μblog: engineering from the trenches

Designing a stable oscillator can be challenging. The first choice is if you want something like a ring oscillator that will switch between two output values at a fixed frequency, or if a sinusoidal output is desired. The basic idea is that the oscillator is a feedback system where the total loop gain has to be greater than (equal to) unity and a loop phase of a multiple of 360 degrees for a ring (sinusoidal) oscillator. This is known as the Barkhausen criteria for oscillation. Here is a small application note from Microchip that outlines some of the theory that I promised to apply a long time ago with some older logic gates.  I will make another post later with some more practical designs employing transistors and logic gates and will hopefully have a interesting design to show off.

( 00943a.pdf )

del.icio.us | digg