AC EQUIVALENT CIRCUIT OF CRYSTAL:-

R=FRICTION LOSSES

L=INERTIA

C=SHIFTNESS

C'=MAUNTING CAPACITANCE

Principle of crystal Oscillator:-

• A materrial such as a quartx which is having an unique properties called as a "piezo electric " property.
• it states that if we applied a force to this crystal then it generates a electric potential.
• also if we applied an electric signal to crystal then it shows the vibrations mechanically.
• The biggest advantage of a crystal oscillator is its frequency stability.
• frequency of the crystal oscillator is remains so stable with any changes in temp,voltage,humidity, or other parameters.

OPERATION:-

1. Colpitt oscillator modifed to act as crystal oscillator.Only change is addition of crystal (y) f/b network.
2. circuit shows parallel resonance circuit of crystal,for this impedence of crystal is maximum.
3. Hence maximum energy transfer through feedback network.
4. since here feedback is positive ,180 degree phase shift is produced bu crystal oscillator and further 180 degree produced by capacitor volage divider from input crystal.
5. even smallest deviation from fp will cause oscillator to act as effective short, so it is example of extremly stable oscillator.

Resonant frequencies:-

• There are two resonant circuits in a eqiuvalent circuit of a crystal oscillator.
• RLC circuit forms an series resonant circuit and RLC with C combines the parallel resonant circuit.
• resonant frequency of RLC circuit is given by:$ fs = {1\over 2\pi\sqrt {LC} }$

Types of Crystal Oscillator:-

1. Pierce Crystal Oscillator
2. Miller Crystal Oscillator

Advantages:-

1. High frequency stability with respective any changes in parameters like temp,voltage etc.
2. Q factor of crystal Oscillator is too high .It is too high as compare to 100 LC tank.

Disadvantages:-

1. Used at only lowe power circuits.
2. Frequency of circuit can not be changed.

Applications:-

1. Used as a frequency generator in microprocessor and microcontroller kits.
2. The crystal oscillator is used in research and measurement for celestrial navigation, space tracking purpose, in the measuring instruments and medical devices, and so on.
3. Used in a frequency synthesizers.
4. In tv and radio transmitter.
5. The use of crystal oscillator in military and aerospace, is to establish an efficient communication system, for the navigation purpose, electronic warfare, in the guidance systems, and so on.
6. Crystal oscillator is used for engine controlling, stereo, clock and to trip computer, and in GPS system.