In this article Geyer Electronic walks readers of Electronics Sourcing through the process of deciding whether an electronic product would benefit from a crystal or oscillator.
When designing an electronic circuit, engineers must decide between a crystal or oscillator. Considerations include space, frequency stability and cost. Engineers can build any oscillating circuit using a crystal so why, even in simple applications like clock generation, are readily available oscillators often used?
For small quantities, using a more expensive oscillator may be recommended to save design costs. An oscillator eliminates requirements of certain additional external components and might save PCB space. Oscillators are easily available in a variety of packages and microcontroller manuals usually contain information on how to apply an external oscillator.
For larger quantities (or if an IC with internal oscillator is not being used) building an oscillating circuit with crystals and discrete components may be more economical. A Pierce oscillator may be chosen or an oscillator may be created by appropriate feedback of an inverter circuit. Most microcontrollers already contain the elementary components for the clock circuit, requiring only a crystal and other external passive components to complete the circuitry. Microcontroller application manuals should describe the necessary details.
There are other reasons for choosing an oscillator. Oscillators are available in a wider range of frequencies and often offer a choice for low or high frequencies where a certain footprint is required. Frequency stability may also be important along with secured start-up conditions and reliability for specific environmental conditions. Engineers can choose between different types of oscillator—TCXO, VCTCXO or VCXO—when compensation in temperature or voltage is required and where tight temperature tolerances are requested.
Effort is required to adapt a circuit to a crystal and secure a reliable start-up performance. Whilst oscillators do not require external circuitry—the capacitors and resistors are already incorporated—they are more sensitive to EMC, requiring engineers to follow certain HF design rules. Oscillators also require low power consumption.
Whether engineers choose a crystal or oscillator, Geyer Electronic has over 4000 components over >100 product ranges to choose from, including ultra-miniature devices with tight specifications. If the exact specifications are not found, the company’s Munich-based Design & Test Centre can design a bespoke option including consultation, circuit validation, final testing and ongoing support.