What is a Crystal Oscillator? An Introduction to the Basic Knowledge of Crystal Oscillators

Every standalone chip system contains a component called a crystal oscillator. So what exactly is a crystal oscillator? How much do you know about it? This article will provide an introduction.

1. What is a crystal oscillator?

A crystal oscillator primarily refers to a quartz crystal oscillator. This component consists of a thin slice cut from a quartz crystal at specific orientations, commonly known as a chip, and serves as the most critical element in clock circuits. The quartz crystal resonator, abbreviated as quartz crystal or simply crystal, is a component that integrates an IC within its package to form an oscillation circuit.

2. What is the working principle of a crystal oscillator?

A crystal resonator is a resonant device primarily fabricated using the piezoelectric effect of quartz crystals. When an electric field is applied across the quartz crystal's electrodes, mechanical deformation occurs. Conversely, mechanical pressure applied to the crystal's sides generates an electric field in the corresponding direction—a phenomenon known as the piezoelectric effect. When alternating voltage is applied to the crystal's electrodes, mechanical vibrations are induced, which in turn produce an alternating electric field.

Under normal conditions, the amplitude of mechanical vibrations in a wafer and the alternating electric field are extremely small. However, when the frequency of the applied alternating voltage reaches a specific threshold, the amplitude increases significantly, far exceeding that at other frequencies. This phenomenon is known as piezoelectric resonance, which closely resembles the resonance behavior of an LC circuit. The resonant frequency depends on factors such as the wafer's cutting method, geometric shape, and dimensions.

III. What are the functions of crystal oscillators?

1. Provide basic clock signals

Typically, a system shares a single crystal oscillator to ensure synchronization across all components. For example, in some communication systems, the baseband and radio frequency operate on separate oscillators, with electronic frequency adjustment maintaining synchronization.

2. Provide the system's required clock frequency

Crystal oscillators are typically paired with phase-locked loop (PLL) circuits to deliver the system's required clock frequency. When different subsystems require distinct clock frequencies, multiple PLLs connected to the same crystal oscillator can be employed to meet these needs.