Crystal is a very high Q device. Ok, the non-sinusoidal noise, you talk about has a sinusoidal component to it. One of the components is at the resonant frequency of the crystal. See the model of the crystal, that should help see how it starts if you inject a small sinusoidal voltage across the crystal model. Don't forget the capacitors on the ends of the crystal.sandeep kumar said:How is the oscillator initiated?How a noise ,though non-sinusoidal can effect a sinusoidal output?
How is the saturation condition in oscillator circuits is decided by circuit parameters?