Oscillator is an electronic ckt used to generate sinusoidal signal at the o/p without any i/p. oscillator is basically an amplifier with positive f/b.

The fig shows block diagram of a amplifier with positive f/b. in which the overall gain with positive f/b is given as

Af = $\frac{A}{1-A\beta}$ ------ (1)

Where,

Af = $\frac{vo}{vs}$ is gain with f/b

A = $\frac{vo}{v1}$ is gain without f/b

p = vf/vo is feedback factor.

The oscillator ckt works on barkhauson's criteria, which states that an amplifier can be converted into an oscillator provided that following conditions must be satisfied.

1) Amplifier must have positive f/b

2) In order to achieve positive f/b, overall phase shift around the levp should be 0˚ or integral multiple at 2 $\pi$

3) | AB | ≥ 1 i.e. Loop gain value should be greater than or equal to one.