Oscillation

Oscillation is the periodic variation, typically in time, of some measure as seen, for example, in a swinging pendulum. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes is used to be synonymous with oscillation. Oscillations occur not only in physical systems but also in biological systems and in human society.
The simplest mechanical oscillating system is a mass, subject to the force of gravity, attached to a linear spring. The system is in an equilibrium state when the weight of the mass is balanced by the tension of the spring. If the system is displaced from the equilibrium, there is a net restoring force on the mass, tending to bring it back to equilibrium. However, in moving the mass back to the equilibrium position, it has acquired momentum which keeps it moving beyond that position, establishing a new restoring force, now in the opposite sense and this time due to gravity. The time taken for an oscillation to occur is often reffered to as being the oscillatory period.
The specific dynamics of this spring-mass system are described mathematically by the simple harmonic oscillator and the regular periodic motion is known as simple harmonic motion. In the spring-mass system, oscillations occur because, when at the static equilibrium displacement, the mass has kinetic energy which is converted into energy stored in the spring at the extremes of its path.

Voltage-controlled crystal

A voltage-controlled crystal oscillator (VCXO) is used when the frequency of operation needs to be adjusted by a relatively small amount, or when exact frequency or phase of the oscillator is critical, or, by applying a varying voltage to the control input of the oscillator, to disperse radio-frequency interference over a range of frequencies to make it less objectionable. Typically the frequency of a voltage-controlled crystal oscillator can only be varied by a few tens of parts per million (ppm), because the high Q factor of the crystals allows only a small "pulling" range of frequencies to be produced.
A temperature-compensated VCXO (TCVCXO) is normally used so that temperature does not alter the piezoelectric effect, thereby causing frequency drift due to heat buildup inside of a transmitter.

crystal oscillator

A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters.
Using an amplifier and feedback, it is an especially accurate form of an electronic oscillator. The crystal used therein is sometimes called a "timing crystal". On schematic diagrams a crystal is sometimes labeled with the abbreviation XTAL.

Backward wave oscillator

A backward wave oscillator (BWO), also called carcinotron or backward wave tube, is a device that is used to generate microwaves and terahertz radiation. It consists of a vacuum tube that provides 1 mW to 50 mW of power. Some types can produce frequencies in a range of 200 GHz to 1.1 THz. It sustains the oscillations by reflecting the traveling wave backwards against the beam. It is derived from the traveling wave tube. It has two main subtypes, the M-type (M-BWO) and O-type (O-BWO). Carcinotrons are used as powerful and stable microwave sources. Due to the good quality wavefront they produce, they find use as illuminators in terahertz imaging.
It is an amplifier with a wide tuning range. The electron gun generates an electron beam that passes through a slow-wave structure. The generated electromagnetic wave moves in the direction opposite to the direction of the electrons. The output signal is coupled out near the electron gun

Self inducing oscillations

Some systems can be excited by energy transfer from the environment. This typically occurs where systems are embedded in some fluid flow. For example, the phenomenon of flutter in aerodynamics occurs when an arbitrarily small displacement of an aircraft wing (from its equilibrium) results in an increase in the angle of attack of the wing on the air flow and a consequential increase in lift coefficient leading to a greater displacement before, at sufficiently large displacements, the stiffness of the wing dominates to provide the restoring force that enables an oscillation.

Coupled oscillations

The harmonic oscillator, and the more complicated systems for which it stands as a simple model, has a single degree of freedom. More complicated systems have more degrees of freedom, for example two masses and two springs. In such cases, energy is converted between the respective inertias of each degree of freedom and the several restoring forces in the system. This leads to a coupling of the oscillations of the individual degrees of freedom. For example, two pendulum clocks mounted on a common wall will tend to synchronise. The apparent motions of the individual oscillations typically appears very complicated but a more economic, computationally simpler and conceptually deeper description is given by resolving the motion into normal modes

Electronic oscillator

An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave.
A low-frequency oscillator (LFO) is an electronic oscillator that generates an AC waveform between 0.1 Hz and 10 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.

Types of electronic oscillator

There are two main types of electronic oscillator: the harmonic oscillator and the relaxation oscillator.

Harmonic oscillator

The harmonic oscillator produces a sinusoidal output. The basic form of an harmonic oscillator is an electronic amplifier with the output attached to a narrow-band electronic filter, and the output of the filter attached to the input of the amplifier. 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.
A piezoelectric crystal (commonly quartz) may be coupled to the filter to stabilise the frequency of oscillation, resulting in a crystal oscillator.
There are many ways to implement harmonic oscillators, because there are different ways to amplify and filter. For example:

• Hartley oscillator
• Colpitts oscillator
• Clapp oscillator
• Pierce crystal oscillator
• Phase-shift oscillator
• RC oscillator (Wien Bridge and "Twin-T")

HARTLEY OSCILLATOR

The HARTLEY OSCILLATOR is an improvement over the Armstrong oscillator. Although its frequency stability is not the best possible of all the oscillators, the Hartley oscillator can generate a wide range of frequencies and is very easy to tune. The Hartley will operate class C with self-bias for ordinary operation. It will operate class A when the output waveform must be of a constant voltage level or of a linear waveshape. The two versions of this oscillator are the series-fed and the shunt-fed. The main difference between the Armstrong and the Hartley oscillators lies in the design of the feedback (tickler) coil. A separate coil is not used. Instead, in the Hartley oscillator, the coil in the tank circuit is a split inductor. Current flow through one section induces a voltage in the other section to develop a feedback signal.

Colpitts oscillator

A Colpitts oscillator is the electrical dual of a Hartley oscillator. In the Colpitts circuit, two capacitors and one inductor determine the frequency of oscillation. The Hartley circuit uses two inductors (or a tapped single inductor) and one capacitor.

clapp oscillator

A variation of the Colpitts oscillator. An added capacitor is used to eliminate the effects of stray capacitance on the operation of the basic Colpitts oscillator.

Pierce Crystal Oscillator

The Barkhausen criteria states that for a positive feedback system, oscillation will occur when the loop gain (product of forward gain and feedback gain) has a phase shift of zero (180 degrees for negative feedback systems) and a magnitude of unity. In practical oscillator circuits, the analysis should indicate a loop gain magnitude greater than one, which will cause the amplitude of oscillation to grow exponentially until clipping or other nonlinear phenomena cause the gain magnitude to decrease to unity.

phase-shift oscillator

An oscillator in which a network having a phase shift of 180° per stage is connected between the output and the input of an amplifier

RC oscillator

Electronic oscillators are often designed around an LC tank circuit, a tuned circuit formed with an inductor and a capacitor. But use of an inductor is not a requirement. Instead, the tuned circuit can be built using just resistors and capacitors. Such an oscillator is referred to as an RC oscillator.

Relaxation oscillator

The relaxation oscillator is often used to produce a non-sinusoidal output, such as a square wave or sawtooth. The oscillator contains a nonlinear component such as a transistor that periodically discharges the energy stored in a capacitor or inductor, causing abrupt changes in the output waveform.
Square-wave relaxation oscillators can be used to provide the clock signal for sequential logic circuits such as timers and counters, although crystal oscillators are often preferred for their greater stability.
Triangle-wave or sawtooth oscillators are used in the timebase circuits that generate the horizontal deflection signals for cathode ray tubes in analogue oscilloscopes and television sets. In function generators, this triangle wave may then be further shaped into a close approximation of a sine wave.
The multivibrator and the rotary traveling wave oscillator are another types of relaxation oscillators