The harmonic, or linear, oscillator produces a sinusoidal output.
The basic form of a harmonic oscillator is an electronic amplifier connected in a feedback loop, with its output fed back into its input through an electronic filter. When the power supply to the amplifier is first switched on, the amplifier's output consists only of noise. The noise travels around the loop, being filtered and re-amplified until it increasingly resembles the desired signal. Very quickly the signal in the loop becomes a sine wave at a single frequency.
In inductive-capacitive or LC oscillators, the filter is a tuned circuit (often called a tank circuit) consisting of an inductor (L) and capacitor (C) connected together. Charge flows back and forth between the capacitor's plates through the inductor, so the tuned circuit can store electrical energy oscillating at its resonant frequency. The feedback from the amplifier creates a negative resistance that compensates for the internal resistance of the LC circuit, sustaining the oscillations. LC oscillators are typically used when a tunable frequency source is necessary, such as in signal generators, tunable radio transmitters and the local oscillators in radio receivers. Typical LC oscillator circuits are the Hartley, Colpitts and Clapp circuits. On-chip inductors usually don't have a high enough Q-factor to use in the tuned circuit.
A piezoelectric crystal (commonly quartz) may take the place of the filter to stabilise the frequency of oscillation, this is called a crystal oscillator. These kinds of oscillators contain quartz crystals that mechanically vibrate as resonators, and their vibration determines the oscillation frequency. Crystals have very high Q-factor and also better temperature stability than tuned circuits, so crystal oscillators have much better frequency stability than LC or RC oscillators. They are used to stabilize the frequency of most radio transmitters, and to generate the clock signal in computers. The Pierce oscillator circuit is often used for crystal oscillators. Because the crystal is an off-chip component, it adds some cost and complexity to the system design, but the crystal itself is generally quite inexpensive.
Surface acoustic wave (SAW) devices are a kind of crystal oscillator, but achieve much higher frequencies by establishing standing waves on the surface of the quartz crystal.[citation needed] These are more expensive than crystal oscillators, and are used in specialized applications which require a direct and very accurate high frequency reference, for example, in cellular telephones.
The basic form of a harmonic oscillator is an electronic amplifier connected in a feedback loop, with its output fed back into its input through an electronic filter. When the power supply to the amplifier is first switched on, the amplifier's output consists only of noise. The noise travels around the loop, being filtered and re-amplified until it increasingly resembles the desired signal. Very quickly the signal in the loop becomes a sine wave at a single frequency.
In inductive-capacitive or LC oscillators, the filter is a tuned circuit (often called a tank circuit) consisting of an inductor (L) and capacitor (C) connected together. Charge flows back and forth between the capacitor's plates through the inductor, so the tuned circuit can store electrical energy oscillating at its resonant frequency. The feedback from the amplifier creates a negative resistance that compensates for the internal resistance of the LC circuit, sustaining the oscillations. LC oscillators are typically used when a tunable frequency source is necessary, such as in signal generators, tunable radio transmitters and the local oscillators in radio receivers. Typical LC oscillator circuits are the Hartley, Colpitts and Clapp circuits. On-chip inductors usually don't have a high enough Q-factor to use in the tuned circuit.
A piezoelectric crystal (commonly quartz) may take the place of the filter to stabilise the frequency of oscillation, this is called a crystal oscillator. These kinds of oscillators contain quartz crystals that mechanically vibrate as resonators, and their vibration determines the oscillation frequency. Crystals have very high Q-factor and also better temperature stability than tuned circuits, so crystal oscillators have much better frequency stability than LC or RC oscillators. They are used to stabilize the frequency of most radio transmitters, and to generate the clock signal in computers. The Pierce oscillator circuit is often used for crystal oscillators. Because the crystal is an off-chip component, it adds some cost and complexity to the system design, but the crystal itself is generally quite inexpensive.
Surface acoustic wave (SAW) devices are a kind of crystal oscillator, but achieve much higher frequencies by establishing standing waves on the surface of the quartz crystal.[citation needed] These are more expensive than crystal oscillators, and are used in specialized applications which require a direct and very accurate high frequency reference, for example, in cellular telephones.
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