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AR# 15162

FPGA/CPLD - What is the difference between an oscillator and a crystal?

Description

Keywords: FPGA, CPLD, difference, oscillator, crystal

What is the difference between an oscillator and a crystal?

Solution

An oscillator is a complete solution for a clock. It is typically housed in a metal or plastic package with at least four pins: two for power, one for output, and an extra for mechanical seating. A benefit to using an oscillator is that an output is already buffered (high output drive).

On the other hand, a crystal is simply a single component of many that will comprise an oscillator. You must create the other components such as the inverting amplifier, trim caps, proper output buffer, etc. You must also determine the parameters of the crystal (such as the type of resonant cut and loading parameters) so you can choose the proper loading caps, etc. As this can take a great deal of time, many engineers choose to use a completed solution rather than manage the details of using a crystal. (We do not have recommendations on how to build an oscillator out of a crystal.)

The decision to use either a crystal or a pre-constructed oscillator should be based on whether a reliable and stable clock can be provided and whether the resulting clock adheres to the data sheet specification for the given device.
AR# 15162
Date Created 09/03/2007
Last Updated 09/13/2007
Status Active
Type General Article