Consider the last computer you purchased. Was it a laptop, desktop, or something more exotic, like the Raspberry Pi? Your new computer's ability to execute computing tasks is based in many of its features and specs, but one of the most important factors is called clock speed. We measure this speed in hertz (Hz), or cycles per second—or in the computing world as megahertz or gigahertz—and a device called a crystal oscillator usually sets this frequency.
We can classify electronic oscillators as devices that put out a signal at a set time interval. A clock pendulum, for instance, oscillates at a 1 Hz frequency as it swings back and forth once per second. You can even make an oscillator out of a tuning fork that "sings" at ~440Hz.
Modern electronics, however, require more advanced methods. While lower-frequency oscillators are available, you'll often encounter oscillators with a radio frequency (RF) range of roughly 100 kHz to 100 GHz. We'll go over a few of the options below.
Types of Oscillators: Harmonic Oscillators & Crystal Oscillators
Harmonic or linear oscillators produce a sinusoidal output where a signal increases and decreases at a predictable level over time. Two basic types are RC, or resistor/capacitor circuits, as well as LC, or inductor capacitor circuits.
1. RC circuits are ideal for lower frequencies.
2. LC circuits are better for higher frequencies.
Both circuit types use an arrangement of complementary components to generate an oscillating output. As with any oscillator, power cycles back into the system to compensate for losses during the process.
The third class of this device, called a crystal oscillator, uses a quartz crystal as the vibrating element, which mechanically distorts when voltage is applied. When the voltage stops, the quartz crystal snaps back into shape and generates an electric field, allowing it to act as a resistor, inductor, capacitor circuit (RLC). This is the most common type of linear oscillator, and you can often find RLCs in small metallic units like the ones in the image above.
We can find RLCs at work in devices such as:
- Electronic watches
- Computers
- Radio equipment
- Arduino boards
These oscillators are very stable, and the (US) National Bureau of Standards even used them to dictate the official time before the transition to atomic timekeeping. Quartz technology continues to advance and become more affordable, leading to the quartz crisis or quartz revolution. During this era, electronic clock and watchmaking largely replaced mechanical methods.
Other Types of Oscillators in Electronics
- Negative-resistance oscillators cancel the resonator's internal losses and don't require an active amplifying element. These oscillators are most appropriate when the application requires high-speed oscillations.
- Relaxation oscillators consist of energy storage elements that produce non-sinusoidal output, but also add a non-linear switching device. This device can produce different types of output shapes, such as square waves and sawtooth signals.
- Voltage-controlled oscillators (VCOs) can vary their output frequency depending on the input voltage or current.
Oscillators come in a wide variety of implementations and speeds. With the right combination of components, oscillators can even offer custom solutions for your device or application. Whatever your implementation, there's probably an off-the-shelf or ready-to-build solution to fit your needs.