TABLE OF CONTENTS This chapter begins with an introduction to sinusoidal oscillators. Subsequently, we will discuss the RC phase-shift and LC oscillator families, and we will describe the Armstrong, Hartley, Colpitts, crystal, and the crystal-controlled Pierce oscillators.
An oscillator may be defined as a class of wave generators that produce sinusoidal, square, triangular, and sawtooth waveforms. Non-sinusoidal oscillators are known as relaxation oscillators. In Chapter 5 we introduced the Wien bridge oscillator, and in Chapter 7 the family of multivibrators. In this chapter we will be concerned with oscillators that produce sinusoidal waveforms. An oscillator is essentially an amplifier circuit that provides its own input signal. Oscillators are classified in accordance with the waveshapes they produce and the circuitry required to produce the desired oscillations. Henceforth, unless otherwise specified, the term oscillator will mean a sinusoidal oscillator.
As the name implies, a sinusoidal oscillator produces a sine-wave output signal. An ideal oscillator should produce an output signal with constant amplitude with no variation in frequency. But a practical oscillator cannot meet these criteria, the degree to which the ideal is approached depends on the class of amplifier operation, amplifier characteristics, frequency stability, and amplitude stability. Sinusoidal oscillators generate signals ranging from low audio frequencies to ultrahigh radio and microwave frequencies. Many low-frequency oscillators use resistors and capacitors to form their frequency-determining networks and are referred to as RC oscillators. These are used in the audio-frequency range.
Other types of employ inductors and capacitors for...
