17 - The ins and outs of oscillator action

Abstract

This chapter reviews the detailed functioning of an LC oscillator to reveal unsuspected sophistication to its operation. In particular, a radical difference between the operation of conventional transistor oscillators and their vacuum tube predecessors is shown to be of fundamental importance in understanding their relative merits and limitations. This chapter also discusses that a good RF oscillator circuit should simultaneously fulfill a number of requirements, such as excellent medium- and long-term frequency stability, low harmonic content, and low phase noise, to name a few. These are not easy to achieve even in a fixed frequency oscillator, and if an oscillator is tunable over a frequency range of more than a few percent, it is even more difficult. Furthermore, in an oscillator covering an octave or more, it is desirable that the output amplitude should remain constant or at least very nearly so over the tuning range. In any case, if the amplitude varies widely with the tuning, the other parameters mentioned will be compromised.