I'm trying to understand how the Pierce oscillator works. Thanks to How does a Crystal work?, I've managed to understand almost all, but I'm still struggling to grasp, what causes the crystal to begin to oscillate at the very beginning? There's still no feedback AC coming into it.
Someone says that it's the "noise" causing the crystal to oscillate, but what noise? Audio noise? Electric noise coming from the circuit?
I would really appreciate if someone could help me to understand this "instant zero" of the Pierce oscillator.
Best Answer
"but... what noise? Audio noise? Electric noise coming from the circuit?"
Every circuit (except for superconductors. Maybe) has noise. Every resistor produces a noise voltage, as thermal energy jostles the electrons in it. It's called Johnson noise. This is why, for instance, very-low-noise amplifiers are often characterized by the effective temperature of their inputs.
It's a direct consequence of a) the fact that charge is quantized, and b) thermal energy manifests itself as thermal motion.
There are other sources of noise as well, but that will do for a start.