INTRODUCTION

Radio-frequency (RF) oscillators play a very important role in every electronic communication system. By definition, an oscillator is a circuit capable of continuously generating a repetitive waveform of the desired frequency. Depending on the application, the repetitive waveform may be either sinusoidal or rectangular in nature. If an oscillator requires no external input signal or trigger to produce the desired output waveform, it is said to be self-sustaining or free-running. Those oscillators requiring an external input signal are called triggered or one-shot oscillators. In this chapter, we will deal only with self-sustaining or free-running oscillators. Also included in this chapter is the coverage of frequency synthesizers which are special frequency-generating circuits encountered in the most modern electronic communication systems. Like the oscillator, a frequency synthesizer produces a repetitive waveform of the desired frequency. Because a frequency synthesizer uses a phase-locked loop (PLL) as a basic building block, complete coverage of phase-locked loops is provided prior to the coverage of frequency synthesizers.