IC oscillators

Chapter IC oscillators

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • This is sometimes called a multivibrator circuit, although that is technically a mis-nomer, the term being more appropriate to various digital signal-generating circuits.Two N-channel JFETs are connected to form an oscillator as shown in Fig. 25-10.Each “stage” amplifies the signal in class-A, and reverses the phase by 180 degrees.Thus, the signal goes through a 360-degree shift each time it gets back to any particu-lar point. A 360-degree shift results in positive feedback, being effectively equivalent tono phase shift.The frequency is set by means of an LC circuit. The coil uses a ferromagnetic core,because stability is not of great concern and because such a core is necessary to obtainthe large inductance needed for resonance at audio frequencies. The value of L is typi-cally from 10 mH to as much as 1 H. The capacitance is chosen according to the formulafor resonant circuits, to obtain an audio tone at the frequency desired.Quiz469IC oscillatorsIn recent years, solid-state technology has advanced to the point that whole circuits canbe etched onto silicon chips. Such devices are called integrated circuits (ICs). The op-erational amplifier (op amp) is one type of IC that is especially useful as an oscilla-tor. Op-amp oscillators are most commonly employed as audio oscillators. Integratedcircuits are discussed in chapter 28.QuizRefer to the text in this chapter if necessary. A good score is at least 18 correct. Answersare in the back of the book.25-10 A “multivibrator” type audio oscillator.