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Specifying Quartz Crystals

A typical surface mount quartz crystal specification reads like this:

The following notes define each element of the specification:

Frequency

Frequency is normally specified in kilohertz (kHz) up to 999.999kHz and in megahertz (MHz) from 1.0MHz. All our computer-generated transaction documents follow this standard convention automatically.

The frequency should be described to seven significant figures. If seven significant figures are not used, we assume that any figure that might follow those given may be taken as zero. Thus a frequency given as 16.6MHz will be taken as 16.60, not 16.66667.

Some specifiers extend the use of kHz to all crystals operating in fundamental mode, reserving MHz for overtones. To minimise the possibility of misunderstanding it is best to use the standard method and specify fundamental or overtone mode separately.

Please contact the sales office for details of developed frequencies.

Holder Style

Before manufacture of the crystal can start, the holder style must be defined. Each holder style covers a frequency range which is defined in the relevant specification.

For leaded versions, the holder information should also cover any mechanical variant required such as a top wire or cropped leads. The following variants for example are available for most crystals, either singly or in some cases, in combination:

• 3 lead base
• Top wire
• Insulating sleeve
• Taped and reeled
• Fitted insulator
• Cropped leads
• Formed leads
• Frequency Tolerance

The cost of manufacture depends partly on the accuracy required at reference temperature (which in the case of the AT-cut crystal,is usually 25°C).

Where high initial accuracy is important the additional manufacturing cost should be weighed against the cost of including a frequency trimming facility within the oscillator.

Frequency Stability

Frequency stability is normally specified as a frequency tolerance over a defined operating temperature range with respect to the frequency at reference temperature. The temperature ranges are defined for each crystal in the relevant data sheet. However the majority of crystals will continue to operate quite satisfactorily outside the temperature range for which they are specified, but with a possible degradation in the value of frequency stability. Under normal conditions this will not damage the crystal.

A crystal designed for operation over a restricted operating temperature range, (such as from 0 to 50°C) has a better frequency stability over that range than one designed for operation over a wide operating temperature range. Therefore it is important not to over specify the temperature range, as doing so will result in inferior performance for the same or greater cost; or greater cost for the same or inferior performance.

Generalised frequency vs temperature curves for the AT-cut crystal types are illustrated where appropriate. These indicate that, without compensation, a crystal specified for operation over a wide frequency range will probably have an inferior performance over a narrower range than one whose design was optimised for the narrower range. The angle of cut of the quartz blank from its quartz stone determines which curve will be followed; the chosen angle being subject to its own tolerance. Thus, since manufacturing cost is tolerance-dependent it is wise not to specify a wider operating temperature range than is actually needed unless some sacrifice of stability, or an increase in cost, can be accepted.

Standard Frequency Tolerances and Stabilities

• ±5ppm
• ±10ppm
• ±15ppm
• ±20ppm
• ±30ppm
• ±50ppm
• ±100ppm

Operating Temperature Ranges

The standard operating temperature ranges for a crystal are:

• 0 to 50°C
• –10 to 60°C
• –20 to 70°C
• –30 to 80°C
• –40 to 85°C
• –55 to 105°C
• –55 to 125°C

When the required temperature range is symmetrical about 25°C, it is indicated in the specification by the lower figure, i.e.: –20 to 70°C would read ‘20’ as shown in the example. If the required temperature range is not symmetrical about 25°C, both figures are used, i.e: –55 to 85°C and appear in the additional text code section (T).

Circuit condition

The characters ‘SR’ are used to denote calibration of the crystal at series resonance. If it is to be calibrated at load resonance the characters represent the circuit load capacitance in pF.

Packaging Codes

Tray packaging is available as an option for some products outlined in the individual data sheets.

Unless individual data sheets state Bulk packaging, surface mount versions will be Tape & Reel packed. Please note: only complete reels are sold.

• BU = Bulk packed
• TR = Tape & Reel packed
• TY = Tray packed

Additional Text Code

If the product is non-standard, the letter ‘T’ will appear at the end of the product specification. This refers to additional text on the quotation/sales order to identify the special requirements.

Outline Drawings

Dimensions on the crystal outline drawings are shown only as a guide. Precise dimensions of crystal holders are available from our Factory upon request. All dimensions are shown in mm and are nominal unless otherwise stated.

Soldering Conditions

Recommended solder pad layouts are shown on each data sheet. For typical soldering conditions, please see the relevant page in Application Notes.

Marking

Where possible the frequency of operation will be marked in full on the crystal. On the smaller types the full frequency may not fit in the available space and will therefore be truncated. Please refer to the despatch packaging for the relevant crystal to see the frequency in full.

Ordering Information

See individual data sheets