Chapter 1: Introduction
For the past several years, analog and digital design engineers have continually been developing and refining circuits for increasingly higher operating frequencies. Analog circuits for wireless communication in the low to high gigahertz (GHz) range and concomitantly the rapid improvement of clock speeds of microprocessors, memory chips, and peripheral units in high-performance mainframes, workstations, and personal computers exemplify this trend. Global positioning systems require carrier frequencies in the range of 1227.60 and 1575.42 MHz, wireless local area networks and HiperLAN operate at 2.4 GHz, and optical communication channels can transport data of up to 40 gigabits per second (Gbps). The low-noise amplifier in a personal communication system (PCS) may operate at 1.9 GHz and fit on a circuit board smaller in size than a dime. Satellite broadcasting in the C-band involves 4 GHz uplink and 6 GHz downlink systems. In general, due to the rapid expansion of wireless communication, more compact amplifier, filter, oscillator, and mixer circuits are being designed and placed in service at frequencies generally above 1 GHz. There is little doubt that this trend will continue unabated, resulting not only in engineering systems with unique capabilities, but also special design challenges not encountered in conventional low-frequency systems.
This chapter reviews the implications as one migrates from low- to high-frequency circuit operation. It motivates and provides the physical rationales that have resulted in the need for new engineering approaches to design and optimize these circuits. The example of a mobile phone circuit, components of which will be analyzed in more detail in later chapters, serves as a vehicle to outline the goals and objectives of this textbook, and its organization.
The chapter begins with a brief historical discussion explaining the transition from direct current (DC) to high-frequency modes of operation. As the frequency increases and the associated wavelengths of the electromagnetic waves becomes comparable to the dimensions of the discrete circuit components such as resistors, capacitors, and inductors, these components start to deviate in their electric responses from the ideal frequency behavior. It is the purpose of this chapter to provide the reader with an appreciation and understanding of high-frequency passive component characteristics. In particular, due to the availability of sophisticated measurement equipment, the design engineer must know exactly why and how the high-frequency behavior of his or her circuit differs from the low-frequency realization. Without this knowledge, it will be impossible to develop and understand the special requirements of high-performance systems.