OSCILLATOR

An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave.^[1][2] Oscillators convert direct current (DC) from a power supply to an alternating current signal. 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.^[1]

Oscillators are often characterized by the frequency of their output signal:

• A low-frequency oscillator (LFO) is an electronic oscillator that generates a frequency below ≈20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.
• An audio oscillator produces frequencies in the audio range, about 16 Hz to 20 kHz.^[2]
• An RF oscillator produces signals in the radio frequency (RF) range of about 100 kHz to 100 GHz.^[2]

Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters.

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

Harmonic oscillator

Block diagram of a feedback linear oscillator; an amplifier A with its outputv_o fed back into its input v_f through afilter, β(jω).

The harmonic, or linear, oscillator produces a sinusoidal output. There are two types:

Feedback oscillator

The most common form of linear oscillator is an electronic amplifier such as a transistor or op amp 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 signal to get oscillations started. The noise travels around the loop and is amplified and filtered until very quickly it becomes a sine wave at a single frequency.

Some of the many harmonic oscillator circuits are listed below:

Active devices used in oscillators and approximate maximum frequencies^[5]

Device	Frequency
Triode vacuum tube	1 GHz
Bipolar transistor (BJT)	20 GHz
Heterojunction Bipolar Transistor (HBT)	50 GHz
Metal Semiconductor Field Effect Transistor (MESFET)	100 GHz
Gunn diode, fundamental mode	100 GHz
Magnetron tube	100 GHz
High Electron Mobility Transistor (HEMT)	200 GHz
Klystron tube	200 GHz
Gunn diode, harmonic mode	200 GHz
IMPATT diode	300 GHz
Gyrotron tube	300 GHz

• Armstrong oscillator
• Hartley oscillator
• Colpitts oscillator
• Clapp oscillator
• Pierce oscillator
• Phase-shift oscillator
• Wien bridge oscillator
• Cross-coupled oscillator
• Vackář oscillator
• Opto-electronic oscillator
• Tri-tet oscillator
• Robinson oscillator

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• Relaxation oscillator

  
  
  A nonlinear or relaxation oscillator produces a non-sinusoidal output, such as a square, sawtooth or triangle wave.^[3] It consists of an energy-storing element (a capacitor or, more rarely, an inductor) and a nonlinear switching device (a latch, Schmitt trigger, or negative resistance element) connected in a feedback loop. The switching device periodically charges and discharges the energy stored in the storage element thus causing abrupt changes in the output waveform.
• Some of the more common relaxation oscillator circuits are listed below:
  • Multivibrator
  • Pearson-Anson oscillator
  • Ring oscillator
  • Delay line oscillator
  • Royer oscillator

  Voltage-controlled oscillator (VCO)

  
  
  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 infilters, 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