuators. This chapter deals exclusively with switches, and various aspects of these components are described. An excellent overview of these circuits as well as of switching devices can be found in References [1–8].

7.1.1 Switch Parameter Definitions

Because of finite impedance of the switching devices and finite losses of the connecting circuitry, the fabricated switch circuits do not have ideal performance. The performance of a practical switch can be expressed by specifying its insertion loss and isolation as the basic design parameters.

7.1.1.1 Insertion Loss It is defined as the ...