An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave. They are widely used in many electronic devices. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters , clock signals that regulate computers and quartz clocks , and the sounds produced by electronic beepers and video games. Oscillators are often characterized by the frequency of their output signal:.
Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters.
The harmonic, or linear , oscillator produces a sinusoidal output. The most common form of linear oscillator is an electronic amplifier such as a transistor or operational amplifier connected in a feedback loop with its output fed back into its input through a frequency selective electronic filter to provide positive feedback. When the power supply to the amplifier is first switched on, electronic noise in the circuit provides a non-zero signal to get oscillations started.
The noise travels around the loop and is amplified and filtered until very quickly it converges on a sine wave at a single frequency. Feedback oscillator circuits can be classified according to the type of frequency selective filter they use in the feedback loop: In addition to the feedback oscillators described above, which use two-port amplifying active elements such as transistors and operational amplifiers, linear oscillators can also be built using one-port two terminal devices with negative resistance ,   such as magnetron tubes, tunnel diodes , lambda diodes and Gunn diodes.
Negative resistance oscillators are usually used at high frequencies in the microwave range and above, since at these frequencies feedback oscillators perform poorly due to excessive phase shift in the feedback path. In negative resistance oscillators, a resonant circuit, such as an LC circuit , crystal , or cavity resonator , is connected across a device with negative differential resistance , and a DC bias voltage is applied to supply energy.
A resonant circuit by itself is "almost" an oscillator; it can store energy in the form of electronic oscillations if excited, but because it has electrical resistance and other losses the oscillations are damped and decay to zero. The negative resistance of the active device cancels the positive internal loss resistance in the resonator, in effect creating a resonator with no damping, which generates spontaneous continuous oscillations at its resonant frequency.
The negative resistance oscillator model is not limited to one-port devices like diodes; feedback oscillator circuits with two-port amplifying devices such as transistors and tubes also have negative resistance.
A nonlinear or relaxation oscillator produces a non-sinusoidal output, such as a square , sawtooth or triangle wave. The switching device periodically charges and discharges the energy stored in the storage element thus causing abrupt changes in the output waveform. Square-wave relaxation oscillators are 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. They are also used in voltage controlled oscillators VCOs , inverters and switching power supplies , dual slope analog to digital converters ADCs , and in function generators to generate square and triangle waves for testing equipment. In general, relaxation oscillators are used at lower frequencies and have poorer frequency stability than linear oscillators.
Ring oscillators are built of a ring of active delay stages. Generally the ring has an odd number of inverting stages, so that there is no single stable state for the internal ring voltages. Instead, a single transition propagates endlessly around the ring.
An oscillator can be designed so that the oscillation frequency can be varied over some range by an input voltage or current. These voltage controlled oscillators are widely used in phase-locked loops , in which the oscillator's frequency can be locked to the frequency of another oscillator.
These are ubiquitous in modern communications circuits, used in filters , modulators , demodulators , and forming the basis of frequency synthesizer circuits which are used to tune radios and televisions. Radio frequency VCOs are usually made by adding a varactor diode to the tuned circuit or resonator in an oscillator circuit. Changing the DC voltage across the varactor changes its capacitance , which changes the resonant frequency of the tuned circuit.
Voltage controlled relaxation oscillators can be constructed by charging and discharging the energy storage capacitor with a voltage controlled current source. Increasing the input voltage increases the rate of charging the capacitor, decreasing the time between switching events.
Probably the first people to observe an effect due to an electrical oscillator were Auguste Arthur de la Rive , who observed a hissing arc in ,  and David Edward Hughes , who observed the humming telephone effect in Ernst Lecher in showed that the current through an electric arc could be oscillatory.
Independently, in the same year, George Francis Fitzgerald realized that if the damping resistance in a resonant circuit could be made zero or negative, the circuit would produce oscillations, and, unsuccessfully, tried to build a negative resistance oscillator with a dynamo, what would now be called a parametric oscillator.
He attached an LC circuit to the electrodes of an arc lamp, and the LC circuit tuned the frequency of the sound. Duddell demonstrated his oscillator before the London Institute of Electrical Engineers by sequentially connecting different tuned circuits across the arc to play the national anthem " God Save the Queen ". In Danish physicists Valdemar Poulsen and P.
Pederson were able to increase the frequency produced into the radio range, inventing the Poulsen arc radio transmitter , the first continuous wave radio transmitter, which was used through the s.
The vacuum tube feedback oscillator was invented around , when it was discovered that feedback "regeneration" in the recently invented audion vacuum tube could produce oscillations. At least six researchers independently made this discovery and can be said to have some role in the invention. Round patented amplifying and oscillating circuits in The first and most widely used relaxation oscillator circuit, the astable multivibrator , was invented in by French engineers Henri Abraham and Eugene Bloch.
Vacuum tube feedback oscillators became the basis of radio transmission by The first of these was the Barkhausen-Kurz oscillator , the first tube to produce power in the UHF range. The most important and widely used were the klystron R. Varian, and the cavity magnetron J.
Mathematical conditions for feedback oscillations, now called the Barkhausen criterion , were derived by Heinrich Georg Barkhausen in The first analysis of a nonlinear electronic oscillator model, the Van der Pol oscillator , was done by Balthasar van der Pol in He originated the term "relaxation oscillation" and was first to distinguish between linear and relaxation oscillators. Further advances in mathematical analysis of oscillation were made by Hendrik Wade Bode and Harry Nyquist  in the s.
Kurokawa derived necessary and sufficient conditions for oscillation in negative resistance circuits,  which form the basis of modern microwave oscillator design. From Wikipedia, the free encyclopedia.
In some types the negative resistance device is connected in parallel with the resonant circuit. The negative resistance of the diode excites microwave oscillations in the cavity, which radiate out the aperture into a waveguide. Retrieved March 1, Electronics fundamentals And Applications. Kung's website, Multimedia University. Retrieved October 17, From Fractal Spots to Energetic Condensation. Springer Science and Business Media. American Journal of Science. Tuttle, Morehouse, and Taylor Co.
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Retrieved May 15, Retrieved December 5, Retrieved December 8, Barkhausen stability criterion Harmonic oscillator Leeson's equation Nyquist stability criterion Oscillator phase noise Phase noise.
Phase-shift oscillator Twin-T oscillator Wien bridge oscillator. Butler oscillator Pierce oscillator Tri-tet oscillator. Blocking oscillator Multivibrator ring oscillator Pearson-Anson oscillator basic Royer. Cavity oscillator Delay line oscillator Opto-electronic oscillator Robinson oscillator Transmission line oscillator klystron oscillator cavity magnetron Gunn oscillator. Retrieved from " https: Views Read Edit View history. In other projects Wikimedia Commons.
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