Crystal Oscillator

Nov 2 21:40 2008 Piter Print This Article

A crystal oscillator is an electronic circuit that produces electrical oscillations at a particular designed frequency determined by the physical characteristics of one or more crystals generally of quartz positioned in the circuit feedback loop

A crystal oscillator is an electronic circuit that produces electrical oscillations at a particular designed frequency determined by the physical characteristics of one or more crystals,Guest Posting generally of quartz, positioned in the circuit feedback loop.

Crystal Oscillators is the base of many electronic and communications systems that depend on accurate time measurement and coordination. They are used to provide stability to time-frequency generators, which in turn provide carrier and pilot signals for electronic communication and navigation systems. Crystal Oscillators also provide the clock signals used by data processing equipment, as well as the reference signals for other special-purpose systems. The required accuracy and stability of oscillator output frequency depend on the application, ranging from about ±1000 PPM in the case of simple microprocessor clocks, to less than ±5 PPM for applications requiring very precise frequency control.

A Crystal Oscillator consist of an amplifier and feedback network that selects a portion of the amplifier output and returns it to the amplifier input. The oscillator circuit is dependent on two key conditions: First, the gain loop needs to be greater than losses around the oscillator loop, or equal to unity. Second, the loop phase shift must be equal to 0 or 360 degrees. Loop phase angle shifts determine the frequency at which the oscillator will work. A little bit of change in net loop phase angle results in a change in output frequency of the oscillator circuit. In order to minimize the net phase shift, a quartz crystal is placed in the feedback loop. Because of the changes in impedance of the quartz crystal due to changes in applied frequency, all other components of the circuit should be considered constant reactance resulting in an adjustment of the quartz crystal frequency to a reactance that satisfies the loop phase characteristics.

Crystal oscillator circuits using crystal have a number of advantages in actual application since crystals show high frequency stability and stable temperature characteristic as well as excellent processing ability. Also crystal oscillator can achieve a high degree of accuracy and frequency stability.


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