EasyElectronics

  A Crystal oscillator is basically a tuned circuit oscillator using a piezoelectric crystal as a resonant tank circuit. Crystal oscillators are used when accuracy and stability of oscillation frequency are important. When a mechanical stress is applied across the faces of the crystal, a potential difference develops across opposite faces of the crystal. This property of a crystal is called the piezoelectric effect. ·          Similarly, when a.c. voltage is applied across one set of faces of crystal, they vibrate at a frequency of the applied voltage. The main substances that produce the piezoelectric effect are quartz, Rochelle salt and tourmaline. The following fig. shows the electrical equivalent circuit of a crystal along with some of the practical oscillators available in the market. ■        In the above circuit we will have two resonant frequencies. ...

  ·          Wein Bridge Oscillator The Wein bridge oscillator is the standard and simple oscillator circuit for low to moderate frequencies (10 Hz to 1 MHz). It is most frequently used type of audio oscillator. It is found that the oscillator is free from circuit fluctuations and ambient temperature. The oscillator circuit consists of an amplifier and an RC bridge is used in the feedback network of an oscillator. Following fig. shows the circuit of Wein Bridge Oscillator. •       Wein bridge oscillator is essentially a two-stage amplifier with RC bridge circuit. •       The transistor Q1 serves as an oscillator and amplifier, while the other transistor Q2 serves as an inverter i.e. to produce a phase shift by 180 0 . •       This circuit uses positive and negative feedbacks. •       The positive feedback is through R 3 C 3 , R 4 C ...