Standard Guidelines For Constant Electrical Parameters Of Quartz Crystals

Normally, Quartz Crystals are manufactured according to industry standard guidelines.

1. Mode of Operation

2. Equivalent Series Resistance

3. Shunt Capacitance and

4. Drive Level.

Above given parameters may vary slightly between manufactures.

1. Mode of Operation (Resonance Frequency):

A Quartz Crystal has two basic modes of operation comprising Fundamental and Overtone Modes. For frequencies below 30MHz, a crystal manufacturer will use the Fundamental Mode of operation. For frequencies exceeding 30 MHz, overtone modes are suggested. Using Overtone Modes in production therefore reduces manufacturing costs for higher frequency applications. A good rule of thumb is to assume the a Crystal manufacturer will produce a Fundamental Crystal below 30MHz, and an Overtone Crystal above 30MHz. If higher frequencies are required in the Fundamental Mode, please contact FOX ELECTRONICS.

2. Equivalent Series Resistance (ESR):

The Equivalent Series Resistance is the resistive element of the quartz crystal equivalent circuit. This range is normally found to be 25-100 ohms for most Quartz Crystals and is usually specified as a maximum value. Typically, these values are specified according to frequency ranges and are very similar across multiple manufactures because similar holder types, electrodes, modes of operation, and mounting structures are used in achieving specific frequencies. Point to be noted that ESR values at a given frequency for an AT-strip cut crystal and it is commonly used in SM devices.

3. Shunt Capacitance:

The electrodes present in a Quartz Crystal, plus the stray capacitance of the holder, form a capacitance in parallel with the LC model. Generally, the Shunt Capacitance is required to be as low as possible in manufacturing the device, as some oscillators cannot tolerate an excessive value. Because Shunt Capacitance may vary according to the size of the Crystal, manufacturers will normally designate a maximum value usually at 7.0pF. If a lower value is required, we suggest contacting FOX Engineering Support.

4. Drive Level:

Specified by Quartz Crystal manufacturers to provide a guideline for maximum values, the Drive Level should be held to a minimum to avoid problems with Aging, Stability, nonlinear coupled modes, and other nonlinear effects. Improvements in phase noise performance can be realized with increased drive levels; however, so careful consideration should be given to this Electrical Parameter when approaching the maximum suggested level.

by: Fox Online

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