Simple Oscillator Design Procedure

Chapter Simple Oscillator Design Procedure

Complete Electronics Self Teaching Guide with Projects
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Complete Electronics Self Teaching Guide with Projects

  • SIMPLE OSCILLATOR DESIGN PROCEDURE423D. Three: the Colpitts, Hartley, and the Armstrong.E. Nothing: The oscillations should start spontaneously if the component values in the circuit are correct.The main practical problem with building oscillators is selecting the coil. For mass production, a manufacturer can specify and purchase the exact coil required. But in a lab or workshop (where you are building only a single circuit), it is often difficult or impos-sible to find the exact inductor specified in a circuit design. What usually happens is that you use the most readily available coil, and design the rest of the circuit around it. This presents three possible problems: ■ You may not know the exact value of the inductance. ■ The inductance value may not be the best for the wanted frequency range. ■ The coil may or may not have tap points or extra windings, and this may cause a change in the circuit design. For example, if there are no taps, then you cannot build a Hartley oscillator.Because Colpitts is the easiest oscillator to make work in practice, and provides an easy way around some of the practical difficulties, you can focus on that oscillator.You can use almost any coil when building a Colpitts oscillator, provided it is suitable for the frequency range you want. For example, a coil from the tuner section of a televi-sion set would not be suitable for a 1-kHz audio oscillator because its inductance value is outside the range best suited to a low-frequency audio circuit.SIMPLE OSCILLATOR DESIGN PROCEDURE27  Following is a simple step-by-step procedure for the design of a Colpitts oscillator. The Colpitts can work over a wide frequency range. (A Hartley can be designed using a similar set of steps.)By following this procedure, you can design an oscillator that works in the majority of cases. There is a procedure you can use that guarantees that the oscillator will work, but it is far more complex.Book Authorc09V107/04/2012 3:23 PM c09.indd 4237/4/2012 3:24:51 PM