Introduction to crystal oscillators and how to test them with a multimeter

Crystal oscillators are core components used to generate precise clock signals in electronic devices. Its working principle is based on the piezoelectric effect of quartz crystals, which can provide very stable frequency output. The following will introduce the principles, classifications, characteristics and applications of crystal oscillators in detail, and explain how to use a multimeter for simple testing.

Principle of crystal oscillator

Quartz crystals have piezoelectric properties, that is, they generate electric charges when subjected to mechanical stress. When an appropriate excitation voltage is applied to both ends of the crystal, the crystal will produce mechanical vibrations and generate electric charges on its surface. This process is reversible, and the charges generated by the crystal vibration will in turn exert pressure on the crystal, causing it to continue to vibrate, thus forming a positive feedback loop, causing the crystal to continue to vibrate at a fixed frequency.

Classification

Crystal oscillators are mainly divided into two categories: passive crystal oscillators and active crystal oscillators.

Passive crystal oscillator
A passive crystal oscillator does not contain a built-in oscillation circuit. It is just a quartz crystal that needs to be used in conjunction with an external oscillation circuit. Passive crystals usually have two pins for connecting to the feedback network of the circuit.

Active crystal oscillator

The active crystal oscillator (Active Oscillator) has an oscillation circuit built in, usually in the form of an integrated circuit, also known as a crystal oscillator IC. In addition to containing a quartz crystal, it also integrates components such as a crystal driver, a temperature compensation circuit, and a voltage regulator. The clock signal provided by an active crystal oscillator is more stable, accurate, and has lower phase noise.

What characteristics does a crystal oscillator have?

Frequency stability: The frequency of a crystal oscillator is very stable, and its deviation is usually calculated in ppm (parts per million).

Temperature influence: The frequency is affected by changes in ambient temperature, and some high-end products provide temperature compensation.

Load capacity: The crystal oscillator can withstand a certain load without significantly affecting its frequency.

Start-up time: The time from power-on to stable oscillation of a crystal oscillator is called the start-up time.

Where can crystal oscillators be used?

Computers and servers: Crystal oscillators provide precise clock signals to coordinate the operation of the CPU, memory, and various peripherals.

Communication equipment: In communication equipment such as mobile phones, wireless routers, and satellite communication systems, crystal oscillators are used to generate and synchronize signals.

GPS and Navigation Systems: GPS receivers and other navigation devices rely on accurate clocks to calculate location and time information.

Digital Electronics: Crystal oscillators are often used in digital cameras, MP3 players, smart watches and other devices to synchronize digital clocks.

Industrial Control and Automation: In industrial control systems, crystal oscillators are used to ensure the accuracy of timing operations and process control.

Medical Equipment: Many medical instruments, such as electrocardiographs and magnetic resonance imaging (MRI) equipment, require a high-precision clock source.

Military and Aerospace: In military radars, missile guidance systems, and avionics, crystal oscillators are used to ensure the accuracy of communications and navigation.

How to Test a Crystal Oscillator with a Multimeter？

Testing a crystal oscillator with a multimeter is mainly to detect whether it is connected and whether there is a short circuit or an open circuit. Here are the simple test steps:

1. Turn on the multimeter and set it to resistance measurement mode.

2. Disconnect all connections between the crystal oscillator and the circuit board.

3. Connect the two probes of the multimeter to the two pins of the crystal oscillator.

4. Observe the reading of the multimeter. If the reading is zero, it may mean that the crystal oscillator has an internal short circuit; if the reading is infinite, it may mean that the crystal oscillator has an internal open circuit or damage.

5. If you are not sure which connection a pin corresponds to, please refer to the crystal oscillator's data sheet for confirmation.

It should be noted that this method can only roughly determine whether the crystal oscillator has obvious electrical faults, but cannot evaluate its frequency stability and performance. More accurate testing requires specialized instruments such as frequency counters or oscilloscopes.

Well-known crystal oscillator manufacturers:

KDS - Daikoku Seiko Co., Ltd. is a Japanese company that specializes in the production of quartz crystals and ceramic resonators.

NDK - Citizen Electronics Co., Ltd. is a well-known crystal oscillator manufacturer in Japan, known for its high-precision and stable crystal oscillators.

TXC - Taiwan Crystal Corporation is a Taiwanese company that mainly produces quartz crystals, ceramic resonators and VCXO (temperature compensated crystal oscillators).

EPSON - Seiko Epson Corporation is a Japanese electronics company whose crystal oscillator products are known for their high performance and reliability.

SiTime - is a brand of Eaton Corporation in the United States, focusing on the production of MEMS (micro-electromechanical systems) clock devices, providing solutions to replace traditional quartz crystal oscillators

Vishay - Vishay Intertechnology, Inc. is a global semiconductor and passive component manufacturer that also produces crystal oscillators and related products.

Murata - Murata Manufacturing Co., Ltd. is a Japanese company that focuses on the production of electronic components, including ceramic filters, resonators, and crystal oscillators.

These brands enjoy a high reputation worldwide and have rich experience and innovation in crystal oscillator technology. When choosing a suitable crystal oscillator brand, it is usually necessary to consider factors such as application requirements, cost, supply stability, and technical support from the manufacturer.

Summary

Crystal oscillators are key components in electronic devices. They provide accurate and stable clock signals, which are essential to ensure the normal operation of the entire system. Understanding the basic principles, classifications, characteristics and applications of crystal oscillators can help us better design and select suitable oscillators.

When using a multimeter to perform a simple test on a crystal oscillator, we can check whether there is a short circuit or open circuit by measuring the resistance between its pins. However, this resistance measurement cannot fully evaluate the performance of the crystal oscillator, because its frequency stability and operating characteristics are usually more important than a simple on-off state. Therefore, for comprehensive testing and evaluation, it is recommended to use specialized test equipment, such as a frequency counter or oscilloscope, to measure its actual output frequency and performance indicators.