TABLE OF CONTENTS This Chapter utilizes the principles presented earlier to study oscillators from the designer's perspective. For each case we begin with a specification, discuss the design qualitatively and then proceed with the actual design. Each case is an oscillator which satisfies a typical application requirement.
Certain characteristics are unnegotiable in good oscillator designs. Failure to achieve these basic objectives is an indication of design flaws which often manifest themselves in unpredictable and undesirable ways. Achieving these basic objectives is an indication of design quality. Among these desired objectives are the following.
The output level and frequency should change smoothly with supply variation from the start of oscillations up to a supply voltage which threatens device thermal, voltage or current failure. Neither the output level or operating frequency should jump or make sudden changes with smooth changes in the supplies.
There should be no discrete frequency components in the output spectrum other than the desired output, integer harmonics of the desired output or harmonics of the line frequency. In addition, reasonable levels of electromagnetic interference from external sources are to be expected in the spectrum. For example, the author's lab is within sight of a 50 KW AM broadcast station operating at 750 KHz and sidebands at this offset are often observed in oscillator outputs.
Other undesired spectral components are fractional harmonics of the desired output such as 1/2, 1/3 or 1/4. These arise from parametric pumping of tuning capacitors or active device junction capacitance. Periodic variation of...
