Armstrong oscillator

The Armstrong oscillator^[1] (also known as Meissner oscillator^[2]) is named after the electrical engineer Edwin Armstrong, its inventor. It is sometimes called a tickler oscillator because the feedback needed to produce oscillations is provided using a tickler coil (T in the circuit diagram) via magnetic coupling between coil L and coil T. Assuming the coupling is weak, but sufficient to sustain oscillation, the frequency is determined primarily by the tank circuit (L and C in the illustration) and is approximately given by . In a practical circuit, the actual oscillation frequency will be slightly different from the value provided by this formula because of stray capacitance and inductance, internal losses (resistance), and the loading of the tank circuit by the tickler coil.

This circuit is the basis of the regenerative receiver for amplitude modulated radio signals. In that application, an antenna is attached to an additional tickler coil, and the feedback is reduced, for example, by slightly increasing the distance between coils T and L, so the circuit is just short of oscillation. The result is a narrow-band radio-frequency filter and amplifier. The non-linear characteristic of the transistor or tube provides the demodulated audio signal.

Armstrong oscillator schematic

The circuit diagram shown is a modern implementation, using a field-effect transistor as the amplifying element. Armstrong's original design used a vacuum tube triode.

Analog temperature controlled crystal oscillator

In physics, an Analog Temperature Controlled Crystal Oscillator or Analogue Temperature Compensated Crystal Oscillator (ATCXO) uses analog sampling techniques to correct the temperature deficiencies of a crystal oscillator circuit, its package and its environment.

Typically the correction techniques involve the physical and electrical characterisation of the motional inductance and terminal capacitance of a crystal blank, the knowledge of which is used to create a correction polynomial, or algorithm, which in turn is implemented in circuit blocks by Electronic Design Engineers. These circuit blocks are usually simulated in a mathematical modelling software tool such as SPICE, to verify that the original measured data can be corrected adequately. Once the system performance has been verified, these circuits are then implemented in a silicon die, usually in a bulk CMOS technology. Once fabricated, this die is then embedded into an oscillator module along with the crystal blank. Due to the sub 1ppm accuracy of this type of crystal oscillator specialist packaging must be used to ensure good ageing and temperature shock characteristics Example applications are for use in low power or battery operated consumer electronic products such as GSM or CDMA mobile phones, or GPS satellite navigation systems.

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 at a frequency below ≈20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator.

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

The waveform generators which are used to generate pure sinusoidal waveforms of fixed amplitude and frequeny are called oscillators.

Types of electronic oscillator

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

[edit] Harmonic oscillator

The harmonic, or linear, oscillator produces a sinusoidal output. The basic form of a harmonic oscillator is an electronic amplifier with the output attached to an electronic filter, and the output of the filter attached to the input of the amplifier, in a feedback loop. 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 take the place of 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:

• Armstrong oscillator
• Hartley oscillator
• Colpitts oscillator
• Clapp oscillator
• Delay line oscillator
• Pierce oscillator (crystal)
• Phase-shift oscillator
• RC oscillator (Wien Bridge and "Twin-T")
• Cross-coupled LC oscillator
• Vačkář oscillator
• Opto-Electronic Oscillator.

[edit] Relaxation oscillator

Main article: 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.

Other types of relaxation oscillator circuits include:

• multivibrator
• ring oscillator
• delay line oscillator
• rotary traveling wave oscillator.