Answer 5—To create an oscillator, it’s necessary to set up a circuit with feedback that has a total of 360° of phase shift at the desired frequency and a net gain of exactly unity.

There are many ways to create the phase shift. Most commonly, an inverting amplifier is used to provide 180° of shift, along with feedback components that provide the other 180° at the desired frequency.

Similarly, there are many ways to stabilize the gain. The most common arrangement is to design excess gain into the circuit and then allow the amplifier to saturate, which limits the overall gain to unity but introduces distortion. To get low-distortion sine waves, a linear (or quasi-linear) mechanism must be used to provide gain feedback, as in a Wien bridge oscillator.

Contributor: David Tweed