Crystal Oscillator: Crystal oscillator use conveniently cut quartz crystals. The property interconnecting the mechanical and the electrical behaviours of a crystal is reffered to as the piezoelectric ehect. When a proper alternating potential is impressed on [iezoelectric crystal, the later vibrates mechanically. If the frequency of the applied alternating voltage and the natural frequency of the crystal are equal, the amplitude of the mechanical oscillations attains maximum.

In circuit Fig.b has two reonant frequencies.

$\therefore W_SL-\dfrac{1}{W_SC}=0$ or $f_s=\dfrac{1}{2\pi\sqrt{LC}}$

At frequency fs, the impedence of the series arm is pure resistance. At frequencies greater than fs, the reactance of the series arm is inductive. At some frequency fp>fs

We have,

$W_PL'=\dfrac1{W_PC'}\\ \therefore W_PL-\dfrac1{W_PC}=\dfrac1{W_PC'}\\ OR\\ f_p=\dfrac1{2\pi}\sqrt{\dfrac{C+C'}{LCC'}}$

fp is parallel resonant frequecy of the circuit.

The frequency of oscillation of the crystal oscillator is the parallel resonant frequency fp which is determined by the crystal parameters. The quality factor or (=WL/R) of the circuit is very high. These exceptionally high values of Q and the stability of the quartz characteristics with respect to time and temperature account for the remarkably high frequency stability of the crystal oscillator.

Crystal oscillator

A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a constant frequency.This frequency is often used to keep track of time, as in quartz wristwatches, to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers. The most common type of piezoelectric resonator used is a quartz crystal, so oscillator circuits incorporating them became known as crystal oscillators. However, other piezoelectric materials including polycrystalline ceramics are used in similar circuits.

Crystal Oscillator

A miniature 16 MHz quartz crystal enclosed in a hermetically sealed HC-49/S package, used as the resonator in a crystal oscillator.