![]() ![]() As the oscillator circuitry amplifies signals from the crystal, frequencies near the crystal’s resonant frequency will become stronger and will eventually dominate the oscillator output. The quartz crystal can also be viewed as a highly frequency-selective filter in that it will only pass a narrow range of frequencies centered around the resonant frequency and attenuates everything else. The positive feedback in the system amplifies any electrical noise in the circuit that effectively ramps up the oscillation. When the energy of the generated output frequencies matches the losses in the circuit, the oscillation continues.ĭuring startup, the circuit puts the quartz crystal into an unstable equilibrium. The surrounding circuit sustains oscillations by taking the voltage from the quartz crystal, amplifying it, and feeding it back to the crystal. The mechanical vibrations result in electrical output and voltage drop across the crystal makes it vibrate. Mechanical and electrical characteristics of a quartz crystal in an oscillator circuit are a two-way street. The geometry of this crystal determines the fundamental or characteristic frequency. Two parallel surfaces have metal plates bonded to or deposited onto them for connection to the electrical circuit. The quartz crystal is a small wafer accurately milled to size and shape. (Specific behavior over temperature will depend on the mode of vibration and the angle at which the quartz is cut relative to its crystallographic axes.) A crystal such as quartz that exhibits the piezoelectric effect can be used to good effect in an oscillator.Īn important attribute of an oscillator circuit is its stability, by which is meant that its frequency remains constant regardless of changes in ambient temperature, electrical load and dc power supply voltage. Quartz is well-suited for this application because it is inexpensive, being abundant in nature and suitable for milling. The quartz crystal schematic symbol and a simple equivalent circuit for a quartz crystal in an oscillator. These properties make it possible for a quartz crystal to facilitate stability in an oscillator circuit. Consequently, a quartz crystal behaves like a circuit composed of an inductor, capacitor and resistor, with a precise resonant frequency. Removing the field lets the quartz generate an electric field as it returns to its previous shape. This property is known as electrostriction or inverse piezoelectricity. It was further observed that when voltage was applied, the crystal changed shape. Researchers found that when a weight was placed on a quartz crystal, electrical charges could be measured at its surface. The piezoelectric effect was first described in the early 1880s. If the property is to be manifest on any but an atomic level, the material must be a crystal, with the atoms organized in a lattice. ![]() They are said to exhibit the piezoelectric effect. Some materials acquire an electrical charge when they are compressed or otherwise dimensionally stressed. ![]()
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