Crystal Oscillator

• The cryatals are either naturally occuring or synthetically manufuctured, exhibiting the piezoelectric effect means under the influence of the mechanical pressure, the voltage gets generated across the opposite faces of the crystal

Crystal


• If the mechanical force is applied in such a way to force the crystal to vibrate, the a.c voltage get generated across it. Conversely, if the crystal is subjected to a.c voltage, it vibrates causing mechanical distortion in the crystal shape.

• Every crystal has its own resonating frequency depending on its cut. So under the influence of the mechanical vibrations, the crystal generates an electrical signal of very constant frequency. The crystal has a greater stability in holding the constant frequency
• A crystal oscillator is basically a tuned-circuit oscillator using a piezoelectric crystal as its resonant tank circuit. The crystal oscillator are preferred when greater frequency stability required. Hence the crystals are used in watches, communication transmitters and recivers etc
Pierce oscillator using crystal
• The main sustances exhibiting the piezoelectric effect are quartz Rochelle salt and taurmaline.
• Rochelle salt have the greatest piezoelectric activity. For a given a.c voltage, they vibrate more then quartz or tormaline. Hence these are preferred making microphones associated with portable tape recorders, headsets, loudspeakers etc. Rochelle salt in mechanically weakest of the three and break very easily.
• Tourmaline shows least piezoelectric effect but mechanically strongest. The tormaline is most expensive and hence its use is rare in practice.
• Quartz is a compromise between the piezoelectric activity of Rochelle salt and the strength of the tourmaline. Quartz is inexpensive and easily available in nature and hence very commonly used in the crystal oscillator.