From The Editor | April 15, 2024

Oscillators 101

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By John Oncea, Editor


Oscillators are fundamental components in electronics that generate repetitive waveforms. They're crucial in various applications, from generating clock signals in digital circuits to producing audio tones in music synthesizers.

Oscillators are mechanical or electronic devices that produce periodic signals with a specific frequency based on energy changes. Ever used a computer? It has an oscillator. What about a watch? Or a radio? Or a clock? Oscillator, oscillator, oscillator.

Heck, oscillators have even played a role in the creation of music by Led Zeppelin and Taylor Swift.

Unsurprisingly, oscillators work on the principles of oscillation: a periodic fluctuation between two things based on energy changes. There are many types of oscillators (more on that in a bit) but they all, according to TechTarget, “Operate according to the same basic principle: an oscillator always employs a sensitive amplifier whose output is fed back to the input in phase. Thus, the signal regenerates and sustains itself. This is known as positive feedback. It is the same process that sometimes causes unwanted ‘howling’ in public-address systems.”

The frequency of an oscillator is typically determined by a quartz crystal. When a direct current is applied to the crystal, it vibrates at a frequency that depends on its thickness and how it is cut from the mineral rock. Some oscillators use combinations of inductors, resistors, and/or capacitors to determine the frequency, but the most stable oscillators are those that use quartz crystals.

In a computer, a specialized oscillator known as the clock acts as a pacemaker for the microprocessor. The clock frequency, or clock speed, is usually measured in megahertz (MHz) and plays a crucial role in determining how quickly a computer can execute instructions.

All Kinds Of Oscillators

The principle that drives the operation of an oscillator is a combination of positive feedback –a mechanism where a section of the output signal is fed back into the input of the system in a way that strengthens the initial signal – and an amplification process. For an oscillator to begin and maintain its operation, the total loop gain of the system, which is the product of the amplifier gain and the feedback loop’s gain, must be equal to or greater than one.

Moreover, the phase shift around the loop must sum up to a multiple of 360 degrees to ensure that the signal reinforces itself with each cycle, leading to sustained oscillation. According to How Stuff Works, oscillators can be broadly categorized into two main types: linear (harmonic) oscillators and relaxation oscillators.

  • Linear oscillators: A harmonic oscillator produces a sinusoidal output. It relies on the principle of resonance, where an LC (inductor-capacitor) or RC (resistor-capacitor) circuit is used to determine the frequency of oscillation. The most common types include the Colpitts, Hartley, and RC Phase Shift oscillators.
  • Relaxation oscillators: In contrast, relaxation oscillators generate a non-sinusoidal output, such as a square or sawtooth wave. They work by charging and discharging a capacitor through a resistor at a rate determined by the RC time constant. The unijunction transistor (UJT) oscillator and the 555 timer in astable mode are examples of relaxation oscillators.

There are beyond these two broad types of oscillators many more specific ones, notes Elprocus. These include:

  1. Armstrong oscillator: This is an LC electronic oscillator using the inductor and the capacitor. It is known as the tickler oscillator because the individual features of the feedback signal should produce the oscillations that are magnetically coupled to the tank indicator.
  2. Clapp oscillator: One of several sorts of LC electronic oscillators constructed from a transistor and a positive feedback network using the blend of an inductance with a capacitor for frequency determinations
  3. Hartley oscillator: This is also an electronic oscillator, and its frequency is determined by the tuned circuit which consists of a single capacitor in parallel with the two inductors which are in series. From the center connection of the two inductors for oscillation purposes, the feedback signal is taken.
  4. RC oscillator: This oscillator is a combination of resisters and capacitors like an RC filter type to produce sine waves, but it is more difficult to generate a pure sine wave shape using a resistor and capacitor.
  5. Colpitts oscillators: This oscillator is a combination of both inductors and capacitors. The features of the Colpitts Oscillator are the feedback for the active devices, and they are taken from the voltage divider and made up of two capacitors which are in series across the inductor.
  6. Crystal oscillator: An electronics circuit that is used to generate an electrical signal of precise frequency by utilizing the vibrating crystal’s mechanical resonance made of piezoelectric material.
  7. Wien Bridge oscillator: A type of phase-shift oscillator that generates sine waves. It is composed of four arms and connected in a bridge fashion.

Additional types of oscillators are cross-coupled, dynatron, Meissner, optoelectronic, phase shift, Robinson, and tri-tet.

One More Thing

Digital systems rely on oscillators to generate clock signals that synchronize the operations of various components. They are used in transmitters and receivers for generating carrier signals and local oscillators and are employed in signal generators for testing and measurement purposes, as well as in audio synthesis for creating musical tones.

Oscillators should produce a consistent frequency over time and environmental conditions. In applications requiring precise timing, such as telecommunications and navigation systems, the oscillator's frequency accuracy is crucial.

Understanding oscillators is essential for designing and troubleshooting electronic circuits across a wide range of industries and applications. Whether designing a simple clock circuit or working on complex communication systems, understanding oscillators is fundamental. Choosing the right oscillator depends on factors like power requirements, frequency precision, and board space.