A quartz oscillator generates a signal at a specific frequency using a quartz crystal’s piezoelectric property. It is used in cell phones, GPS, radios, watches, and computers. The crystal changes shape when voltage is applied, generating a voltage when returning to its original shape. The oscillator operates at the resonant frequency of the crystal, which can be affected by external factors. Additional circuitry can compensate for these factors, and some oscillators have a controlled oven to compensate for temperature changes.
A quartz oscillator is an electronic circuit that generates a signal at a determined frequency from a quartz crystal made up of silicon and oxygen. The piezoelectric property of quartz makes it an excellent resonator from tens of Kilohertz (KHz) to hundreds of Megahertz (MHz). A quartz crystal oscillator is typically designed to operate at only a single precise frequency. These oscillators are used to create stable frequencies in cell phones, Global Positioning System (GPS) receivers, and two-way radios. They are also used for precise timekeeping in watches, computers and other electronic equipment.
A crystal of piezoelectric material such as quartz can change shape slightly when a voltage is applied to an electrode on the crystal. Once that voltage is removed, the crystal can return to its original shape and generate a voltage while doing so. Discovered in 1880 and called piezoelectricity, this property is fundamental to the functioning of an oscillator. Over time, experiments were conducted with different crystalline materials, and the first quartz oscillator was assembled in the late 1910s. Since the 1920s, quartz crystal oscillators have been frequently used in amateur, commercial, and military radio equipment and watches.
When a quartz oscillator is first turned on, the circuit introduces a random noise signal to the crystal. Some of that noise will always be at the resonant frequency of the crystal, causing the crystal to oscillate. The voltage produced by the crystal as it changes shape is amplified by the crystal oscillator circuit and fed back to the crystal resonator. As this process repeats, signals within the limited frequency band of the crystal will get stronger while other frequencies will be filtered out. Once this “warm up” period is completed, the oscillator will operate at exactly its designed frequency.
The shape, size and cut of a quartz crystal determine how quickly it expands and contracts. A quartz oscillator can operate at this rate, which is called the resonant frequency. It can also operate at a harmonic frequency, which is a multiple of the resonant frequency. While quartz crystals occur naturally in the environment, very large numbers are produced to increase the yield and supply of physically usable crystals.
The output frequency from a quartz oscillator can be affected by a variety of external factors including temperature and even sudden acceleration. Radiation will also affect the frequency, whether it comes from cosmic rays in a spacecraft, X-rays, or a pulse of ionizing radiation. Some of these factors can be compensated for with additional circuitry that monitors conditions and adjusts the oscillator output accordingly. Some quartz oscillators include a precisely controlled oven with the crystal inside to compensate for temperature changes. Quartz crystals can also be “swept” or hardened against radiation by firing them in a specialized atmosphere and electric field.
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